Test SAFT batterys under load as a well as by voltage

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arsharpe
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Test SAFT batterys under load as a well as by voltage

Postby arsharpe » Mon Aug 02, 2010 6:05 pm

This maybe obvious to some of you, but I have included here as it gives real data to back up the practice.

Before examining my Berlingo batts, I ran the vehicle until low charge light came on (at about 45%) to help identify the weakest cells. All cells (within the middle pack) were within 0.02v apart from one which we replaced. Anyway, we ran around the other cells with a battery tester set to 125A and tested for about 5 seconds not expecting any issues. However, one of the cells dropped by just under a volt over the 5 sec period, even though it was in a low state of charge and its voltage was within 0.02 of the others at the start of the test.

So the moral of the story is that it is worth doing a load test of 125A for 5 secs even if the voltage looks ok.

Summary :-

Dudd cell
...o/c voltage = within 0.02 v of other good cells.
...125A 5 sec load volt drop = approx 1 v
...recovery time to 0.02v of other good cells = TBC

Good cells
...o/c voltage = 6.02v (50% charge)
...125A 5 sec load volt drop = approx 0.25 v TBC
...recovery time to 0.02v of other good cells = TBC

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ChrisB
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Re: Test SAFT batterys under load as a well as by voltage

Postby ChrisB » Tue Aug 03, 2010 12:31 pm

Might also be worth carrying out a capacity test as it may well be that the battery has just become "un-blanaced" from the rest of the pack.

As you say terminal voltage cant be used an indication of condition, load testing or better, capacity testing is always a safer bet.

ChrisB
I reject reality and substitute my own !!!!!!

arsharpe
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Re: Test SAFT batterys under load as a well as by voltage

Postby arsharpe » Tue Aug 03, 2010 12:42 pm

That is the plan ;-)
The unbalancing is unlikely as I did part initialisation charge (which only got me an extra 10%)
I will take more accurate readings when rerunning tests.

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ChrisB
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Re: Test SAFT batterys under load as a well as by voltage

Postby ChrisB » Wed Aug 04, 2010 7:23 pm

Really depends how far out of balance a battery or even a cell has become from the rest of the pack.

The fact it just sagged underload makes me think there may not be a lot wrong with it, that say an extended charge wouldnt fix :? Dunno these Nicads are funny old beasts but todate I've really only ever had them fail or work with nothing much in between.

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Cogito
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Re: Test SAFT batterys under load as a well as by voltage

Postby Cogito » Tue Aug 24, 2010 6:21 pm

Were the modules fully charged before load testing?

Collapse of voltage when almost discharged is normal. Try reconditioning by cycling at 5 amps down to a threshold of 2 volt. Pulse charging at very high efffect of 150A kan also help to skift to capacity under 5 volt up to a more useable voltage.


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