ERA 289FIA alternator replacement

[patrickt]

Originally Posted by Dangerous Doug

Patrickt: I'm showing a discharge---the ammeter is going negative. You'd expect your regulator to compensate for the load and the ammeter to return to zero---you're not drawing excess current from your battery. This drained by battery down in 20 minutes such that I didn't have sufficient current to crank the starter...

I don't think the ammeter is lying to me. It's never lied before...

DD

My previous post was for when you have an alternator that is strong enough to carry the entire load. When that happens, by having your new lights load on one side of your ammeter, and the rest of the load on the other side of the ammeter, you could show a partial "charge" but actually be discharging (if the amount of indicated "charge" is less than the amperage draw of the lights that are now on the battery side of the ammeter). The fact that you are showing a discharge now is an indication that your alternator is not carrying the load at all.

[patrickt]

If your new lights drain off 20 amps, and the ammeter only shows 5 amps of current going through the ammeter to those lights from the alternator, then the battery is supplementing the needed 15 amps (discharging it), but your ammeter still shows a nice healthy charge of 5 amps! That's why you generally don't put a load on the battery side of the ammeter.