while i have the HV battery out of my gen1

He is doing it right and there is no problem. I would only go up to 8V and then do a discharge to 7.8-7.9V. Then do the same for the three replacement modules. Now comes the hard problem, finding the weakest modules.

The approach is to put a known load, say a tail light bulb, on each individual module for a fixed period, say 60-100 seconds using an accurate watch, and see which modules drop the greatest voltage. The two weakest are dropped from the reassembled pack. You also use this survey to pair the strongest and weakest module pairs with the strongest pairs in the middle and weakest on the ends.

Now pairing the modules, two strategies come to mind but it isn't clear to me which makes most sense:

• closely paired modules with strongest pairs in the middle and weaker on the end
• strong and weak modules paired and using the average to stack stronger in middle and weaker on ends

Of the two approaches, I'm leaning towards the first but can't give a strong reason why. If a weaker pair fail, having the two together might simplify a future repair . . . planning for the end game of the NHW11 modules. However, the second strategy, especially if the stronger is always on one side so they isolate the weaker ones, might minimize weak module heating concentrating. I'm certainly open to other suggestions.

Before assembly, be sure and clean the terminals with distilled water and throughly dry. Also, make sure the buss bars are clean and free of corrosion. Be careful with the sense wires as any corrosion makes them fragile and subject to breaking. Easy to repair but . . .

It sounds like you have a high probability of being on the road early next week! Just work carefully because you really don't want to do this again.

Bob Wilson

 

John,
You are correct. I was wrong. (That's what I get for skimming to fast and multitasking!)
Since they are in parallel, it is safe (.05 amp per module). And yes, it still will take a long time.

 

An easy mistake and something we are all guilty of from time to time "I know I am". The important thing is you were using caution and trying to keep things safe obviously important with the voltage and current capabilities of 38 modules in whatever configuration.

John (Britprius)

 

Don't worry too much about the least significant digit of a VOM.

From the data you've posted, I see two candidates for replacement. It makes sense to test the two apparently weakest modules with the three replacement ones in a parallel charge to equalize and then discharge test. Keep the top three and put the bottom two aside as weak.

Now if the three replacements do not arrive today, I would take the time to use the discharge through light test for a fixed interval, 100 seconds. Unlike self-discharge, the fixed load will put a significant load for a finite time on the modules and should more reliably identify the weaker modules.

One last balance charge, parallel, for all modules and then reassemble and put in the car. Work careful on the reassembly. I would put the longer buss bar assembly on first. If I remember correctly that also includes the sense wires. It is easier to test the sense wires to the plug now than later in the car.

Because the split buss bar has a jumper that won't be in, your voltage risk is 'less bad'. Carefully reassemble . . . "one hand rule." Button up and back in the car.

Bob Wilson

 

Hummm, you might find a quick refresher on the tags to make a table. For now, assume that "*" is the same as "[".
*table]
*tr]*th]header_1*th]header_2*th]...*th]header_last
*tr]*td2]data_1*td2]data_2*td2]...*td2]data_last
*/table]

So with the "[" you get:

	Column 1
0	[tr][th]header_1[th]header_2[th]...[th]header_last
1	[tr][td2]data_1[td2]data_2[td2]...[td2]data_last

Bob Wilson

 

These are the one I'd probably look at:

	Column 1
0	[tr][td2]38[td2]7.76[td2]7.60
1	[tr][td2]8[td2]7.77[td2]7.60
2	[tr][td2]19[td2]7.77[td2]7.60
3	[tr][td2]28[td2]7.77[td2]7.60

The next set may also be weak as the least significant digit is the only real change. Module #38 looks the worst only because of the self-discharge. The others are just suspect.

Let's go over some of the engineering. Your 2.28A lamp for 60 seconds was 2.28*(1/60) Ahr load, 0.038 Ahr discharge. Small steps are always best but they also give a clue as to what sort of values make sense (and are safe.)

Take the above candidates and parallel balance them back to 8.0V. Then using the lamp for 10 minutes, 0.38 Ahr, report the starting and stopping, unloaded voltage. The 10 minutes puts a fair load on the modules and the voltage difference gives us a rate of dV/dC (C amp hour.) This will give a solid ranking of the strength, the amp-hour capacity, of these modules . . . a definitive assessment.

There is another approach, put the load on and measure how long it takes to reach a common, target voltage, say 7.2-7.4V. Just use the measured time and dV to calculate the dV/dC. . . . Often there is more than one way to 'skin a cat.' It might be easier than trying to hit 10 minutes. <grins>

Use the same approach with the replacement modules to figure out the best set. Then parallel charge the selected 38 modules to 8.0-8.1V and you're ready to go.

Bob Wilson

 

Correct.

Your earlier tests suggests the charge should be fairly quick, less than an hour, and four, 10 minute discharges, another hour. This will give a better idea of the health of those four modules. The idea is to be able to rate their capacity and compare to the three coming in. Eventually the top three, one for the failed module, and the next two for the strongest set.

My back of the envelope suggests two hours should handle it. Remember, this is just to get the pick of the litter.

Bob Wilson

 

Looks like you've got your order and #38 looks the strongest of the lot . . . a keeper. The others are so close, not hardly one worse than the others although #8 might be a flea's hair weaker. But we have enough information to estimate the Ahr capacity.

~0.65V/(2.28*(10/60)) = 0.65/0.38 = 1.7V/Ahr
8-6 ~ 2V normal range (conservative)
2/1.7 ~= 1.17 Ahr . . . fairly weak, an estimate

What is important is you now have a credible test, with stronger, more trustable results than the single digit earlier tests, to evaluate the modules.

Bob Wilson

 

Even if you keep them as spare, you still want to know how good/bad they are.

Bob Wilson