Prius Battery rebalance thread

This is an amazingly valuable thread. Respect to all, both for the info, and even for the debates. Good stuff with real analysis.

I've been trying to get things working right with an IMAX B6. I set the capacity cutoff for 7250 mAh, and it cuts off every charge cycle. How do folks get it to run through three cycles?

Also, with a discharge voltage cutoff of 6V, I was only seeing 4000-ish mAh the first and second cycle. I haven't made it to a third yet, because the charger kept cutting off for capacity (see above.)

What am I missing here? Thanks for your help!

 

Not sure about that charger, but on the hitec X4 charger you have to set the number of charge/discharge cycles and start it from that screen. If you start it on the charge settings screen it will only charge. Starting it from the discharge settings screen will only let it discharge.

 

I Did that. Set it for three cycles. It discharges properly, then charges up to the cutoff, and stops with an alert beep because it reached the capacity cutoff. It doesn't continue the cycle.

 

Did you set the safety timer to off?

I would also lower the capacity cutoff to around 6000 to start and then move to 7000 if the modules are in good shape (ie modules take full capacity without any heat)

 

Yes, the safety timer is off. Your suggestion of reducing the capacity cutoff seems contrary to my issue. My problem is that it is REACHING the capacity cutoff and stopping. I'm reluctant to raise the limit higher, but I need it to make it through three cycles without manually resetting it each cycle.

 

Settings just to double check......
NiMH, 7.2v, 7000 mAh, 2.0A charge, 1.0A and 6.0v discharge, DCHG>CHG 3

NiMH Sensitivity: Default
Temp Cutoff: Off
Waste Time: 5 mins
Safety Timer: Off
Capacity Cutoff: 7000 mAh

Beyond that the only reason I can think of as to why your charger is stopping is that your input power source is dropping below 10V during the cycles........if you have a B6 (not B6AC), what are you using to power it?

 

I checked and those are indeed the settings I'm using. When it beeps to stop, it is flashing "CAPA" and the mAh counter says 7250 (which was my capacity cutoff setting).

 

Are you sure you have a legit Imax B6 charger because I know that charger has been knocked off extensively and I would be concerned about extending the capacity cutoff beyond what it is now. If you have some test modules you can try that on them but I wouldn't do it on the main pack until you can get it to cycle as expected. You can always bite the bullet and get a Hitec X4AC and be done 4 times faster but not sure how to help you beyond this because it should cycle properly with those settings.

 

Okay, I purchased the "legit" HiTEC X4-80. It hasn't been cutting off for current capacity, so that's good. So I hooked it up to four batteries in my pack (all disconnected). I used the settings above (I think) and the cells keep coming up as "DRY." So I tried C>D, and they'd charge a few hudred or a few thousand mA, and then discharge and say "DRY" again. I tried another four cells, and got similar results. I'd used cheap-er Amazon banana plug wires, so I re-soldered them, and that didn't fix it either.

Not sure what I'm doing wrong, but clearly something is amiss. 8 batteries in my pack couldn't all be dead. I replaced the one "bad" cell when I first removed it from my vehicle, about a year ago.

The only thing I couldn't set according to the instructions above was the "Nominal Voltage" - there's nowhere to tell the charger what the voltage of the battery "should be." I assume it's just looking for the charge curve to respond properly, and it decides that it's charged from that. But it feels really weird to not tell the charger what the optimal voltage is.

So...what could be going wrong here? Help please!

 

The instructions can be a little unclear. It seems like the setting for nominal voltage is in user setup, but I don't remember. I'll try to look it up tomorrow if I get time. The "dry" message I believe is the waiting period between charge/discharge or vise-versa. It's adjustable, whatever you set it to.

 

Thanks! Okay, not worried about "DRY." Here is the data from the four batteries. It looks like it's not discharging maybe? I have Discharge set to 2.0A, 6.0V for all of them. And running D>C.

Battery# Discharge1 Charge1 Discharge2 Charge2 Discharge3 Charge3 Discharge4 Charge4 Discharge5 Charge5
28 16 6064 268 2561 303 1595 304 1344 310 941
26 206 4692 321 1189 294 1605 255 1593 231 1485
24 117 4875 154 1278 126 1365 100 1043 82 1793
22 64 5092 159 1083 149 1502 120 1091 112 1360

(Sorry, it seems to ignore spacing in the table)

 

I have my spare battery on my work bench cycled all cells three times. But I fear it's still not exactly what I would wish for, I been thinking since the battery rebalancing/ grid charger charges at a 350 mAh rate that I could use my 4 NiMH chargers to do something simular, I could use a 0.3A charging rate for a few hours to equalize the modules, but the catch is since its not installed what would, you guys recommend to keep the modules cool
terramir

 

I have charged them at 6 amps and 6500mAh max and discharged them at 1.5 A to 5V then dis charged them at progressively lower rates to 4.8 until I used a 0.1 A discharge then depending on the capacity discharged I brought them down to either 4V 3.5V 3V or 2.4V at a 0.1A rate which should be fairly safe to fight crystalline buildup on the plates. A discharge rate of 1/65 of C should have been safe for all but the most damaged modules. I figure they are all charged now but have been resting for 1 to 2 weeks and now need the top off and equalization charge b4 I slap it in my car and attempt to rescue the pack inside my car which can go from purple to green with-in 5 minutes. At times. Then I plan on either putting my original pack in or keeping the one on my bench or pick and choose the highest capacity cells it all depends on what I learn about my original pack once this one is inside.
terramir

