Nothing, just direct wired.  Not saying a fuse wouldn’t be a good idea though. Like someone already said, something just over the alternator rating.  You are protecting against internal short to ground alternator failure.  It would not protect against overvolt failure though.  Those are pretty rare.

In your case, the solenoid may have both caused the alternator failure and then acted as fuse to protect against shorting the battery to ground.

Tracy

Sent from my iPad

> On Aug 2, 2018, at 11:02, Jeff Whaley jwhaley@datacast.com <flyrotary@lancaironline.net> wrote:
>
> Hi Tracy, that is an interesting comment.  Sounds like a fuse would have been a better bet than the alternator solenoid - but what do you replace the battery solenoid with?
> Jeff
>
> The sequence of failure is a question.  The relay failing and going open might have been the first in the chain.  Many alternators will fail internally when all load is removed due to over volting.  Most Automotive alternators were not designed for no load operation.
>
> I've never been an advocate for either battery or alternator solenoid use.  They cause more problems than they solve.
>
> Tracy
>
> -----Original Message-----
> From: Jeff Whaley
> Sent: August-02-18 10:41 AM
> To: Rotary motors in aircraft
> Subject: Alternator Damaged - Internal Short
>
> Last Thursday I decided to try my cooling on a hot day 32C (90F); orbiting the airport, the cooling wasn't too bad but while waiting for the temps to stabilize I smelled smoke so landed immediately.  Saw a bit of smoke exiting the oil cooler plenum so thought I was baking some fiberglass.
> On the weekend I did a more thorough inspection and found the battery mains cable burned where attached to my alternator cut-out relay and the relay fried to the point that the input terminal was loose.  The connections stayed in place but open-circuited the relay - so the engine never skipped a beat and I was unaware there was an electrical problem at the time. Only reporting this now as it took me a while to get the alternator tested.
> Jeff
>
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