DIY V2 Grid Charger/Discharger
For less than $75

Latest updates:  7/27/2023 Added warning about non Honda IMA battery packs.
                         8/10/2023 Old style light bulbs not being sold any more.

Note:  If you want to host any of this material please use a reference to this website. TNX.

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

There are dangerous high voltages inside the charger and IPU.  You can be KILLED if you are careless and don't follow the safety instructions while building the charger and when installing the charging harness.

At the same time, if the IMA battery breaker switch is OFF and you follow the warnings given in this article and in installing the charging harness from installation instructions given from the web, it is quite safe to work on this high voltage system. If you are not comfortable working around high voltage, try to enlist the help of someone that knows what to do.  (Or just wear latex gloves.)

7/27/2023  In the course of time going by, it has been found on the Insight forum that discharging some non Honda IMA battery packs to low (below ~90 volts) or even zero volts may not be good for them.  So determine if your battery is an original or a non Honda replacement battery to play it safe when determining what voltage you want to discharge to.  One indication if your battery is an original Honda issue is the light orange color of the heat shrink that is covering the cells.  This color can be seen when the cover of the IPU box lid is removed. .  

10/19/2023  I've been informed that some non Honda IMA battery packs have the light orange heat shrink.  If your pack has that color I would ask where you bought the car from about the manufacturer of the pack. One of the reasons why I bought the Insight I have is that the glove compartment was full of the dealer invoices for oil changes and other maintence work done on the car for the original owner.  My battery is a Honda waranty replacement battery which was installed in my car in January 2013.  It loves a discharge to zero volts overnight.

Select articles from the list below.

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 battery is 144 volts.  A pack will typically run between 156 to 165 volts while in use.  Ni-MH cells have a rather high self discharge rate of up to 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.

The IMA battery pack is normally charged (if needed) 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.

More information about all this can be found at the  Do a search for "grid charger".  I also have a forum link if you have any relevant questions concerning the V2 charger or usage.

The battery control module (BCM) has many features to safely control the charging of the battery so that it operates between 20% and 80% of the IMA battery 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.

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 24 to 35 hours. This 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 maintance grid charged once a few times a year 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 gets it's input power from the normal home power grid (the wall sockets).  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 are not correct for our purpose.

The grid charger also powers the normal Insight 12 volt IMA battery cooling fan to insure that the IMA battery pack doesn't overheat due to the extended low level charge. There is also a fan inside the grid charger to cool its components.

General features of this charger

This article is an idea provoking one to present how my V2 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 etc will vary in size from the parts I used. And truthfully I don't want to encourage people to copy my designs 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 online, eBay and if you are into building electronic devices, probably from your junk box.  If you are familiar with reading schematics, soldering and using hand tools you should have no problem building your own charger.  You also have to open the battery box (IPU) behind the Insight seats under the hatch storage area to install a charging harness.  You can find information how to install the harness (some with videos) on the Insight Central forums.

When I built this charger in November 2019 the Mean Well HLG-60H-C350A LED power supply cost me $36.  I had all the other parts in my "pre-owned" [junk] boxes including the used computer power supply case, a 3" square cooling fan to replace the huge original fan, the switches and other parts.  Naturally your cost will vary depending upon how many parts you already have.  The total parts price is typically less than $75.

One of the aims of designing the V2 grid charger was to eliminate the terminal strip and some of the other discrete parts used on V1 charger.  I accomplished those goals with V2.

If you can find a local computer repair shop you can probably buy a junked ATX power supply with a top mounted fan for the charger case, 3" square fan and the AC line cord etc.

The Mean Well power supply is much longer than the average PC computer power supply case.  The Mean Well supply will normally not fit in a side mounted fan case.  I have some junk power supplies and one of the supplies was rated at 450 watts output. That case is slightly larger than lower wattage supplies. The length and width of the 450 watt supply is 6.125" x 5.875" measured at the bottom of the case. By bending three of the power supply mounting tabs upwards the supply will diagonally fit into the slightly oversize case.  This is shown in the pictures further down this article.

You will need to replace the huge top mounted fan on the power supply case you use with a smaller fan to gain more vertical space inside the case. Since the grid charger really doesn't generate much heat that needs to be dissipated a smaller fan will work fine.  So bring a ruler when buying a junk power supply.  If you don't have a 3" square cooling fan you may have to buy another junk supply to get the rear mounted 3" fan.  Top mounted fans tend to be much thicker and run slower than the smaller fans.

One builder, MparkH, a member of the insightcentral forum, mounted his Mean Well power supply rotated so one side of the supply lays on the bottom of a normal computer sized case.  The case he used also has the fan located on the side instead of on top of the case.  To read his excellent description of how he built his charger for about $59 (not including s/h) from these plans, click the following link,

With luck you may find some of the parts on the computer junk power supply printed circuit board to use in your DIY charger/discharger. I found the 100K ohm resistor on one junk power supply PCB.  If the PC computer power supply board uses 4 individual diodes mounted close to each other on the AC high voltage side of the PC board, one those diodes may be used in the grid charger (see schematic further down this article).  You should remove the small 2 pin connector on the PCB that the fan wires connect to.  It will be used on the grid charger to connect the charger cooling fan to the charger 12 Vdc power supply.

