DUVAC Alternator and Suitable Replacements

[Guest Potholepicker]

Hello,

Our duvac alternator went out last week. I went to the truck supply and got what they said was a suitable replacement, Delco 24SI. I installed it and saw that some of the old connections had no place to connect on the new alternator.

I started the engine and the alternator wasn't charging. Upon turning the ignition key off the engine kept on running. Not good! I tried cutting off air to the engine, no joy. Called the truck supply no joy. This went on for 30minutes, then I prayed and retrieved a wire jumper and connected (temporarily) the ignition terminal on the new alternator to an unused terminal on the new alternator, which allowed the key position (off) to take effect. Whew, the engine stopped running.

I have ordered a DUVAC alternator for 550 from Amazon, and am waiting for the part.

I think Van mentioned another Delco alternator which may replace the DUVAC. Anyone know the model of that and the wiring for that one.

Thanks for reading and commenting.

Jeff

02 Executive Tag, 500 ISM

[jacwjames]

Here is a good post from IRV2 on the subject, several of the posters are very knowledgeable.  https://www.irv2.com/forums/f115/eliminating-the-duvac-system-539048.html

If you have already ordered a replacement you might consider taking the old one and having it rebuilt.  That is pretty much what conventional wisdom suggests and what I did in ~10 years ago when my alternator failed.  Got a recommendation of a good shop, dropped it off, 24 hours turn around, $185.  Still running strong.

[vito.a]

It's possible to swap in a new style alternator but there are so many issues.  

Just have the original alternator rebuilt.  It's so much easier.  

[Guest Potholepicker]

Thanks for the suggestion to rebuild. Closest shop was 100+miles away. May consider for a spare though.

[JJMonaco]

I recently replaced my DUVAC with the Delco on my 2002 Signature.  No problems so far.  If you go to my post, it addresses the issues you may be having.

Good Luck,

JJ

 

[Bjohnsonmn]

I had nearly the same experience with my 2000 Windsor 32PB (A.k.a Loaf, A.k.a. "Shorty No-slides")

The newer alternator will work, but you will need to do a few things to simplify the system.

I ended up having only four connections: 1. Negative, 2. Battery Positive, 3. Remote sense, 4. Relay (Controls the Alt Fail light)

I had originally connected the ignition wire. The newer alternator ign connection is bi-directional and will let voltage on the line AND detect ignition on.

Two choice: 1. Leave it disconnected, 2. Install a Diode

Our RV didn't have the big blue battery isolator of doom. It had a trickle (from the factory) charge green box that allowed voltage to charge from the chassis to the battery and a large solenoid that was connected to a momentary switch to act as a "booster" bridging the systems for a self-contained jump.

I talked with a tech at Delco about how the internals of the SI alternators worked. Very interesting.

If you have that big blue box of unhappiness, then you do have some other work to do. But, if you are setup as I was from the factory, it is a MUCH easier system to support with the SI series as those are on the shelf and affordable to acquire at any good truck service location.

[jimc99999]

I had already replaced my battery isolator with the BlueSea ML-ACR, partly because I suspected alternator problems. There are no alternator rebuild shops nearby, so I ended up with a Delco 28si. The alternator is self-exciting, just needs to rev over 500 rpm to start working. Occasionally the startup doesn't rev quite high enough so I have to tap the throttle to get the alternator charging. 

I'm pretty sure I only attached +/- charge and tach sensor, leaving the ignition and voltage sensing wires disconnected. Not being a DUVAC alternator, the new alt doesn't have a separate voltage sense post. It does have the ignition sense but it isn't required on my 97. 

So far 5K+ miles with the new alternator and ML-ACR and no problems. 

The DUVAC alternator was only necessary because of the voltage drop across the diode-based battery bank isolator. If you don't have the old-style battery bank isolator you don't need a DUVAC alternator.  If you do have a diode-style battery bank isolator you should consider replacing it. The ML-ACR takes the place of the diode-based battery bank isolator, the boost relay (mine was also failing), and the trickle charger that keeps your chassis batteries charged while on generator or shore power. 

