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You could modify Bob's latest overvoltage module to do what you need. Change the trip point to 13.5 volts, and remove the SCR.

From schematic 9003-630-IP6:
Change R7 from 13.7K to 11K
Remove Q ...

I don't like the key switch. If you turn it off with the engine running it could cause a load dump by disconnecting the alternator from the battery. Use a DPDT key switch to turn off the alternator ...

Hi Gerry,

I just finished my Tailwind this year. I went with a simple Z-11 approach.

The main feed from the battery contactor should be routed carefully to prevent compromise. If you smel ...

I would tie the ground pin (signal ground) to ground regardless of whether it is tied internally to case ground.

Snipping the shield ground on one side is appropriate. Don't re-connect, this pr ...

It looks like you need a DP3T switch. Do a search for them. It seems that it is a 4PDT switch with a jumper. You can search for those also.
The selection seems to be limited. There are several w ...

That looks like it should work.
I'd pull the feed for switch input pin2 from before the dimmer and use one fuse.
I assume there are series resistors as part of the cabin LEDs to limit current? If, ...

I used one of these: [url=https://www.connectorconcepts.com/bu15reteatcf14.html]Bussmann 15712 Rear Terminal ATC Fuse Panel, 20 position, w/Circuit Breaker Cover

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Without knowing the details, this is purely speculation, but this sounds like a scenario I was concerned with and posted about a month ago:
The potential exists that in a user modified automotive alt ...

Hi Bob,

Thanks for your response. But, remember in this case we are dealing with a user modified alternator, not factory. The two failure events you list are linked in a chain so their probabil ...

Yep, you would have to cycle master power first.

On Tuesday, September 26, 2023 at 10:09:42 AM CDT, user925 ...

If you really want an OV indicator it is easy to do. I think this was shown already. Just connect an LED fed by a separate source of 12 volts and a 270 ohm 1/2W resistor to the RED20 terminal of the ...

I've been luring on this list for years and this is my first post.
I've recently completed my plane (Tailwind) and have if flying.
I used the previous version of the OVM crowbar circuit and I have m ...