Battery packs exposed

The construction of the two packs is examined and compared, as well as some tips on keeping the pack in good condition.
WARNING, you can be killed or hurt fooling with the battery pack. Don't even think about working on or removing the pack if you are not fully confident in your knowledge of electronics. Get the service manual and electrical manual, and follow the procedures for safely removing the pack from the car.
The HV switch needs to be off whenever the pack is being worked on. The development of tools and hardware to replace defective cells will also be discussed.

Cleaning the corroded buss bars from a Prius battery pack


Cleaning the Prius hybrid battery buss bars

The prius hybrid batteries have been having cronic issues with the copper buss bars between modules getting corroded by Potasium Hydroxide weeping through the terminal seals. The effect is a crust of hard material that is non conductive, eventually causing battery failure.
I want to build up more of the 48V modules for my EV's, and wanted to find a way to clean the strips more efficiently than sanding and using steel wool, which can take as much as several minutes of hard work each.
I remembered my Dad showing me how to make old copper pennies shine buy dunking them in muriatic acid (Hydrochloric acid). I still had a container of the stuff which can be bought at most hardware stores, so I gave it a try. It immediately causes the crust to dissolve in a flory of bubbles, and then it stops, and the strip is mostly shiny copper. A thorough wash in running water finishes the job by washing off all the acid. Time will tell as to how it look a year from now, but it looks good now.

Forever solar desk lamp


Recycled Insight battery cells

We lost our power a week or so ago, and the usual search for a flashlight with good batteries was a pain in the A**.
In researching the Insight subpacks, I had to remove a weak cell from the stick to examine it. That left 5 pretty good D cells, the only problem being that they are welded together. I carefully used a dremmel grinder to grind off the welds, and in the end had 5 nice high rate NIMH cells. A few short pieces of heat shrink, and they were ready to be put to work. I installed them in a cheap LED emergency lamp, and made a small 4 cell solar charger.The solar panel current was passed through a diode so it would not discharge the cells at night. Now I am ready for the next power outage

Making a Cheap battery State Of Charge gauge more accurate


Making the SOC meter more useable

I had to buy some speed controllers and other EV parts for my yard machine, so I took a chance and got what was supposed to be a 36 Volt system battery SOC gauge.
kelly controller SOC gauge

I took out a variable voltage power supply, and checked the led display's SOC against a Trojan battery company equivalent voltage chart, and found that it was not even close. I could not use it as it was, and the thing was glued together with no way to get inside.I took my band saw and cut the outer tube so the back could be removed. The circuit looks like a series of resistors that make up a voltage divider and some op amp comparators to turn on the leds when the voltage rises over the voltage divider taps. This type of comparator can be quite accurate, but it depends on voltage references and precision resistors,which this unit does not use. What was most interesting was that there is a potentiometer on the circuit that can adjust the divider current to make the whole scale move up or down. I set the power supply to the 100% SOC voltage according to the trojan chart, and then adjusted the pot so the 100% led just came on. I then adjusted the power supply down until each led went out, and noted where the 50% SOC was so I knew when to get to a charger. While this setting may be a bit temperature sensitive, it at least made the gauge usable.
To gain access to the pot, without cutting open the whole case, drill a hole in the indicated place on the back cover and you should be able to adjust the gauge without cutting it open. Of course one could calculate the precision resistor values required for accurate SOC throughout the range, and replace the 10% resistors that they used, but relative SOC is all I need so simply getting the 100% and 50% points will be sufficient accuracy for me.

Solar headlight


carbon free light for years

Headlights are a great way to save energy, by taking your light with you rather than turning on room lights. I modified this headlight by punching a small hole in the side, and carefully soldered to the battery end terminals. The wires are run to a two terminal piece of some breakaway .1" on center headers. The solar panels are in series, and a diode is in series on the + lead, to prevent discharge of the cells at night. with 750MHA NIMH AAA batteries, a full day of sun will give several hours of light per evening. The batteries should last for years.

Insight Battery pack turbo cooler


Insight Battery Turbo Cooler

As any owner will tell you, when you are pumping charge in and out of the pack with MIMA, it can get hot, especially in summer. The battery is cooled with a two speed fan that draws air into the battery pack from behind the passenger seat inlet vent.MIMA will force the two fans on at full speed when the temperature of the battery gets over 95F.
I made a Turbo Cooler for my pack by ducting the passenger foot AC outlet to the battery pack input duct. I set the fan on high, and the duct to foot only. The driver side vent is ducttaped over, so that all the air comes out of the passenger side.
The increased air flow helps a lot, with mild MIMA use, but if you are really pushing the hybrid ratio to the electric side, the pack can still get into the 100 F range. Because of the large thermal mass of the heavy batteries, it takes a lot to cool them even a few degrees. To Turbo Cool the pack, I wait till I am going down hill, so the power is nearly free, and turn on the AC to full, set to 60 F. A long hill and you can cool the pack several degrees.

Those useful Prius subpacks

Prius NIMH batteries are called on to produce over 100A, and can be charged at 100A as well. I have been collecting the batteries and have quite a few, and have been finding some nice uses for them. I have several vehicles that I only use occasionally, and keeping a good 12V battery in each is wasteful, and is not that good for the batteries. I tend to carry a battery to the vehicle whenever I use it, and remove it when finished. Lugging a 50-75 lb battery over 100 feet is a lot of work. Just to see how it would work, I connected two 7.2V prius subpacks in series, and using a 100A Anderson connector, plugged them into a dodge caravan. The car cranked just like a new 12V battery. I put a connector on my 1965 John Deer tractor, and bang, it cranks effortlessly.
My lawn tractor uses the same configuration. The batteries do not need charge regulation, as the alternator or vehicle charging system will regulate to 13.6V , about 80% SOC on the NIMH.
A 5 lb starting battery compared to a 50 lb one. What a labor saver.


prius subpacks start van