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Preparing case to build charger

The original power supply printed circuit board should be removed and discarded.  If the case has a 115-240 AC voltage input selection switch mounted near the AC power cord socket it should be removed.  The rectangular switch opening left in the case can be used to mount the panel mount fuse holder by enlarging the opening with a hand tapered reamer.  Luckily my case has a rear mounted power ON-OFF switch which is now used as the power switch for the charger.  If your case doesn't have a power switch you will need to buy two SPST switches (SW1 and SW2).  One switch is used as the charge/discharge switch and the other for the charger AC power ON-OFF switch.

I used #4-40 sized hardware to mount the various front panel parts and power supplies to the bottom of the case.  After the charger was built and tested I installed four rubber feet on the bottom of the case where the PCB mounting holes were located.  The rubber feet keep the bottom mounted screw heads from snagging on the car's carpet while charging the battery and allow space on the bottom of the charger for air flow to act as an additional heat sink for the Mean Well power supply..

For the V2 simple grid charger I've switched to a dual volt/amp meter since the V1 meter isn't available on eBay anymore.  The volt/amp meters sold now on eBay can't sense or display the (negative) discharge current. The volt meter will show the battery voltage while discharging but the ampere meter will show 0.000 ma [discharge].  Such is progress.  :-(

If you want to see a preview of what meters are available do an eBay search for "200V 10A 4 digit meter". I've done a several hour eBay search several times but haven't found any of the dual meters that can read the discharge current.

So for now I would stick with the cheaper 4 bit dual red meters that do not display discharge current.  By using the light bulb vs current chart (way down this article) you can select what current you want to flow at the beginning of the discharge. Or you could buy a dedicated current meter and wire it up on your discharge load.  If you don't have or can't buy 2 old style light bulbs buy a 500 ohm, 100 watt wire wond resistor as the dummy discharge load.  I would mount it on a good sized heat sink because it will get very hot at the start of a fully charged IMA battery discharge.

The dual reading meter is powered by a separate small isolated switch mode power supply with an output voltage between 4 to 30 volts at less than 30 ma requirement.  I used a small 5 volt, 100 ma cell phone wall wart charger to power the meter.  The meter power supply must have the output isolated from the AC input and chassis ground.  This is necessary because the meter negative DC power lead (thin black wire) is internally connected to the thick black lead which is used to measure the voltage and current of the charger.

The IMA battery charging voltage is created by the Mean Well  which delivers 100 to 200 volts (depending upon the battery voltage) at 350 ma constant current.  The V1 charger used two 45-90 V, 350ma current limited supplies wired in series but they are just not offered on eBay anymore.  The Mean Well supply will not taper the charge current as the battery reaches 100% (~174 volts) since the voltage is in the area of constan current.

The Mean Well supplies are normally used to power strings of LEDs for lighting or special affects. The Mean Well supply is protected for short circuit, over temperature and other features which are desirable. The power supply case is aluminum and will dissipate heat much better than the plastic cases used on other LED supplies.  Even more heat can be dissipated by mounting the supply on the bottom of the metal case of the grid charger.  The Mean Well is a well designed, sturdy supply which is much better than the cheap supplies used in V1 of the grid charger/discharger.

I use a series output diode on the positive DC output lead of the Mean Well to keep the IMA voltage from back biasing the supply when the front panel switch is set to discharge mode. This allows you to read the battery voltage while discharging the battery.  The 100K resistor is used to speed up the discharge of the high voltage of the Mean Well supply when you switch to "Discharge" or power OFF.  Without the resistor (commonly called a "bleeder resistor") the supply will take much longer to reduce the high voltage to safe levels if you need to tinker inside the case.  I connected D1 and R1 right near the charging harness socket on the front panel.

If a diode(s) is used on the charging harness or within the IPU case 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(s) inside the IPU case.   For that reason I you should not install any diodes in the high voltage portion of the charging harness.

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 housing with a space up to 1/4" wide along the fan sides.  Use some RTV or other flexible caulking to fill in the gap to increase the cooling affect of the fan.

As a safety feature I would install a fuse on the positive high voltage lead when you install the charging harness in the IPU.  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.  The 2 amp fuse should be rated for 250 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!  A DC fuse can generally be identified by the white ceramic looking body between the metal end caps.

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Construction and description of how to build a grid charger

V2 charging battery

This is a preview of what the V2 grid charger looks like while charging my battery.  You need to use a 4 digit meter so tenths of a volt are shown. As the charge proceeds the battery voltage rise decreases drastically.  The V2 version charge current is 350 ma, the battery voltage rise will slow to 0.2 volts per hour after reaching ~172 volts!  Without seeing the 1/10s volt display you would not realize that the battery still needs to be charged for a good bit of additional time.

