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OUPower.com • View topic - An interesting battery.

An interesting battery.

Do you have a project you're working on that doesn't fit into any of the forums above? Please post about it here.

An interesting battery.

Postby mael » Tue Dec 22, 2009 3:36 pm

I've been trying to fix a 42 A/h car battery.

When it came in it seemed reasonably fit. The end cells were a little weak and the rest were about all right.

Then I put it on a pulse and kept it at about 15.3 V for nearly three days. And then I tested it for power. It seemed to have only 60% of its rated capacity. Then I charged it after the test and measured the electrolyte and was very surprised to see all the cells were registering about 1100.

???

I told the owner of tha battery that I was sorry but there was something wrong with the battery that I couldn't fix. and he then said he'd overfilled the battery after it failed to start his car - a few months prior. I mean he filled the cells to the top. (I don't know exactly what he did or what he put in it).

So I said I'd see if I could adjust the mix, and that I'd get back to him in a few days.

I ended up putting a startling amount of acid in to get the cells to around 1280, and then did a charge - but it didn't need charging so I set it to work on a discharge test. And it scored about 90%.

So I charged it after the test and I have just measured the cells again and they are sporting electrolyte measuring about 1180 each. all the same!

And another funny thing is that it's been resting for a day and the voltage is around 13.4 and holding.

And, I did a short test with a 6 A load and the voltage didn't plunge at all - rather it went down to 13.1 after a few minutes, and climbed straight back to 13.4 in less than a minute.

Then after the short discharge test I put it on a charger, and it took 7 A and rapidly went down to negligible. ie - it behaved well.

So I'm really confused.

If the electrolyte is in the red then the resting V should be low.

I became confused when, after the first test and charge after pulsing, the electrolyte was so weak the float was barely sticking out of the liquid. And this was before I added anything at all. I was confused because when I first got it the electrolyte was basically all right.

And now, after 400 cc or so of pretty concentrated acid (around 1600) added to the whole battery after a measured amount was removed from each cell, the SG is an improvement over how it was after I charged it, but by the looks of it it'll need another 300 cc of the same to get it approaching the green zone (1250).

... BUT!!! If I do that, then what's the resting voltage going to be like? 14???

* Has some as yet unknown (to me) substance found its way into the battery? Did the man who filled the battery use some weird additive which alters the SG of the electrolyte, but still makes it pack a punch? I'm sure he wouldn't know even if he did.

What is happening?

The guy's coming tomorrow, but I'm going to tell him his battery is not right - which is true. But what isn't right is that it is packing far too much power. (If it's too good to be true, then something's wrong).

I can see me removing some more acid and adding stronger stuff so that the contents satisfy the SG requirements, but the results so far indicate that if I do that then the voltage is going to be way too high.

Suggestions?
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Postby mael » Tue Dec 22, 2009 4:34 pm

I put it on 'charge' anyway. the charger I'm using with it is a transformer-type and has an open v of 15.3. The battery is on it now and the terminal V is about 15. Not that this means much to anyone except me, but this means the battery is drawing milliamps and is quite happy at that elevated voltage.

there is bubbling, but only the tiniest of bubbles, and the battery case temperature is no diferent from the ambient.
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Postby mael » Wed Dec 23, 2009 9:07 am

Well - I'm going to boil-down some electrolyte and add this to the cells after I've removed a measured amount from each one.

Then we shall see. I'll get the acid prepared as from about now. It'll take a few hours to boil it down enough for my liking beforfe adding it to the electrolyte.

Any suggestions?

* I thought maybe the plates had become detached and the sulphur was on the shed material so it couldn't be zapped back to the electrolyte. But it's got a lot of power so this doesn't seem to be the case.

But it must be something???
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Postby redriderno22 » Wed Dec 23, 2009 3:07 pm

If i were you mael id keep that battery

and study it

give the guy a diffrent one

very intresting
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Postby mael » Wed Dec 23, 2009 5:49 pm

I have adjusted the electrolyte. All cells are about 1280-90.

I put it on a discharge test an hour ago. On a 5.5 A load, the V dropped from 13.5 to 12.90, where it is at now.

I'm going to just let it discharge until I wake up, which will hopefully be in about 7 hours. I wonder how it will be?
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Postby mael » Fri Dec 25, 2009 3:04 pm

Well the battery wasn't anything remarkable in a good way.

I got the SG at about 1280 and charged. It took longer than it normally does to charge to 14.4 V.

... Tried it on a discharge of 5.5 A and thought it looked good for being over 100% of spec.

The initial V was around 13.6, and under load it went down to about 13.1.

But unfortunately it didn't sit there. Rather it gradually dropped and after three hours I noticed the V was about 10.0 and pulled the plug.

The V soon went back to 12.7, and it has sat at that mark for the last 15 hours.

So it's poked. I suppose the electrolyte has swallowed a fair bit of my available acid, so I want to save the electrolyte out of it before sending it to the dump. But I am not too sure about what might have found its way into that mix, as the battery was certainly acting strangely.

So that's about it I suppose.

End of report.
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