DIY Grid Charger/Discharger
For less than $70! (Hurry, the price keeps going up!)

                       Latest update:  6/22/16 

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(Now that I have your attention, please read the next sentence carefully.)

There are dangerous high voltages inside the charger and IPU.  You can be KILLED if you are careless and don't follow all the safety instructions when working on either unit.

At the same time, if you follow the instructions it is quite safe to work on these high voltage systems.  If you are not comfortable working around high voltage, try to enlist the help of someone that knows the precautions to take.
If you have any questions about this article etc please post them here.

Select articles on this page from the list below.

Much of this article is based on reading many-many hours of posts on the I want to give everyone credit that have spent days/weeks experimenting and posting their findings on the forum.

The first generation Insight high voltage IMA battery is composed of 120 special ~"D" sized Ni-MH individual cells arranged in 20 "sticks" of 6 cells each. The nominal voltage of the IMA battery pack is 144 volts.  A new pack will typically run 156 to 165 volts while in use.  Ni-MH cells have a rather high self discharge rate of 1% per day and over time the capacity of the individual cells will vary.  At the same time the internal resistance of the cells will tend to rise and not be equal between all the cells. This causes the pack to become out of balance and the full capacity of the battery can't be utilized while driving. More information about all this can be found at the  Do a search for "grid charger".

If needed, the IMA battery pack is normally charged by the kinetic energy of the car when slowing down or coasting to a stop while in gear. This is called "regeneration".  The battery can also be charged while the engine is running in what is called a "background charge".  The background charge does not always show up on the dashboard instrumentation.  Normally there is no way to charge the IMA battery with an external charger.
The battery control module (BCM) has many features to safely control the charging of the battery so that the battery operates between 20% and 80% of it's capacity. If the capacity of the battery goes below ~10% the BCM will not charge the battery or allow it to assist the IMA system.  This is done to protect the battery.  The digital dashboard will also display a "Check engine" warning and an error code will be stored in the OBDII system.

Over time the IMA battery will loose capacity or become badly out of balance which results in reduced time the battery can provide assist and other problems.  This will be discussed in detail further down this article in "Why and how to make a discharge load".

Enthusiasts on have devised a way to rebalance the battery cells by slowly charging the pack to 100%.  Many of the  2000 to 2006 Insight IMA batteries can be brought back to life by giving them this low current charge for an extended period of time. Typically 0.20 to 0.35 amp is used for 18 to 30 hours. The low level charge allows all the cells of the battery to become fully charged without overheating the better cells of the pack which will reach full charge first. The battery will charge to ~174 volts.

Even new batteries ought to be grid charged once every 3 or 4 months after they are 6 or 9 months old.  This keeps them balanced and will help them last longer.

The charger that does this is called a "grid charger" because it derives it's input power from the normal home power grid (the wall socket).  The charger is basically what auto mechanics call a "trickle charger" because it charges at a very low rate.  A normal 12 volt car battery charger can NOT be used on the IMA battery because the voltage and current is not correct for our purpose.

The grid charger also powers the Insight 12 volt IMA battery cooling fan to insure that the IMA battery pack doesn't overheat due to the extended low level charge or discharge. Some Insighters say you don't need to cool the battery while discharging.  That may be true, but it is common practice to start a discharge after having charged the battery to 100% to balance the cells first. I've found that the IMA battery pack will continue to rise in temperature for many hours after a grid charge with the fan OFF.  For that reason I allow the battery to rest for an hour with the cooling fan running before starting another grid charge (with the fan still running).  The cost to run the cooling fan is far less than ruining even one cell of the series connected battery pack.

There is also a fan inside the grid charger to cool its components.

Purpose of this article

This article is an idea provoking one to present how my DIY grid charger looks and to present the schematic with a parts list so you can build one for yourself.   I am not going to give a detailed mechanical dimensions of where to drill holes etc because the parts you buy, the case you use, the individual parts, power supplies etc may vary in size from the parts I used. And truthfully I don't want to encourage people to copy my design to sell  [6/11/13].

Ready to use grid chargers from simple to very elaborate computer controlled models can be bought through  and eBay. This article describes a simple grid charger (no fancy computer control) that can be built from components found on eBay etc.  If you are familiar with reading schematics, soldering and using simple hand tools you should have no problem building your own charger.  You also have to open the battery box (IPU) behind the Insight seats to install a charging harness.  The charging harness is basically 4 wires (of different colors) approximately 4 feet long with a 4 pin connector on the free end to plug into the grid charger.  You can find information how to install the harness (some with videos) at the Insight Central forums.

When I built this charger in February 2013 the main electrical components cost me less than $30 not including the used computer power supply case with it's fan, the switches and other mechanical parts.  Naturally your cost will vary depending upon how many parts you already have.  I had most of the parts.  The parts price now is typically less than $70.  You can usually find a local computer repair store to buy a junked ATX power supply for the case, fan and  the AC connector etc. Try to get a power supply that has the larger top mounted fan.

The original power supply printed circuit board(s) and wiring were removed and discarded.  The original printed circuit board threaded mounting spacers (PEMs) in the case are used on my first grid charger.  Luckily I found a nice case in my used parts collection that had ventilation slots on the top and one side.  This allows me to position the charger on various sides and still have enough air flow.  You might be able to use some of the components from the power supply PCB.

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Features of this charger

The unusual features of this simple charger are that two LED meters are used and it has a connector to plug your discharge load into. A 2 pin discharge connector allows you to use the built in volt/current meter to monitor the charge/discharge voltage or current. The "charging harness" can be used to charge or discharge the battery with no extra adapters (other than a simple discharge load).

The high voltage (HV) meter is a dual function meter that has a front mounted push button that allows the meter to display either 0-199.9 volts or 0-500 ma. Do yourself a favor and buy a 4 digit multimeter so the voltage can read 1/10s of a volt at 170 volts. When the pack is nearing full charge the voltage will change only ~0.2 volt per HOUR! So you need the 1/10 volt capability to read the change.