I found that the dual meters with a blue LEDs are almost impossible to read outside during the day when viewed at an angle to the front panel. For that reason I strongly recommend buying a 4 digit meter with both displays being red.

The 0.5 digit in the above picture appears to not be lit properly.  It really was lit to the eye when the picture was taken.  Even though the meter updates many times per second the camera shutter was even faster and it caught the .5 not quite fully lit.

The left side 4 pin Molex connector is the charging harness socket.  I used the normal computer power supply convention of the yellow wire being a higher voltage than the red wire.  The two black wires are not common ground connections but rather the left black wire is the isolated from the chassis negative lead for the high voltage (yellow) wire and the right black wire is the chassis negative lead for the 12 volt fan voltage (red) wire.

The SPST switch is the charge/discharge switch which turns OFF the Mean Well supply during discharge, the dual meter and finally the two pin discharge cable socket.  The AC power switch is located next to the rear 120 Vac socket on this power supply case.

For convenience to identify which switch I'm writing about I will call the charge/discharge switch the "mode" switch from now on.

To make it easy to remember what mode the switch is in I would mount it so when the switch handle is pointed upwards that is the charging mode. Down will be the discharge mode.  Easy to remember, up to charge, down to discharge the battery.

When the mode switch is set to the charge mode with the charging harness not connected the volt meter will read ~200 Vdc and zero current flow. If the charging cable is plugged in the meter will indicate the IMA battery voltage and the charging current accurate up to 3 decimal places as 0.350 A (350 ma).

When the mode switch is set to the discharge mode with the discharge load -not- plugged in the volt/amp meter and current meter will both read zero.  While discharging the meter will display the battery voltage and 000.0 A discharge current.

To see an enlarged view of these pictures, left click on the picture.
Rear panel

This is the rear of the charger showing the rear mounted ON-OFF power switch, the panel mount fuse holder and the 120 Vac socket.  Use a 2 Amp DC fuse.

The fuse holder is mounted where the original 120-240 voltage switch was located.  I used a hand reamer to enlarge the rectangular opening so the fuse holder could be mounted in place of the switch.

You will probably want to mark the underside of the cover where the AC socket etc is located so the cover mounting screw holes will line up with the holes on the front and rear panels of the case each time you put the cover on while trial fitting the cover with the 3" fan mounted so it doesn't interfere with the internal parts.
cell charge

This picture shows where the power supplies are mounted. The small roundish 5 volt power supply is used to power the front panel meter.  It is mounted to the bottom of the charger case with the original screw that holds the top and bottom covers together.

There no mistaking the huge Mean Well 200 volt, 350 ma power supply. It is bolted to the case with two #4-40 bolts, one at each end with washers and nuts.  The case was used for a 450 watt power supply and is a little larger than most cases at 6.125" x 5.875".

The rectangular box near the AC fuse holder is a 12 Vdc, 1.25 Amp isolated switching power supply that runs the charger and IMA cooling fans.
LED spacing

This picture shows the top cover mounted onto the bottom of the case. The horizontal line near the bottom of the cover is where the top cover panel is indented and is tucked in behind the lip of the bottom of the case.  You should not mount the Mean Well right up against that lip or the top cover won't fit properly.

LED supply spacing

This view shows the left side of the front panel.  The socket on the left of the picture is the discharge socket,  The dual meter is in the middle and the green switch is the mode switch..  I used hot melt glue to hold the meter and wires in place.  The case metal is so thin that the normal meter tabs couldn't properly hold the meter tight to the front panel. Hot glue came to the rescue for that.
AC wiring

This is the right side of the front panel. The male 4 pin Molex connector assembly which I sawed off the corner of a junk hard drive is hidden under all the wires!  D1 and R1 are connect directly to the high voltage pins of the charging harness socket.  This eliminated the terminal strip.

The small 2 pin male-female connector is the 12 Vdc to the cooling fan. The 12 Vdc power supply is partially visible to the right of the Mean Well power supply. The 12 volt supply is held to the bottom of the case by two #4-40 screws. Be careful and do not run the screws into any of the power supply components.


This is a close up of the 4 pin Molex socket showing where D1 and R1 (see the schematic) are mounted.  This eliminates the terminal strip that V1 of the charger used.

The curved white 2 conductor wire goes from the 12 Vdc switching type power supply  to the 12 Vdc fan +/- pins of the charging harness socket.

The socket is mounted on a piece of the socket mounting metal from the corner of the hard drive which in turn is fastened to the front panel with two #4-40 screws.
The picture to the left shows the small 3" square cooling fan mounted in place of the huge original cooling fan opening.  The original fan was so thick that it wouldn't allow the top cover to be properly mounted to the bottom of the case because of the height of the Mean Well power supply underneath the fan..

