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.
Well I cooked some more prius subpacks. This time was 10A for several hours. I am not going to do this again. I have a lot of microswitches in my surplus drawers, so I will add a switch in series with the pack charging path that will sense the first sign of internal pressure build up (adjustable), and kill the charge when the first swelling is detected.This seems to be around the 100% SOC point.
Carolyn Coquillette from Luscious Garage in San Fransisco, ( http://www.lusciousgarage.com/ )was kind enough to send me a first gen Prius battery pack. The pack was bad and the codes indicated two bad subpacks. Carolyn attended one of the Hybrid classes that I was involved with, and is a highly qualified hybrid auto technician.If you live in the bay area, and have a hybrid, you should consider Luscious Garage for all of your service. I have not had the opportunity until now to examine a Prius subpack that was actually bad, so I immediately labeled the subpacks, and removed them from the enclosure. A quick voltage test showed two subpacks that were a full 1.2V or more lower than the rest, and one that was about .7V lower. I put the two bad subpacks on a charger to see if the subpacks would recover, but shortly after the charge seemed to be complete, the subpack dropped back to the same condition, indicating that the subpack likely had a shorted cell. I used my milling machine to expose the cell to cell connections, and indeed, one cell was at 0 volts while the rest were fully charged. One must be very careful playing with charged NIMH batteries in a milling machine. My end mill managed to hit the plates of one of the good cells, and the current lit up the shorted area cherry red. In my RC modeling days, when a NICAD cell would short, it usually was a symptom of a plate to plate short caused by a nickel whisker.The trick we used to do was to blast away the short by discharging a big capacitor into the cell. Sure enough, I took the shorted cell, and blasted it with 250V from a 6100uf cap, and the cell was able to be charged. Next I took the other subpack with the same problem, and blasted the whole subpack with the same capacitor. While I do not expect the blasted subpack to be equal to a good subpack, it was nice to see that the initial response was to fix the shorted cell. If ever there were an imbalance condition, this is it. one cell started at zero charge while the rest were fully charged. I will give the subpack some time to equilibrate, and then compare it under load with a good subpack in a series configuration. While blowing out some plastic chips from the machined subpack, some of the potassium hydroxide electrolyte sprayed past my glasses into my left eye. It burned a bit, and I immediately flushed my eye with a lot of water, and my eye is fine. Batterys are dangerous in many ways.
Well it happened again. I put my dual prius subpack on my 6A 75V solar panels for a quick recharge between the solar dish runs, and forgot it for several hours. When I finally remembered it, the black tape holding the subpacks together had nearly ripped apart and the cells swelled up with a lot of internal hydrogen pressure. Usually the subpacks are clamped tightly so they cannot swell, so they would vent the gas instead. I measured 140F between the packs, and submerged them in water to cool them. Even after an overnight cool down, the subpacks were still swollen. I drilled six holes in two boards, to clear the locating tabs, so the clamping pressure would be uniform, and squeezed the subpacks together. Several hours of clamping, and the cells were back to normal shape, with no signs of any fluid venting. I used the same packs to run my next canning run, and also to run a 30A 12V heater, and they seem to
Have been using the same dual pack in my lawn tractor for the last 2 years and they are working fine. Some tough batteries for sure.
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.
Back in 2001 when I first started being active in the Insight on line community, I was concerned about the life of the battery pack, especially the issue of recalibrations. Our understanding of the reasons for the "recals" have not advanced much since then. I designed a battery monitoring system that used relays for isolation to read each of the 14.4v monitoring points in the pack. The connection to the pack was accomplished with a special spring loaded back probe that just clipped onto the battery. A Labview based data acquisition card and software scanned the taps and recorded the voltage graphically. I fully expected that my pack would eventually start having the recal issue and wanted to be ready. I am now nearly at 100K on my car, and still have not experienced a single recal. Honda says that gradually accumulating errors in the coulomb counting SOC software is the reason that recal's happen, but I ask what causes the errors? My intuition says that one cell in a subpack is of lower capacity, and since the pack is one long 120 cell series string, that one cell will cause the whole pack to have less capacity than the system expects. When the BCM senses the weak cell dropping voltage as it becomes depleted, the system stops assisting and starts charging to prevent the cell from becoming reverse charged which is instant death. A smart system would have the ability to balance the pack by charging that cell more than the others. Unfortunately since the cell is in a 6 cell subpack, that is not possible with either the Honda or Toyota systems.
The Prius battery system is made up of 6 cell subpacks that are cooled and mounted in a much more practical fashion. The subpacks each have a thermal well, and high current connections. The bumps and sockets on the subpack sides allow a small air gap for the cooling air to pass through. Because the internal pressure in the cells would deform the plastic sides of the subpack, the whole 40 subpack assembly is compressed between two metal plates, so the pressure cannot deform the subpacks, and each subpack has a pressure relief valve. A cleaner easier to service pack for sure.
Genesis One, LLC
If you would like to get involved or support any of these projects, please contact me at (860)935-5569.