Warm alternator when using charger

[US1Fountain]

Have a guy state his alts get warm whenever he is plugged in shore power with the battery charger on. Thinking about this, I see the connection. Standard mercruiser motors. Alt output lead goes directly to starter lug, which is where the battery cable attaches. Defective alts? Do they have diodes internally to address this very issue that may be bad?

Any thoughts on this? Thanks

[sy_gilana]

Sounds like the field lead is hot when charging, or diodes faulty.
Disconnect field wire, not hot = regulator problem
Disconnect field wire, still hot = diode problem
They can get really hot, enough to start a fire...

[smac999]

if the alt had a constant field or ign power it would get warm but it would do it whether the charger is on or not.

if it only happens when the charger is on something is pretty weird.

[US1Fountain]

Thanks, passing the info along. It's my understanding happens only when plugged into shore power and the batty charger is on.