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Old 12-19-2012, 06:14 PM   #1 (permalink)
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Default Cell conditioning

I've got my battery broken down to the sticks ans need to know how to do the conditoning.
I know they go through a series of discharge charge cycles.
How far down should they be discharged to be considered empty?
My discharger is a super brian 977, there are settings for total mAh, delta mV
and time. For charging same thing.
Any suggestions on settings?
Max charge and discharge for this model is 4 or 5 amps.
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Old 12-19-2012, 09:46 PM   #2 (permalink)
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Quote:
Originally Posted by Subdewd2 View Post
I've got my battery broken down to the sticks ans need to know how to do the conditoning.
I know they go through a series of discharge charge cycles.
How far down should they be discharged to be considered empty?
My discharger is a super brian 977, there are settings for total mAh, delta mV
and time. For charging same thing.
Any suggestions on settings?
Max charge and discharge for this model is 4 or 5 amps.
I have the Superbrain 989. I have been quite successful using these setting in the charge/discharge mode:
Battery type: NiMh
Cells:6
mAh: 6500
Amp(charge):1000mA
Amp(discharge):2000mA
Cut Off Delta Peak(charge) mV:6
Cut off V(discharge): 1v/cell
Cut off Temp: 130
Trickle: 350mA

Since there is just one temperature probe, just strap it to a middle cell, these are usually the warmest since the ends lose heat more easily. Don't let the stick lay directly on a flat surface, support both ends with small blocks of some type. Make sure there is at least a bit of air flowing around the stick. Nothing fancy needed, I just turn on my ceiling fan over the table.

I recommend 3 charge/discharge cycles. Be sure to keep notes. you will need them when you start to analyze the results. Let the cells sit for at least 2 weeks to test self discharge, then give the cells one more cycle to measure the self discharge. Internal resistance is also important, but I don't know an easy way to check that. It doesn't seem to be a major failure mode anyway. BTW, the square end is the positive, the hex the negative.

Last, the 989 stores the charge/discharge values. I suspect the 977 does the same. After the charger shows "end" then these values can be brought up on the display by pushing the left arrow.

Good luck,
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Last edited by jime; 12-19-2012 at 09:56 PM.
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Old 12-20-2012, 02:49 AM   #3 (permalink)
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Here's a couple threads I reviewed when doing my pack:

Analyzing, refurbishing/repairing a dead hybrid battery pack (2000 Honda Insight) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

Spare IMA pack: Rebuilding/testing the IMA battery

I used the SB989, which has a 10 amp charge and discharge. From what I've read, most people have done a 10 amp discharge and a 5 or 7 amp charge. I've read that you should charge and discharge as fast as possible, that that's part of the refurbishing strategy. 3 cycles should be enough to indicate whether you need to do additional cycles, most likely on only some of the sticks. I used a 5mV delta V and a 0.9V discharge cutoff... If the 977 is like the 989, you need to write down the cycle results before you move to the next stick, as they're not saved once you end the cycling...

So, program an automated 3 cycle routine, write down the results, move through the rest of the sticks, graph the results. The graphs should indicate which sticks will need additional cycling. Here's a link to an excel workbook I used for my pack. It also includes others' results. It's probably a little too cryptic to understand in places:
https://dl.dropbox.com/u/20136699/MI...cling_data.xls
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Old 12-20-2012, 03:03 AM   #4 (permalink)
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....Internal resistance is also important, but I don't know an easy way to check that. It doesn't seem to be a major failure mode anyway....
I think high internal resistance is probably the most significant failure mode. I read that you can calculate internal resistance by change in voltage over current: A) note voltage before beginning discharge, start discharge, B) note voltage after voltage drop stabilizes - use a consistent amount of time from stick to stick, I used 1 min. - then subtract B from A and divide by current, such as 5 amps... Supposedly this should at least give you some indicator of the variation in internal resistance from stick to stick. Yet my results didn't seem to suggest anything...
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Old 12-20-2012, 10:21 AM   #5 (permalink)
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I think high internal resistance is probably the most significant failure mode. I read that you can calculate internal resistance by change in voltage over current: A) note voltage before beginning discharge, start discharge, B) note voltage after voltage drop stabilizes - use a consistent amount of time from stick to stick, I used 1 min. - then subtract B from A and divide by current, such as 5 amps... Supposedly this should at least give you some indicator of the variation in internal resistance from stick to stick. Yet my results didn't seem to suggest anything...
I would like to see your data

