Super Brain 989

The packs are 6.5Ah. So depends how much time you have. But you can research NiMH charging rates. I would recommend C/10 charging rate (ie. 650mA) but the critical thing is temperature and not causing venting. It is going to depend on the starting cell voltage and you should also monitor the dT/dt (temp change over time)

Are you charging individual modules outside of the battery pack?

This paper might be interesting:
http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/2a_2002_01_1962.pdf

 

Make sure they are under compression when you charge them or you will have balloons when its done.

 

It depends if your modules are Gen II or Gen I modules.

But you should set the programmer to at max 6500mAh rating. (If the modules are old, I wouldn't even assume they have that much capacity and it may try to over charge them). 1.5A discharge and charge is fine, but if gets too hot, then cut charge rate that in half and take the extra 5 hrs per cycle. As far as temperature settings go for limits, please read that paper.

If they are outside the pack, you might want to consider making a jig to hold the packs together and bookend boards on each end to compress them, as you risk physical expansion from thermal effects, and you will want a fan hopefully as you will be dealing with 10 watts of heat from each module.

I wouldn't go below 15% SOC, so use that as your low voltage set point. None of the Toyota traction battery charges do, and the vehicle never goes below 15%.

Toyota Prius Battery Specs - EAA-PHEV



This is a generic graph and each module has 6 cells, so 15% SOC or 20% SOC would be around 1.18V per cell.

However, the curve here depends on the discharge rate, and like I recommend a 0.1C rate has a different curve at different temperatures than a 0.25C rate.

Read this paper that shows the dependance on temperature and rates which can determine the capacity you are leaving the battery with:
Inaccuracies of Estimating Remaining Cell Capacity with Voltage Measurements Alone - Application Note - Maxim




Anyways, I recommend these settings:
1 amp charge and discharge
6000 mah capacity
run 3 cycles
1.18v min per cell discharge
5mv per cell dv charge
100 degree F temp limit


I wouldn't charge these unless clamped into a module holder so the sides don't expand. And do it in ventilated space.

 

I rebalanced my 27 Gen2 modules successfully with a similar unit (SuperMate DC6). I let the unit decide when to stop the discharge (5 watt discharge to 1v per cell) and limited the charging to 7200 mah ( a slight overcharge helps rebalance the cells but be careful not to overheat a module). When working with modules outside the HV battery assembly, I clamped a module between two pieces of wood with a c-clamp.

The modules did get above 8v at the end of the charging cycle, but quickly relaxed to about 8v when resting a couple of days. They then slowly self discharged to about 7.8 volts over the next two months - a good measure of Module condition.

JeffD

 

If a module has some SOC as 7.6 v says. it should be able to handle reasonable discharge current. If not it is toast. We have seen two very different HV battery failure modes:

1. In cool climates and not too hilly - one or two modules get out of balance and at a low SOC one cell gets reversed and the ECU detects the 1.2 volt drop in that module pair. The remaining modules are usually useable, but probably need to be rebalanced. That is what happened to my 2004 Prius in CT.
2. In hot climates and/or mountain regions - the battery dies due to elevated temperature and ALL of the modules are not reusable.

An additional problem occurs in Gen1 batteries. The modules leak electrolyte, the bus bars get corroded and the modules loose moisture which weakens them.

JeffD

 

Read those charts for NiMH.. and multiply by 6 cells in a module. If you aren't on that chart anywhere, the cell is probably damaged. It is very possible those cells are totally ruined since they have no charge in them and won't take a charge, the chemistry just goes bad when they sit or are exposed to high heats.

I supposed you can read up on some threads here about maybe drilling some holes and adding some distilled water if the module it dead anyways.

I mean you can google how to revive dead NiMH batteries. They are all the same chemistry just this one is larger. A voltage below 6V might be more salvageable than what you are reading which is high voltage no current.

 

It is too high. It probably is out of electrolyte. Please don't put 1A into a dead module which is at 9V... Do you even have this physically supported? It could be outgassing hydrogen, maybe even rupture. I guess you've never seen a bad rechargeable AA and what it can do when it goes bad....

