charge battery while battery still connected?

Just would like to know if it is ok to charge a car battery while the battery is still connected in the car. (Engine and all switchable electrics off). Is the output wave of the charger likely to zap the car electronics?

The reason I ask is that an elderly person needs to switch off and unclip the charger croc clips after the battery is charged overnight.

They are not up to reconnecting the battery main earth by themselves.

Thanks

Reply to
dave
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Well, the car alternator manages this and it has a far higher output than a domestic battery charger.

That's fine. Just remind him to switch the mains off before unclipping.

No need to anyway. It might be prudent with one of those vast trolley mounted garage fast chargers - but even then I doubt it.

Reply to
Dave Plowman (News)

it will be fine, don't worry about it. A new battery may prevent having to do it again. However, if it is going to be a regular occurence you might want to get a modern intelligent charger and leave it connected to the battery permanently. the modern ones will not draw anything out of the battery and just need to be plugged into the mains. this would obviate any reversed connections that old folk do quite often (probably due to poor colour vision) , they also do not need to be turned off after so many hours, and can be left switched on and connected indefinitely, and they prolong the useful life of the battery.

Mrcheerful

Reply to
Mrcheerful

Agist remark. ;-) Youngsters who don't know their a**e from their elbow are equally as likely to. Especially when so many cars don't use red and black for the battery connections. And use brown for ground.

Reply to
Dave Plowman (News)

I agree, lots of people do it, but I have found that elderly people do it more often, and even with sparks flying they carry on trying to connect !!! Ever watched someone non technical trying to use jump leads? it is like bonfire night.

Mrcheerful

Reply to
Mrcheerful

:-) thanks.

Reply to
dave

DP will tell you otherwise but when my battery went very flat it wouldn't charge while still connected to the car.

Reply to
adder1969

In all the times I have recharged batteries on cars (many hundreds) I have not come across that, so although you have. it seems it may be a rare occurence, possibly something on that particular vehicle sucking all the current that the charger could put out?

Mrcheerful

Reply to
Mrcheerful

My charger will refuse to charge a battery that's below a certain level. Perhaps yours is the same and the draw from the car's clock or whatever was just enough to drop the battery below the threshold.

Mind you, if the battery's that flat, it's probably doomed anyway. I managed to resurrect a totally flat one sufficiently to drive to the scrapyard once by connecting jump leads from a good battery for half an hour and then topping it up with the charger, but it wouldn't have got me much further.

Reply to
Willy Eckerslyke

And never ever let someone you don't know connect their jumpleads to your battery. DAMHIKIJD OK

-- Malc

Reply to
Malc

I've charged batteries without disconnecting on dozens of cars without any problems. I'm still using a charger about 40 years old, inherited from my father, who taught me the basics of car maintenance all those years ago.

I used to service my uncle's Minis and he once had a new battery fitted (can't remember by whom), and they had actually fitted it the wrong way around, i.e. positive to negative and negative to positive! Fortunately I spotted this and corrected the problem, which involved repolarizing the alternator (or was it a dynamo in those days?). Luckily, no harm was done. This is one of the catalogue of disasters I've experienced with so-called garage 'servicing'. I never allow my car near a garage unless I absolutely have to. I carried out my own services for over forty years and never had any problems until I bought a newish car and had to have it serviced at the dealer under the terms of the guarantee. This is when my problems started - too numerous to go into detail. The incompetency I've experienced is beyond belief (and it's grossly expensive).

Terry D.

Reply to
Terry D

Not Gamages brand by any chance? I only threw mine out quite recently when the case had rusted to an embarrassing state. It's the new one that's fussy about not charging totally flat batteries, I suspect because its polarity checking won't work unless there's enough charge to give it an indication.

Well there wouldn't be, would there. They probably thought they were doing your uncle a favour by converting his old Mini to negative earth. Can't see why you'd want to change it back unless there was a radio fitted.

Reply to
Willy Eckerslyke

That's a feature of smart chargers, the dumb ones still work. (The smart ones need a little voltage to check the battery's the right way round.)

Reply to
Duncan Wood

Some battery chargers require a few volts from the battery to pull in a relay in them - basically to prevent reverse connection. So if the quiescent load from the vehicle was such as to pull down those last few volts I can see this happening. Not sure that battery would ever be ok again, though.

Reply to
Dave Plowman (News)

Used to be a common occurrence with UK cars overseas or in the UK with non UK owners - as many countries never changed to positive earth as much of the UK makers did between about the '30s through to the '60s. The change back to negative earth was due to solid state electronics. Before those electronics nothing would be damaged by incorrect connection - but the dynamo wouldn't charge.

Reply to
Dave Plowman (News)

I recently had a hair-raising experience doing this - the battery caught on fire, and I had two-foot flames coming out of it very close the fuel lines. It even ignited the lining of the bonnett. What happened is that I had been charging it for a few hours, and when it came to disconnecting the crocodile clips I think there must have been a spark (I had the negative on the chassis near the little vent pipe on the battery) and this spark must have ignited the gas that all batteries give of when you charge them. The instructions with chargers always say to charge batteries in a well-ventilated area away from the car. Mine did say in an emergeny you should only charge in the car after disconnecting it from the car electrics first. I am sure they say this because of the fire risk, and you ignore the guidelines at your own peril! GTS

Reply to
GTS

Some cheap battery charges, are crude devices. They often employ half wave rectification of a stepped down 50 Hz supply. As they are not usually regulated suffice to say my the rise in potential accross the battery, as it charges, hence a drop in current. It is possible, if a lot of arcing occurs when connceted, the the voltage spikes generated, could damage sensitive silicon devices, such as IC's in some management systems. As someone stated, not a good idea to connect with the supply on!

Incidentally, alternators are usually 3 phase, with full wave rectification, and are both voltage and current regulated, therefore cannot really be compared to a battery charger, unless is is a reasonably sophisticated device.

Mr Popular LOL

Reply to
Pat Crouch

This why you don't connect both the clips to the battery, then you can disconnect well away from the battery, just in case. Same with jump leads.

Mrcheerful

Reply to
Mrcheerful

The idea of connecting the negative to the chassis is to do it away from the battery. Certainly not anywhere near a pipe venting explosive gasses that you're trying NOT to ignite.

Reply to
David Taylor

Let me get this quite clear. You remove the battery from the car before letting the car alternator charge it? Something not quite right there...

Reply to
Dave Plowman (News)

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