Alternator exciter wire issue

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

Re: Alternator exciter wire issue

Reply #50 – July 23, 2025, 12:20:46 pm

What I don't understand is that the original isolator came with the coach back in '89. (the rust surrounding the isolator and frame mounts give that impression of age. No witness marks from anything else mounted there.
The alternator came with the coach when we bought the coach about12-14 years ago.
Never had any problem with this alternator, even the first rebuild. But, after some dumbass (no name here, please) in the dark of the storage place, accidently hooked up the second start battery back-asswards. WOW!! Lots of spark and smoke there for about 10 seconds!!
So, now 1 newly rebuilt (and very recently double checked) anternator puts out 14.4 volts on the test stand but only reads about 11.5 on the coach dash gauge (a needle indicator not an idiot light).
So, what is the opinion? Did I blow the isolator? If the excite post wired to the engine battery post worked all these years, should I just hook a new (untoasted burnt) wire from engine bat post to the excite post and see what happens?? {The old wire got cremated because the hot "excite" wire touched the black ground wire the dumbass had removed off the alternator and didn't know the excite wire was HOT!!}

Re: Alternator exciter wire issue

Reply #51 – July 23, 2025, 01:24:23 pm

Try Brett's idea of hooking the alternator B+ cable directly to the engine battery post on the isolator. This takes the isolator out of the equation. You would then be able to use a short excite wire from the B+ post on the alternator to the excite post and see if it starts charging.

Re: Alternator exciter wire issue

Reply #52 – July 23, 2025, 02:47:47 pm

Now I am really confused. Brett, I looked up the alternator on your last post. It shows two yellow wires connected to two of the small posts on the lower recess on the back of the alternator but NO "exciter" post at all.
My alternator doesn't have those two wires but does have those three small posts AND the "exciter" post above them.
Now I am worried that if I try your idea of changing the wiring I might "blow" the alternator or some other item.

Re: Alternator exciter wire issue

Reply #53 – July 23, 2025, 03:18:11 pm

Quote from: nitehawk – July 23, 2025, 02:47:47 pm

My alternator doesn't have those two wires but does have those three small posts AND the "exciter" post above them.

Does it look more like the alternator in photo below?

Leece-Neville Alternator 2670LC (543-10347) | eBay

Your alternator has the older model voltage regulator. See your Reply #2 in this thread. It was apparently later replaced with a different regulator.

Alternator: Regulator change 102200 to 103450 - All Things Foretravel

Re: Alternator exciter wire issue

Reply #54 – July 23, 2025, 03:55:44 pm

You will NOT hurt anything by directly wiring the alternator B+ to the wire to the chassis battery.

This will just remove the diode-based battery isolator from the equation (the isolator could be failed and if working correctly, it WILL have a .7 VDC voltage drop). That voltafge drop across the isolator is the reason for the remote sense wire (which tells the regulator what voltage is reaching the chassis battery.

Re: Alternator exciter wire issue

Reply #55 – July 23, 2025, 03:59:05 pm

So what should I do? Make a jumper wire from the "excite" post to the center smaller post just below?

Re: Alternator exciter wire issue

Reply #56 – July 23, 2025, 05:25:00 pm

If you hook up the B+ directly to the chassis battery cable at the battery isolator end (just move the chassis battery cable and ADD IT to the cable from the B+), then if you do need 12 VDC to the excite terminal (not saying you do or don't, as the description and what you see are different) then a short jumper from alternator B+ to the excite terminal will do it since you not have chassis battery voltage at the B+ terminal.

Anyone else concur/disagree???

Re: Alternator exciter wire issue

Reply #57 – July 23, 2025, 06:44:02 pm

Brett is saying to move the chassis battery cable from its post on the isolator to the center terminal on the isolator and then try it to see what voltage you have with the engine running.

Re: Alternator exciter wire issue

Reply #58 – July 23, 2025, 07:37:33 pm

Quote from: red tractor – July 23, 2025, 06:44:02 pm

Brett is saying to move the chassis battery cable from its post on the isolator to the center terminal on the isolator and then try it to see what voltage you have with the engine running.

Yes, thanks for the clarification, I went back and added:

B+ directly to the chassis battery cable at the battery isolator end

Re: Alternator exciter wire issue

Reply #59 – July 23, 2025, 09:11:56 pm

Got it, but I have an issue with all the standing water on our drive and on the lawn. We got 2-1/2" of rain this afternoon, and more predicted for tomorrow.
So, knowing that water and electricity don't mix, I will hold off awhile.
How do I know? When I was about 12 my farmer uncle told me and my cousin that the electric fence on the dew covered clover hay field wasn't on. (He was wearing rubber boots) My cousin and I started to straddle the low electric wire and discovered that my uncle had lied. My voice didn't come back down for two years.

