Lamar Alternator Contact/Relay Troubleshooting

[CarbonFlyer]

Recently had a spat with a charging system and a new Cessna with a G1000 package. The charging system was INOP but if I would cycle the alternator switch off then on, the system would turn back on for a period of time then shut off. After a bit of throwing parts at it; alternator then ACU, I replaced the contactor. Problem solved. Field voltage was getting to the alternator. The ACU & contactor had voltage through both and correct resistance.

Does anyone have a troubleshooting document or home built troubleshooting test to test the contactor or ACU for fault? After all said and done and the plane left, I thought of jumping the relay with a simple wire to see if that would work. Any ideas or advice?

Thanks

 

[Dan Thomas]

Recently had a spat with a charging system and a new Cessna with a G1000 package. The charging system was INOP but if I would cycle the alternator switch off then on, the system would turn back on for a period of time then shut off. After a bit of throwing parts at it; alternator then ACU, I replaced the contactor. Problem solved. Field voltage was getting to the alternator. The ACU & contactor had voltage through both and correct resistance.

Does anyone have a troubleshooting document or home built troubleshooting test to test the contactor or ACU for fault? After all said and done and the plane left, I thought of jumping the relay with a simple wire to see if that would work. Any ideas or advice?

Thanks

Yup. We use this thing:

It's made specifically for the Lamar MCUs used in the restart Cessnas. Expensive.

In my toolbox I have a strip of plywood with a bunch of screws in it that have long lengths of wire, each soldered at one end to one of the screws and at the other are alligator clips. When I need to troubleshoot a charging system, I connect those clips to ground, field output, alternator output, battery positive, and so on. With a few more wires you could connect to both sides of the alternator contactor and to its coil terminal. Sit in the airplane with that board in your lap, run the engine, and take voltage readings between the ground screw and the others to see what the system is or is not doing. Turn heavy loads on and off to see that the field voltage rises and the output voltage stays steady. See that the battery is reading the same as the alternator output.

 

[CarbonFlyer]

Thank you very much. Very helpful.