Battery Charger problem

snipped-for-privacy@XnospamXpaulhsimon.plus.com(Paul Simon) mumbled:

The big lumpy thing is the transformer which drops the AC voltage to something useful. The thing with plates is the rectifier which converts to DC.

First off, pinch a bulb out of the courtesy lamp or somewhere else easy and stick the croc-clips on each terminal. If it doesn't light up and you're sure the fuses are OK then it's prolly knackered.

Take this advice and you will live longer. Don't much about with mains powered equipment if you don't know what a "big lumpy thing" is for. The big lumpy thing is either the tranformer or the diode pack either way it changes lumpy big electricty into nice flat little electricity -- big lumpy electricity = danger.

Quite a few chargers these days rely on a small current from the battery to pull in a relay via a diode - to protect from polarity reversal or sparks when connecting if switched on. And without that tiny current from the battery, they won't give any output.

but most modern chargers have stupidity circuits built in, especialy the ones that have a fully charged light (means they're aimed at people who don't own or know how to use a hydromiter and/or avo meter)

but the anti stupidity protection circuit in the battery charger works by not allowing any current to flow untill it is sure it's connected up correctly to a battery, and of the correct voltage battery too.. (some people do connect up 12 volt chargers to 6 volt batteries.. so the charger needs 8 or more volts at the terminals before it will switch on)

of course if the battery is totaly dead, the charger thinks it's connected to a 6 volt battery, or none at all, so nowt will happen,

the way round this.. you need some jump leads and a good battery, connect the dead battery to the good battery for a few minutes, if it's on a car you can have the engine running if you want, you just need to get a few more volts into the dead battery, they wont stay there long, but usually there's enough light surface charge left when you connect the charger up again, it'll read the battery as the correct type and start charging.

Dave Plowman mumbled:

There's a thought. Not much I can offer then if the bloke doesn't already recognise the bits inside his charger.

If the battery is so flat it can't supply a few milliamps at 8 volts, I doubt it's worth bothering trying to charge it - it will be knackered.

I'd like to say a big Thank You to all who contributed on this thread.

Special thanks to CampinGazz who got it spot on. The battery was showing only 4 volts on Sunday afternoon, obviously too low to allow those 'stupidity' circuits to let the charger operate.

I finally got my reluctant sister to come round tonight to get some reasonable voltage in.

First thing I did was check the charger on her good battery. It worked perfectly, confirming CampinGazz's theory.

Next I connected jump leads and ran her car for 5 minutes. My battery then read 12 volts, so I could probably run it less to get up to the suggested

Connected the charger up and it seems to be working perfectly.

Thanks again to all. What would we do without newsgroups.

Incidentally, is there likely to be any long term damage to the battery? It did drop down to 1 volt prior to recharging.

I'd find a new dealer...

No.

Any lead acid charger will charge any lead acid battery. Fully sealed gel types like you get in house burglar alarms could be damaged by a basic charger, though, as they require a constant voltage charge.

There a few websites re car and leisure batteries. Worth a look. Aparently a new leisure battery (don't know what the expert view is on vehicle batteries) if allowed to drop below ten volts will probably suffer permanent damage, at least one cell will fail and it will never fully recharge. DaveK.

I've had a sealed 8 year old battery drop down to 4v (stupid high drain car alarm) when left for a few weeks. Charged up again happily but I suspect it had lost some capacity but no cell failure.

I have a feeling that what kills lead acid batteries is leaving them in a discharged state for a long period of time.