Re: Alternator exciter wire issue

Reply #60 – July 24, 2025, 08:53:40 am

Was going to go out and start moving wires around this morning. BUT!!!! The humidity is way, way up there. I thought I saw a school of small minnows go by my office window a few moments ago.
So am putting off any working outside until maybe this afternoon, altho rain is predicted--AGAIN.

Re: Alternator exciter wire issue

Reply #61 – July 24, 2025, 09:12:04 am

Just wear rubber boots like your uncle

Re: Alternator exciter wire issue

Reply #62 – July 24, 2025, 01:36:53 pm

Quote from: red tractor – July 16, 2025, 07:35:25 pm

On some models of the earlier rear engine diesel engines the alternator had to be revved up to a little over a 1000 rpm to start charging. That has been too long ago for me to remember the wiring, they didn't have duvac alternators then. I know this isn't much help. I wonder what would happen if you hooked up an ignition hot to that terminal and tape off the small wire that is hot all the time.

Just reading your post , my original alternator was a leece Neville 160 amp output with this duvac system that I've read about , anyway after lengthy searching ,I came up with a leece Neville alternator which I was told was the correct one , so I bought it had it shipped to UK probably 4 or 5 year ago now , it looked identical but it was only a 120 amp version so I knew it was wrong , but I wasn't too bothered I thought oh well IL fit it anyway and when i started the engine obviously it wouldn't charge , I think it's because of the battery isolator ,and because there is no direct power direct from the battery to the alternator it wouldn't self excite hence why the duvac system is important , a normal vehicle without a separate battery system like all the rvs have would be connected direct to battery , anyway someone said to me all I need to do to get the alternator charging was to run a hot wire onto one of the spare terminals I have on the alternator which I did and as soon as I started the engine all I did was strike one of the smaller terminals with a hot wire just quickly and that was enough to get the alternator charging , so once I discovered that ,rather than go through all the hassle of sending the alternator back and getting the correct one, cause I can't really remember who's fault it was mine or whoever I bought it from now but what I did in the end I connected 1 wire to the terminal that set the alternator charging and ran it all the way underneath up into the dash and connected to a spring return switch and the other to a hot wire , so all I have to do now is start the engine ,press the switch just for a fraction of a second and let go and that gives me just enough power for the alternator to start charging, and it will stay charging till I switch engine off , and the next time I start the engine I have to do the same, it works fine ,I was a bit concerned that it was only a 120 amp alternator, but it is plenty I have no issues with the system at all works fine even if I was driving at night with headlamps on there is still enough power to keep the batteries fully charged ,and also I do have the solar panels fitted on the roof which I bought from windy nation ,was recommended this company by one of the forum members ages ago , IL take a photo of my alternator in a bit ,I mean for all I know it has got a duvac system fitted to it without my knowing and maybe if I wired it up differently it would start charging without having to flick the switch , mind you I have done this so many times now that it just comes naturally , turn the key flick the switch , at first I would sometimes forget until I looked at the voltmeter , IL send this and then I will take a photo of my alternator and upload , I can't even see any numbers on it , maybe the numbers are there but I have over the past few years sprayed with water resistant spray which contains PTFE ,which helps keep moisture out , I'm always going around with spray grease ,it's probably had that many coats of it that it's just covered the label maybe ,IL have a look in just a sec and send the photo kev

Re: Alternator exciter wire issue

Reply #63 – July 24, 2025, 02:30:00 pm

Well, I did what Brett told me to do. I connected the alternator cable to the black #2 battery cable, along with the two red wires.
Then I went in the coach and started it up.
YAHOO!!!! Absolutely amazing. My meter now reads 14.3 volts!!
So now I am waiting on the selector switch to mount on the foot of the bed. (here tomorrow)
Got to go shopping for 4Ga cable and ends later today.
Thank you Brett and all the rest of you for helping a dumbass (no name here, please)
How times change-- only 36 years old and the battery isolator craps out. What is the world coming to?

Re: Alternator exciter wire issue

Reply #64 – July 24, 2025, 02:40:12 pm

Quote from: nitehawk – July 24, 2025, 02:30:00 pm

Well, I did what Brett told me to do. I connected the alternator cable to the black #2 battery cable, along with the two red wires.
Then I went in the coach and started it up.
YAHOO!!!! Absolutely amazing. My meter now reads 14.3 volts!!
So now I am waiting on the selector switch to mount on the foot of the bed. (here tomorrow)
Got to go shopping for 4Ga cable and ends later today.
Thank you Brett and all the rest of you for helping a dumbass (no name here, please)
How times change-- only 36 years old and the battery isolator craps out. What is the world coming to?