There are some nice looking 4 digit dual (volt/amp) reading meters on eBay now. I finally bought a 200 volt, 10 amp meter with the shunt built in (piece of heavy wire) to see if it would be suitable for a grid charger/discharger meter. It does display 500 ma full scale as 0.500 amp. Unfortunately it can't display the discharge as negative current. Basically it can only show the charge current and displays 0.000 while discharging. For that reason I do not recommend those meters at all.

The HV multimeter I used has the micro processor set up to use an external shunt that originally allowed the meter to display 0 to 50.0 amp.  I use a different value shunt (0.15 ohm) which allows the meter to display a reading of 0 to 500 ma. Unfortunately the decimal point is preset and will be in the wrong position when reading current.  The meter will be displaying 0 to 50.0 which is really 0 to 500 ma..  Otherwise it works fine and displays the discharge as negative numbers (-50.0 for instance).

The multimeter is very handy to monitor the IMA battery system while charging or discharging it.  The multimeter requires a separate small power supply with an isolated output voltage between 6 to 15 volts at less than 50 ma to power it.  I used a small 6.25 volt cell phone charger supply but that is not a common voltage. I listed a 6 to 15 volt wall wart in the bill of materials further down this page.  

The meter power supply must have the output isolated from the AC input because the HV DC negative lead of the meter power supply is connected to the negative lead of the high voltage being measured by the meter.  This connection is made within the meter and can not be separated. Switch mode power supplies have the output leads isolated from the AC input wiring.

The IMA battery charging voltage is created by two "LED driver" supplies wired in series.  These supplies are normally used to power strings of LEDs for lighting or special affects. Each supply I used  is rated to deliver 45 to 90 volts and each are rated to limit the maximum output current to 300 ma. Please note that these are not constant current supplies but rather (maximum output) current limited supplies.  Because of that the charger will more than likely not charge at the rated limited current on the label.  The voltage output will be whatever the battery voltage is at that time during the charge.  Apparently some of the LED supplies will make a whistling noise when the battery voltage is very low after a discharge. The noise stops after the battery voltage rises near the minimum output voltage the supplies are rated at. I usually wait an hour before starting a charge after a discharge and the battery voltage normally rises above the minimum voltage my supplies are rated at.

The grid charger will output ~178 volts no load and ~265 ma when charging the battery. The supplies I used are also protected for short circuit and over temperature. The cases of the supplies are aluminum and will dissipate heat much better than plastic cases.  By mounting them to the metal case of the charger more heat can be dissipated. The supplies do not feel abnormally warm to the touch after charging for many hours.  In use I have found the charger supplies run at whatever the ambient cooling temperature is.

A good feature of the LED supplies I used is that they have an internal diode connected across the output leads. When the two supplies are used in series as a grid charger they will be protected if one of them quits working (as an example, from overheating).  The charger won't output any charge current but at least it won't let the magic smoke get out of either of the supplies. If you find supplys that don't show having a diode on the output you can wire a 1N4004 through 1N4007 diode across the red and black wires of each supply. Make sure the diode marking band (the cathode) is wired to the red lead of each power supply.  If you don't use diodes and one supply stops working it is possible for that supply to have reversed voltage applied to it from the working supply if the battery voltage is very low after a battery discharge. That situation will certainly cause internal damage to the supply that isn't working.

I also use a series HV output diode within the grid charger to keep the IMA voltage from being present on the supplies when they are not operating.  This allows the charger multimeter to display the no load IMA battery voltage when the charger/discharger is connected to the car but not charging.  This also allows you to read the voltage and discharge current while discharging the battery with no back voltage applied to the power supplies.

The 12 volt, 2 amp rated switching supply I bought seems to be a typical Chinese supply in that it really doesn't put out 12 volts AND 2 amps at the same time.  12 volts is output with a 1 amp load.  At two amps load the voltage drops to 11.1 volts.  On the other hand, even 11.1 volts at 2 amps will run the Insight 12 volt Insight battery cooling fan and the BCM if you want to run both while charging the battery.  I set the no load voltage to 13 volts with the built in calibration potentiometer.

  1. If a diode(s) is used within the IPU to prevent battery voltage from appearing on the charging cable, the multimeter will not be able to read the IMA battery voltage when the battery is not being charged.  Unfortunately you will also not be able to do a discharge cycle of the battery to increase it's life with a diode inside the case.   For that reason I would recommend that you not install any diodes in the charging harness. Just be careful and don't touch the pins of the charging harness.  They will have the full battery voltage on them at all times with the ignition ON and the IMA master disconnect switch in the ON position..
  2. While you have the IPU open to install the charging cable, check the gap around the battery cooling fan. Typically there will be a ragged gap in the plastic shroud housing with the gap up to 1/4" along the fan sides.  Use some RTV or flexible caulking to fill in the gap to increase the cooling affect of the fan.
  3. As a safety feature I would install a fuse on either high voltage lead when you install the charging harness.  A fuse holder can be mounted outside the IPU case or a panel mount fuse holder can be mounted on the IPU case so you can change the fuse without opening the IPU case.  I prefer the panel mount fuse because you are trying to protect the harness wiring inside the case if there is an external short.
  4.  I used a 2 amp slow-blow DC fuse in line with the positive battery lead charging harness.  Use a fuse rated for at least 200 volts DC.  A DC fuse is designed to quench any arcing if the fuse blows to prevent it from starting a fire inside your car!
  5. I will probably not install a 12 volt meter on future supplies because the voltage never changes.
  6. The HV multimeter being lit will easily tell you when the charger is turned ON so a separate pilot lamp is not needed.
  7. To allow the exhaust cooling air from the IPU to have an more direct exit from under the IPU I have removed the black flexible container in the tire well.
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How to build the grid charger/discharger

grid charger side fan 2nd supply top fan

These two pictures are a preview of what two chargers I've built look like when turned ON with a no load.  The charger on the left is described in detail below and is is my proof of concept charger.  The right side picture is a charger I built for a local Insight owner and is how I would build more chargers (minus the 12 volt meter).  

