OT Car batteries going flat.

[Dave Plowman (News)]

Yes. The theoretical 2.2v a cell fully charged may not be so on an older battery which still works OK.

[Dave Plowman (News)]

It's said not to be good for the engine, though. Best to take it for a drive.

My old car has a very accurate voltmeter across the battery. And the charge voltage drops as the battery gets full. After a cold start, it will read 14.4v. By the time the engine is fully hot it will drop to 13.8v

[Marland]

What does this BSi control module do?

Reason for asking is that the particular elderly couple whose battery died have had a problem with their auto gearbox doing strange things like dropping into neutral at inconvenient points such when you pull away from stationary such as entering a roundabout and several garage visits both main dealer and an independent have not come up with a cure, about a £1000 spent on diagnostic charges and some electronic bits so far and it is still doing it. One of the reasons they hadn?t used it much even before the present lockdown as they have reached the stage of feeling it too dangerous to drive having had the thing drop into neutral just as they entered a busy fast dual carriageway where you really need to maintain progress as the traffic is moving swiftly all the time.

Be ironical if it turned out the fault originated with the battery all the time.

GH

[AnthonyL]

I've measure this current at 0.05A which will flatten a small car battery in about a month.

[AnthonyL]

My front disks severly corroded because the car was often stationary outside and the water trapped behind the pads. The mechanic couldn't see the funny side of my suggestion of spraying some WD40 to stop it from happening again.

[tabbypurr]

who knows what that means.

[Paul Cummins]

I drive a little(ish) car with a little battery - only 40Ah. It's not a clever calcium battery either.

As long as my battery reads 11.8v, the car will start first kick in normal conditions. It needs 12.2v in a British winter (0c or less).

Within 5 minutes of starting the car, the (actual) battery voltage exceeds 13v, and the alternator is throwing 14.4v at it from startup.

If I run everything electrical, all at the same time, the alternator output drops to 13.9v. So it's STILL charging the car if required.

[T i m]

That's why, if you have the opportunity (you park your car outside in the sun, at least for part of the day), and especially if your ciggy lighter socket stays live when the ignition is off, a small (2W) trickle charger solar panel should be more that enough.

100mA charge even for a couple of hours a day will help enormously and has on a couple of our motorcycles that are outside and used infrequently.

Cheers, T i m

p.s. We fitted an electric fence around daughters rabbit hutch because a fox was seen trying to get at them in the night. Because it was remote it ran from a small lead acid battery that would only last a week. We fitted a 5W solar panel and controller and even though the panel only got the sun over the top of a house and in the morning, in the summer the solar panel would pretty well keep up with the demand. It would also stretch out the time between charges in the winter. I could have fitted the panel in a more receptive position but that wasn't easy and we had spare batteries to swap to with a mains charger if required.

[ARW]

TBH she did it last time and read TMH's book whilst sat in the car.

I usually give it a run to work after the van has broken down.

[ARW]

Drivers door not bonnet with a Scudo.

[harry]

The car is forty odd years old. Dunno if they had such stuff back then

[Brian Reay]

Cars seem to vary when it comes to how long the battery will hold up.

Our CRV was pretty hopeless, even with a new battery. The Smart Car, which has a small battery, is very good, even on a battery several years old.

One thing to consider if relying on driving to charge the battery- modern cars often have smart alternators. They limit their output voltage. It is worth googling the problem.

[Dave Plowman (News)]

The discussion was about car battery chargers...

A plain SMPS may well not have a switch of any sort. The switch on these battery chargers changes the mode.

[Dave Plowman (News)]

Neighbour had one of those on his little used 911. Often saw the AA called out to start it.

[Dave Plowman (News)]

The Kienzle was common before quartz days. Car electric clocks before it - usually made by Smiths, and also used on earlier Rolls - not very accurate. Think that model of Kienzle was only made for a few years, though. Rover used them too.

[ARW]

VH Cavaliers locked the doors when you connected a battery. Not much fun if the keys were in the ignition switch.

My solution opened up all Cavaliers doors.

[Dave Plowman (News)]

Just about every dynamo and alternator ever made limits its output voltage. The internal resistance of a lead acid is so low, you've no option.

[John]

A supercapacitor-based jump starter harnesses power from the weak battery power of your car recharge the supercapacitors within the unit. This happens within a minute or so to push a large amount of current into the alternator of your car and start your engine. Car battery still has enough charge but cannot get it out fats enough. The supercap charger gives instant output.

Supercapacitor car starters:

[Harry Bloomfield, Esq.]

williamwright has brought this to us :

True, up to a point. Full charging capability is available at a tick over, but only if there is little additional load on an alternator. Start loading it up and the voltage will reduce and hence the charge current going into the battery.

[Harry Bloomfield, Esq.]

[e-mail] formulated on Saturday :

That is only applicable to a new/ good battery. As a battery ages, those voltages decline.

A gassing battery produces a perfect hydrogen and oxygen, to create H2O. Which means it is even more explosive than hydrogen mixed with air.

To jump start, it is always best to connect positive to positive, then finally chassis to chassis (or engine to engine) so there is no sparking close to a battery. Disconnect in reverse order.

Likewise when connecting a battery on a car, positive terminal put on and tightened first and removed last. That way a stray spanner shorted positive to car body will do no damage.