Greetings all, About 18 months ago, I purchased a 2011 Gen III Prius (base model, about 201k miles) from my stepson. It was flying the Triangle of Death at the time. After driving it around on the ICE since then (short & local trips only, low mileage), I finally felt I had adequate knowledge & available time to open up the hybrid battery, this message board helped a lot with that. The bus bars and some associated wiring was showing some extreme corrosion in places, I cleaned the bars and connective wiring to the best of my ability and reassembled with a very light coating of dielectric grease. I assembled a DIY grid charger with APC 35-350 modules and a discharge device with an old porch light and a couple 100 watt incandescent bulbs, per instructions elsewhere on this site. I went through some charge/discharge cycles. Full charge first, then down to about 150 volts on first discharge, down to about 60 volts on second discharge, down to about 20 volts on third discharge. Charged it up again and this is what I'm seeing when I test each cell pair (below). My question is, is there anything here I should be concerned about? Or is it time to take the batt. off the bench and slap this bad boy back together for in-vehicle testing?
Modules 9-10 is too high of voltage relative to other blocks... It also failed the load test... If I were you I'd trickle charge and balance the pack over night and then wait a few days for self discharge voltages, then load test each individual module for 2mins with 50w / 12v bulb. Hopefully you get lucky and don't have to replace module 9 or 10... You could potentially swap modules with 13-14, which are your lowest voltage modules to better balance the pack. But currently a voltage diff of 0.54 is going to throw warning lights once it gets a tiny bit worse.
Correction: modules 9-10 pre-load should be 16.05 - not 16.5 That's a typo, my bad. How does that change things? I'll see if I can update the graphic.
If the dielectric grease is on the faying surfaces, that might impede electrical flow? It's good to use for sealing and lubrication, but where the bus bars clamp with the nuts should bare/clean metal?
Well, if there's a way to update the image I'm not finding it. Here's an update with the 9-10 module voltage corrected.
My understanding of dielectric grease is, it exists to protect surfaces and impede corrosion w/out interfering with the flow of electricity. I did consult an electrician friend who consulted someone else and the received answer, why not use some dielectric on parts that are prone to corrode and develop questionable electrical connections as a result of corrosion. It's a very light coating anyway, doesn't seem to interfere with charge/discharge cycles or voltage tests. Not enough there to drip or run if things get warmish.
Bottom of chart where it says: "Voltage diff." is now at 0.18v As long as it stays in that range you have a healthy pack. Easiest way to monitor "voltage diff." in real time is with with Dr. Prius App.... This is the main number to monitor. Once it gets up in the 0.54v range it will fluctuate even higher and then you get warning lights and car shuts down hybrid system.
Yay, sounds like I can start putting things back together. And thank you for the tip on that Dr. Prius app, I'll check that out.
Make sure you buy a decent OBD2 reader or Dr. Prius app won't work... Here's buyer's guide: Hybrid battery diagnostic and repair tool for Toyota and Lexus
That might not be a good idea. Some compounds called "dielectric" grease are conductive but many/most are not. If you don't know which kind you used, you should try to find out. The original dielectric grease was designed to be packed around bare exposed conductors and was specifically made to NOT be conductive so that it could be packed into multi-conductor connectors without causing a short between adjacent pins. I personally think that science and experience dictate that what you are doing will just be a waste of time and money but I too will be watching for the results......just for curiosity.
What I have was purchased from NAPA many years ago. It didn't seem to interfere with charge/discharge cycles or with voltage measurement tests. And as I said earlier, it's a very light coat. If it causes problems days, weeks, or months from now it won't be too difficult to pop things apart and clean everything up with some lacquer thinner now that I have a better idea of how all of that goes & works together.
SitRep: Hybrid batt. is in the car, all electricals connected but not much else re-assembled yet. I still need to finish some cooling fan op tests but initial indicators (Dr. Prius app) are that the 1034 bulb wasn't a heavy-enough draw, the app is reporting a .34 volt diff across the hybrid battery and there is a P0A84 error code IIRC, it may be an old code though. Still need to reset and retest that. Assuming the .34 volt differential is correct, can any addition life be gained by rearranging the individual modules to balance things out a bit better? Or is that a wasted effort or worse, recipe for destruction? How about replacing the most problematic modules? Is there anyone selling decent-quality used modules at a reasonable price?
We'll try a better OBD2 reader for my friend's new Prius when it returns from the installation of the new tires from 4Wheelonline plus the alignment. The current one he have seems not cooperating with Dr. Prius app.
I found the secret answer elsewhere: Looks like yes, after replacing the 2, 3 or 4 bad modules the new assembly can have all the modules re-ordered to balance things out better on the "book" voltage measurement front. I'm still looking for the best seller of suitable used modules though.
Carista does offer auto diagnostic software, on subscription format IIRC, and fairly substantial scope. But I’ve only used it as “hardware”, with Dr Prius. Might be worth looking into though.
