Batery charging - brain fade day?

Yup

NT

Reply to
tabbypurr
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I've a feeling the first alternator fitted as standard to a Mini had a pretty weedy output too - very little more peak than the dynamo. But obviously producing that at lower revs.

It could well be a larger one had been fitted - this was a common mod where extra lights etc were used.

Reply to
Dave Plowman (News)

Did you have it from new? Could be a previous owner fitted an uprated one. Or the factory ran out of standards ones. ;-)

Reply to
Dave Plowman (News)

This is oft quoted. I've not seen that high a voltage from a standard self contained alternator. Newish ones which are controlled by the car ECU may well do.

The 14.4v IMHO dates from dynamo days and batteries that needed topping up regularly.

Reply to
Dave Plowman (News)

when I fited an alternator to my Anglia, the extra load on the fanbelt tended to cause the pressed steel pulley to break. I discovered that there was a cast one as an "extra". No more problems

Reply to
charles

It was new in 1973, at which point it would have had an alternator according to Adrian, so it's no surprise it still had an alternator when I got it in 1979.

Previous owner was an 80 year old who used it once a week to go and buy the chicken feed for his 24 chickens, and take his wife to the shops. He never got used to releasing the built-in steering lock (something his previous Morris Minor didn't have), so he always left the car parked with the key in the ignition.

Reply to
Andrew Gabriel

I'm sure you're right. Though I did encounter a BMW 3 series that put out higher. Battery needed replacing every 2 years.

13.6 x 50A = 680W. I gather you can get far more power out of an alternator if you get rid of the field coil regulation.

NT

Reply to
tabbypurr

I used to connect something or other to ground via a big fat resistor to up the output from the alternator on my old Transit.

Bill

Reply to
Bill Wright

This explains why alternators never really fully charge the battery.

Bill

Reply to
Bill Wright

What a pair of extraordinary statements. Off load alternators will peak out at 40+v.

They are capable of doing over 15v at merely idle revs, at thousands of revs the potential is many tens of volts.

They settle at 14.4v because that is the level at which the battery starts to draw dangerously high charge current - even when fully charged

- and the electronics in the alternator limits the current.

A car alternator is fully capable of fully charging a battery.

Reply to
The Natural Philosopher

They will do, but only after a long run. Both my cars settle down at 13.8v exactly quite quickly. They both have 100 amp or more alternators. At

13.8v it would take some time to get a battery up to full. But you don't really need to in a car. Different matter with leisure batteries, etc.

In a car, it's more important not to cook the battery. And the battery life I expect from both of them is so much better than once was the norm. The BMW one did 11 years.

Reply to
Dave Plowman (News)

13.8 volts is a typical 'float' voltage for keeping the battery charged rather than charging it fully. The typical 'charge the battery fully' from a clever charge system will take the battery up to about 14.4 volts and, once it has reached that, will drop back to the float voltage of 13.8 volts. I believe car alternator charging systems are now likely to do this sort of thing so, just after starting or after the battery has been drained for some other reason, you should see the voltage go above 13.8 volts up to 14.4 volts or thereabouts but then, once it's charged the voltage will drop back.
Reply to
cl

Only with no load. Certainly not connected to a battery.

Meaningless.

Alternators are inherently self limiting as regards maximum current. Unlike a dynamo which would happily self destruct if turned hard on.

Of course. But they don't produce the maximum possible charge rate as the battery approaches full capacity. So the rate the battery is charged at isn't linear.

Reply to
Dave Plowman (News)

Completely wrong. They have electronics to regulate the field coil current.

Well no shit Sherlock. That's what I said. But they still charge at high amps - enough to fully charge the battery.

Reply to
The Natural Philosopher

Its to limit gassing.

Reply to
TomSawer

Precisely

Reply to
The Natural Philosopher

So it's entirely possible that a local garage needed to fit an alternator, found an uprated one was not only a straight drop-in but no more expensive, so just did it.

Reply to
Adrian

But that's irrelevant because when charging a battery it is on load. You will never ever have 40V on your car electrics.

But they have built-in regulation.

More like 14.2V I think.

Yes of course, but we we discussing the need to charge a battery fully (or as near fully as possible) in a couple of hours. A normal alternator won't do this because the charge rate drops off far too fast because the voltage is regulated to Yes it will keep a car battery fully charged in normmal use, but it won't put a constant high charge into a battery. That isn't what it's designed for, and if it did it would be undesirable. Smart chargers use a high voltage and current limitation, rather like charging nicads, so they can safely maintain a high charge rate for longer.

Bill

Reply to
Bill Wright

You explained it better than I could.

Bill

Reply to
Bill Wright

But it takes too long! Our man wants to charge his leisure battery from a genny and a charger, and he doesn't want it running all night.

Rest assured you'd have a drive a very long way indeed to fully charge a flat battery from the alternator.

Bill

Reply to
Bill Wright

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