You will have to check the clearance between the fan and fuse holder when mounting the fan.

I have found that the charger power supplies run at the ambient cabin temperature  while charging the battery and there is more than enough air flow with the 3" top mounted fan.  The fan blows air into the case.

This is a short list of the somewhat unusual tools you will need to build the charger, a tapered hand reamer, a hand nibbler, a small hand drill with drill bits and a center punch.  It took me about 38 hours to build the charger.

V2 grid charger schematic

Bill Of Materials
Part designators
F1     (Note 2)
J2      (Note 4)
M1    (Note 1)
PS2  (Note 9)
PS3  (Note 9
R1    (Note 2)
SW1, 2

Description                                                                                   Vendor
1N4007, silicon diode 1amp, 1000  V ........................................... Various suppliers (a 1N4004 through 1N4007 may be used)
250 volt, 2 amp fuse and holder ......................................................Various suppliers, fuse holder
3" square 12 Vdc fan ...................................................................... From a computer power supply with a rear mounted fan
Male line cord plug ......................................................................... Part of power supply case
Molex male 4 pin ............................................................................ Charging connector cut from corner of a HD
Dual red LED meter, 200 volt, 10 amp  ........................................... eBay item, buy a meter with both displays being red
Female 2 pin connector ................................................................... Any 2 pin connector rated for 200 Vdc to match male plug
100-200 volt, 350 ma LED constant current  LED power supply  .... Mean Well HLG-60H-C350A from various distributors or eBay
5 volt cell phone charger  ................................................................ eBay item  (To power the dual LED meter) actually 5-30 volt is OK
12 volt, 1.25 amp minimum regulated switching power supply  ........  eBay item  (To run the cooling fans) the smaller the better
100K ohm, 1/2 watt resistor  .......................................................... Various suppliers  (Any tolerance value will work)
SPST mini toggle switch  ................................................................. Various eBay suppliers (only 1 switch needed if case has SW2)

  1. There are many dual voltage/current meters listed on eBay now, but please, only buy a 4 digit meter that can display 1/10s of a volt.
  2. 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. With luck you may find the resistor and other small parts on the junk computer supply PCB.
  3. Use the case cooling fan connector from the junk computer power supply PCB to match the one on the fan wires.
  4. I cut the Molex 4 pin male connector from a junk hard drive for the charging connector on the grid charger.
  5. I used a  male 4 pin Molex female computer power supply connector on the end of the charging harness.
  6. I have found flexible covers for the harness 4 pin Molex female connector on the power leads of Dell computer power supplies.
  7. Instead of using a dedicated 4 wire cable, you can use four lengths of stranded AWG 22 (the minimum size wire) each about four feet long for the charging harness from the IMA battery connections to the charger.  Place the completed harness in insulated tubing.  I found the wire and the split plastic tubing at an auto junk yard.
  8. My charging cable comes out of a gap at the bottom of the rear right corner of the IPU case next to the floor of the car body.
  9. I used two small wall warts for the low voltage power supplies.  They must be isolated DC output switching type power supplies.
  10. Since normal 20 watt light bulbs are made out of unobtainium now I would buy a 500 ohm, 100 watt wire wound resistor as the discharge load.

First check of grid charger

Where possible I test each power supply as I get them mounted and wired partially into the circuit.  I use a normal AC power cord with alligator clips on each lead to temporarily connect the power supplies to 120 Vac and measure the output voltages with an external voltmeter.

You can calibrate the charger meter before it is mounted in the case.  And it's easier to get at the calibration adjustments.

But first, here are a few bits of information:
  1. In the calibration instructions of the charger I will use the term "DVM" to indicate a known accurate VOM or DVM for calibrating the charger voltage and  current meter.  You can also use several meters and average the readings to calibrate the charger meter.
  2. While working on the charger it is OK to disconnect the charger cooling fan. Don't forget the fan connector is polarized positive and negative so you must connect it properly to the 12 Vdc supply circuit.  I marked the plastic fan connectors with a red marking pen so I have a quick guide for connecting the fan correctly.  I have found that the temperature of the various charger power supplies are basically the ambient temperature inside the car.
  3. If the cover is off the grid charger, be aware that there are exposed 120 Vac connections in addition to the 200 Vdc connections just waiting to shock the didily out of you.  The charger no load DC voltage is higher than the IMA battery voltage!  So be careful.
  4. To work on the charger I always set the mode switch to discharge first and wait until the HV meter shows less than 15 Vdc.  Then I turn the power switch OFF and unplug the AC cord before sticking my hand(s) into the grid charger.
  5. R1, the 100K resistor causes the high voltage to discharge quicker than just the bleeder inside the Mean Well supply. I found it on a junk power supply PC board.
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Calibrating the multimeter

You will probably need to check the accuracy of the charger multimeter.  The meter current calibration pot is labeled IR and the voltage calibration pot is labeled VR.  You will need a very small, short flat blade insulated handle screw driver to set the calibration pots.  The C350A version of the Mean Well power supply has an internal constant current adjustment potentiometer located under a flexible plug located on the top of the case.  I found that I did not need to adjust the current output of the supply.

