Visit our Popular Forums

ayates · 02-08-2022, 14:54

Configuration is an engine alternator connected to both an engine start battery and a house batter. Simplified schematic shown.

The house battery is fully charged. The engine is started at 11:25am, and the alternator is maintaining a charging voltage (blue line in the top graph) and keeping up with the house load (bottom graph).

Then at about 12:20am, the alternator looks to dropout, with the voltage dropping, and the house battery starts supplying some of the current.

While I don't have an exact time match, I also received reports of tachometer issues. As this is a diesel engine, the tachometer is driven from an alternator signal.

I am wondering perhaps if we are seeing early indications of a alternator regulator failure?

**Jammer** · 02-08-2022, 17:03

I would imagine that you're seeing the failure of the diode bridge, not the regulator.

goboatingnow · 03-08-2022, 02:00

It’s it diode failure in my view. Run the graph on further and see what happens. Ie repeat the sequence. What sort of regulator is on the alt , stock internal or external

Regulator failure usually results in higher then expected battery voltages when the battery is full or nearly full, in my case I saw 16 v from a failed regulator.

goboatingnow · 03-08-2022, 03:24

Sorry , it’s NOT a diode failure

Sailmonkey · 03-08-2022, 05:17

This doesn’t look like early indication to me…..it looks like failure.

What regulator is fitted?

Why is the alternator float voltage so low?

What size alternator?