At the very least leave it alone for 10 hours, then try again.

 

You really need to consider getting a set of good gen2 or gen3 modules for your gen1 battery or get a ReInVolt (they do the rebuild correctly with Gen2 or Gen3 modules).

JeffD

 

I would recommend this guy. He seems to know what he's doing. These batteries are already conditioned.

Toyota Prius 7.2V Nimh Battery Cells 6.5ah 01-03 | eBay

 

I'm using an MRC 989 to recondition a set of NHW11 modules from my old pack. They'd been sitting idle since November of 2009. I'll try to update with the results but this is my 'memory dump:'

• 6 cells, NiMH
• 5800 mAhr capacity ~= 6500 / 1.12 :: the MRC 989 has a 12%, undocumented 'pad'. Reduce the set capacity by 12% to get an absolute cutoff or in this case, 6.5Ahr.
• 100F, peak temperature ... this is too high as I'm still seeing them come in the +90F range
• 3 mV - dV/dt threshold (default I think)
• 2.5A charge - based upon my expected application but may be too high for reconditioning
• 7.5A discharge - based upon my expected application
• 2 cycles - autodischarge/charge
• 5 ma tickle with a 1 minute interval

What I'm finding are:

• D1 - 200-600 mAjr after two years idle, the residual charge
• C1 - running about 3,400 mAhr but varies, it did use dV/dt cutoff
• D2 - about 3,000 mAhr
• C2 - 5.5-6.5 Ahr charge, only the ones under 6.5 used dV/dt cutoff. Those that used capacity cutoff are often at ~90F and in the compression plate assembly, they have tried to expand

I've surveyed 20 modules and only one looked suspect. Of the remaining 19, I'm going to pull the 10 weakest and run an enhanced series on them after I complete my first survey. Meanwhile I'll put the six best for my first, test string.

For the next set of 10, again +2 years idle, I'm going to experiment with:

• 600 ma charge - this is to limit any charge heating and reduce gas generation
• 4900 mAhr capacity ~=5.5 Ahr lowered to avoid any overcharge heating and gas
• 4 cycles :: the first discharge is 'throw away' so this will give four, full charge and three full discharge cycles
• 7.5A discharge - again based upon my expected application

I recently read a paper on reconditioning that recommended:

• 0.1C charge - this inhibits surface effects including gas generation and leads to a deeper penetration of the hydrogen into the electrodes.
• 1C discharge - in my application I'm expecting a 7.5-15A discharge rate. So I'm using little over 1C, 1.36 C = 7.5/5.5 as the discharge load. There is a "bounce" in the voltage when it reaches the 6V/cell lower limit but I don't see it doing any harm.
• ambient+10F - typically 77F in the work area so I'll set the threshold down to 90F if it will go that low. With the lower charge rate, I'm expecting much lower peak temperatures. Also, I'll do them 1, 4, 7, 10, 2, 5, 8, 3, 6, 9 order to minimize adjacent module heating.

Bob Wilson

 

You can use your SuperBrain to charge/discharge the new module to match the others.

JefD

 

These modules had been cycled shortly after being taken out of service to measure the residual capacity, ~5.5 Ahr:

Column 1

0

[th]ID[th]D1[th]C1[th]D2[th]C2[th]D2/C2%[th]hh:mm[tr][td]6[td]523[td]5857[td]5020[td]6508[td]77.1%[td]2:26[tr][td]8[td]424[td]5403[td]5064[td]6472[td]78.2%[td]2:21[tr][td]7[td]289[td]4861[td]5087[td]6499[td]78.3%[td]2:16[tr][td]4[td]850[td]6345[td]5284[td]6520[td]81.0%[td]2:35[tr][td]9[td]1099[td]6193[td]5341[td]6365[td]83.9%[td]2:34[tr][td]2[td]1086[td]6301[td]5386[td]6394[td]84.2%[td]2:36[tr][td]1[td]612[td]5878[td]5509[td]6520[td]84.5%[td]2:31[tr][td]3[td]187[td]6520[td]5531[td]6520[td]84.8%[td]2:33[tr][td]5[td]547[td]5841[td]5591[td]6479[td]86.3%[td]2:30