The first check of the charger meter is done with not having anything connected to the chargers output connectors.  
  1. Connect the AC power cord
  2. Set the power switch to ON
  3. The voltmeter should show close to 200 Vdc and 0.000 ma current with no load on the charger.
At this point you could calibrate the voltage portion of the meter by connecting an acurate DVM to the high voltage output of the charger and adjusting VR pot on the meter to read the same voltage as the DVM is showing.  To adjust the current pot (IR) you need a load that can handle up to 200 Vdc and 350 ma DC. The load needs to be able to dissipate a maximum of 70 watts.  Several choices are available, the 500 ohm, 100 watt dummy load wire wound resistor, the two bulb dummy load (see information how to build the load below) or the IMA battery itself.

I origianlly used two 60 watt 115 Vac light bulbs as the discharger load to calibrate my meter.  One builder found that his Mean Well supply would not output any voltage or current with the two 60 watt bulb discharger load.  Yet his charger does charge the IMA battery OK.  In that case use two 40 watt bulbs to calibrate the meter current reading.

The Mean Well charger will not output any voltage or current if the load will present a load that would require less than 100 Vdc within the 350 ma current limiting capability of the supply.  Apparently the supply outputs a test voltage to see if the load (the IMA battery or dummy load) would result in less than 100 Vdc at 350 ma.  If that combination of voltage/current is detected the supply shuts the output down until that load is removed or the battery voltage rises above 100 volts. This will be discused in more detail further down this article.

When you turn the Mean Well AC power off after an overload, it resets and will work properly when the output voltage is (again) above 100 volts.

I sometimes use an aluminum cased 500 ohm, 100 watt wire wound resistor mounted on a large heat sink with a fan to cool the resistor as the dummy load.  The Mean Well will output 175 volts at 0.350 Adc using the 500 ohm resistor.  This means the charge current will not taper off when the battery is 100% charged.

The twin 60 watt light bulbs dummy load should show ~130 Vdc and 0.350 Adc vs 175 Vdc using the 500 ohm resistor.  This is because the lit resistance of the bulbs are not 500 ohms when they are driven by the 350 ma constant current supply.  Old style light bulbs exhibit a lower resistance when cold vs when they are hot and drawing current.

You can also connect the charger temporarily to your IMA battery to calibrate the dual meter using the procedure listed below.  For a short test you do not need the battery cooling fan running.

Be very careful, the charger will have 120 Vac AND up to 200 Vdc voltage floating around inside the case waiting to shock you if you touch an energized wire when the power and the mode switch is set to charge.  If you want to play it safe wear a pair of latex gloves, no metal wrist watch bands etc

Here is how to calibrate the dual volt/amp meter using the light bulb discharge load and two external calibrated DVMs.  Temporarily wire the two DVMs, one to read the discharge load voltage and the other read the charging current.  (Or use one meter and reconnect it as necessary to read Vdc or the current.)
  1. Set the power switch to OFF
  2. Connect the two 40 or 60 watt light bulb discharge load to the discharge port of the grid charger with a DVM meter wired to read the charge voltage or current
  3. Set the mode switch to Charge
  4. Set the power switch to ON
  5. The meter should show ~130 Vdc and ~0.350 Adc (be careful the bulbs will get pretty hot after a bit) when using two 60 watt bulbs
  6. If the readings are not close to the DVM values you will need to adjust the VR and IR pots to calibrate the meter.
My RL chart (shown below) was done with a variable high voltage power supply and two DVMs, one reading the voltage and the other current.  You can use various combinations of bulbs as the dummy load as long as the combo will draw 0.350 A.  You want to draw as close to 0.350 A as possible because that is the current the IMA battery will draw while being charged.

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How to make a discharge load (the dummy load)
8/10/2023 Note:  Now that the old style light bulbs are not being sold in stores I would recomend using the 500 ohm, 100 watt resister shown in the discharge data chart.  Mount it on a large transistor heat sink.  Be careful because it will get very hot at the beginning of a discharge.

The actual discharger I use consists of two old style light bulbs and two ceramic light sockets 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 is made by using 120 volt light bulbs of various wattage combinations wired in series. Nothing exotic about that, just wire the two sockets in series like Christmas tree light bulbs and attach the 2 wire discharge cable to each of the single free terminals on each socket.
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 go between the sockets.  There is another short trench from one socket for the two wire discharge cable to leave the board.  I used a matching 2 pin male connector on the end of the cable to plug into a 2 pin female connector on the grid charger.
The picture on the left 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

I used a long two wire cord from a vacuum cleaner (with the plug changed) so I could have the discharger sitting in my closed garage to have an idea how the discharge is going. Since I took these pictures I have added two short nails sticking up between the sockets with one nail wired to the positive lead of the discharge cable and the other nail connected to the negative lead of the discharge cable.  This allows me to have the discharge load in my garage with a voltmeter connected to the nails to read the battery voltage remotely.

