Causes of alternator burn out

[Gryphon2]

Yesterday our charge light failed to go out so after some head scratching we went to a marina and they arranged an "electrista" to diagnose the problem .It turns out the relatively new Prestolite 70 Ah had burnt out windings. I am now the proud owner of a new one and lighter by several hundred Euros.
I have a Sterling smart charger and solar panels with a effective regulator.

My non existant spanish could not ask if the electrista had any ideas why it had happened.Any suggestions ?

The ignition warning light and sound have often come on if starting with low revs in the past. But otherwise charging has been good for the 2 years of my ownership.

 

[pvb]

It could just be one of those unfortunate random failures. Prestolite alternators are generally excellent products. Did you install the alternator temperature sensor for the Sterling booster?

 

[William_H]

I would say the electrician replaced the alternator as a simpler and more profitable fix for him. I have never heard of an alternator burning out. As in windings fused and melted. If it was it would smell and look very burnt. Conceivably a failure of the field coil on the rotor would give similar symptoms. The outer 3 phase windings not likely. You can check this with a meter on ohms from one slip ring to the next. Most failures however occur with failure of the brushes to contact the slip rings. Usually fixed with a clean up of the slip rings and or new brushes. (or just free the brushes). According to this forum diodes can fail though I have never seen this happen. If indeed an diode fails it usually gives just lower current out put and light will go out.
S0o don't throw the alternator away. FIx it or get it fixed at an auto electrician and keep for a spare. ol'will

 

[lw395]

The most likely route to actually burning out an alternator would be to load it very hard in a hot engine compartment.
If the airflow through it is hampered by a build up of belt dust that will contribute too.

If you have a windlass or bow thruster, you might consider whether the alternator is being overloaded by these?
Some yachts with a battery at the bow forthe windlass give the alternator a very hard time when that battery starts to show its age.
It might be interesting to have the old one apart.

Another popular way to destroy an alternator is connecting the battery or jumpleads the wrong way around.

 

[Gryphon2]

The windings were melted. The "electrista" showed me them.
I take the point that the windlass or the bow thruster may give the alternator a hard time. The windlass has not got a battery of its own but the bow thruster does and it is a bit tired....

 

[lw395]

The windings were melted. The "electrista" showed me them.
I take the point that the windlass or the bow thruster may give the alternator a hard time. The windlass has not got a battery of its own but the bow thruster does and it is a bit tired....

Depending on the detail of the installation, the load will be shared by the local battery, alternator and probably house battery.
If it worked happily for two years while the thruster battery was new/newer, then upgrading that might be prudent. But obviously I can't see your boat so can only make vague general comments.

 

[geem]

If you take the Prestolite alternator model number and do a google search you should be able to find the Prestolite details of your particular alternator. My own Prestolite alternator is rated as heavy duty with a high temperature rating. If yours has the same rating as mine then you can rule out the overloading aspect. It is possible that it isnt rated for the kind of use you are imposing on it especially with a smart reg driving it harder in a high temperature environment