Electrical Problems.

[Brian Cloke]

Hello.
Just bought this motorhome and had the starting battery die on the way home.
Bought a new battery and came on home.
Now looking into my problems found the alternator was not working. Have now installed a rebuilt Delco Remy 160 amp same as the old one. This alternator has one large red wire that goes to the battery isolator the other heavy black wire goes to ground. Underneath is a plug in connection on a single small wire that fell apart with corrosion.On that wire a few inches from the end is a diode.
Where does this wire come from and what is it for?
On start up the alternator does not seem to be charging. any ideas would be welcome. Thank you.
Brian

[jacwjames]

This might be an exciter wire that basically starts the alternator to charge.

[Mr_D]

Originally Posted by jacwjames

This might be an exciter wire that basically starts the alternator to charge.

Either that or the tach wire, but I'm guessing the exciter wire as above.

[Piker]

On a delco, I think the field (exciter wire) and sense (basically remote voltage sensing) wires would be the two prong blade type connector located along the outside edge at the back of the alternator.

Your alternator may be a self exciting one-wire type unit that does not use either of those two connections. All that is required is a hot wire from the battery and a ground.

If your alternator does not immediately start charging, but then starts to charge once the engine rpm is bumped up a little bit... this is normal operation for a self exciting alternator. Ours starts charging once the engine hits around 1000 rpms or so.

Below is a picture of our alternator... the arrow points to the field/sense wire connection. On a self exciting unit, these are normally just capped off.

-cheers

[gatorcq]

Depending - the newer 160 Amp are only 2 wires and not 3 wires. Verify your alternator.

needs it,
When I went from 130 to 160 amp, i dropped the 3rd wire

[Piker]

Originally Posted by gatorcq

Depending - the newer 160 Amp are only 2 wires and not 3 wires. Verify your alternator.

needs it,
When I went from 130 to 160 amp, i dropped the 3rd wire

Yes... verify the alternator. On some models, you cannot differentiate between a 1 wire and 3 wire setup. The only real difference is the internal regulator, but the connections look the same.

I believe our alternator (in the picture) is the original 1 wire self exciting style - 22 years old. Even though the connections for the field and sense wires are there, they are simply not used.

-cheers

[Brian Cloke]

Thank you gentlemen for your comments and suggestions.The picture is exactly the same alternator that I have. From what I can gather it would seem my single small wire is the field/sense that plugs into the two prong position on the back of the alternator.
My heavy red wire goes to the middle terminal of the battery isolator which does not feed voltage to the alternator. This is why the single wire is used. I tested the diode on this wire and found it open/ not working. Will try to get a new diode on tuesday. report back then. British Columbia long weekend . Cheers.
Brian.

[Brian Cloke]

RE my electrical problems.
Decided to hook up the exciter wire minus the diode. Sure enough it now charged back to normal. On trying to shut down the engine it would not stop running.After searching around a now hot engine found the fuel shut down solenoid and disconnected the wiring that stopped it . Pulled the exciter wire off started engine. It now switched off at the key.
Now I know what the diode is for. Obtained a diode hooked up and all is well. Thank you gentlemen for all your help.
Cheers
Brian.

[Piker]

Good deal!

Have fun.

-cheers

[camperkids]

Yep now you know, I at work did a lot of Delco conversions on heavy equipment and without the diode they won't shut down. Glad you conquered it.