• 5020-5591 mAhr (D2) - discharge capacity
• Ahr limited final charge - the dV/dt did not happen (C2)

So the next set had been left idle since Nov. 2009:

Column 1

0

[th]ID[th]D1[th]C1[th]D2[th]C2[th]D2/C2%[th]hh:mm[tr][td]27[td]416[td]3357[td]3670[td]4253[td]86.3%[td]1:36[tr][td]32[td]265[td]3152[td]3461[td]5150[td]67.2%[td]1:39[tr][td]30[td]518[td]3510[td]3800[td]4608[td]82.5%[td]1:42[tr][td]28[td]302[td]3670[td]3907[td]4379[td]89.2%[td]1:41[tr][td]34[td]216[td]3836[td]4087[td]4603[td]88.8%[td]1:44[tr][td]29[td]482[td]3802[td]3968[td]4732[td]83.9%[td]1:46[tr][td]31[td]138[td]3779[td]3695[td]4835[td]76.4%[td]1:42[tr][td]36[td]351[td]3630[td]4017[td]5343[td]75.2%[td]1:49[tr][td]35[td]236[td]4047[td]4042[td]5598[td]72.2%[td]1:54[tr][td]33[td]199[td]4539[td]4192[td]6485[td]64.6%[td]2:06

• 3670-4192 mAhr capacity (D2) after first cycle
• dV/dt stopped all but one charge (C2)

So I ran this set through a second series:

Column 1

0

[th]ID[th]D1[th]C1[th]D2[th]C2[th]D2/C2%[th]hh:mm[tr][td]27[td]2394[td]4213[td]4115[td]5060[td]81.3%[td]2:09[tr][td]34[td]2545[td]4460[td]4385[td]6148[td]71.3%[td]2:23[tr][td]30[td]2422[td]5845[td]4433[td]6267[td]70.7%[td]2:34[tr][td]28[td]2353[td]4885[td]4475[td]6520[td]68.6%[td]2:28[tr][td]29[td]2414[td]4857[td]4536[td]6161[td]73.6%[td]2:26[tr][td]32[td]2713[td]5658[td]4861[td]6397[td]76.0%[td]2:40[tr][td]36[td]2958[td]5494[td]4909[td]6316[td]77.7%[td]2:40[tr][td]33[td]3436[td]5639[td]4921[td]6384[td]77.1%[td]2:46[tr][td]31[td]2471[td]5487[td]4933[td]6520[td]75.7%[td]2:38[tr][td]35[td]3118[td]5684[td]5010[td]6520[td]76.8%[td]2:45

• 4115-5010 mAhr (D2)
• 20% were capacity limited and 80% still showed dV/dt (C2)

I calculated the cycle time using:

• 7.5A - charge
• 2.5A - discharge
• 1 minute tickle

The high-numbered set did not recover to similar capacity as the low-numbered set. The only difference was the low-numbered set was 100% cycled shortly after being taken out of service and stored at that level. In contrast, the high-numbered set had started storage at the ~60% capacity when removed from service. After a second conditioning cycle, the high-numbered set are running about 500 mAhr low compared to the low-numbered set.

My goal is the maximum, recoverable capacity from these modules so I am trying a different conditioning cycle:

• 2.5A -> 0.6A charge :: some literature suggests a lower charge rate reduces the risk of gas formation that can block the exposed surface area.
• 2 -> 4 cycles :: this will run the same number of cycles as the low-numbered and high-numbered set.

The charge cycle will take four times longer and it had already been 3/4ths of the original cycle time. So we are looking at about three times longer, close to eight hours per cycle compared to two and a half. The unanswered question is whether or not we'll see a higher end capacity.

Bob Wilson