Alternator exciter wire issue

Topic: Alternator exciter wire issue (Read 2251 times) previous topic - next topic

Re: Alternator exciter wire issue

Reply #25 – July 17, 2025, 05:14:40 pm

OK!! Except I have to remove a platform one of the previous owners installed as a place to coil up the 50A cord when the temperatures drop. Kind of tests one's patience, no??

Re: Alternator exciter wire issue

Reply #26 – July 17, 2025, 05:29:30 pm

Right now I just got the alternator in place and managed to thread the two bolts that hold the alternator in the bracket. Little different from some coaches. We have a rear radiator, so I have to assemble a platform under the bed (after raising the bed) and then drag all the necessary tools under with me. Drop one and I have to crawl out of that cavity, go outside and try to find the bolt or tool under the rear end of the coach--and hope the item didn't drop somewhere up in the framework.
Of course, lots of dropsy with my arthritic thumbs so lots of "calisthenics" climbing in and out at 83. For some reason I am not as spry/limber as I was last year.

After dropping the alternator two times (just down on to the frame) I got a brain strain. I took the bolt that goes thru the slotted adjustment arm and chamfered the threads about 1/16x45*. Went right in and held the alternator while I fished around for the pivot bolt holes on the bottom side. Now back out to put the three belts on, tension and then tighten the bolts, then hook up the wires-----after finding out where the "little red wire" goes. I will need to cut cable ties and get the wire out of the protective ribbed sheathing.
Temp outside is 78* and my brain temp is 140* Wonder why.

Re: Alternator exciter wire issue

Reply #27 – July 17, 2025, 07:57:45 pm

Well, alternator is in. Small red wire goes from exciter post on the alternator down to the right post on the Powerline Model PL1-130-2
Duh. Didn't check which large red wire is under it on the post on the Powerline.
Just checked and the little red wire from the "exciter" post is on the same post as the black cable going to the starter?

Re: Alternator exciter wire issue

Reply #28 – July 17, 2025, 11:49:53 pm

Quote from: nitehawk – July 17, 2025, 07:57:45 pm

Small red wire goes from exciter post on the alternator down to the right post on the Powerline Model PL1-130-2
The little red wire from the "exciter" post is on the same post as the black cable going to the starter?

Schematic found in our Excellent Forum Library. I added the "little red wire" that melted.

Note that the 2 GA "black cable going to the starter" connects directly to the 000 GA BLACK cable, which is connected to the POS (+) terminal on the ENGINE battery.

Therefore this black cable would be HOT all the time with ENGINE battery voltage.

Since the black cable is HOT all the time, it follows that the "little red wire" would be HOT all the time with ENGINE battery voltage.

Re: Alternator exciter wire issue

Reply #29 – July 18, 2025, 08:14:57 am

Something strange here. There is ANOTHER little red wire on the same post, right under "my" little red wire, and it disappears in the maze of wiring under the driver's side of the engine. So, what does THAT wire do? I guess I will have to trace it thru all the grease and 36 years of accumulated gunk.
If I reconnect a red wire from the (-) terminal to the "EXCITE" terminal then there should be a constant draw on the battery, should then cause my battery to see gradual voltage loss. And that is what has happened ever since we got the coach.
The red wire seemed to have been done very well at the factory, and not an add-on.

Re: Alternator exciter wire issue

Reply #30 – July 18, 2025, 04:33:51 pm

Does that little red wire that you found have voltage all the time or only when the ignition is on? Maybe it is supposed to have a duvac alternator and someone before you put on the wrong one.

Re: Alternator exciter wire issue

Reply #31 – July 18, 2025, 08:22:13 pm

Being clamped on the same post as the main battery cable I believe it has/had constant voltage.
But the Leese/Neville alternator is set up with an "excite" post on the back and thus should not be "hot" all the time, even when the engine and ignition are off.
So, should I run a new wire to the accessories position on the ignition switch?
No matter what, what is causing my system to only register about 11.5 volts?

