cloudmaster_321

I am troubleshooting an alternator problem. I have battery voltage on the bigger gauge wire at the alternator. I also have battery voltage on the smaller red wire on the alternator, which I see CP Performance website labels as "sensor". What is the "sensor" wire for? The purple wire, which they label as "excitation" is less than battery voltage. About a volt drop on that line. Where is the excitation wire coming from? Why am I getting a voltage drop on that wire? I believe the purple wire only gets voltage when the ignition is on, so could be a voltage drop from the load of various systems turned on with the ignition?

I do notice that if i load the buss with blowers fans, lights, etc., I can get a voltage drop of close to 2 volts when compared to the battery voltage. I cleaned the main rear mounted round connector on the back of the engine. I know the power wire is run to the front of the boat with a 10 gauge wire or so.

I wasn't expecting to see this much of a voltage drop. I'll be running the boat tonight on the hose to check alternator out for 14volts since cleaning that connection, and the alternator regulator connections. I opened up the male pins on the round plug, as they were pretty loose in the female pins.

Thoughts?

Thanks.

apollard

The red wire is the voltage sensing line which the alt uses to monitor the voltage of the system. The alt adjusts output according to what it sees on this line.

The purple wire is the wire that turn the alternator on. Drop of a volt or two won't matter on that line; the alt will generate power when it starts turning if voltage is on this line.

apollard

BTW, make sure you have a good ground on your alternator. An actual wire, not just grounded through the mounting bolts. I nearly burned (it was smoking) an alt up this weekend when the ground wire broke. Repairred the ground and made it through the w/e ok, but output at low speeds is down, so I'm sure i fried a diode or two.

cloudmaster_321

Thanks for the info. It does have a ground wire. I did not check the integrity however.

I wondering where the biggest voltage drop from batterys up to the power bus takes place. I haven't traced down where the power comes from. I did see there is a power junction on the starter. I'm not sure if that is the place the feed wire for the power bus in the front comes from or not yet. But either way, it may be a good idea to take that junction apart, clean, and reassemble. Same with the grounds.