The switch on the upper left is the master switch that turns on the 12 volt supply, the 6.25 volt supply for the HV LED meter, the grid charger fan and the IMA battery cooling fan.  The right hand switch turns on the high voltage power supplies.  If you want to run the BCM while charging the IMA battery you have to apply the 12 volts to the BCM before applying the charging voltage.  This allows time for the BCM computer to boot up and do its chores.

The voltage or current selection push button for the multi-meter is located at the lower right hand corner of the meter bezel. If you look closely through the ventilation slots you can see that the NE-2 neon bulb is glowing to indicate that the high voltage power supplies are energized.  The neon bulb also acts as a low current bleeder to discharge the two power supplies output capacitors when switched off. When the neon bulb goes out the high voltage is a little below 80 VDC. You should wait ~20 seconds or more for the secondary bleeder resistor to drain the voltage below 10 volts or so.

Lately there are dual display volt/current meters listed on eBay that would require modification to read 500 ma.  They display the volts and current at the same time.  Please notice that all of the dual display meters I've tested do NOT display tenths of volts over 99.9 volts though.  It is much better to have tenths of volts shown as  173.6 volts instead of 174 volts  so you have a more accurate voltage reading to get an idea how the charge or discharge is going along.  None of the dual meters I tested will display the discharge current at all. They read 0.00 when discharging the battery.

I've bought several different dual display meters and only the one I list on the bill of materials (with the small push button to switch between reading voltage or current) will display the discharge current properly.  So as nice as the two color dual display meters are they are unsuitable for a grid charger.  I would not recommend them at this point.

To see an enlarged view of these pictures, left click on a picture or right click and select "View Image".
top view

This is an overall top view of the grid charger.  Notice the 3/4" w x 1/8" thick aluminum strip of metal that holds the two LED power supplies in place. The strip also is a mount for the 6.25 volts cell phone charger supply and the 12 volt, 2 amp supply.  All the supplies are high efficiency switch mode type power supplies.

The two LED driver supplies are mounted at an angle because that is the only way they would fit in the case.  Notice the 1/4" spacing between them so cool air can circulate around the cases.

cell charge

This is a close up of the 6.25 volt power supply which is used to power the larger LED front panel meter.  It is mounted on the hold down strip with a #4-40 nut/bolt and hot melt glue.  I cracked the case open so I could solder the AC input wires to AC terminals on the left side of the PC board.

The hold down strip also is used to mount the 12 volt, 2 amp power supply located in the lower left of this picture.  One of the mounting screws for the supply is partially hidden and is located just above the small yellow voltage adjustment potentiometer.
LED spacing

There is a spacer located under each end of the LED supply hold down strip. The spacer length is chosen so the lower side of the hold down strip is ~1/16" below the top of the LED supplies.  This clamps the supplies in place and also helps to dissipate some of the heat they produce.

The hold down screw for the 12 volt supply is located on the right bottom of the supply below the green LED. The green and white heat shrink is used to protect the LED high voltage leads when the cover is placed on the case.

LED supply spacing

This is the other end of the hold down strip showing the spacers and the screw that also mounts this end of the 12 volt, 2 amp supply.  The spacers are just hollow tubes that the mounting screw passes through.  The PEM studs attached to the case are threaded for metric screws.

The 12 volt supply has many holes in the cover for ventilation so it is OK to mount it against the case with its ventilation holes.  If your case doesn't have ventilation holes in that area space the 12 volt supply away from the case.
AC wiring

The AC input wiring is on the left of this picture.  Also shown is an end view of the 7 lug terminal strip I used.  All the output voltage wiring connects to the terminal strip or the green stand off which is the high voltage positive output terminal.


This is a close up of the terminal strip with the high voltage wiring on the 4 left end lugs and the two 12 volt wires on the 2 right end lugs. The 5th lug is the mounting (grounded) lug. It is located under the green stand off terminal in this picture. The stand off terminal is not part of the terminal strip.

The fuse holder is mounted where the 120/240 switch was originally located.  A normal computer power cord is used.

After these pictures were taken I installed a female 4 pin Molex connector on the "front" side of the case for the charging harness to plug into the charger.  A 2 pin discharge connector is also mounted on the front panel.
top panel meters

The case is made of steel so you will have to find a way to cut the two rectangular holes for the LED meters. I used a hand "nibbler". It took quite a bit of careful measuring to make sure the larger meter clears the fan.  The fan fits into the clear area above the meter and to the left of the switches in this picture. The two calibration pots can be seen on the multi-meter. The two white connectors and wires came with the meters.

Inside view 2nd charger

These two pictures are of the top mounted fan grid charger I built for a friend.  The case is a standard ATX power supply.  The main advantage of  the top mounted fan is that it allowed mounting the meters and the two switches on the front side of the case rather than on the removable lid. That eliminated all the wiring from the cover except for the two wires for the fan. I used the normal fan 2 pin connector so the top cover can be completely removed & placed out of the way when building or calibrating the charger.

The LED supplies are bolted to the bottom of the case which eliminated the hold down strip the first supply used.  The two amp ventilated cover of the supply is mounted to the rear panel with #4 hardware.  I cut away a good bit of the two amp power supply's ventilated cover where it touches the rear panel to increase the air flow through the supply. The supply cover is mounted to the rear panel first and the supply is then slid onto and under the cover from the right side of this picture.  Note that the terminal strip is also mounted on the supply. All of these details take a lot of measurements and trial fittings before you drill any holes.

The cell phone charger with the brown PCB is mounted with two long #4 screws using several #4 nuts to space the supply above the LED supplies.

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2nd supply outside

A short charging cable with a 4 pin male Molex connector comes out the back of the case near the 120 Vac plug.  The charging cable coming from the IPU case uses the normal ATX power supply female Molex connector.