Re: Alternator exciter wire issue

Reply #32 – July 18, 2025, 10:45:48 pm

Quote from: nitehawk – July 18, 2025, 08:22:13 pm

So, should I run a new wire to the accessories position on the ignition switch?

Since you don't know the model number of your alternator, it's anybody's guess how it should be wired.
If you could determine the alternator model number, then it should be easy to find wiring instructions online.

Re: Alternator exciter wire issue

Reply #33 – July 18, 2025, 10:56:01 pm

I will call the rebuilder Monday. Thanks

Re: Alternator exciter wire issue

Reply #34 – July 19, 2025, 12:00:16 am

It's very probable that one small post is the sense , and another is the excitement post.
I would use a fused jumper from 12v to each post and see which one turns on the charge circuit .

Re: Alternator exciter wire issue

Reply #35 – July 19, 2025, 12:35:49 am

At the rebuilder's facility he showed me how, when zero voltage is on the "excite" post there is zero voltage being generated. When he applied 12V to the "excite" post the alternator output read 14.4 Volts.

Re: Alternator exciter wire issue

Reply #36 – July 19, 2025, 01:30:26 pm

How many post are there ?

Re: Alternator exciter wire issue

Reply #37 – July 19, 2025, 07:38:39 pm

I believe nitehawk said that the alternator is a powerline. This is a knockoff to a Leece Neville. I believe that some people who had worked for Leece Neville left and started the power line company. If your rebuilder understands a duvac alternator, then he can probably modify it to be a duvac alternator. You could take a volt meter and check the large positive terminal with the engine not running and it should have no voltage. Take a jumper wire from a 12 volt source to the excite terminal with the engine running and see what the voltage is then. I do think that you will have to have it modified in order to get proper charging to the engine and house batteries. Wish I was close, I would come and help you.

Re: Alternator exciter wire issue

Reply #38 – July 19, 2025, 09:10:26 pm

Sorry Red, my alternator says Leese/Neville right on the nameplate. The isolator is a Powerline Model PLI-130-2.
The rebuilder demonstrated that my (+) terminal on the alternator put out ZERO voltage until 12V was touched to the Excite terminal. Then He got 14.4 volts from the (+) terminal.

Re: Alternator exciter wire issue

Reply #39 – July 20, 2025, 10:01:25 am

Most vehicle alternators use an "excite" or other means to get the alternator started. Usually it is part of the charging warning lamp system. Having a failed bulb can cause the alternator to "not" turn on. It is possible that the excite circuit is fuse protected. Most likely it is powered from the ignition for fuel stop circuit.

Re: Alternator exciter wire issue

Reply #40 – July 20, 2025, 07:25:20 pm

Sorry I didn't understand the power line regulator.

Re: Alternator exciter wire issue

Reply #41 – July 21, 2025, 12:57:24 pm

Quote from: nitehawk – July 18, 2025, 10:56:01 pm

I will call the rebuilder Monday.

Let us know if you are able to determine the alternator model number.

Re: Alternator exciter wire issue

Reply #42 – July 22, 2025, 07:34:48 am

DUH! Totally forgot to call yesterday. Too many things going on here, but none serious. Just forgetful on my part.

Re: Alternator exciter wire issue

Reply #43 – July 22, 2025, 06:56:04 pm

I called this afternoon. Greg will get back to me, hopefully tomorrow (busy, busy).
So today I proceeded to dismantle and clean ALL the cable connections and then reconnected them After I get all done, protective anti-corrosion spray.
Voltage went up a little bit on the house battery gauge after cleaning and reassembly. 12.6V

Re: Alternator exciter wire issue

Reply #44 – July 22, 2025, 07:05:11 pm

Quote from: nitehawk – July 22, 2025, 06:56:04 pm

Voltage went up a little bit on the house battery gauge after cleaning and reassembly. 12.6V

What do you mean by "the house battery gauge"? Are you talking about the instrument panel volt meter, or another gauge?

