Skip to main content ↑ ↓
Topic: Alternator -DUVAC- isolator - explanation please (Read 2644 times) previous topic - next topic

Alternator -DUVAC- isolator - explanation please

I changed my Leese alternator last year and feel I'm not hooking it up correctly.
I thought I read that a straight 12v wire from the battery's to the DUVAC terminal would work the best. My problem is a battery drain. I resorted to disconnecting the wire after I got to my destination.
Should the wire to the DUVAC terminal be activated with the ignition key? Is this why my battery's would drain when parked?
I checked my isolator today thinking I could wire the DUVAV to one of the posts. (all tests were done with alternator disconnected)
When the key is off: (4 terminals from front to back) , 13.3v - .3v - 13.3v - 12.5v
When the key is on and engine off and running (same readings) , 13.3v - .3v - 13.3v - 12.5v
Where have I errored?
Where is a good place to tap 12v for the DUVAC terminal?
1995 U320C SE 40'
Jeep 4x4 Commander - Limited - Hemi
"The Pack"  Yogi and Diesel our Airedales -  Charlie our Boxer/Akita mix. Gone but NEVER forgotten Jake our yellow Lab.
NRA Law Enforcement Firearms instructor - Handgun/shotgun
Regional Firearms instructor for national Armored Transp. Co.

Re: Alternator -DUVAC- isolator - explanation please

Reply #1 –
Unless you have already had it done, the regulator has to be re-wired from the inside of the alternator for duvac. Then, the sense wire from the start battery post on the isolator runs through a 20 amp reset-able fuse to the duvac post on the regulator. I don't have an exciter (ignition switch) wire on mine. Just the sense. You may not either.  I had exactly the same problem as you until I took it to an auto electrician that knew how to wire it for duvac.
1994 U280, Build 4490
Deming, NM.

Re: Alternator -DUVAC- isolator - explanation please

Reply #2 –
Lon,
When you changed you alternator did you go back with a Leece-Neville?
If you did here is a link to how it should be wired up for a Duvac system and shows how to convert a non Duvac.
The thing is you have 4 terminals on the back of your alternator so this is how it should be set up internally.
Technical Services
Pamela & Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Alternator -DUVAC- isolator - explanation please

Reply #3 –
We only have a "sense" wire on our alternator - we do not have a "exciter" wire.  I had to look up DUVAC to see what you are discussing.  Found this info/diagram - perhaps it will be helpful in diagnosing the problem:

http://www.dixie-electric.com/tsb/TSB_704.pdf
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Alternator -DUVAC- isolator - explanation please

Reply #4 –
Lon,

Looking at the diagram I linked (above), I think you are correct in wiring the DUVAC lead direct to the POS terminal on the "start" (engine) battery.  Or, it could be attached to the "start" battery terminal on the isolator - should be the same thing.  The other small connector on the alternator should be wired to a "switched" ignition source - it should only see voltage when the ignition key is "ON".

With the ignition key "OFF", check voltage at both small contacts on the alternator.  Should see "start" battery voltage on the DUVAC terminal, nothing on the IGN terminal.  Turn key to "ON" - should read same voltage on both small terminals.

If this checks out, I think (opinion) your alternator is correctly wired, and you should not be seeing a drain on the batteries through the alternator.

I did see (in my quickie Google search) a couple references to having a relay in the DUVAC wire (one is in the source I linked above).  Apparently this would prevent the alternator from seeing any voltage on the DUVAC terminal unless the ignition switch was turned "ON" (which would power the relay).  I'm not clear why some applications would need a relay, and others would not.  Requires further research...
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Alternator -DUVAC- isolator - explanation please

Reply #5 –
Thanks for the help!
The alternator is a Leese. It is wired for the DUVAC system ( at least that's what I was told) It has 4 terminals.
I will go try it again today and do the checks you suggested.
1995 U320C SE 40'
Jeep 4x4 Commander - Limited - Hemi
"The Pack"  Yogi and Diesel our Airedales -  Charlie our Boxer/Akita mix. Gone but NEVER forgotten Jake our yellow Lab.
NRA Law Enforcement Firearms instructor - Handgun/shotgun
Regional Firearms instructor for national Armored Transp. Co.

Re: Alternator -DUVAC- isolator - explanation please

Reply #6 –
I'm getting 12v with the ign. key ON and OFF at the ign. wire at the alternator.
This does not seem correct.
I have ,3v at the main 12v lug with engine off.  Full 14+v engine running.
I have a direct to start batt, DUVAC wire at #2 post (12v)
I have 12v at all times at the ign. wire #3
I have ground at lug #4.