The two advantages to using the top mounted fan case are the fan is very quiet and there are no permanent wires or switches attached to the cover. Since the fan and cover is removable the charger was easier to build and if necessary, will be easier to repair later.

This charger has a neater layout and mounting set up compared to the first supply which I built for myself. The first charger was actually a proof of concept test charger.

I have found that the LED supplies run at the ambient air temperature while charging the battery and there is more than enough air flow with the top or side mounted fan.  The top mounted fan makes a much nicer looking power supply internally and externally. The fan discharges the air upward.

Just to the left of the 12 volt meter you can see the covered hole where the original computer DC power leads came out of the power supply.

  Schematic  (Click on the schematic to see a larger, clearer view of it.)
grid charger sch

Grid charger harness connections   (P2 connector with pin numbers as P2-x)

P2-1   Positive high voltage to forward end of white resistor in IPU box. (use "Y" spade lug adapter).
P2-2   Negative high voltage to resistor in IPU box (Install a "Ring" spade lug under the bolt holding the orange cable with black band on end).
P2-3   Positive 12 volts to battery cooling fan (blue lead from fan itself).
P2-4   Negative 12 volts to battery cooling fan (black lead from fan itself).

Installation of the charging harness

A short youtube silent video with subtitles showing how and where charging harness wires go can be found here.

A #30 Torx bit is used to remove the special IPU cover screws.  The small bolt next to the battery switch takes a 8mm wrench and you have to remove it to get the cover off. The flat spade connector you have to remove from the white resistor has a locking button on it. I was not able to get the connector off by hand even after pushing on the release button. I finally used a long screwdriver as a pry bar and was able to remove the connector.

With all due respects to the video's author, after 4:17 into the video I started seeing mistakes and things I wouldn't do.  i.e. Run the harness out the right side of the case and don't take the chance of sharp metal cutting into the HV wire insulation. The normal charging time is from 24 to 35 hours to fully balance the battery. The final charged voltage will vary depending upon the battery and ambient temperature. The harness fuse should be installed close to or on the IPU case to protect the wiring inside the IPU.  

Leave the flexible box insert out of the tire well and the trap door open while charging the battery. This will insure the best cooling of the battery. I don't have the insert installed in my car to help reduce the battery temperature when driving the car. I don't have to always remove the insert before charging the battery. I just open the trap door and connect the harness to the charger.

Naturally your harness wire colors will vary from the video but the connection points shown are correct.  To make it easier for me to remember which way to plug in the 4 pin polarized charge/discharge harness into the charger I used a red wire for the low (12 volt DC)  and a yellow wire for the high (IMA battery voltage) connections on the 4 pin Molex ex-computer power supply female connector. The ground wires are electrically isolated from each other and use different color wires.

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Bill Of Materials
Part designators
PS1, 2 (Note 1)
PS4     (Note 2)
SW1, 2

Misc hardware       

Charging harness     
Description                                                                                   Vendor
1N4007, silicon diode 1amp, 1000  Vr  ......................................... Various suppliers
2 amp fuse, 250 volt and holder ......................................................Various suppliers, fuse holder
12 volt fan ....................................................................................... Part of power supply case
NE-2, neon pilot lamp  ................................................................... Various suppliers (Not absolutely required but nice to have)
Male line cord plug ......................................................................... Part of power supply case
Molex male 4 pin ............................................................................ Mate to computer Molex hard drive power connector
Dual red LED meter, 199.9 volt, 50 amp  ....................................... eBay item  (Note 2)
3-30 volt red LED meter  ................................................................ eBay item (Not absolutely required)
Female 2 pin connector ................................................................... Any 2 pin connector rated for 200 Vdc for discharger cable
45-90 volt, 300 ma LED driver switching power supply  ..............  eBay item   (I used a gold anodized LED driver w/aluminum cover)
6 to 15 volt, 50 ma cell phone charger  ........................................... eBay item (Cheapest supply to power the dual LED meter)
12 volt, 2 amp regulated switching power supply  .......................... eBay item (To run the cooling fans and BCM) See note 3.
1 megohm, 1/4 watt film resistor  ................................................... Various suppliers  (Any tolerance value will work.)
220 k ohm, 1/4 watt film resistor  ................................................... Various suppliers  (Any tolerance value will work.)
0.15 ohm precision resistor  ............................................................ Various suppliers (Must be +/-2% or better for meter stability)
SPST mini toggle switch  ................................................................ Various suppliers  (Look on eBay.)

You will need two terminal strips and mounting hardware. One terminal strip should have 6 terminals plus 1 or 2 ground lugs and another strip with 4 terminals plus 1 or 2 ground lugs.

For the charging/discharging harness you will need a circular lug to fit the the negative IMA battery terminal bolt and a two male one female "Y" spade lug adapter.  I found a package of the "Y" lugs at Radio Shack. I later found a "Y" connector on a junk clothes washing machine.
You will also need at 4 pin male-female pair of connectors. I used the normal 4 pin female Molex power supply connector on the free end of the charging harness.

