OT Car batteries going flat.

[Andy Burns]

That happens every wet weekend with modern discs.

[Marland]

snip

You could of course, but in these times where people are confined to barracks those who live in such areas where the only parking is on street in the first vacant spot may well be a little on edge anyway from tensions inside the home, having someone from up the road then revving a car up outside their front room window for30 mins or so might just tip them over the edge to the extent that any brick in the car will have entered through a window and won?t be resting on the accelerator.

GH

[Harry Bloomfield, Esq.]

[e-mail] formulated the question :

No need, you just don't see the dimming as vehicles come to a stop these days, unless the system is under very heavy load. Checking the actual voltage is a much better indication and mine remains stable at

14.2v during tick over, unless presented with a very substantial load.

[Harry Bloomfield, Esq.]

charles was thinking very hard :

Yes. Some ecu's will lose their learned settings, but will quickly regain those over a few miles. You may also need the radio code and to retune the stations.

[Harry Bloomfield, Esq.]

Not a problem if you park under cover, where the discs are protected from bouncing rain and a wet atmosphere.

[Andy Burns]

Don't think it's much of a problem to start with, by the time you've driven off the drive and braked once, the rust may have caused a graunchy noise, but it's gone ...

[Dave Plowman (News)]

You can buy, for not a lot, a device called a battery disconnect. Permanent fit between the battery earth terminal and the lead. Large thumbscrew which you undo a couple of turns to disconnect. Just needs tightening to connect again.

Also useful for checking quiescent current. Use a DVM to connect to the battery initially, and there's a chance the inrush current will blow its fuse. Also saves powering down things that need constant volts.

With this device you wire the DVM across it, then use the 'switch'. No interruption to the supply.

[NY]

"Harry Bloomfield"; "Esq." [e-mail]> wrote in message news:r6790g$982$ [e-mail]...

I'm surprised that ECU and radio settings (except security code) aren't held in permanent memory - eg pen-drive type memory - to allow for the battery being disconnected during routine maintenance.

[Dave Plowman (News)]

Lots of people seem to think it causes all sorts of problems if you disconnect the battery. I've yet to experience this.

Lets hope if your radio has a security code you have it. Otherwise you'll be in trouble when it's new battery time.

[Dave Plowman (News)]

If you draw extra current with the engine idling, there's a good chance the volts will drop. This doesn't mean they're not as high as possible with the engine idling and only charging the battery. No modern alternator will use the full 150 amps or so just to recharge the battery. They are limited to 14.4 volts or so.

[Paul]

Exactly. Car electrical systems are still just a "hunk of iron". There's no sophistication there.

For battery charging, you can use one of these.

No claims for using it for long periods. Don't clip it on for ten years, and then complain about the outcome.

Works best if the engine compartment has cooled off, and the charger and battery are at the same temperature. It's possible it is temperature compensated inside (has the internal table of [voltage,temp] versus fill_level).

Turn off the courtesy (dome) light in the car, so state of car doors doesn't make a difference.

I have one of those chargers, but it's only clipped on for a few days at a time (as needed). Since I got a brand new alternator (not a rebuild), I haven't needed it. The leads and connection method, leave a bit to be desired.

You might not find one of those at the car parts store. But have a look around, I'm sure there's a local design available somewhere.

Paul

[Dave Plowman (News)]

I reckon many modern cars have the idle speed rather higher than it could be. To make sure the battery is near always on charge.

[tabbypurr]

Mine dim a bit at idle, yours might not. The only way for each car owner to know is to try it.

NT

[tabbypurr]

and that the display still works so you can enter it.

Nah, plug another battery into the cig lighter socket, switch it on then change the main battery

NT

[Fredxx]

That's if you can anticipate a battery change. I've had an alternator fail with no ignition light and with reducing volts the first thing to fail was the radio.

A number of procedures for work on the car often involve removing a battery connection.

[John Kenyon]

On 03/04/2020 09:01, harry wrote: <snip>

If you own a Peugeot or Citroen, there's a good chance you'll screw up the BSi (aka body control) module, if you don't follow the correct disconnect and reconnect procedure.

[Paul]

For routine maintenance, I use a "holder".

It's a DC source, with a diode for one-way current flow.

Once the holder is hooked up, when I disconnect the battery, there is sufficient voltage left to maintain car radio codes and ECU.

Before doing this, switch off the dome light in the car, as you'll be in and out of the driver area while working on the car. The lighter socket is one place to hook up for your holder.

The holder is only for battery maintenance. Do not try to insert the ignition key in the drivers position while the holder is holding up the electrical system voltage. The holder is just for battery maintenance (change-out of battery, take battery to side of car before charging, that sort of thing). The fuel pump can draw 20 amps, and if you accidentally trigger the fuel pump to start running, that'll cause your holder to shut off on overcurrent (or potentially burn the series diode you fitted it with).

I mainly tried this, because I wanted to see if it would work.

Paul

[Chris J Dixon]

Some of them are. The most recent one I mounted in my caravan seems to have adequate non-volatile memory, which is handy because caravan electrics automatically isolate the interior supply when towing.

Chris

[Chris J Dixon]

I went to some trouble to make sure I had the code for the radio in one of my used cars. When I needed to remove it from its housing, there was a piece of paper helpfully stuck onto its casing. :-(

Chris

[Dave Plowman (News)]

Of course they are. They might take a short time to adapt to the octane of the fuel being used, though.