Problem?
1995 U320C SE 40'
Jeep 4x4 Commander - Limited - Hemi
"The Pack"  Yogi and Diesel our Airedales -  Charlie our Boxer/Akita mix. Gone but NEVER forgotten Jake our yellow Lab.
NRA Law Enforcement Firearms instructor - Handgun/shotgun
Regional Firearms instructor for national Armored Transp. Co.

Re: Alternator -DUVAC- isolator - explanation please

Reply #7 –
Lon,

That .3 volt at the alternator main POS terminal could be your "battery drain" voltage, or it could be "back feed" voltage coming from the alternator lug on the isolator.  While doing some electrical work on our coach, I discovered there is always some small amount of voltage on the alternator lug at the isolator.  I initially thought this was a problem with the isolator, but later decided it was doing no harm.  That subject was discussed in GREAT detail here:

Bad Isolator?

But to get back to your problem, in that link I posted earlier, it clearly states, "There should be no voltage to the ignition terminal with the key off. There should be 12V to the terminal with the key on (with or without the engine running)."  I also read another reference when I was doing my research this morning (can't find it now) that said having the IGN terminal on the alternator constantly powered would result in the battery being drained through the "sense" wire (DUVAC wire).

I believe I have read here on the Forum that on some coaches the alternator IGN wire is powered off the "Start Engine" panel in the engine compartment.  I think when you turn your ignition key to "ON" it sends power to the engine compartment start panel (which then allows you to start the engine).  As an experiment, you could remove the wire that is now attached to the IGN terminal on the alternator, and run a temporary jumper from the engine start panel to the alternator.  This would insure the alternator IGN terminal ONLY gets power when the key is "ON".

If this solves your problem, you could route the new wire more permanently.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Alternator -DUVAC- isolator - explanation please

Reply #8 –
12v wire with ignition off will drain battery.  But it is important to see if the 12 v reading is coming from ignition or from alternator.  Disconnect ignition wire and with it not connected to anything, does the wire still read 12v with ignition off.  With wire still disconnected from alternator, does the alternator small bolt post read 12v?

Re: Alternator -DUVAC- isolator - explanation please

Reply #9 –
Quote from: Barry & Cindy –
12v wire with ignition off will drain battery.  But it is important to see if the 12 v reading is coming from ignition or from alternator.  Disconnect ignition wire and with it not connected to anything, does the wire still read 12v with ignition off.  With wire still disconnected from alternator, does the alternator small bolt post read 12v?

The wire reads 12v disconnected
No reading on alternator when disconnected..
1995 U320C SE 40'
Jeep 4x4 Commander - Limited - Hemi
"The Pack"  Yogi and Diesel our Airedales -  Charlie our Boxer/Akita mix. Gone but NEVER forgotten Jake our yellow Lab.
NRA Law Enforcement Firearms instructor - Handgun/shotgun
Regional Firearms instructor for national Armored Transp. Co.

Re: Alternator -DUVAC- isolator - explanation please

Reply #10 –
A simple fix. You can stub that wire off so it's not used. On your remote start panel in the engine compartment is an hour meter. This meter only runs when the key is on. Run a wire from the + of this meter to the Ign post of the alternator. Now, the alternator will only get hot with the key on. See if this solves your problem. OR.........you can trace that hot wire and see WHY it is hot with the key off and correct it.
1994 U280, Build 4490
Deming, NM.

Re: Alternator -DUVAC- isolator - explanation please

Reply #11 –
Perfect and straight forward fix.  Alternator is ok.  Just find a new place to connect the ignition wire.  Behind the remote start panel is an ignition source and there are other ignitionsources in the engine compartment.  Don't know why the current connection is hot when ignition is off.

Re: Alternator -DUVAC- isolator - explanation please

Reply #12 –
Went and did battle with the beast today!
I ran a new wire from the engine hour gauge, GREAT SUGGESTION!
When I hooked everything up I had a new problem, the engine would not shut down. I had to remove the DUVAC wire that runs from the batteries to the alternator to get the engine to shut down.
I finally decided to check the alternator voltage regulator to see if the 12v all the time problem was there. IT WAS!
Apparently when the voltage regulator was initially installed the 2 wires inside were trapped inside the 2 spring coils. the insulation had been torn and the wires were grounding to the spring coils. I repaired the worn wire insulation and re-installed the regulator. WAA LAA, the alternator post (ign.) no longer was live.
I left everything hooked up and will monitor it tonight to see if the start batteries drain, all looked good when I last checked.
I hope the voltage regulator is good, it is charging, but the charging voltage on the dash and the plug in cigarette lighter voltage gauge show about 15v at a fast idle, it does drop at idle to about 14v, Maybe too much?