  1. "eBay item" are links to the current supplier of those parts at the time I built my charger. Use the pictures of the parts to find current vendors. The vendor that I used previously for the two LED drivers isn't on eBay anymore. I have linked to another eBay vendor that seems to have the same 45-90 volt drivers I used. Do not buy similar looking units that do not output 45-90 volts DC. There seems to be many more drivers now that have either too high or too low a voltage range than when I built my chargers. You need 45 to 90 volts DC output at ~300 ma. The total no load output voltage of the series connected supplies should be 175 volts to 179 volts.
  2. The original vendor I used for the dual meter is not on eBay now. I have listed an eBay vendor who has what appears to be a very similar meter. You will have to remove the thick wire shunt and replace it with the 0.15 ohm current shunt. The meter appears to have the two calibration pots. Hopefully can calibrate the current meter with the 0.15 ohm shunt  But you may have to experiment with the shunt resistance value.
  3. If you don't want to power the BCM you can buy something similar to this 12 volt supply eBay item  for PS3 & PS4.
  4. I've had good luck buying parts from B&G Micro for many years and you will find most of the small parts on their website.
  5. I used a Molex sized 4 pin male connector cut from a junk hard drive chassis as the grid charger output 4 pin connector. I tapped the metal for #4-40 screws and mounted the connector on the meter side of the case.
  6. I used a normal Molex 4 pin female connector from a computer power supply cable on the charging harness free end from the IPU. You need to use a well enclosed female connector because the full IMA voltage is on the pins at all times. I cover the connector with a flexible cap that many Dell PCs have on the unused 4 pin Molex power supply connectors.
  7. The charging harness can be made with AWG #20 minimum sized wire about 4 feet long of four various colors. You can use 4 separate insulated wires and place them in insulated tubing instead of a dedicated 4 wire cable. Use stranded wire, not solid wire.
  8. I routed my charging cable out of the IPU case at the gap under the bottom of the right rear corner of the case. Use a tie wrap on the inside and outside where the cable passes under the box.
  9. Do yourself a favor and buy a 4 digit multimeter so the voltage can read 1/10s of a volt at 170 volts. When the pack is nearing full charge the voltage will change only ~0.2 volt per HOUR! You will need the 1/10 volt capability to read the change.
  10. The multimeter I used reads current when the push button is released (OUT) and voltage when it is pressed and stays IN. Ignore the decimal point when reading the current. It is preset by the meter uP and from what I can determine it can't be changed

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First check of grid charger

The multimeter will read voltage when the small button on the lower right side of the meter bezel is pushed IN and current when the button is pushed again so it is OUT.  Do not connect the grid charger to the car's charging harness at this time.
  1. Push the multimeter selector button so it stays IN.
  2. Set both switches to OFF and connect the AC cord to the charger.
  3. Plug the AC cord in to a wall 120 Vac socket.
  4. Set SW2, the power switch ON.  The power supply fan should run and both meters should light with the smaller meter showing ~12 volts DC.  If desired you may be set the 12 volt, 2 amp power supply to 13 volts or more with the pot on the 12 volt power supply.
  5. If the fan doesn't run or the meters don't light etc then trouble shoot and correct the problem. (Check the wiring and then individual components.)
  6. Set SW1, the high voltage [HV] switch ON.  The multimeter should show ~178 volts.  There's no power supply adjustment for this voltage.
  7. If you installed LP1, the 1/4 watt neon lamp it should be lit whenever the HV switch is ON and the voltage is above ~80 volts.
  8. Set both switches to OFF and read the notes below.
  1. If the charger is not being used to charge the battery is is OK to disconnect the charger cooling fan while working on the charger. If you use a two pin fan connector don't forget the fan connector is polarized positive and negative so you must connect it properly to the 12 Vdc supply.
  2. If the cover is off the grid charger, be aware that there are open 120 Vac connections in addition to the 178 Vdc connections just waiting to shock the didily out of you.  So be careful.
  3. To power down the charger I always turn the HV switch OFF first and wait until the HV meter shows less than 20 Vdc.  Then I turn the power switch OFF and unplug the AC cord before sticking my hand(s) into the grid charger.  The neon bulb LP1 will remain lit until the HV falls below ~80 volts.  But 80 Vdc can still shock you so have patience and wait for the HV meter to go down below 20 Vdc or so.
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Calibrating the multimeter

Once the initial power supply checks have been done you need to calibrate the multimeter.  The voltage calibration pot is closest to the multimeter power connector at the lower edge of the meter PCB.  The current calibration pot is located at the top of the PCB.  You will need a very short flat blade screw driver to set the 10 turn calibration pots.  You can also use a small needle nose pliers to set the pots.

The current calibration is done first.  An accurate DVM is used as the calibration standard to set the multimeter. To simplify calibrating the current meter and to not have to use a high wattage load, I use an adjustable low voltage power supply to light a small 12 volt pilot type bulb.  The bulb should be rated to draw at least 1/4 amp at 12 volts.

In affect the low voltage power supply takes the place of the LED drivers and the 12 volt light bulb simulates the IMA battery being charged. The multimeter doesn't care what voltage is being used when reading current.  The low voltage supply is fine for calibrating the meter and avoids having 180 Vdc floating around in the charger while sticking your hands into it.  Just be careful and don't touch the AC power terminals etc.

How to connect the external low voltage supply to the charger.
  1. Do not plug the AC power cable into the charger at this time.  Set both power switches on the grid charger to OFF.  Set the external power supply to OFF.
  2. Connect the positive voltage lead of the external variable power supply to J2-1.  (The "-1" or "-2" is the pin number of the connector).
  3. Connect the negative voltage lead from the external supply to J2-2.  (J2 is the grid charger output connector to the charging harness.) 
You can also connect the external supply leads to other appropriate points inside the charger case.

How to connect the DVM and 12 volt light bulb (dummy load) to the charger.
  1. Connect one lead of the bulb to P1-1, the positive terminal.of the discharge connector.
  2. Connect the other lead of the bulb to the DVM positive lead.
  3. Connect the negative lead of the DVM to P1-2, the negative terminal.of the discharge connector.
Note:  You can use jumper wires to connect to other appropriate points inside the charger.

