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dodgy lead acid battery

Have one of those 12v jump starter light compressor things, don't know wher e it came from. The allegedly 17Ah battery in it showed no output, so hooke d it up to an old dumb unregulated charger & left it, walking by it now & t hen. Charger put out about 15v.

It began to take a tiny trickle of charge, hardly any. Then to my surprise I saw it sucking up 3A of charge! What's more it appeared to work, at least on a 1W load. But the charger switches every so often between 4A charge an d near zero, with the built in battery voltmeter showing about 11v when 4A, 15v when near zero amps. With charger disconnected the battery sits at abo ut 8v - I've not yet measured its terminal volage when it's behaving better .

Obviously the battery is in a sorry state, but what exactly is wrong with i t? I don't expect to replace it, not worthwile.

NT

Reply to
tabbypurr
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ere it came from. The allegedly 17Ah battery in it showed no output, so hoo ked it up to an old dumb unregulated charger & left it, walking by it now & then. Charger put out about 15v.

e I saw it sucking up 3A of charge! What's more it appeared to work, at lea st on a 1W load. But the charger switches every so often between 4A charge and near zero, with the built in battery voltmeter showing about 11v when 4 A, 15v when near zero amps. With charger disconnected the battery sits at a bout 8v - I've not yet measured its terminal volage when it's behaving bett er.

it? I don't expect to replace it, not worthwile.

It is hard to say without measuring individual cell voltages, but I bet you have one cell shorted and the others may not be in very good shape. Takin g current doesn't mean it is storing the charge. The question is how much current can your draw? But with a no load voltage of 8 volts it obviously isn't going to do much.

Rick C.

Reply to
gnuarm.deletethisbit

where it came from. The allegedly 17Ah battery in it showed no output, so h ooked it up to an old dumb unregulated charger & left it, walking by it now & then. Charger put out about 15v.

ise I saw it sucking up 3A of charge! What's more it appeared to work, at l east on a 1W load. But the charger switches every so often between 4A charg e and near zero, with the built in battery voltmeter showing about 11v when 4A, 15v when near zero amps. With charger disconnected the battery sits at about 8v - I've not yet measured its terminal volage when it's behaving be tter.

th it? I don't expect to replace it, not worthwile.

ou have one cell shorted and the others may not be in very good shape. Tak ing current doesn't mean it is storing the charge. The question is how muc h current can your draw? But with a no load voltage of 8 volts it obviousl y isn't going to do much.

I didn't have any half decent tools or instruments with me, will get more i nfo soon. 8v might be enough to run the compressor, but I suspect ESR will say no. Sometimes it gives around 12v, sometimes 8.

NT

Reply to
tabbypurr

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