Generator switch off

[mike.smith]

I just have an in-line fuse. If there is an over voltage the fuse breaks the circuit. I carry a few spare fuses. It's the only fuse in my entire system. I have combination switch/breakers for all my other switches, except the mag switches that are mechanical on/off.

[NWade]

I just have an in-line fuse. If there is an over voltage the fuse breaks the circuit.

Fuses are great at protecting against over-amperage (AKA over-current) conditions; but AFAIK they don't protect against a voltage rise, such as what happens when your voltage regulator fails.

--Noel

[Rynoth]

I installed the full overvoltage/relay kit that Noel linked above, and the amp draw is indeed very low when engaged.

I actually tested this today using my installed Ammeter, when I turned on the alternator relay with the engine off, amp draw only went up by something between 0.1 and 0.2 amps. This shouldn't be any different in flight.

[mike.smith]

I just have an in-line fuse. If there is an over voltage the fuse breaks the circuit.

Fuses are great at protecting against over-amperage (AKA over-current) conditions; but AFAIK they don't protect against a voltage rise, such as what happens when your voltage regulator fails.

--Noel

The fuse is between the VR and the battery. I know it works because a couple of years ago there was an issue with the stator, and the fuse blew. Fixed the problem and replaced the fuse. No damage to the battery or the rest of the electrical system.

[Rynoth]

Fuses are great at protecting against over-amperage (AKA over-current) conditions; but AFAIK they don't protect against a voltage rise, such as what happens when your voltage regulator fails.

--Noel

The fuse is between the VR and the battery. I know it works because a couple of years ago there was an issue with the stator, and the fuse blew. Fixed the problem and replaced the fuse. No damage to the battery or the rest of the electrical system.

Fuses are by no means a guarantee against over-voltage, they are intended to limit current.

[radfordc]

Fuses are great at protecting against over-amperage (AKA over-current) conditions; but AFAIK they don't protect against a voltage rise, such as what happens when your voltage regulator fails.

--Noel

The fuse is between the VR and the battery. I know it works because a couple of years ago there was an issue with the stator, and the fuse blew. Fixed the problem and replaced the fuse. No damage to the battery or the rest of the electrical system.

Fuses are by no means a guarantee against over-voltage, they are intended to limit current.

Do we understand the "E = I x R" formula? For a given resistance (ie, the battery) a rise in voltage always produces a rise in current. Like love and marriage you can't have one without the other.

[Kai]

Speaking of which: I have a solid state Icom 200 COM in #0525, and a King KT76A TPX (not solid state). In fact, it is the third TPX; the others have failed with depressing regularity. They fail when for some reason I need to stop the engine and forget to switch off the avionics. When I start the engine again, and then release the starter switch: scratch one TPX. I am am told releasing the starter relay produces over voltage in the system that kills the 'cavity' in the TPX. Is this true? Comments? Is there any way to protect against this? (apart from switching off the avionics bus). Thanks.

[sonex892.]

Speaking of which: I have a solid state Icom 200 COM in #0525, and a King KT76A TPX (not solid state). In fact, it is the third TPX; the others have failed with depressing regularity. They fail when for some reason I need to stop the engine and forget to switch off the avionics. When I start the engine again, and then release the starter switch: scratch one TPX. I am am told releasing the starter relay produces over voltage in the system that kills the 'cavity' in the TPX. Is this true? Comments? Is there any way to protect against this? (apart from switching off the avionics bus). Thanks.

Its true Kai. Releasing the starter button will produce a voltage spike without a diode across the relay coil. That said I've never have one on my starter, I must add that job to the list.
https://en.wikipedia.org/wiki/Flyback_diode
Steve Sonex 892

[GordonTurner]

This never made any sense to me either.....but here’s a pretty easy to read explanation. And it has PICTURES, critical for pilot comprehension.

https://en.m.wikipedia.org/wiki/Flyback_diode

Gordon

[N190YX]

You never, ever want to have any avionics on when starting the engine. While the starter is engaged, the battery voltage is low and going up and down with the compression strokes of the engine varying the RPM of the starter and therefore the load it is drawing from the battery, and when you disconnect the starter, the chemical reaction in the battery to provide the large load to run the starter takes a (small) period of time to stop, meanwhile the voltage spikes high, going from low volatage and osclillating to high volatage (momentarily). This circumstance damages avionics. I would not even have any LED lights on during engine start (Nav lights, flashing strobe style LED lights, etc.). I damaged the frequency indicater electronics on a KX-155 Nav/Com by accidentally leaving it on when my engine stalled after landing and I started the engine back up without turning off that radio! Recommend you learn from my mistake!