How to do the current calibration.   (Use caution since there are exposed 120 Vac terminals inside the charger.)
  1. Set the DVM to read at least 500 ma (current).
  2. Set both power switches on the grid charger to OFF and then plug the AC power cord into the charger.
  3. Set the charger power switch SW2 to ON, leave the HV power switch SW1 OFF.  The grid charger fan should run. The 12 volt meter should show ~12 volts or whatever you set the 12 volt power supply to.  You can disconnect the fan for current and voltage calibration if you want to.
  4. Set the multimeter to read current by pushing the bezel button so it stays OUT.
  5. Set the external supply to the lowest output voltage and turn the supply ON.  Slowly increase the voltage until the external DVM current meter reads 250 ma (1/4 A).  The light bulb may only glow at this low current and that is OK since we are only interested in the current.
  6. If necessary adjust the multimeter current calibration pot to read the same current as displayed on the DVM.  Ignore the decimal point as it is pre-wired in the meter and can't be turned off when reading current.  (250 ma will read 25.0)
  7. Set the charger power switch (SW2) and the external power supply switch to OFF.  
  8. Remove the external power supply, the DVM and the light bulb.

How to do the voltage calibration  
(The HV output of the charger can't be changed but we do want to calibrate the multimeter.)
  1. Set both power switches on the grid charger to OFF.  Do not plug the AC cord in the charger.
  2. Set the DVM to read at least 200 volts DC.
  3. Connect the positive  lead of the DVM to J2-1, the HV positive terminal.of the HV output of the charger. 
  4. Connect the negative lead of the DVM to J2-2, the HV negative terminal.of the HV output of the charger.
  5. Push the multimeter button so it is IN to read the HV.
  6. Connect the AC power cord to the charger.
  7. Set the charger power switch SW2 to ON. The meters should be lit and the 12 voltmeter will read voltage.
  8. Set the HV power switch SW1 to ON.  The DVM should read ~178 volts.  As long as the voltage is above 175 volts the charger will correctly charge the IMA battery.
  9. Set the multimeter voltage calibration pot to read the same voltage as displayed on the DVM.
  10. Turn both power switches to OFF and disconnect the DVM.
  11. Your meter is now calibrated.    -- Enjoy! --
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How to make a discharge load.

My discharge load device consists of two ceramic light sockets wired in series and mounted on a short piece of 1" x 6" board.  One socket has a pull chain ON/OFF switch on it. The actual discharge load can be made by using 120 volt light bulbs of various wattage combinations. Nothing exotic about that, just wire the two sockets in series like Christmas tree lights with a single length of wire and attach each wire of the 2 wire discharge cable to the single free terminal on each socket.  For people in countries with 240 volt AC systems just use one socket with a switch.

I used a long 120 volt power cord from a vacuum cleaner as the discharge cable so I can have the light bulbs inside my garage to keep an eye on the discharge while it is running. I used a polarized 2 pin male connector on the end of the cable to plug into a the matching polarized 2 pin female connector on the grid charger. After these pictures were made I added two brass nails partially hammered into the wood board and soldered a red wire to the positive lead of the two wire cord to one nail and a black wire soldered to the negative lead to the other nail.  This allows me to connect a voltmeter inside the garage to read the battery voltage.  If you want to get fancy you could also wire a milliamp meter on the discharge board.

Before I could wire the ceramic bulb sockets I had to route out an area on the board underneath where the sockets would mount with a ~1/2" wide trench between the sockets for the wires to pass between the sockets.  There is another short trench from one socket for the two wire discharge cable to leave the board.

The left picture shows the routed out area underneath where the sockets mount.  The right side picture shows the sockets mounted on the board.

Discharger openDischarger sockets mounted

Some people have used a dual bulb "Y" socket designed for wall mounting.  They have two wires on each socket that can be wired in series.  You don't have to route the board out as much with a "Y" socket. The problem with the "Y" socket is that there is no switch on the ones I've seen.  I like the remote cut off feature of having a switch on one of the sockets.

What wattage bulbs should you use as the discharge load?

The current drain when using light bulbs will vary in a non linear fashion depending upon the battery voltage. 

Normally Ni-MH battery cells are considered discharged when they read 0.9 volt per cell. It has been found that bad cells can reversed charged when the total pack voltage is above 0.9 volts per cell.  This is true because good cells can be above 0.9 v/cell while bad cells are already in reverse charge. This can result in the total pack voltage to be more than 0.9 x 120 =  108 volts.  For this reason I would like the discharge current to be less than 200 ma at 110 volts.  My tests show that a combination of a series combination of a 20 watt and a 40 watt bulb will discharge at ~168 ma.

If you want to change the discharge rate, vary the wattage of the two bulbs as the current changes depending up on what final current you want to discharge at that point in the discharge.  Lower wattage bulbs give lower discharge currents.  If you live in the UK or other countries that have 240 VAC bulbs you can use just one bulb as a discharge load.  But you will have to do your own experiments to see what current various watt bulbs draw.

I did some bench tests on various wattage incandescent light bulbs to help understand the current vs DC voltage curves. I also checked the current flow using a 500 ohm, 100 watt resistor for comparison. The data is presented on the chart below. Use this chart as a guide to what wattage bulbs to use depending upon what current you want to discharge the battery at.

While using a resistor as a discharge load will work; you do have to take into consideration that the resistor will be dissipating up to 60 watts when starting the discharge with a fully charged pack.  Even mounting an aluminum cased 100 watt resistor on a 3" x 5" finned heat sink did not keep it cool enough so it wouldn't cook your finger if you touched it.  A computer fan did not help much.  As a test I finally used a microprocessor dual heat pipe heat sink with a large shrouded fan to be able to keep my fingers on the resistor for a short while.  

Again, I recommend using two 120 volt light bulbs in series.  We know they are going to be hot and generally don't put our fingers on them.  And they do give some indication of how the discharge is going along.  Also two bulbs in series aren't likely to blow out when the battery voltage is above 120 volts. It takes long enough to do a discharge and you will waste time if a bulb blows stopping the discharge.

Click on the chart to see it full size.

I vs V for light bulbs * 100 Ω resistor

I would use the chart currents as a close approximation of what the discharge currents will be using light bulbs as a discharge load.  With the current meter built into the grid charger you can check the actual discharge current and perhaps use different size bulbs in various combination to get the current you want at any point of the discharge.

