"jumpstart" starter eliminates the need for a battery charge

Quite.

The message from Tech&Tool contains these words:

Since when?

It's an American thing. As an acr17 could survive the experience any modern alternators fine.

The message from Duncanwood contains these words:

Quite. I've driven off after jumpstarts from utterly flat batteries in a wide variety of vehicles many times and never suffered. The very worst that would happen is that it would work at its rated maximum for a while.

driving it. Charge the battery.

In which case you also have an unregulated alternator that was stuffed anyway. Probably the reason that the battery went flat in the first place.

Well I've always had the greatest respect for Mr hillier, but I can't accept that. If that was the case, when you jump started something, it would need jump starting again and again until the battery was "removed and bench charged". But as we all know, that doesn't happen.

Steve

Quote:

If the battery is discharged to a point where it cannot crank the engine; and in consequence the engine has to be started by other means, then will be impossible for the alternator to recharge the battery. When it is in this condition the battery must be removed and bench charged because the voltage needed to restore it is higher than the output given by the charging system of the vehicle.

VAW Hillier. "Fundamentals of Automotive Electronics"

He's wrong.

HTH.

cheers, clive

In the particular case of a totally flattened maintenance free bettery it's possible. For most sealed gel-cel, flooded wet batteries, AGRM etc it's no longer the case and an alternator will happily charge a bettery with the

The message from "Ben Doon" contains these words:

Bollocks. I've done it dozens of times and I'm sure there's plenty of others here who have.

While the jump leads are connected enough charge makes it into the battery to up the voltage enough to keep the field coils alive and kciking.

And even if there isn't sufficient oomph to crank the engine, there will still probably be enough to do that without jumpleads - hence push starting works.

cheers, clive

Ben Doon ( snipped-for-privacy@l0vettg1.freeserve.co.uk) gurgled happily, sounding much like they were saying :

How's a battery charger charge a battery?

It puts about 14-15v across the terminals of the battery.

How's an alternator charge a battery?

It puts about 14-15v across the terminals of the battery.

So - why can a battery charger charge a battery if an alternator can't?

The only time that you *could* have a problem is if the battery is SOOOOO flat that the alternator's getting to field charge.

If that's the case, then the engine won't run anyway, because the battery won't have enough charge to run the injection/ignition.

I think you'll find plenty of people in the real world who have found this not to be so.

That applies to a heavily sulphated battery - ie one which has been

He got that one wrong, then.

Something like this happened to me once many years ago - flew off to the sun for three weeks and left the car (P6 Rover 3500S) in a long term car park near Gatwick. Came back to find the battery so flat not even a glimmer from the interior light. Turned out (afterwards) to be the electrically wound clockwork clock which had stalled and was drawing a fairly large current. Got a jump start and drove back to S London - perhaps 45 minutes. The battery was still totally flat. Thank gawd I didn't stall the car.

I installed a spare battery and left the other one on charge for about a week using an ancient 4 amp charger with no regulation apart from a series resistor to limit the current - so probably produced quite a high voltage into a high impedance source. The battery then was ok for at least a year until I sold the car.

Ben Doon wrote on Mon, 31 Oct 2005 14:51:04

-0000:

Well, despite what the book says, I _have_ recharged my battery through the alternator when the battery was discharged to a point where it cannot crank the engine.

So it's rather definitively wrong, at least as a categoric statement.

Dave Plowman (News) ( snipped-for-privacy@davenoise.co.uk) gurgled happily, sounding much like they were saying :

I've done it a few times when things have ceased charging - jump start, and try to limp home. You know you're in trouble when the damn thing misfires as you brake, because there aren't enough sparks for brake lights AND coil...

By "other means" he may be referring to push starting. I've jump started at least 3 cars in my time and at least two of them had no subsequent problems. The other car got the driver to work and then died again that evening; it was an old, old battery and the car couldn't even be jump started the second time. A new battery sorted it.

Does the "Magic eye" on a sealed battery go back to green after a flat battery? I haven't seen one do it... thought the car starts and runs fine after the initial flat battery where the indicator was black.

I have always been told a battery would not FULLY re charge on the vehicle, it many work for some time after the initial flat battery ....but does it FULLY re charge?

Does the "Magic eye" on a sealed battery go back to green after a flat battery? I haven't seen one do it... thought the car starts and runs fine after the initial flat battery where the indicator was black.

I have always been told a battery would not FULLY re charge on the vehicle, it many work for some time after the initial flat battery ....but does it FULLY re charge?

Maybe that word is missing from Mr Hillier's statement?