RC Charger for HV Battery module charging

I use SuperMate DC6. However, you can use a 12V battery charger and charge 2 at a time in series. A dumb 12V charger is better, like an analog version that will do 10 amps, to get the charging voltage up to around 15V. You are only looking to add 1 amp hour or so. Do you have an old wheel cart-type 12V charger? I've got a Schumacher 10/40/200 with a mechanical timer -- I love it, completely old school -- a setup like that is what you could use.

 

Disconnect all of the bus bars on one side -- the side with the sense wires. If you have linesman's gloves and insulated tools, use them for this step, as you have 200V at your fingertips. Once off, you have 19 battery pairs.

The computer will be unhappy if it detects more than 1.2V difference from the highest to lowest pair. It can resolve imbalances that are smaller than that. You shouldn't have a problem, unless you have a bad module, which is possible. If you like, you can take voltage readings of all 38 modules and post them here for comment.

The problem that you face is this: if you are putting on a partial charge, you can only do this in pairs, because that is how the battery computer manages the string. It can resolve a charge imbalance from one pair to the next, but it cannot resolve an imbalance inside the pair, and that can lead to the higher module being overcharged or the lower module having a cell reverse.

 

A SuperMate DC6 can be used to carefully discharge those modules with higher voltages to match the voltage on the lower charged modules (one at a time, Seilerts has 14 of them ). Use a separate digital voltmeter to monitor the module being discharged and remember that the module voltage will bounce back up a bit when the discharging current is stopped.

JeffD

 

Here's the setup that I was describing. A 10A analog 12V charger will converge to 0A at around 15.5V. I tried 40A for grins, but it made the charger trip.

 

First, check all terminal voltages. If non are more than 0.1V off the average, then you should be good to go. If you have one or more that is 1.2V less than the others, then they should be replaced.

The charger can put out 5 amps or 50W, whichever comes first. Since you have a smart charger, you do not need to do this pair-wise. Simply add the same amount of charge to each module. I suggest 2500 mah. You can set this in the user defined settings. Then go back to the NiMH charging menu, and select 6S, 5 Amp charge, and turn it loose. You will then need to move the charger up to the next module every half an hour.

 

Hi. Sorry to bring an old thread from the dead but I've recently started cycling/checking my battery. I'm using a Dynam DC6 charger. I have one question I wasn't able to find. What should I set the delta peak shut off to? I'm using "Default" which is 7mVbut I don't know if that is the best option.

Thanks

 

You'll need to have multiple protections:

• ~5 mv/cell - threshold
• ~100F - temperature limit
• 3.5 Ahr - initial charge limit (unknown, used cells)

If they charge to 3.5 Ahr and not the other limits, let them sit for a day or so before cycling that one again. Up the limit and try the next module.

Bob Wilson

 

Thanks Bob. That translates to 3500mAhr right? Why so low? Just to be safe since as you said they are unknown?
What amperage would you recommend I charge at. I've seen from other threads-
5a charge
.7 discharge to 6v

 

Correct. I've seen weak modules, especially after the 3d cycle, lose the dV/dt notch. Resting 24 hours seems to bring it back. So I typically like to see two charge/discharge cycles, initial survey. Then two more after tweaking any charger parameters as needed.

Good, fast, cheap . . . pick two. Personally, I like the charge to be 1/10th estimated C . . . close to 10 hours. But then I have enough inventory and time to be patient. Still:

• charging is exothermic - they get warmer
• resistance heating is the current squared - also leads to warming

My recommendation is experiment and try to make it match your ordinary schedule.

Bob Wilson

 

Well, I would definitely pick good/cheap. I've got another car to drive in the meantime. So I'm not in a particular rush. Though of course I don't want it to take too long. My plan is to try and get some more use out of this pack. If all goes well, I will try to get my hands on a couple 2nd gen packs and rebuild with gen2 cells. I'm running 4 chargers.
So do you think 5a is too much?

 

My interest was in module capacity measurements, the first full discharge after an initial charge. That typically is done at 1/10th C. So I soon learned used modules have significantly decreased capacity, often in the 2.5Ahr range or less if any. But these were experimentally determined. But I'm not trying to force any given protocol as much as 'this is what I used'.

Try the 5A, experiment, and let us know how it works.