Old fashioned incandescent light bulbs are getting hard to find and CFL bulbs will NOT work.  Halogen flood lights work fine and have the same curved discharge current vs voltage as the normal old fashioned bulbs.

You really should run the IMA battery cooling fan when starting a discharge right after  finishing a battery charge.

In the past I recommended always running the fan while discharging the battery but on further tests I found the reason I thought that was desirable is because after a normal grid charge the battery temperature continues to rise for many hours in warm S. Florida. In that case if you have just finished a charge or the IPU case is very warm, it is best to run the fan for the discharge.

In South Florida the ambient temperature is normally well above 45F in the Winter and above 95F in the Summer.  During the summer I usually start a grid charge in the early evening to avoid the heat of the day.

Recently I started a grid charge at 7 PM with the outside air temperature being ~85. At noon the next day, with the fan running and the tire well trap door open the battery temperature was at 122F.  I felt that was hotter than I wanted to continue the charge so I turned the charger off to allow everything to cool off.  At 7 PM that evening I remeasured the battery temperature again. At that time the battery temperature had continue to rise and was reading 129F!  Unfortunately I didn't think to measure the inside cabin temperature but the outside air temperature was still in the mid 80s.

After not charging or running the car that day, the next morning the battery was still at 91F with the outside ambient at 80F.  This illustrates how much heat is stored in the mass of the battery that can be released for many hours.  With the car closed and in the sun you have to be aware of how hot the battery can get while charging.  And to some extent this also applies to discharging the battery. Let's not cook our batteries.

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Information about rejuvenating a battery

But first, you might ask, "Why even discharge the IMA battery?"  Good question.

Ni-MH batteries are known to not deliver their highest capacity when first put into service until they have been charged and discharged several times. It  is normal to find instructions on small AA or AAA Ni-MH batteries to charge them for 16 hours before using. Many RC enthusiasts charge, then discharge and charge their batteries several times before using them. They do this to get maximum performance the first time they actually put them into service. I found that each time I grid charged my "new" Honda battery that the car maintained the battery at higher SOCs afterward.

In use the individual cells of the IMA battery will tend to deteriorate over time and the cells will have different levels of watt hour capacity. This is called an "unbalanced battery".  When driving the car, the weaker cells limit the time and amount of assist the battery pack can deliver.  The batteries can usually be brought back to usable capacity by properly grid charging them.  This is called "balancing the battery" or "a balancing charge".  New batteries ought to be grid charged three or four times a year after the first 6 months to a year of use. This helps to keep the battery pack balanced over time. Consider the periodic grid charge as part of your car maintenance and more importantly to extend the life of your [expensive] IMA battery.

To rejuvenate an Insight IMA battery it has been found through experimentation that discharging packs down to near zero volts per cell gives very good results to regenerate battery packs. There is a technical paper here that indicates that there is some merit in this approach.  The results are encouraging on batteries that had to be grid charged very frequently.  But at this time the Insight Central forum experimenters aren't sure if this is a long term fix or not.
A complete regeneration cycle would be a balancing charge to 100% followed by a discharge to near zero volts followed by another 100% charge. Packs that are on their last legs will sometimes recover more capacity by doing two rejuvenation cycles.

Unfortunately when discharging an unbalanced battery pack the weak cells will discharge to 0.9 volts much quicker than the good cells.  In fact really weak cells will not only discharge to 0 volts but they can be slightly "reversed" charged by the discharge current while the good cells in the pack continue being discharged. When discharging a weak pack to zero volts it is obvious that many cells may be reversed charged.

At high current levels, reverse charging cells is not good!  Using too high a discharge current with cells reversed charged can result in those cells overheating with venting which will cause all sorts of problems over time. (Another reason to run the IMA cooling fan during a discharge.)

Through experimentation, the general consensus on the  forum it has been found that if cells are reversed charged at low current, that minimum or no damage will occur.  What that low current  is, is still up for some debate.  But 200 ma or less at the end of the discharge should be OK. And if your battery is on it's last legs anyway it may be worth to do this procedure on the chance you will get more life out of it.

As the say in the TV advertisements, "But first .........."  
If you have installed one or two diodes in the high voltage charging harness you will NOT be able to discharge the battery. So if you want to  or later need to discharge the battery remove any diodes in the HV lead(s) of the charging harness.

Some additional information and hints about Ni-MH batteries that have been left uncharged for long periods of time.

It has also been reported on the forum that batteries that have sat unused for several years and have self discharged to very low voltages were brought back to life by doing several rejuvenation charge/discharge cycles.  Individual sticks of 6 cells that were in very weak condition were also brought back to life after sitting for long periods of time by cycling them.

Storing a stick or a complete battery for a long time doesn't seem to be a problem.  There is no danger of a cell becoming  reverse charged by allowing a battery pack to self discharge for a long time with no load on it.  Ni-MH batteries self discharge about 1% per DAY.  If you are planing on storing a battery or the car I would grid charge the pack to balance the cells and then store it in a cool location.  I would probably be a good idea to switch the battery master switch to OFF for long term storage.

"eq1" an  member has done a lot of battery research and has come up with some very good results by completely discharging battery packs. I would highly recommend reading this post of his and this one on how he sets his discharge current.

When the battery pack voltage gets to 50 volts or lower during the discharge the current will also go down in value.  You may want to change the light bulbs to ones with a higher rated wattage rating (at 120 volts) to raise the discharge current back up again.  I tend to keep the discharge rather low when going below 50 volts.  My idea is to give the chemical reactions within the batteries time to complete.

Be careful when changing the bulbs. The bulbs may be dim at the lower voltages but they are still very hot if you change them without wearing work gloves.  I would turn the discharge off with the socket switch, wait awhile for the bulbs to cool off, change them to higher wattage bulbs and then start the discharge again to the final volt level for that cycle. I also made a shorted adapter to replace one of the bulbs that also works nicely.

