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Bryan1

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Joined: 22/02/2006
Location: Australia
Posts: 1450

Posted: 12:14am 28 May 2011

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Hi Guy's,
I do remember reading on the net ages ago by supplying a small current one can restore old sla batteries. I do have 5 old 12 volt 7ah ones here that just went flat over time of no use so I grabbed a 68 ohm resistor and hooked the battery to my nife bank. At first the battery was just reading the nife bank voltage so I thought the battery was dead but I left it on anyway. A fortnight later the battery was showing 11.78 volts so I took the negative lead off and left it for a couple of days. The voltage reading was 11.56 volts. Put the lead back on and 3 weeks later 12.67 volts. I took the negative lead off again and put a 75 watt 12 volt spotlight on for 3 minutes and checked the voltage drop. 11.98 volts 3 minutes later 11.87 volts.

It does look like the battery is on the way back so I'm going to leave it connected and eh it might take another month at that small current but if this trial does workout it will save buying new batteries for my electric fence. I do know I won't get the 7ah again but eh even if it's half that it will be a bonus.

Cheers Bryan

RossW
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Joined: 25/02/2006
Location: Australia
Posts: 495

Posted: 02:21am 28 May 2011

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Bryan1 said Hi Guy's,
I do know I won't get the 7ah again but eh even if it's half that it will be a bonus.

I took 400Kg of them to the recyclers not that long ago, Bryan. You could have taken a bunch of them for the price of scrap mate!

I'm not running a heap of "small" 3KVA UPSs any more, so unlikely I'll collect more than a few dozen over the next year - do you want me to keep any?

(Reminds me - I have to get about 2 tons of old SLAs out of the garage and down to the recyclers while they'll pay me something for the lead, rather than charge me to get rid of them)

Bryan1

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Joined: 22/02/2006
Location: Australia
Posts: 1450

Posted: 06:26am 28 May 2011

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Hi Ross,
I'll chat wiff ya in IRC over that stuff mate.

Anyway I put the battery onto my smart charger ( the siliconchip Mk2 one) and charged it twice. The resting voltage was 12.8 volts so I put the spotty on and the voltage dropped to 11.9 volts and stayed around that until I took the spotty off. Then it went back to 12.7 volts at rest. I put the battery back onto the nife bank with a 27ohm resistor which is supplying 70-75mA's of current to top it up.

I reckon this first trial has been a success and I have put 3 of the other batteries on now too. I'll leave the battery on the nife bank for another week then I'll do a discharge test and see if this has all worked out.

Cheers Bryan

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