Here's a post with before/after pictures for ML-ACR installation. I still haven't wired up the remote yet, I just leave it on auto and it's fine. The only thing I ever needed the battery boost for was starting the generator when the house batteries were low, and with the space cleared up from installing the ML-ACR, I just switched the generator start circuit to the chassis batteries (the way it always should have been).

 

Edited April 20, 2023 by jimc99999

[Guest Potholepicker]

Howdy,

I received the Delco 28si and the ML-ACR and have installed them both. Our 12V box was alot different from the pics shown by Van.

I spent some time checking cable continuity to verify what I could.

Battery voltages are sufficient at 12.74.

Problem is I cannot get the power to the house system, no Lights or indications on the inverter panel.

Not sure I have the whole picture. Any help would be appreciated.

[jacwjames]

1 hour ago, Potholepicker said:

Howdy,

I received the Delco 28si and the ML-ACR and have installed them both. Our 12V box was alot different from the pics shown by Van.

I spent some time checking cable continuity to verify what I could.

Battery voltages are sufficient at 12.74.

Problem is I cannot get the power to the house system, no Lights or indications on the inverter panel.

Not sure I have the whole picture. Any help would be appreciated.

Have you installed the ML-ACR & Alterator???

Have you checked power coming through the battery disconnect.   Disconnect has to be on.  I'd get out a meter and check power from the batteries all the way through the system. 

[Guest Potholepicker]

Yessir. New 28si. Dx switches on. Power to and through ml-acr. 
not getting batt voltage at back of alternator. 
not sure what to do with heavy cables that came off isolator. 

[JJMonaco]

Did you hook up the ground wire connection bolt on the alternator to a good common ground?  
 

[Guest Potholepicker]

Yes.  Bright metal and tight connections. I need a decent schematic. 

[JJMonaco]

I recently installed the same alternator on my 2002 Signature. That alternator is self exciting -so it should have 14 .1 volts with engine running at the output when testing between the + and - on the back of the alternator - if the ground connection is good. You don’t even need to use a 12v sense wire or have the tachometer feed wire hooked up for it to work. It may need to have bump up in the rpm to get the self excitation to kick in. Otherwise it may be a defect.  

[Guest Potholepicker]

So, haven’t started engine yet. Trying to determine why no power in Coach ( lights, inverter, etc. )

did you remove the isolator and maintainer and the boost solenoid?

I did and that may be where the problem is. 

John

care to share a pic of your 12volt center with the the big boy?

[jimc99999]

 

59 minutes ago, Potholepicker said:

Yessir. New 28si. Dx switches on. Power to and through ml-acr. 
not getting batt voltage at back of alternator. 
not sure what to do with heavy cables that came off isolator. 

21 minutes ago, Potholepicker said:

So, haven’t started engine yet. Trying to determine why no power in Coach ( lights, inverter, etc. )

did you remove the isolator and maintainer and the boost solenoid?

Power to your inverter should be coming from the batteries to the cutoff switch, across the ML-ACR house-side post, to the inverter. So the house-side cable from the inverter to the isolator should now be connected to the ML-ACR house-side post, as well as the house battery.

The boost solenoid and cables can just be removed.

I removed my maintainer as well, because with the ML-ACR in auto mode, charging current from the inverter/charger will cause the ML-ACR to connect the banks and both sides will receive charging current.

The engine side should be similar. Chassis battery to battery cutoff switch to ML-ACR to alternator. The big cable from the alternator to the isolator should now be connected to the chassis post on the ML-ACR, along with the cable from the battery cutoff switch.

On my ML-ACR, house is left side, chassis is right side. The thick cable coming from the right side of the ML-ACR heading downward goes directly to the back of the alternator. The copper bars I used on the ML-ACR came from the boost solenoid I removed.

Edited April 25, 2023 by jimc99999

[Guest Potholepicker]

Thanks for the pic. Your cutoffs are visible where as mine are not in the box. Are the four fuses to the left of the Ml-acr connected to ground?

