Motorola Alternator not charging when installed

[pvenuti]

I'm working on a 35amp Motorola alternator attached to an A4. It's not charging the batteries while in the boat but was taken to a shop and tested ok on the bench.

When I put a meter on the + lead on the back of the alternator with the engine running I can read 12 volts but I assume this is from the batteries.

From the regulator there seem to be 3 other connections.

1 Yellow wire with a black plastic connector going to the coil(positive I presume).

2 Brown wire(I think) grounding reg to the case.

3 Green (I think) running off somewhere else I should know but I don't.

So assuming the bench test was accurate and the alternator is good what other testing can I do to troubleshoot this issue?

I plan on metering the positive alternator connection again with the engine and ignition off then just ignition on to prove that the connection to the batteries is good(no bad fuse etc).

I also plan on metering the positive alternator connection with the engine running and the wire to the battery disconnected to see if it produces any voltage(I expect it wont).

Any suggestions would be appreciated

[Don Moyer]

Pvenuti,

Motorola alternators are very unforgiving of operating without a load. The large output diodes tend to blow out if the alternator is disconnected (as in going to "OFF" on the master battery switch) while the engine is running. Therefore, and since I can't be sure that your alternator is currently connected to the batteries, my first advice is to connect the output terminal on the alternator directly to the large battery cable on the starter solenoid. Then measure the DC voltage anywhere in the system for 13.4 volts.

Don

[CalebD]

Recommended reading

Nigel Calder's "Boatowner's Mechanical and Electrical Manual" has a whole section on alternators: how they work, are connected and troubleshooting and is full of diagrams.

[keithems]

can anyone tell me where to connect the various wires coming out of the motorola 55 amp alternator with built in regulator attached?

[Don Moyer]

There should only be two wires to consider: the large output terminal connects either to the ammeter in the cockpit or the big battery cable on the starter solenoid (preferred by most), in which case you can monitor alternator performance by checking the DC voltage. Your Motorola should be maintaining approximately 13.5 volts anytime the engine is running. If it is a very late aftermarket 55 amp model, you might see 14.2 volts in the DC circuit with the engine running.

The second wire is a field flashing lead that connects to the positive terminal of the coil. This is a smaller wire and is usually provided with a quick-disconnect.

Don

[keithems]

thank you, don -- not only for this but for all your help in getting this motor running in my boat