alternator wiring question

Bubblehead · #1 04-10-2009, 07:34 AM

I am installing an EIS 4000, and just like many of my projects when I opened that little can a whole lot of worms stampeded out! I've managed to get a lot of them back in the can by rewiring, rerouting, adding cable ties etc. but I found one thing that I ahve not figured out. I have a 60 amp alternator with 3 wires hooked to it. One is the battery or high current wire, and then two smaller 16 ga or so wires in one three pronged connector.

When I traced the smaller wires to make sure where they went, one traced back to the breaker panel to the field breaker. That makes sense. The other one traced back to the panel lighting circuit. That did not make sense.

I checked the Van's wiring diagram the builder of the plane used but it shows the older style alternator that has a separate regulator. I also checked Plane Power's website and found a diagram for their 60 amp alternator that shows two wires from the connector that both go to the "Alternator Field" circuit.

Any ideas about this? Is that the proper place for it to go? Should I reroute it to the Alternator Field circuit?

N131RV · #2 04-10-2009, 09:16 AM

If it is a standard vans with internal regulator, the big wire goes to your bus, the field wire goes to a the field breaker (or switch) and the other wire is used to indicate alternator failure. It produces a current when running and is ground when not working.

So, your alternator failure light has power from the battery on one side and connects to the alternator failure line on the other. When the alternator is offline you get power through the lamp. When it is online, the currents "cancel" and you get no light.

Clear as mud?

If if is not a standard vans alternator, I have no clue.

JP

Brantel · #3 04-10-2009, 10:17 AM

The Plane Power one works the same way. That third wire should pass thru a light bulb then to a breaker or fuse and then to the power buss.

Sid Lambert · #4 04-10-2009, 11:04 AM

Just keep in mind if you do decide to use the dummy light you will not be able to turn the alternator off in flight without killing the master and alt. (you can bring the master back up without the alt and it will not continue to charge) The power going through the light will energize the alt fields and keep the alternator charging even if you disconnect the field circuit.

I think the EIS 4000 can give you warnings of low voltage so I would not use the light.

Note: This is for the retrofitted car alternators. I'm not sure how the certified alternators handle it and I can't say that I've ever seen a certified alt with a dummy light leg anyway.

Bubblehead · #5 04-10-2009, 04:17 PM

Excellent info. I am putting a current sensor in on the alt line so will be able to alarm on low/no current from the alternator as well as low voltage so I won't need the indicator light.

It is a standard alternator with built in regulator.

Thanks for the info. I think I will temporarily put a toggle switch in that line and when I test run the system I can see if alternator output changes when I interupt the line to instrument power.