[jimc99999]

The 4 fuses to the left are on the house battery positive side. The top goes to the salesman switch solenoid, the second is generator starter power, I assume the bottom is +12 to inverter. 

The old isolator and now ML-ACR handle only positive 12V, the grounds all connect to the chassis. Some systems use battery cutoff switches on battery negative instead of positive but mine does not. That’s something you’d want to double-check on yours. 

[Guest Potholepicker]

That salesman switch might be an issue too. Don’t know where the solenoid for it is located. 

[jacwjames]

Salesman switch normally just controls the 12 volt circuit used for the house circuits.  The inverter is connected through a large fuse, in my case I believe it is a 300 amp  fuse. 

Find the larger wire that feeds the inverter and back trace toward the MLACR. 

[jimc99999]

2 hours ago, Potholepicker said:

That salesman switch might be an issue too. Don’t know where the solenoid for it is located. 

You've mentioned you have no power to the inverter and no interior lights, which are 12V separate from the inverter.  So likely your problem is not the salesman switch solenoid or the inverter, but the power supply to both of them. In my coach, the power supply to both 12V lights and the inverter is that bar with fuses left of the ML-ACR. The thick cable that feeds that bar used to cross the house side of the isolator. 

In this "before" picture, the isolator is the blue device at the top. The alternator 12V+ is the center cable on the isolator. That is now connected to the chassis post on the ML-ACR. The house power crosses the left post of the isolator, and feeds the house side power (12V lights/fans and inverter). There are no ground cables in this photo, it's all +.  I know your setup is going to look different but the concept should be the same. The isolator, battery boost, and maintainer that the ML-ACR replaces are all positive side, no ground wires.

The alternator ground runs to the chassis near the alternator. Battery grounds connect to chassis, and there will be a big ground strap connecting the engine block to the chassis.  From any of these +12V wires you can check voltage to a clean spot on the chassis. Even if your ML-ACR isn't working in auto mode, you should still have 12V from house batteries to inverter and house 12V circuits, and 12V from engine batteries to alternator + post.  Obviously battery disconnect switches interrupt those circuits.

[Guest Potholepicker]

Thanks for the pic. In my checking of the wiring some cables were grounded. Will recheck between rain showers today. Will report back once it is working. 

[Guest Potholepicker]

Hi

our 4 fuse with the buss bar is ground in our system. 
 

started engine and alternator works. 
no house power. 
no inverter power. 
generator runs with partial ac to house outlets. 
 

ideas please. 

[JJMonaco]

I can see from the photo that your old setup was the same as my 2002 Signature was before I changed over to Lithium (LifePO4) batteries for my house battery bank.  In my case I did not want to have the alternator charge the house batteries directly. I have a dc to dc charger coming from my chassis batteries to my house bank that can charge the house bank when the engine is running. In your case you want that option to combine both battery banks assuming both of your battery banks are lead acid types.
The double buss bars on the bottom of the photo are for you house battery distribution to the circuits you want the house batteries to feed. It appears you have nothing feeding that bus.  It needs to be fed directly by the house battery bank. In your case you want to  have the option to combine the two banks.   
I believe all you need to do is identify the large red cable that is the direct feed from your house batteries and connect it to the double buss bar in the photo. (not to the input of the ML ACR) That will power the house. Then run another same sized red cable from the switchable output of ML ACR to the house bus bar. That should allow you to combine both banks when needed.  However, I would not keep them combined all the time.  You will need a way to charge the house batteries by themselves to their specific charge parameters when you are not plugged into shore power and unable to use your inverter/charger to charge the house bank.  House batteries and chassis batteries have different charging needs.

JJ

[Guest Potholepicker]

JJ,

The double buss at the bottom ohms out as negative through the chassis ground and the negative battery terminals. I had thought that it was related to the house power.

I dont know how to connect a positive cable to the negative buss without creating a welder. Our Batteries are AGM.

Am I mistaken in this supposition?

Jeff

 

[jacwjames]

Did you take any pictures before you started??  Can you post them.