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Old 2nd May 2009, 03:34 PM   #21
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Quote:
Originally posted by Steerpike

I have only a cheap car battery charger (transformer - rectifier - thermal cutout); even a 'dead' battery always manages to get about 2 to 4 amps from it, but a dead battery never fully charges - even after several days. Hydrometer testing always shows 5 fully charged cells and one flat cell.
I had several batteries like that, where one cell is lower than the rest. After long, and slow overcharges, it eventually equals them out.
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Old 2nd May 2009, 07:02 PM   #22
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Quote:
Originally posted by EWorkshop1708


I had several batteries like that, where one cell is lower than the rest. After long, and slow overcharges, it eventually equals them out.
Oh really? How long is 'eventually'? I gave up after about 72 hours, but maybe I should have left it longer. This is ALWAYS the reason I have to buy a car new battery - was that a waste and I could have restored the battery by charging long enough?

I keep meaning to build a low current charger (les than an amp) that I can leave on 24/7/365.
 
Old 2nd May 2009, 09:32 PM   #23
star882 is offline star882  United States
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Quote:
Originally posted by Steerpike
I keep meaning to build a low current charger (les than an amp) that I can leave on 24/7/365.
Just take an unregulated 12v wall wart and connect it to the battery.
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Old 4th May 2009, 09:16 PM   #24
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I'm in the process of trying this out on a completely dead battery that was in a car I've had sitting for a long time. I tried charging it with my car charger but it just keeps cycling on/off.

I was trying to get a 60w bulb hooked up to the circuit, but getting a wire attached to the steel base of the bulb proved to be an excesses in futility. I ended up using a 7.5uF motor-run cap instead.

When I first plugged it in the voltage was around ~17V and has slowly dropped to ~12.4V (and still dropping). Current draw measures around 270mA.

I will post back with my final results later.
 
Old 5th May 2009, 12:48 PM   #25
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Success!

I left the "desulfator" on the battery for around 5 hours at which point the voltage was ~12V. I felt this was high enough for my automatic charger to take over so I set it at 6A and left it over-night.

After the charger completed it's charge cycle the voltage was ~13V with the charger in trickle charge mode. I then connected the battery to a transformer out of a an old linear regulated 12V 10A supply (with a rectifier of course). After just a few minutes the voltage was at ~15.5V and the electrolyte was boiling rapidly. I think I need to put some resistance in series, the transformer is capable of too much current.

Anyway, it seems to have worked on this >5 year old battery. I will probably do a slow discharge and charge it back up again before putting it back in the car.
 
Old 5th May 2009, 05:13 PM   #26
jkeny is offline jkeny  Ireland
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moderators, why am I getting no email notifications from this thread even though it says I'm subscribed?
 
Old 7th May 2009, 02:57 PM   #27
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Quote:
Originally posted by theAnonymous1
Success!

I left the "desulfator" on the battery for around 5 hours at which point the voltage was ~12V. I felt this was high enough for my automatic charger to take over so I set it at 6A and left it over-night.

After the charger completed it's charge cycle the voltage was ~13V with the charger in trickle charge mode. I then connected the battery to a transformer out of a an old linear regulated 12V 10A supply (with a rectifier of course). After just a few minutes the voltage was at ~15.5V and the electrolyte was boiling rapidly. I think I need to put some resistance in series, the transformer is capable of too much current.

Anyway, it seems to have worked on this >5 year old battery. I will probably do a slow discharge and charge it back up again before putting it back in the car.
Sweet! Glad to see you got that old battery to take a charge.

7.5uf, pretty sweet. Is there any heating of the capacitor, or does the circuit remain cool?
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Old 7th May 2009, 06:02 PM   #28
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Quote:
Originally posted by EWorkshop1708


Sweet! Glad to see you got that old battery to take a charge.

7.5uf, pretty sweet. Is there any heating of the capacitor, or does the circuit remain cool?
The cap and rectifier remained completely cool.

I'm not too good at this stuff, but doesn't the cap form a first order high-pass filter? If so, according to the current draw I measured (~270mA), shouldn't the cap be dissipating around ~32W? It didn't feel like it was dissipating any power at all.

I would like to find another battery and try this again with a slightly larger capacitor.

EDIT: Oops, there was a flaw in my above thinking. I didn't measure the current draw on the AC side, I measured it on the DC side when the voltage was under 12V. That would make it more like 3W of dissipated power in the cap, correct?
 
Old 7th May 2009, 06:18 PM   #29
luka is offline luka  Slovenia
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cap be dissipating, well cap don't dissapate anything [not 100% true], it blocks, slows, however you want it... it is not like resistor
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Old 7th May 2009, 06:41 PM   #30
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Originally posted by luka
cap be dissipating, well cap don't dissapate anything [not 100% true], it blocks, slows, however you want it... it is not like resistor
Oh, I thought it acted like a resistor below Fc. So actually, if it does work as a high pass filter, the higher the internal resistance of the battery (due to sulfation) the more current flow there is in both the battery and the capacitor.

I have no clue what I'm saying.
 

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