alternator field breaker triped

[Paul 5r4]

The alt field breaker has tripped twice on my 7A in the three years I've had it flying. Both times I had switched on the current hungry landing lights, (12 amps each)! I have the standard light kit from vans and they draw 150 watts each. As long as I leave the landing lights off it never trips. I'm thinking of replacing my 12 amp lights with the BAJA LEDs which draw only 3.3 amps each. My question is this. Assuming there is nothing else causing the problem, will decreasing the current draw stop the tripping problem when they are switched on? Like I mentioned, it's never tripped as long as I leave the landing lights off. I have the standard vans 60 amp alternator.

[rv7charlie]

What's the current rating of the breaker? There's no reason for a field breaker to trip in normal operation, unless there's a real fault somewhere, or the breaker's bad. That would be true even if total electrical load exceeds the alt capacity (you just drain the battery faster than the alt can replenish).

Just to be sure, you're not talking about the breaker that actually protects the B lead, right? (It's not uncommon to hear about B lead breakers tripping under high load, because the breaker is rated at or below the alt's capacity.)

Charlie

[Carl Froehlich]

If this is the alternator output breaker, I suspect you put in a 60 amp breaker. If so, this should be a 70 amp breaker for a 60 amp alternator.

Carl

[lr172]

Increase the Alt Fld breaker size and wire, if necessary. I have a 50 amp alternator and followed the advice here that 5 amps is more than adequate for a fld breaker. One day, early in my Phase 1, I ran the battery down a bit starting the engine. When I do this, I see 45+ amps of cuurent. during that flight, i noticed my voltage was low and sure enough the fld breaker tripped. I kept pushing it in and it would pop in 15 seconds. Had to do this all the way back to the airport.

I replaced the breaker with a 7.5A unit and never had a problem again, even when drawing 49 amps. It is possible that my breaker was defective, but I believe the field current requirement is higher than 5A for these bigger alternators. Remember, the greater the output of the alternator, the greater the field current requirement is. This is how the VR regulates that output.

Larry

[flyinga]

You didn't mention alternator or regulator type, but it could be an overvoltage situation for some reason. If you have a "crowbar" type of overvoltage protection the field CB will trip if an overvoltage occurs.