I produced a decent battery by stick reconditioning with the 989 without any accurate measurement of internal resistance. I tried your approach with the 989 and the results were scattered all over the place and did not correlated with cells which performed well when later installed in a 20 stick battery. I'm not inclined to strongly disagree with your point that it is very important, but I don't know how to measure it. Mike Dabrowski talked to me about using special equipment, but he apparently doesn't agree that the 989 is adequate to measure internal resistance. So what equipment is adequate?

One thing which Mike suggested was a high current load, such as a 50-60 amp nichrome wire load. I have the wire, but have not yet built the load. The high current load would be more indicative of what the car sees in actual operation.
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Old 12-20-2012, 12:37 PM   #6 (permalink)
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I would like to see your data...
Data to back up my opinion that high internal resistance is probably the most significant failure mode?, or my IR calculations from my pack? The latter is in that workbook I linked to in post 3, I think 3rd sheet, row 32... The former is just sort of obvious observing how pack voltage changes under load and what the car has to do to work around it (reduce current), not to mention that that's what happens to old worn NiMh batteries...
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Old 12-20-2012, 05:05 PM   #7 (permalink)
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Rinternal = (Vx - Vy) / (Ay - Ax).

The second voltage in particular should be taken at as high an amperage as possible. Both readings should be taken once the sticks voltage has stabilized during the lower rate discharge.

Our internal resistance test uses ~20A and then ~90A.

An IR test really needs to be done at the cell level to be meaningful anyway, IMO. It's the same conundrum as trying to test for.. just about everything.. on the stick level... your picture of the stick is very muddied by the 6 cells. You could have 5 cells with low IR and one with high IR that is the problem cell, but you can't see it because its mixed in with data from the rest of the cells.

High IR is called power fade and is interpreted by the systems as low capacity. It does seem to be the biggest cause of battery failure, especially in 10-12 year old packs. It's also the primary reason why testing sticks at 5-10A is hit and miss at best. It's just not comparable to what the batteries see when used in the car.

Our testing rig just got a major upgrade and can now charge at up to 70A and discharge at up to 160A.

You can almost feel the stock sticks trembling as they are brought near.
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Last edited by Eli; 12-20-2012 at 05:14 PM.
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Old 12-20-2012, 05:29 PM   #8 (permalink)
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It's also the primary reason why testing sticks at 5-10A is hit and miss at best. It's just not comparable to what the batteries see when used in the car.

That is basically what I saw when I tried testing internal resistance with the Superbrain 989. The numbers were "hit and miss." I basically made my decisions on leakdown after 2 weeks rest time and on third cycle discharge capacity. That seemed to work fine. If there is a bad cell in a stick, it won't stand up to these tests anyway. I don't really care that there is a bad cell or two cause the stick is trash anyway,and it doesn't get used.

The pack I built is better, based on Dabrowski charger/discharger, than either of the 3 packs in my cars. I do want to build a high current load since that would more nearly simulate what happens in the car.
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Last edited by jime; 12-20-2012 at 05:34 PM.
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Old 12-20-2012, 05:33 PM   #9 (permalink)
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Yeah, the self discharge test is going to be the most telling with the Superbrain method of stick cycling. It's relevant even with the higher rates of charge/discharge, since it's not something that gets measured during the actual cycling.
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Old 12-21-2012, 10:50 AM   #10 (permalink)
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I've been able to cycle 4 sticks so far and found one that dropped like a rock whenI put it through the initial discharge cycle. Only been two cyles now but cell capacity has incresed 700 mAh. So if This trend continues what are the odds of this stick staying balanced if put back in service. If I decide to return it to service would it be advisable to force it to a higher SOC than the remaining sticks in hopes that it will help it stay balanced?
The last charge took 4.025 Ah, according to the smart charger.
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