Alternator prob


Well-known member
6 May 2004
Evening stars
tonights devious question is
Can an alternator if it is malfunctioning or maybe wrongly installed exert a large load on an engine, if so what is the fault within the alt
further symptoms in tonights earlier question
thanks all


New member
10 Sep 2004
Theoretically I guess the alternator could 'brake' if it went tits up, like shorting a wind generator to slow down the blades. How likely in practice this is I don't know.

If you really suspect it, try removing your fan belt and running the engine without the alternator, this should at least take it out of the equation.

It could be mechanical, the alternator bearing might be seizing as they get hot, but quite how much this could affect a running engine is anyones guess.

Worth a look though.

I would suspect your governor personally, maybe a split diaphragm /forums/images/graemlins/frown.gif


Well-known member
28 Jul 2003
West Australia
Here is a story probably not relevant but. it concerns an aircraft with an orinary alternator but with a switch which switches power to the field after the engine is started.
the anti hero (engineer) had just fitted a newly overhauled alternator. This one had an auxilliary terminal. (not used in the previous installation) ( often used for tacho output, it is a connection to the centre of the 3 phase star connected windings) There was a spare earth lead floating free so our antihero connected the earth to the aux terminal. Engine running, switches alternator on - no charge. Removes the alternator and just before sending back under warranty notices broken wires of the stator through the cooling slots. Further investigation showed the whole centre section despite being clamped by the end sections had rotated to break all the wiring to the stator coils. The mechamical load on the stator coils completely shorted out when field power was applied was enough to twist the guts out. However this was on a directly coupled alternator.
So your question is not stupid however I imagine the belt would slip before any damage was done in your case. so remove the belt drive and or remove all the wiring to confirm if the engine is being loaded load by the alternator. needless to say without a belt the alternator should spin by hand qute freely, if not then you8 have crook bearings. good luck olewill


Active member
15 Apr 2004
Yes, it could even stall your engine.
First remove the belt and turn the alternator by hand feeling for any resistance to turning - the alternator should spin quite freely. Next refit the belt and start the engine (alternator cold) and with the aid of a clamp on ammeter measure the output. If the regulator is "goosed" you could be drawing full (or over output) from the alternator which will slow your engine down. If that is O.K. put some load on (lights, invertor, fridge, freezer atc and allow the alternator to warm up while monitoring the alternator output. (regulators can break down when hot). If (when) the engine slows down check the out put to see if it is higher than normal (regulator goosed) If the output is "normal" stop teh engine and quickly remove the belt and check the alternator rotor spins freely. A spray of something like Rocol aerosol grease down the shaft behind the pulley helps as it is usually that one that takes the most punishment. After thought - check the electrolyte level in your batteries.
“I’m as confused as a baby at a topless bar. “