Have you tried measuring the voltage directly at the battery posts?

Re: Alternator exciter wire issue

Reply #45 – July 22, 2025, 10:35:56 pm

Yup. Voltage went from 12.2 up to 12.6 on my little red voltage test instrument. Not a heck of a lot but nothing was different other than newly cleaned wire ends and contact points like battery terminals.
Tomorrow is predicted to be wet and sloppy weather with storms off and on tomorrow and Thursday.

Re: Alternator exciter wire issue

Reply #46 – July 22, 2025, 11:09:25 pm

12.2 and 12.6 is a huge difference when talking battery voltage not being charging

Re: Alternator exciter wire issue

Reply #47 – July 23, 2025, 09:32:24 am

OK, here is the info I got from my rebuilder: Alternator is a Leece-Neville 130A Model 2670LC
Hope this helps. Isolator is a 130A also.

Re: Alternator exciter wire issue

Reply #48 – July 23, 2025, 09:40:52 am

Quote from: wolfe10 – July 17, 2025, 01:27:14 pm

Then it is not the correct alternator to be used with a diode-based battery isolator, as the isolator reduces voltage by about .7 VDC and the remote sense wire (to the chassis battery side of the isolator) compensates for the voltage loss in the isolator by telling the regulator what voltage is actually getting to the chassis battery. Yes, the sense wire can "come from" any location that shows chassis battery voltage-- does not need to be at any particular connection. On many, it is on the chassis battery lug of the battery isolator.

With engine at 1,000+ RPM, check voltage at alternator B+ to ground and then at the center lug of the diode-based battery isolator to ground and then at the two outer lugs to ground. Let us know what you find.

There ARE workarounds that are a lot less $$ than a new alternator.

From post #22. When the alternator is reinstalled, let us know the voltages.

Re: Alternator exciter wire issue

Reply #49 – July 23, 2025, 09:56:53 am

In looking up the specs for your alternator (so I presume Prestolite bought Leece Neville):

2670LC PRESTOLITE LEECE NEVILLE 2600 12V 130A BRUSH ALTERNATOR

PRESTOLITE LEECE NEVILLE 2600 12V 130A BRUSH ALTERNATOR
SPECIFICATIONS
Brand Name   PRESTOLITE ELECTRIC    Condition   New
Voltage (V)   12   Brush or Brushless   Brush
Output (A)   130   Ignition terminal   No
Polarity   Insulated return   Sense terminal   No
Rotation   Reversible   Lamp terminal   No
Mounting type   J-180 (Long)   Pulley fitted (Type,OD)   tbc
Field isolation terminal   No   Overhang position (mm)   tbc
Multipower terminal   No   Product family   2000
Excitation type   Self excite   EAN code   5052629013812
Regulator included   Integrated

SO. that just seems to add to the confusion. Self exciting or needs 12 VDC excitation??? No sense terminal???

As I mentioned earlier, that alternator may work very well, just NOT with a diode-based battery isolator.

Easy to test: Move the battery cable for the chassis battery lug on the battery isolator to the center lug of the battery isolator that is directly connected to the alternator B+. What is the voltage now?

If it 13+ VDC, there are some relatively inexpensive "work arounds". I did one of these "work arounds" a long time ago, not because of a failed isolator, but because I like KISS (Keep It Simple Stupid). I used a Perko simple ON-OFF marine battery switch. Wire from alternator B+ and wire to chassis battery to one lug of the switch. Wire to the house battery to the other lug. Switch off, chassis battery gets charged. Switch on, both banks get charged but can discharge as one. Also serves as an excellent battery combine.
Mount is somewhere that you can easily get to inside the coach or in a basement compartment. On our 1993 U240, I mounted it on the vertical wall at the foot of the bed next to the other electrical equipment. Raise the bed dust cover and it is right there.

Affiliate Notice