A normal VOM won't require any power for it to continuously display the voltage.  I use an old Simpson 260 VOM for this job.  As old as it is it still reads the same as my DVM.

Some people use dual bulb "Y" sockets designed for wall mounting to make the discharge load.  They have two wires on each socket that can be wired in series.  You don't have to route the board 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 by having a switch on one of the sockets.

While the battery is being charged the batteries will get very warm so you MUST run the battery pack cooling fan at the same time. If you turn the fan off after charging the battery temperature will continue to rise for many hours due to the stored heat IN the cells in warm weather.  The cooling fans run any time the charger is switched to ON.

If you want to get fancy you could even have a current meter setup at the dummy load to read the current by connecting an amp meter correctly in series with one lead of the discharge load cable.

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Current vs light bulb wattage at various battery voltages

I vs V for light bulbs * 100 Ω resistor
Click on the chart to see it full size.

I did bench tests on various wattage incandescent light bulbs to help understand the current vs voltage change. I also checked the current flow using my 500 ohm, 100 watt resistor for comparison. The data is presented on the chart above. Use this chart as a guide to what wattage bulbs to use depending upon what current you want to start discharging the battery at.  Typically I starrt near 0.270 ma. using two 40 watt blulbs.

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 my finger if I 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 time.  

If you use light bulbs I recommend using two bulbs wired in series to do a discharge.  If you use one 120 Vac light bulb it will greatly shorten the bulbs life if you start discharging from a battery voltage higher than 120 volts.  If the bulb blows out due to the high voltage you will waste time if you aren't around to monitor the discharge.  As it is, a two cycle rejuvenation is going to take days to accomplish. You don't need another day added to the task if a bulb blows.

You will have to wire up an external current meter to check the actual discharge current and perhaps use different size bulbs in various combination to get the current you want at the beginning or end of the discharge.  Personally I use two 40 watt bulbs and when the voltage gets below 20 volts I replace one of the bulbs with a shorted screw in adapter to raise the current up a bit.

Old fashioned incandescent light bulbs are pretty much impossible to find and CFL or LED bulbs will NOT work. Old halogen flood lights work fine and have the same curved discharge current vs voltage as the normal old fashioned bulbs.

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Information about rejuvenating a battery

First off you might ask, "Why even discharge the IMA battery?" That is a good question.

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. Just like a steel chain, the weakest link (the weakest cell in our case) determines how strong the chain is. This due to the 120 cells being wired in series like Christmas tree lights.

The batteries can usually be brought back to usable capacity by properly grid charging them.  This is called "balancing the battery",  "a balancing charge" [or actually] "a trickle charge".  New batteries ought to be grid charged three or four times a year after the first 6 months to a year of use.  Think of it as a maintenance chore to keep the battery pack balanced over time.  This will extend the life of the battery.  My Honda warranty IMA battery was replaced in Jan 2013 and is still going, not like new but for the way I drive, it does work OK.

The purpose of discharging the Honda IMA battery for a rejuvenation is to discharge all the cells down to a fairly low or even zero voltage. This causes chemical reactions within the cells which in turn will cause the weak cells to be in a condition to gain capacity while being charged again.  Discharges to only 100 volts etc just isn't enough to do much rejuvenation of the cells.

Unfortunately when discharging an unbalanced battery pack the weak cells will discharge to 0.9 volts (the rated "discharged" voltage condition) much quicker than the good cells.  Even when the battery pack reads a little below 144 volts some of the week cells could already be fully discharged.  Typically the weak cells will not only discharge to 0 volts but they will be slightly "reversed charged" by the discharge current while the good cells in the pack continue being discharged.

High discharge current of reversed charged cells is not good!  Using too high a discharge current with cells reversed charged can result in those cells overheating with possible venting and even leaking which will cause all sorts of problems over time.  It has been found that 0.350 A (ampere) discharge current is a safe current to start the discharge.

To rejuvenate a battery you should do 1 or 2 charge/discharge cycles with a final grid charge.  The first cycle starts with a 0.350 A charge of 24 to 35 hours to fully charge the battery to ~174 volts, followed by a discharge to a desired low voltage.

Different discharge cutoff voltages have been put forward by members of the  I used to discharge to 10 to 15 volts.  There is a technical paper by Robert Huggins here (see pages 226 to 233) that indicates that there is some merit to this approach.  By experimentation, Insight Central members have found this procedure does work.

Recently tests have been done by forum members that completely discharge the battery pack to zero volts.  I allow my discharge to go to zero volts by leaving the discharge load on the battery overnight.  After my usual one cycle charge after the discharge the battery is performing better than a discharge stopping at ~12 volts.

It has also been found that batteries that have sat unused for many 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.