I bought this alternator new, When I got it the posts from the regulator were loose. I sent it back to the seller and they SUPPOSEDLY repaired the loose posts. After I installed it again I had the battery drain problem. I worked around it by always keeping a battery charger on it or by disconnecting the start batteries. I finally got around to checking it this week (2 years).

It seems no matter who or where you go for service or repair parts there is a increasing problem with BAD workmanship. Sad but true!
1995 U320C SE 40'
Jeep 4x4 Commander - Limited - Hemi
"The Pack"  Yogi and Diesel our Airedales -  Charlie our Boxer/Akita mix. Gone but NEVER forgotten Jake our yellow Lab.
NRA Law Enforcement Firearms instructor - Handgun/shotgun
Regional Firearms instructor for national Armored Transp. Co.

Re: Alternator -DUVAC- isolator - explanation please

Reply #13 –
Quote from: Lon and Cheryl –
I hope the voltage regulator is good, it is charging, but the charging voltage on the dash and the plug in cigarette lighter voltage gauge show about 15v at a fast idle, it does drop at idle to about 14v, Maybe too much?

Lon,
L/N makes 3 type voltage regulators for the alternator.
1. Non adjustable
2. Adjustable with moving a buss bar. This one is more of a pain than a non adjustable.
3. Adjustable with an external accessible pot. The one I like the best.

 Look at the top of the voltage regulator for a little black rubber plug. If your has it you should be able to remove it and use a small instrument screwdriver to trim it out to what you need.  To make any adjustment you need a good Volt meter as moving this trim pot a small amount will make a big change. Take your reading right off the taps of the alternator.

If you are trying to overcome voltage loss going through a diode based isolator after getting your voltage close right at the alternator then make a final adjustment on the down stream side of the isolator at your battery.

Pamela & Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Alternator -DUVAC- isolator - explanation please

Reply #14 –
Quote from: Pamela & Mike –

If you are trying to overcome voltage loss going through a diode based isolator after getting your voltage close right at the alternator then make a final adjustment on the down stream side of the isolator at your battery.

Pamela & Mike

Correct.  You want to have correct voltage on the chassis battery side of the diode-based battery isolator.  You loose around .7 VDC across the isolator.  So, voltage at the alternator will/should be  just under 15 VDC. 
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Alternator -DUVAC- isolator - explanation please

Reply #15 –
This drawing may have some value to the discussion.

Regards,
Charles
W5CRY
1997 Dynasty - Sold
 

Re: Alternator -DUVAC- isolator - explanation please

Reply #16 –
Quote from: Pamela & Mike –
Lon,
L/N makes 3 type voltage regulators for the alternator.
1. Non adjustable
2. Adjustable with moving a buss bar. This one is more of a pain than a non adjustable.
3. Adjustable with an external accessible pot. The one I like the best.

 Look at the top of the voltage regulator for a little black rubber plug. If your has it you should be able to remove it and use a small instrument screwdriver to trim it out to what you need.  To make any adjustment you need a good Volt meter as moving this trim pot a small amount will make a big change. Take your reading right off the taps of the alternator.

If you are trying to overcome voltage loss going through a diode based isolator after getting your voltage close right at the alternator then make a final adjustment on the down stream side of the isolator at your battery.

Pamela & Mike

I took a closer look today at the regulator, it HAS a very small, clear plastic plug that I didn't see before. This must be the voltage adjustment port you mention.
The engine battery's (3) did not lose voltage sitting connected to the alternator last night. I'm sure my short is fixed.
I still question the regulator, as it is now, The voltage fluctuates from 15+v to 14v. It will not stay steady(engine running at 1000rpm no load) If I turn on the lights or dash lights they flicker.
I will try setting the voltage at the regulator Saturday, hopefully I can get it to stabilize.
1995 U320C SE 40'
Jeep 4x4 Commander - Limited - Hemi
"The Pack"  Yogi and Diesel our Airedales -  Charlie our Boxer/Akita mix. Gone but NEVER forgotten Jake our yellow Lab.
NRA Law Enforcement Firearms instructor - Handgun/shotgun
Regional Firearms instructor for national Armored Transp. Co.