 

Btw 4 rc type chargers,
And I replaced 3 modules one that seemed to have a shorted cell inside and two that seemed to only have like 1.5 Ah or less left. Seems like all the modules have 3 to 5 Ah of capacity without a top off equalizing charge hope to restore a 5+ Ah capacity with an equalizing charge to have a mostly restored pack that doesn't bounce up and down once installed. Will see. Thinking at a 0.3 A rate I might reach 1.43V per cell i.e. 8.58V per module after a few hours without heating the , pack too much and revive this pack some more before installing it.
terramir

 

They are cheapy generic clones of the Imax B6 the neuvoton type I have not yet loaded the custom firmware on them yet.

I charged them at 6.5 Ah to ensure that I would not Iover charge them at a 6A rate.
Because the condition of these cells are kinda a mystery.
130k mile car I was told with one damaged cell turns, out two more were quite weak. But honestly the rest seem quite ok at least 50 % of original capacity with an equalization charge I might actually see quite a bit more.
As for crystalline structure forming NiMH are not as susceptible as nicd but that is actually what causes voltage depression larger crystals, forming on the surface. The deep discharge is what should make it disappear theoretically.
With these cells what I am wondering is how long I will have to float them at 0.3A to ensure a balanced module. Btw 6V to 5 V might have been 100 mAh at the most 200 mAg
terramir

 

The IMAX B6 can't discharge at 1.5A. How did you do that?

If you're worried about condition, you shouldn't be charging at 6A at all. You should charge at 0.6A for 16 hours fixed time (standard formation charge) after a 1.3A discharge to 6V.

You are mistaken about NiMH. Overcharging and short-cycling cause voltage depression. It doesn't form crystals, it changes the phase to include compounds with a lower potential, 0.8V instead of the 1.2V. There's nothing theoretical about eliminating voltage depression. You discharge the cell/battery to consume the capacity stored at the lower potential and return the phase to the proper distribution. Upon recharge the lower potential material is no longer present, and you now have the full capacity at the upper potential. Where this typically fails in Prius modules is when one or more cells have deteriorated below its siblings.

Crystals are a completely different beast, and they can generally only be removed with pulse charging or blasting with a capacitor. if you're successful, they are probably short-lived.

Standard balance (formation) charge for a NiMH battery is 0.1C for 16 hours.

Here is my recommendation to you:

Your B6 clones should be able to handle pairs (12 cells). If all modules were previously charged to 6500mA @ 6A, then I would set the capacity safety to 4800mAh, NiMH sensitivity to 20mV. Charge a BLOCK at 0.6A until it terminates @ 4800mAh. Make sure you isolate the blocks (pull off all the buss bars along one side). Box fan blowing across the charging modules. You're prior charge should have pushed them well north of 50% capacity, and the 8 hour 0.1C charge will push them well past 100% safely.

Do not charge adjacent blocks. If you inadvertently contact an adjacent charger, your fastest path to the common ground may be through the other charger. One or both will likely see higher than 30V and pop the power MOSFET rendering it a shiny blue brick.

Steve

 

My power supply can only supply 12V so I can't charge a block I.e. two modules cause that would require an 18V supply which I dun have.
I was not talking about penetrating whiskers which short NiCD cells I learned that the surface crystals get bigger due to short cycling and a full discharge eliminates this. 0.4V per cell is what I read is, mil-spec. But I also read that taking them down that far when it's in a pack formation can cause reverse charging of individual cells this is why I used the minimum level possible which was 1/65 of C 0.1A.
I set the discharge to 1.5A it bounces in read out to 1.3 to 1.4 during discharge.
There seems to be a, limit in the software as well as physically cause it gets mighty hot.
As for charging modules I usually charge modules 1,7,14,21 then 2, 8, 15, 22.... etc. This way modules don't heat each other besides the short circuit you described.
Bus bars were removed off both sides right when I opened it up to avoid any accidents.
Will 0.3 not be sufficient to equalize the cells ? I do think that I could afford the extra time. Will 4800 be too much or too little if I use that rate, also will I have to adjust the sensitivity up or down 20 mV if I use 0.3A?
terramir

 

Ehhh question since the voltage of a full cell is 1.43 *12 = 17.16 should I terminate the slow charge when it reaches this voltage or is there more to it.
terramir

 

Visual is better than thousands of words. I’ve recently published couple of 7 minute videos in HD to give you visual of what is happening with the batteries in the idle mode, under the load and when the load has been removed. That will give you an idea of why the “individual module replacement” could fail in many cases. Part 3 wich covers balancing and charging is still in production (slightly delayed as I am quite busy helping rebuilder who is now launching their second assembly line and also very busy with Li batteries for EV owners). Enjoy:

Part 1 Prius Individual Module Testing with Voltmeter:

Part 2 Comparative Test of 20 Prius Modules with HV Battery Analyser:

 

Great videos Kiwi - how is part three coming along?

By the way, in your second video I couldn't help but wonder why you would have it analyze 20 modules where there are 28 in the pack.

Is the analyzer limited to only Gen II Prius?

How about Gen I?

Or Lithium Ion?