A few years ago found an Insight that had sat outdoors for 10 years not being driven or run.  The car was in sad condition.  I was allowed to take the battery out of the car to attempt to rejuvenate it.  The complete battery pack measured 8/10 of a volt before I did anything to it!  After two rejuvenation charge-discharge cycles to 15 volts followed by a final grid charge the pack sticks were very well balanced.  Unfortunately the car wasn't in running condition to drive it on the road to test the battery.  

As a test, I allowed the battery to sit with the IMA master switch OFF for two years and the battery voltage was reading 90 volts due to self discharge on 12/8/2023.   I am now grid charging the battery to see if the self discharge changes differently than the first discharge test. .

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 roughly about 1% per DAY.

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.  The cars normal charging current only charges the IMA battery to ~80% SOC (not 100% SOC) and has much too high a current level to do a proper balancing or re-forming of the battery.  A discharged battery caused by sitting unused is a great candidate for a rejuvenation though, so don't loose that opportunity by letting the car charge the battery.  And it is a great bargining chip if you are contemplating buying an Insight with a "shot" 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 switch is located under the rear deck carpet under a small removable panel with a 10 mm wrench.  An error light will light up on the dashboard, this is normal.
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.

The IMA master switch is located under a small cover on the top of the battery box (IPU) at the rear 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 battery disconnect switch that needs to be lifted off the handle so you can switch it OFF.  Replace the clip so you don't loose it.

It is possible to open the IPU battery case and disconnect the two connectors towards the front of the car on the Battery Control Module (BCM) case 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.

Please note that the car will have a much slower acceleration rate at low engine speeds with the IMA battery not being used. The gas engine is tuned so it has to be revved up to develop its peak power (torque) at ~4500 RPM.  Normally the IMA system (electric motor) fills in at the low RPM of the gas engine.  You will get normal high mpg numbers once you are cruising along.

Finally, as they say in some TV advertisements, "But first .........."  
If you have installed one or two diodes in the high voltage charging harness you will NOT be able to read the battery voltage or discharge the battery. You must remove any diodes in the HV lead(s) of the charging harness.  The diode(s) to remove are not inside the charger, but on the connecting harness from the charger to the battery itself.

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Hints to help you use the grid charger

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 were you want to stop the discharge at.  You will find the volts per hour change will start at 4 to 6 volts per hr and will taper off to below 0.5 volt per hour.  A weak battery may drop from 115 to 100 volts very quickly as cells drop out and become reverse charged. This is normal.  With a low current discharge the cells shouldn't be damaged with the cooling fan running.

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 a weak cell(s) becoming completely discharged.  Pay close attention to the battery voltage at that point if you are not discharging to zero volts.

After you terminate a discharge by disconnecting the load, the battery voltage will rise up to some higher voltage rather quickly.  A weak battery discharged below 100 volts will typically rise back to 120 volts or more.  A really good battery will not rise as much. It is permissible to start the discharge again to pull the battery back down to the final goal voltage but keep an eye on the voltage because it will drop to your desired cutoff voltage quicker compared to the initial discharge.

When charging the battery, the high cut off voltage should top out at ~174 volts for a battery in good condition.  The exact voltage will vary depending upon the battery temperature and charge current.  A warm battery will have a lower voltage than a cool battery at the same point in a charge cycle.

A weak battery may show higher than 175 volts due to higher than normal internal resistance (IR) of the cells.  The higher the charge current, the higher IR voltage drop which will cause the total battery voltage to appear higher while charging.  As you can see there are a lot of variables when working with a 120 cells connected in series.

By watching the charge voltage change per hour you will see that the voltage increase rate per hour decreases with time.  My old V1 grid charger with a 265 ma charge rate started at 4 to 6 volts rise per hour and then tapered off to ~0.2 volt per hour after the voltage was above 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 cooling fan off while charging or discharging.

The typical charge time for a good battery is 24 hours to 35 hours. The discharge time varies greatly and is determined by how good the battery is etc. A complete rejuvenation is going to take days to complete.  But if you can get a year or 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 OEM) battery from one of the forum vendors.  One Insight owner posted that he not only paid for the new battery by grid charging (in the gas savings as compared to his other vehicle) but for the Insight too!

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Do a rejuvenation (Finally)

The basic procedure to do a rejuvenation is as follows, the battery should first be grid charged to 100% state of charge (SOC) 174 Vdc to balance the cells as much as possible, then slowly discharge the battery, then charge it again.  That is considered to be one rejuvenation cycle.  Really weak batteries respond better to doing the charge/discharge/charge sequence 2 or even 3 times in a row.  One sequence will take several days to complete. And with simple grid charger/discharges you need to monitor the voltage to turn the charge or discharge off if not going to zero volts overnight.