Bob Wilson

 

I've already run through a few cells. You are right on. I had already run 4 cells through 3 cycles @ 5A/ .7A.
final discharge #s
#1 cell 2434mAh
#3 cell 1993 mAh
#5 cell 2164 mAh
#7 cell 4723 mAh

I've been doing every other cell to help manage heat. These have obviously been disappointing numbers.
thanks for the responses.

 

Any progress on reconditioning your modules? I'm interested to see how much more usable capacity you get after a few cycles.

 

Yes. Here is what I have right now.

Cell# final dischargemA / charge mA after 3 cycles at 5A charge, .7 discharge
1) 2434 / 4281
2) 2001 / 3190
3) 1993 / 3573
4) 2198/ 3819
5) 2164/ 3818
6) 1884/ 3471
7) 4723/ 6511
8) 1847/ 3328
9) 1822/ 3500
10) 2073/3696
11) 1916/ 3458
12) 1752/3694
13) 1673/3500
14) 1655/3664
15) 1664/3328
16) 2096/4109
17) 1606/3207
18)1788/3328
19) 1737/3204
20) 1535/3451
21) 1700/3453
22) 1828/3814
23) 3780/5404(JUST REPLACED THIS ONE)
24)1926/3939
25)3079/5755
26)1693/3500
27)2129/4188
28)1856/3816
29)2022/3943
30) 1877/3776
31) 4356/6204
32) 1935/3451
33) 1780/3907
34)1881/3696
35)2029/3653
36)1963/3583
37)2038/4062
38)2215/4273

Aside from the one I marked as "new", there are a few more that have notably better numbers, those have been replaced within the past year. (I replaced one cell with no charging/balancing. It lasted almost a year then lights came back, replaced 2 more cells and it only lasted a day which is why I'm now doing all this.

I've re-cycled a few that had particularly low numbers with 2-400mA increases.(already reflected in these numbers) I'm re-cycling the ones will less than 2000mA discharges right now.
Any input is appreciated.

 

Are you using gen 1 modules or gen 2? I'm getting some gen 1 modules just to experiment with and learn from and possibly make a battery pack for my ebike with.

HTC Evo 3D

 

	Column 1
0	[tr][th]Ahr[th]cell
1	[tr][td2]4723[td2]7
2	[tr][td2]4356[td2]31
3	[tr][td2]3780[td2]23
4	[tr][td2]3079[td2]25
5	[tr][td2]2434[td2]1
6	[tr][td2]2215[td2]38
7	[tr][td2]2198[td2]4
8	[tr][td2]2164[td2]5
9	[tr][td2]2129[td2]27
10	[tr][td2]2096[td2]16
11	[tr][td2]2073[td2]10
12	[tr][td2]2038[td2]37
13	[tr][td2]2029[td2]35
14	[tr][td2]2022[td2]29
15	[tr][td2]2001[td2]2
16	[tr][td2]1993[td2]3
17	[tr][td2]1963[td2]36
18	[tr][td2]1935[td2]32
19	[tr][td2]1926[td2]24
20	[tr][td2]1916[td2]11
21	[tr][td2]1884[td2]6
22	[tr][td2]1881[td2]34
23	[tr][td2]1877[td2]30
24	[tr][td2]1856[td2]28
25	[tr][td2]1847[td2]8
26	[tr][td2]1828[td2]22
27	[tr][td2]1822[td2]9
28	[tr][td2]1788[td2]18
29	[tr][td2]1780[td2]33
30	[tr][td2]1752[td2]12
31	[tr][td2]1737[td2]19
32	[tr][td2]1700[td2]21
33	[tr][td2]1693[td2]26
34	[tr][td2]1673[td2]13
35	[tr][td2]1664[td2]15
36	[tr][td2]1655[td2]14
37	[tr][td2]1606[td2]17
38	[tr][td2]1535[td2]20

This "whack a mole" module replacement approach risks the good modules from heating by the adjacent, failing modules.

Bob Wilson

 

I'm with you Bob. The first time around was just an experiment. I bought the car knowing it had a bad battery. Just for giggles I replaced the bad cell just to see what would happen. I was surprised when it lasted so long. I kept driving the car with no issues. Then the car sat for a few months, I started her back up, made it about 2 miles and the dash lit up like a christmas tree. So I took it back out, found 2 bad cells and threw 2 more in and well, here I am.

I'm putting more effort in now as a learning experience. If I'm able to make it work I hope to rebuild in the future with Gen2 cells. I work on Toyotas for a living and I consider myself pretty good at what I do. But electrical engineer I am not. As you already know, we don't play with cells at the dealer.