Lead acid battery charger (or alternator) switching to trickle with load present?

How does a lead acid battery charger (or car alternator) know when to switch to trickle charge? I can understand it noticing a drop in charging current if the battery is on its own, but what if a random changing load is connected, as there is in a running car?

Reply to
Commander Kinsey
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The voltage perhaps.

Reply to
Max Demian

Why would the voltage change? That's determined by the alternator or charger. Let's say the charger/alternator gives out 14.4V initially, to charge the battery quickly. It'll just sit at 14.4V forever, providing the charger can give out enough current to charge the slightly flat battery and power any connected loads. If the battery had no loads connected, it would take a lot less current when it became full, but the voltage would stay the same. If the charger monitored the current it was providing, how does it know if the battery is still charging at 10 amps, or if the battery is full and there's a 10 amp load?

Reply to
Commander Kinsey

Definitely. One of the simplest ways to msake a vcarger is to have a constant voltage source in series with somem form of resistor. As the terminal voltage rises so too does the charge current drop.

The problem that brings is when a heavy cirrent is siltanoeusly drawn from the battery.

Which is why car alternator control is a little more spohisticated than that.

Reply to
The Natural Philosopher

Asks the unemployable wanker/troll with a 20 year old worthless degree and a stated IQ of 138. Odd that a few years ago your stated IQ was 142.

Reply to
Mr Pounder Esquire

It doesn't.

Ohm's law.

Reply to
TMS320

It has always been 135. And the degree is 22 years old.

Reply to
Commander Kinsey

Mine does, if I start my car when the battery is say 80% full, the voltage will be 14.4V. After a while, something causes that voltage to drop to 13.8, because something knows the battery is full and should no longer be charged at a high rate.

Explain how an alternator or charger can use ohm's law to distinguish between:

1) A car battery which is full, with a load of 10 amps connected to it, like two headlights. 2) A car battery with no load, which is not full yet and draws 10 amps for the charge.
Reply to
Commander Kinsey

That's a bit *deep* for some people to comprehend.

Reply to
Xeno

To determine current, measure the voltage across a series resistor, duh.

Two resistors?

Reply to
TMS320

Why didn't you wait until I'd finished?

Yes that would work, but not if it has no external sensors (as in external to the alternator).

Reply to
Commander Kinsey

No idea where to find that.

Agreed. And it could well have a sensor in the fusebox etc.

No, all I did was to start the car when the battery was almost full. The battery terminal voltage was immediately 14.4V. 20 minutes later it dropped to 13.8V. I added no loads. I think it actually dropped gradually if that means anything. I actually did that test because someone in one of these groups (although some troll has deleted half the groups, so I've added them back in AGAIN) told me that a car alternator changes voltage, this was in a post 6 months ago.

It could only be mV, but easy enough to sense with modern electronics. Or how about an amp clamp?

Every UK car has 2 or 3 cables on the battery positive. America is infamous for being behind the times. We all know your cars can't go round corners, and get way less HP for the same engine size.

Reply to
Commander Kinsey

You asked.

An alternator is not simply two wire power output. The electronics on the alternator would be to keep everything within acceptable parameters but fine control comes from the ECU.

Reply to
TMS320

No, I said "explain.... distinguish between:" and before I'd listed the two things, you interrupted.

So there are external sensors.

Reply to
Commander Kinsey

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