Various cutoff voltages of the discharge are recommended by different sources.  I typically discharge my battery in one long discharge to below 15 Vdc starting the discharge at 0.350 A.  A full discharge can take many hours depending upon the condition of the battery and the discharge current.  As the battery voltage goes down you may want to change to higher wattage bulbs to keep the discharge current above  10 to 25 ma.

As the battery pack is discharging the weaker cells will discharge quicker and will actually suddenly start being reversed charged by the current caused by the rest of the battery pack. Through experimentation on the InsightCentral forum it has been found that if the cells are reversed charged at a low current (typically no more than 350 ma), that no damage will occur to the cells..

When the battery discharges to the voltage you want, set the dicharge load switch to OFF. The battery voltage will rise to above 100 volts rather quickly. This is normal. and you need to allow it to happen.  My battery voltage normally bounces back to 120 volts or so in less than 30 minutes after removing the discharge load.  Keep the battery cooling fan running at all times.

If the voltage doesn't rise above 100 volts after waiting awhile, this could indicate your battery is really sick. 

Here's why you need to wait until the battery is above 100 volts:
The Mean Well power supply will not charge the battery if it is below 100 volts because a protection mode called "Hiccup mode" kicks in.  The charger will output charge voltage when the voltage rises to more than 100 volts.

If you are trying to rejuvenate a battery that sat for many years and is below 100 volts, go to Charge dead battery to >100 volts which is located below this article for information how to charge the battery to 100+ volts.

I usually let the battery rest for an hour with the IMA fan running to dissipate some of the battery heat before starting the next charge 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 normally don't have to worry about the temperature being too cool.  60 is cold to us!

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Charge dead battery to >100 volts

Note:    If you just discharged the battery to below, 100 volts just disconnect the load and the battery will quickly rise above 100 volts within an hour.

The Mean Well power supply will not charge the battery if it is below 100 volts because a protection mode called "Hiccup mode" kicks in.  The charger will power back up when the voltage rises to more than 100 volts by switching the charger OFF for a few seconds and then back ON again..

What this means is if your battery has sat around unused for a long enough time that the total pack voltage is below 100 volts you will have to charge into the battery to raise the pack voltage a little above 100 volts at a charge rate of 350 ma or less.

If the battery pack is below 12 volts I would recommend that you use either a variable low voltage DC supply or a normal 12 volt battery charger to wake the battery up. By using a variable 12 volt power supply I could keep the charge current to 100 ma by slowly adjusting the voltage higher or lower over about a 1 hour time.

If using a 12 volt battery charger, I would wire a normal low wattage 12 volt car light bulb (for instance a Philips #1895, 12v, 3.8 watt bulb) in series with the positive lead of the charger to limit the charge current to wake the IMA battery up. Don't use a stop light or headlight bulb. They will pass way too much current through a less than 12 volt battery pack.

The bulb should light up fairly bright at the beginning of the wake up period and get dimmer as the IMA battery comes up to 12 volts.

Even a regulated, low current 12 volt phone charger might work without a bulb. Naturally be aware of the polarity of the connections.

Once the battery comes up to near 12 volts I would remove the series bulb and connect the 12 volt charger directly to the IMA battery for another hour. There are chemical reactions going on at even that low per cell voltage.

Now that battery is awake again, here's a way to allow you to get the IMA battery above 100 volts.  

Build the discharger load and install two 40 watt bulbs in the sockets.  Using a VOM or DVM you should see about 60 ohms at the cable end of the discharger harness when the bulbs are cold.  Set the switch on the discharger load to OFF

Follow these steps to start charging the battery to above 100 volts:
1. Set the IMA battery master switch to OFF
2. Temporarily wire the discharger in series with the positive lead of the charging harness to the normal battery positive connection point at the battery. The negative charger lead should be connected directly to the normal negative lead connection point at the battery
3. Set the grid charger Mode switch to discharge
4. Set the IMA battery switch to ON
5. Set the gridcharger AC switch to ON, after a moment you should see the IMA battery voltage of about 12 volts showing on the charger voltmeter but no current flowing
6. Set the gridcharger Mode switch to Charge, wait till you see ~200 volts on the meter (the Mean Well has to go through some self tests before outputing high voltage)
7. Set the discharger load switch to ON, you should see the bulbs light and charging current on the meter
8. Use a seperate meter to read the actual battery voltage since the charger meter won't be showing the true battery voltage with the series discharger load connected.  Allow the charge to continue until the battery shows  ~105 or so volts.  
When the battery has been charged above 100 volts do the following steps:
1. Turn the charger OFF
2. Switch the IMA battery master switch to OFF
3. Wait 30 seconds or more for the charger and battery voltages to drop to zero volts
4. Disconnect the discharger load from the charging harness
5. Reconnect the positive lead of the charging harness to the battery lead connection point.
6. Set the IMA battery master switch to ON.
You can now give the battery a normal grid charge to 174 volts at 350ma with the cooling fans running etc..

I would definitely read and record the stick voltages after waiting an hour or so after each charge to see how balanced the sticks are.

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