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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 insightcentral.net/forums 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 insightcentral.net/forums/ 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.
How to build the grid charger/discharger
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