What's likely to be wrong with this car?

[bert]

[The Natural Philosopher]

The electrics is used to charge voltage - has to be.

Anyway 99% of the electrics is off when car ignition is off.

It

[The Natural Philosopher]

Theres a lot of difference between unable to crank a starter and zero volts

[NY]

Most radios/clocks seem to have a higher threshold that whatever terminal voltage is available while starting, if the battery is almost flat. A flat battery in my cars almost invariably means that the clock resets when I try to start the engine; I think it's very rare that I *haven't* had to reset the clock in that situation. That's in all the cars I've had which have had a digital clock. Luckily most of my cars haven't had a coded radio - there was just one where I had to find the code and the instructions on how to enter it into the radio whenever the battery failed to operate the starter.

Next time I have a flat battery (which I hope will be never!) I'll have to get my voltmeter out and see what the terminal voltage drops to when I start the engine.

I know that the battery is *really* dead if the lights *don't go out, because that means there is so little current available that it won't even operate the relay to switch the heavy duty starter motor current :)

[Clive George]

Bonnet ajar, doors locked - why risky for theft? I might not do it onto a street, but a drive in most places would be fine.

Removing the battery can be quite a PITA. Hefting that great lump around etc. I never bother :-)

[Dave Plowman (News)]

If you can't charge the battery with it connected, how would you get away with jump starting a car?

Hardly. Most cars have room for the charger under the bonnet. So just route the mains lead out underneath the car and shut the bonnet. Might be more tricky if the battery is in the boot, though.

It's a lot more work. ;-)

[Bill Wright]

Assuming there are no poor connections the charge rate won't vary much with the load from lights etc. The alternator maintains the same voltage irrespective of load. The alternator is more than capable of powering the lights, heater motor, etc, and also charging the battery.

I drive a vehicle with digital ammeters and I observe this fact frequently. I turn the headlights on, the voltage and charge rate dip down momentarily, then they resume their previous position.

The idea that you can't charge the battery if you have the lights and the heater blower on is a hangover from the days of dynamos. They had a max output of, typically, 22A, and SFA on tick-over. A modern alternator will produce 20A at tick-over and over 80A when the engine is running normally. The alternator in my 20 year old motorhome will power a 24V

45A microwave and still charge the battery at 20A, power the headlights, etc. (Yes, we use the micro when we're moving)

Bill

[Bill Wright]

Some Jap cars have a 15V alternator output. Doesn't seem to hurt the battery and the charge rate is better. Probably blows bulbs though.

Bill

[charles]

when I fitted an alternator to my Anglia, the extra load was too much for the pressed steel pulley which broke, I had to buy a cast one - which Ford were able to supply.

[Dave Plowman (News)]

I've a feeling many car makers now set the idle speed rather higher than it need be purely to provide enough output from the alternator.

[harry]

The pulley on alternators is smaller than dynamos. The alternator performs better because it runs faster. It can run faster because there's no commutator.