Load Testing and Balancing HV Battery Pack SKYRC iMAX B6AC V2

Do you have the data from your previous work? It's really helpful to put all the data on the same spreadsheet so we can study all the details. Also doing the math and writing out the voltage loss for each module after load testing makes it easier for us to help with a quick glance. I do way too much of this math on my own packs and don't want to have to do it for yours too.

But in general you're in that awkward stage where it's hard to tell exactly which modules are the worst with a low amp load test and way easier to tell when the pack is in the car under high amp loads and throwing codes. Dr. Prius can help with that if you can post screenshots...

Also, discharging all modules down to deeper and deeper levels (5v, 3v, 1v) to recondition them to restore capacity from 50% to 96% will give you more data to find bad modules. Often the next module to fail will be one that discharges much faster than the other modules in the third round or earlier of discharging. What I do is set up 5 multi-testers, soon to be 7 multi-testers and race them against each other while discharging them with 12v lights and watch them side by side to find the weakest module.

Also keep lots of fans blowing on everything, don't let anything get too hot, especially when recharging from the deepest discharge. And if you can get a thermal camera you can sometimes find cells that are running hotter than others so you know it's about to fail.

Here's one of my spread sheets to give you sense of how I set them up:

 

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So.....the car threw a P3015 code..."Block 5 becomes weak"...............but you don't suspect Block 5 to be a problem?

Gen 2 module blocks start with Block 1 being the 2 modules furthest from the ECU. Block 14 being the 2 modules closest tot he ECU.

Block 5 would be the 9th and 10th modules from the end.

 

Well, some people have wired the pack up in parallel, which means connecting all the positive terminals together and all the negative terminals together and then charging the pack the way you would normally charge a single module. But this is a huge amount of electrons you have to pump into the system in this configuration and the SKYRC chargers aren't designed to do that... But maybe if you charged it for long enough it'd work. But it will take a long time and you'll have to have lots of fans to keep everything cool.

 

Charging 28 modules in parallel would be challenging. The 28 modules would divide the available current based on module internal resistance. In extreme cases, one module may get 50% of the current and another may get 1% or less. It's potentially a crazy situation.

Just 2 or 3 in parallel can be a feat of frustration.

 

So you put a 100 amp load for 30 seconds on each individual module? The voltages in your chart show the module voltage immediately prior to load application (7.6-7.8), and then on the right it shows module voltage immediately prior to removing the load, or immediately after removal of the load, or a few minutes after load removal once voltage recovers and steadies out?

On another note, set your charger to discharge/charge mode. Discharge down to 5.8 volts at 1.5 amps (or 0.8 amps if a 5w model), have it wait about 20 minutes, then charge at 2 amps (or whatever you're comfortable with, I suppose) with a max charge of 8200mah. You should be able to just keep whatever default delta is in the setup for detecting when fully charged. When the charge cycle ends, you'll be able to see total mah discharged and total charged back in. If the module is healthy, the discharged number should rise each cycle up until max improvement.

If that's a single channel charger, it's going to take about a month or so (at 24/7) to get through 3+ cycles of 28 modules. I suppose it could be faster if you drain them at 100 amps (or x amps) and then charge them at 5 amps with the charger, but that kind of defeats the purpose of obtaining discharge measurements so you can actually see true module capacities.

 

i have a SKYRC iMAX B6AC V2 also and ... uhm...

the link you posted is interesting but i would disagree with one thing that post says.

"Charge at 5 amps up to 7250mAhr"

im not sure why to charge up to 7250 mahr when the battery was originally rated for only 6.5ah and we shouldnt be discharging to zero. but aside from that....

i would only add this information.......for any stray web surfers who land here... and have a b6ac v2.... . dont depend on the "auto charge" feature to cut off correctly on a prius module., especially when charging at higher amps like this.

i was playing around with a module charging at 6 amps and it wound up at almost 9 volts and slightly physically deformed (bulged out) which is not good. It wasnt completely destroyed or anything, it was just slightly poofy to the naked eye.

my max capacity limit, charge time limit, and temperature limit with temperature probe, were all turned on, but they were all turned on too high so they did not stop the charger soon enough.

i should have lowered those limits since its hard to know the capacity, and the time limit, and the temperature, for an older battery. the battery was not hot, it was mildly warm, and still deformed slightly. it was not 'unattended', i was checking on it every now and then, but not often enough.

 

I keep the V2 skyRC chargers at 4.3 amps and the V1 skyRC chargers at 4.6 amps because they're so much slower. But I backed down to 4.6 from 4.8 because the modules were getting too hot and inflating ballons over the vent covers. Thinking I might go lower on amps again too.

As for measuring mahr, those measurements are a joke. They can't differentiate between voltage that made into the module vs voltage lost to heat. And if you try to get all 6800 mahr in one charging session it makes the module unnecessarily hot even with a really powerful cooling system. I prefer to get to full charge in stages.

In general this is a very primitive way to rebuild packs and you need to invest at least $10K in lab-grade equipment if you want to accurately measure mahr that legitimately made it into the pack.

 

PriusCamper that is very interesting info... thanks.

I really like having the temperature probe for the charger, i have set it down to like 85 degrees F now and feel alot better about my various batteries when i charge. It actually makes me feel better than any of the other limits - voltage detection, mah counter (as you noted this seems a bit off!) and time limit.

really gives an appreciation of what the Toyota / Panasonic teams went through inventing this stuff in the late 90s / early 2000s. Without that battery + battery controller tech nailed down to a science, the whole project would not have worked that well.

 

update for future surfers... ive been charging more modules on the skyrc byac v2 and i noticed that even at low current, like 1 amps, there is an ever so slight physical deformation of the pack. you have to hold it up at a certain angle to see it. It is definitely noticeable if you have a cold module next to one that is just charged at 1 amp.

I am no longer confident in this process (in other words, charging without being inside a properly clamped assembly) and am not sure if it is doing damage to the cell but it seems likely. i would never charge one of these modules unattended and without a working temperature probe on the charger set to a low temperature, and i dont think i would stick one of these back in a car. I'm using them for farting around with hobby stuff where there is minimal danger.

 

Not sure of your description of physical deformation of the pack. But the thin aluminum sides on the modules are only structurally sound if all modules are bolted together / compressed on the rack. Charging modules that aren't compressed with other modules or end caps will cause them to swell up and fail.

That being said, even when modules are compressed on a rack, a bad module that gets hot will still slightly swell and look different, but will return to its normal shape after it cools down. As for monitoring temperature I've found most methods like using a temp probe or a cheap laser temp sensor to be inaccurate/hassle. But a quality thermal camera can help you find bad modules running too hot with nothing more than a quick glance.

 

yeah i waded into a mess... wish i could delete old posts.. oh well. edited to clarify. charging without a properly tightened clamp is a Bad Idea

 

@donbright any hints on getting the SkyRC temp sensor to work? Mine is not detected (yet)... possibly bad but in searching I find various people have tricks for getting it to fire up.

Too bad there are no instructions...

UPDATE: Turns out, saving a few bucks just wasted my time. Essentially *every* LM35DZ (temp sensor chip from National Semi) on Amazon, and elsewhere, and all sensor devices based on those... are 100% bogus. No temp sensor in the "chip" at all: it's an NPN transistor with different lettering.

So, I found a hopefully reputable source, and am starting over on that bit.