Don't be surprised if the battery voltage rather quickly rises to a much higher  voltage with the load removed. Just change the bulbs and the voltage will quickly drop back down. The lower the bounce back voltage is the better the battery pack is. My little over 3 year old Honda battery bounced from 12 volts (0.1 volt per cell) to 50 volts after an hour of sitting.  People with very weak batteries mention bounce voltages of 120 volts.

 Damage can occur by improperly charging a dead battery when starting to use it again.

If you find a car that has sat for many months or several years without running it is recommended that a slow grid charge be done before using the IMA battery again. In other words, don't just start the car and take off on a long trip home with it. By leaving the battery discharged you will have a perfect battery to do a slow grid charge to bring it back to life. The cars normal charging routine has much too high a charge current to do a proper balancing of the battery.
If you have a short trip you can switch the IMA battery master switch to OFF, start the car on the 12 volt battery that has been charged and drive the car home. The IMA master switch is located under a small cover at the center of the battery box (IPU) at the back of the car under the rear carpet. You will need a 10 mm wrench to remove the small cover.  There is a red safety clip over the handle of the switch that needs to be lifted off the handle so you can switch it OFF.  Replace the clip so you don't loose it.

With the IMA battery switched OFF the 12 volt battery will NOT be charged.  So the distance you can drive is limited by how long the 12 volt battery can supply enough voltage to run the gas engine. It is possible to open the IPU battery case and disconnect the two front connectors from the BCM computer box and safely run the car as a gas only car for as long as you want to. The 12 volt battery will be charged and some people have run their Insight for years that way. Instructions how to disconnect the IMA battery can be found at    Google "disconnect battery" on the forum.  It is normal for several dash error code lights to eventually light with the IMA battery disabled.

Please note that the car will have a much slower acceleration rate at low engine speeds with the IMA battery not being used.  How much slower you ask? How 'bout if you are driving along in 5th or maybe even in 4th gear at 45 mpg and you floor the throttle and the car doesn't speed up? Down shifting to rev the gas engine up gets you going again.

The gas engine is tuned so it has to be reved up to develop its peak power (torque) at ~4500 RPM.  Normally the IMA system (electric motor) fills in the low RPM power band when accelerating briskly.  The Insight is also a high geared car to get better mpg, so that also limits the acceleration with the IMA system not working.  Luckily once you are cruising along you will get pretty much the same mpg as if the IMA system was functional.  But 0-60 mph is "Yes, it will do 60 mph."

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Doing a rejuvenation


The method I use to have an idea when it's time to stop the discharge is to record the battery voltage at the start and at each hour thereafter as the voltage drops to the voltage to the point you want to stop the discharge at.

When discharging a weak battery it may drop from 115  to 100 volts very quickly. Although even weak batteries may take 8 hours to completely discharge. It depends upon the condition of the battery and the discharge current used.

My charged 3 year old Honda battery in good condition took 18 hours to discharge to 0.1 v/cell starting at 265 ma. I did one rejuvenation cycle on it because it had started doing a negative recalibration every few weeks. I believe the negative re calibrations are due to the battery self discharge rate increasing and my not running the car everyday. The self discharge isn't seen by the BCM (battery control module) and finally the BCM detects that the SOC is not what it is indicating when one of the stick pairs drops below some level. The BCM would then initiate a negative recalibration.

If you start a discharge on a really weak pack at high current keep an eye on the voltage so you don't reverse charge damage the cells. Even if the total pack voltage is well above 108 volts there could be good cells keeping the total voltage high while weak cells are undergoing a reverse charge. With a low current discharge the cells probably won't be damaged even with the fan running to cool the reversed charged cells.

By recording the volts per hour change as the battery goes below 115 volts you can guesstimate how weak the battery is.  A quick voltage drop of ~1 volt in 5 or 10 minutes is a sign of weak a cell becoming completely discharged.

I usually let the battery rest an hour with the IMA fan running to dissipate some of the battery heat before starting the next phase of a charge or discharge cycle.  I also try to start the charge in the early evening so it runs when the ambient temperature is below 86 F.  Here in South Florida I haven't had to worry about the temperature being too cool since I bought my Insight.

When charging the battery, the high cut off voltage should top out at ~174 volts for a battery in good condition. Some people try to get as much voltage as they can. In one post on the forum  being over 185 volts!  This is not good!  

The exact voltage will vary depending upon various factors; battery internal resistance, charge current and battery temperature being the major considerations. Warm batteries show a lower voltage than if the same battery is cool even with the same SOC reading. If you start a grid charge in the late afternoon and it's cooler in the early morning than the evening before, it is not unusual for the voltage to have only changed a few 1/10s of a volt. As the ambient temperature starts rising throughout the day the battery voltage will tend to drop even though the battery is still taking a charge. As the temperature again drops during the evening the battery voltage will again rise.  As you can see there are many variables when working with a 120 cell series connected battery.

By watching the charge voltage change per hour you will see that the voltage increase rate per hour will start at 4 to 6 volts per hour and then taper off to ~0.2 volt per hour when the voltage is nearing 170+ volts.  At that point the cells of the battery that are are 100% charged will be producing a lot of heat. So it is important to not turn the IMA cooling fan off while charging..

The typical charge time for a battery will be 24 to 30+ hours. The discharge time varies greatly and is determined by how good the battery is, what current you discharge at etc. A complete two cycle rejuvenation is going to take days to complete.  But if you can get a year or two more life out of a weak battery it might be worth it.

The money you save on gas can pay for a new, better than a "new" Honda OEM battery from one of the forum vendors.  One Insight owner says he not only paid for the new battery by grid charging but for the car too!

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Poll of people who are building or finished one of my grid chargers

I would appreciate if you have ordered the parts, are building or have finished building one of my grid chargers that you go to my google spreadsheet. to give me an idea where you're in the build.  This article itself has been the most read of everything on my website so I am just interested in how many people have built a charger from it.  And of course no personal information is saved etc.

Thank you.

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