A mate of mine just swapped the alternator on a "modern" jag. When he starts it and leaves it running, the voltage at the terminals is 15.5, then it suddenly drops to 13.5 after five minutes or so. This cycle repeats when he stops and re-starts it. He wandered if there was something "clever" in the regulating circuit to give it a quick boost every time the starter was used.
Sounds plausible, but I bet someone here knows!
"newshound" gurgled happily, sounding much like they were saying:
Entirely possible. How "modern"?
sounds like a modern ford, oh yes, it is! Yes, they do that on the smart charge system or whatever it is called
Thanks very much. Yes, it's modern enough to be a Ford. By "modern" I meant not a classic.
Yes that is entirely normal- its a Ford thing- called 'smart charge' and entirely necessary on anything fitted with a calcium battery.
You *must* fit a calcium type battery on these cars- anything else can go bang due to the high intial charge voltage.
Tim.
Halfords etc sell 'calcium' batteries for normal cars. Got one on the SD1 which is 25 years old and it works just like any other.
They need a higher charging voltage than "normal" batteries. They'll still work if charged at 14.4V but optimal charging requires 14.8V. Some charge controllers charge at a higher initial voltage then back off as the battery charge approaches 100%. Whereas a calcium battery will work with a standard charge controller, a "normal" battery won't like being charged on the same profile as a calcium battery because it will lead to gassing of the electrolyte.
Be interested to know how much capacity is lost through using with a system not specifically designed for them? Can't say I've noticed any in practice. Nor does my expensive tester show any abnormality.
In the case where the charging voltage is a little on the low side, maybe expect marginally shorter life due to slightly more sulphatation.
John
The main difference I'd expect would be a slower charge rate, so unless you do a lor of short trips you'd not notice any difference.
I would imagine the tolerance of the components used to control the charge voltage would vary by almost as much as the difference between the two systems in any case.
Chris
Eh?
Only if you're buying really crap aftermarket voltage regulators.
As of course the motor industry would.
Chris
No it doesn't.
I've never seen one, what makes you think that?
Eg:
Yes, in the case of generators that's possibly true, but they've got a completely different usage to most cars.
Alternators too. Car batteries rarely reach 100% charge. That would require more expensive electronics than are usually fitted, as well as time.
John
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