Ah brilliant I'm glad you have sorted it out ,IL still send a photo of mine , cause maybe it does have a duvac system on it and I don't know maybe ,that's why it works when I flick the switch on the dash ,but would mutch prefer if I could wire it up so I don't have to flick a switch on the dash , cause occasionally I do forget to flick the switch and then I suddenly remember when I see the voltage has gone down , just been doing a touch of welding , I'm just packing up and IL send that pic of my alternator ,hope you get well soon

Re: Alternator exciter wire issue

Reply #65 – July 24, 2025, 03:56:22 pm

Quote from: kevo0000 – July 24, 2025, 02:40:12 pm

IL still send a photo of mine , cause maybe it does have a duvac system on it and I don't know maybe ,that's why it works when I flick the switch on the dash ,but would mutch prefer if I could wire it up so I don't have to flick a switch on the dash...

Kev,

If you want some help with the correct wiring for your alternator, I would suggest you start a new separate thread on that subject. It will help if you can post some photos of the back side of your alternator, showing the wiring terminals, and a photo of your battery isolator. Getting the alternator hooked up correctly isn't rocket science, but depends a lot on the alternator model and battery charging setup in your coach.

Re: Alternator exciter wire issue

Reply #66 – July 24, 2025, 04:04:08 pm

Quote from: nitehawk – July 24, 2025, 02:30:00 pm

So now I am waiting on the selector switch to mount on the foot of the bed. (here tomorrow).

Here is the switch I used: PERKO Inc. - Catalog - Battery Switches - Medium Duty Battery Disconnect...

Rated for 250 AMPS Continuous, 360 AMPS 5 Mins. Intermittent.

Wiring:

Wire from alternator B+ and wire to chassis battery to one lug.

Wire to house battery bank to the other lug.

Re: Alternator exciter wire issue

Reply #67 – July 24, 2025, 06:23:51 pm

Quote from: wolfe10 – July 24, 2025, 04:04:08 pm

Here is the switch I used: PERKO Inc. - Catalog - Battery Switches - Medium Duty Battery Disconnect...

Rated for 250 AMPS Continuous, 360 AMPS 5 Mins. Intermittent.

Wiring:

Wire from alternator B+ and wire to chassis battery to one lug.

Wire to house battery bank to the other lug.

Yeah I get that , now thanks ,I've been thinking about that one for a long time, as long as that alternator has a direct source of power from the house batteries it will automatically excite , yeah that makes sense cheers ,

Re: Alternator exciter wire issue

Reply #68 – July 26, 2025, 11:21:10 am

Here is a pick of the back of my alternator you can see where I have attached the thinner 18 gauge wire the one that I've run to the spring switch on dash that would probably be the b plus terminal you mentioned ,is that correct please,

Re: Alternator exciter wire issue

Reply #69 – July 26, 2025, 12:18:38 pm

No, the B+ is the large lug on the right marked +. It is the 12 VDC positive that goes to the isolator center lug (assuming you still have the diode-based battery isolator).

Re: Alternator exciter wire issue

Reply #70 – July 26, 2025, 12:25:46 pm

Quote from: kevo0000 – July 26, 2025, 11:21:10 am

Here is a pick of the back of my alternator you can see where I have attached the thinner 18 gauge wire the one that I've run to the spring switch on dash...

Looks like you probably have the same (or similar) type alternator model as nitehawk.

The terminal you have your "thinner 18 gauge wire" attached to is called a "AC tap". It is definitely not a "excite" terminal.

I don't know how your "spring switch on dash" works to turn on your alternator. Not a normal setup, but if it does the job.........why not?

Re: Alternator exciter wire issue

Reply #71 – July 26, 2025, 12:39:15 pm

Perhaps this video will help....or not.

https://www.youtube.com/watch?v=hJB7cMeLwbI

Re: Alternator exciter wire issue

Reply #72 – July 26, 2025, 01:35:02 pm

Quote from: Chuck & Jeannie – July 26, 2025, 12:39:15 pm

Perhaps this video will help....or not.

https://www.youtube.com/watch?v=hJB7cMeLwbI

Yeah will watch now thanks alot

Re: Alternator exciter wire issue

Reply #73 – July 26, 2025, 01:42:11 pm

Quote from: kevo0000 – July 26, 2025, 01:35:02 pm

Yeah will watch now thanks alot

Yeah just watched the video briefly very interesting have subscribed to that channel , Il watch it later when not doing anything else I can concentrate better ,mutch appreciated thankyou

Re: Alternator exciter wire issue

Reply #74 – July 27, 2025, 04:13:42 am

Quote from: Chuck & Jeannie – July 26, 2025, 12:25:46 pm

Looks like you probably have the same (or similar) type alternator model as nitehawk.

The terminal you have your "thinner 18 gauge wire" attached to is called a "AC tap". It is definitely not a "excite" terminal.

I don't know how your "spring switch on dash" works to turn on your alternator. Not a normal setup, but if it does the job.........why not?

Yes I do have the same set up as nitehawk , with the diode battery isolator ,it is attached to the chassis drivers rear, and yes it works fine with the switch,it just needs a mili second of power and you can see the voltmeter go up and working fine , so IL leave well alone at the moment , I find electrics very interesting,

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