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bfam2008 · 06-19-2025, 09:38 PM

We have 02 Monaco Dyn Queen, ISL 400 on a Roadmaster chassis with a Tag Axle.

On trip up to Colorado a couple of weeks ago the alternator was over charging the house batteries and not charging the chassis batteries,(figured that out post shutdown)

There were no Alt warnings.... but about 3 hours into the trip I got a check trans warning as I pulled into a rest area near Quanah TX. The Trans went to limp mode and shifted to neutral and I was able to pull into a parking spot, but when I shut down I had zero power house or chassis.

The tech the Good Sams sent out figured out that if we charge the chassis batteries everything "chassis" worked and we were able to get to his shop about three miles down the road. I had a meeting in Colorado Springs so we left it there and continued in the toad.

I had him replace the old lead acid cells with AGMs while he worked the other problem. Oddly enough everything worked like it was suppose too after he replaced them.

I picked up the coach this morning, and headed towards Dallas. I got a Alternator warning light in Wichita Falls. Stopped at the Loves on the west side to troubleshoot. That alt warning light went out before I got to the parking so I pulled behind the repair shop. Checked the charging at the batteries "nothing"??

All this to ask, what is the best replacement for what looks like an old (original) Leece-Neville but there are no placards to be seen. Is there a straight up replacement or do we have to rig...it. I've seen discussions about the Delco 28si. Are both battery banks 12v out or is the chassis 24v out? This makes the most sense to me. I've always replaced them myself but used the picture that 'I take' to hook them back up. I do understand the house is series/parallel and 12v out! (The first tech wired the house in series (24v out) and I caught it before I turned stuff on)

I had my grandson with me so I had to drive him back home in the toad. The Loves maintenance manager let me put the coach in the lube bay overnight, so I'm heading back in the AM to figure things out with the Tech that was helping me.

I'm going to call the Tech on the way up and would like to give some ideas

Bill

twinboat · 06-19-2025, 09:59 PM

There is no 24 volt systems in you rig, both battery banks get wires for 12 volts.

You charging issue may be due to your battery isolator, if equipped. Your rig was built during the time they were switching from diode type isolators to isolation solenoids.
High charging at the house batteries and no charging at the chassis batteries, from the alternator is a symptom of a bad diode isolator. That will be in the battery control center. It will have cooling fins on it and 3 alternator size cables.

As far as going with a Delco or even a L-N replacement alternator, it will need to be a model with remote sense of Duvac style if you have a diode isolator.

bfam2008 · 06-20-2025, 05:31 AM

The first tech in this sorted story seems to wired both wrong

. I caught the house side but it seems that the chassis side is 24v as well. I'm heading back up to Wichita Falls now I'll check the chassis side and see how he wired it.

I'll check the battery isolator in control box, its on the back of the coach in the engine bay. Any tips on how to test it... I've got a really nice Flute multimeter.

Ideas on where to get one outside of Amazon.???? Are they available in a Auto parts store.

shootist · 06-20-2025, 05:57 AM

Quote:

Originally Posted by bfam2008

The first tech in this sorted story seems to wired both wrong

. I caught the house side but it seems that the chassis side is 24v as well. I'm heading back up to Wichita Falls now I'll check the chassis side and see how he wired it.

I'll check the battery isolator in control box, its on the back of the coach in the engine bay. Any tips on how to test it... I've got a really nice Flute multimeter.

Ideas on where to get one outside of Amazon.???? Are they available in a Auto parts store.

24 volts to the chassis could have done a lot of damage. You have a generator and could have used it to power the entire coach through the inverter just by combining both battery banks

SafariBen · 06-20-2025, 06:43 AM

Yes, if anything was hooked up 24V, all bets are off, take pictures before you touch anything, and measure the voltage overall and at each battery.

Agree with Twinboat, a diode battery isolator is a likely cause of this issue. IF you have a diode based battery isolator, the center post is typically the alternator, one side is chassis and one side is house battery, so easy to measure voltages right there with the engine running. Chassis should be 14V, alternator a little higher, and house is irrelevant at this point. If the alternator voltage is not getting to the chassis terminal, you can re connect the cables right there to bypass the isolator, but then your house use will drain the chassis battery also.

If you have another isolator style, post pics and whatever voltage readings you find.

A Delco 28SI will have a remote sense terminal so it will CHARGE correctly, but you'll need minor modifications to make the warning lights work correctly.

bfam2008 · 06-20-2025, 08:59 AM

Quote:

Originally Posted by shootist

24 volts to the chassis could have done a lot of damage. You have a generator and could have used it to power the entire coach through the inverter just by combining both battery banks

I looked at the cables when I got back to the coach, It would have been mostly impossible for him to do that the way the cables are Routed.

I was worried about it because he wired the house for 24… had him fix that before we fired things up

shootist · 06-20-2025, 09:49 AM

Quote:

Originally Posted by bfam2008

I looked at the cables when I got back to the coach, It would have been mostly impossible for him to do that the way the cables are Routed.

I was worried about it because he wired the house for 24… had him fix that before we fired things up

Awesome!

shootist · 06-20-2025, 09:58 AM

So if you have the older solid state battery isolator you need what they used to call a duvac alternator. Now they simply call it what it is , a remote voltage sense alternator. I would not recommend a 28si. I personally think I will just go back to the Leece Neville. The 40si appears to be a great alternative and has remote sense.
40si 240 amp 12v j180 long hinge , 160 amps at idle,#8600390. The long j180 is the isl standard mount.

The original 200 amp Leece Neville is a A0014884-JB
Ignition excite, mount 1/2-13unc , neg stud 3/8-16 unc pos stud 5/16-18, shaft diameter.8736-.8741. Clockwise rotation. Internal regulator. Distance between mounting flange 8.5. 4800 and 4900 series.

bfam2008 · 06-20-2025, 10:05 AM

Pretty sure we’re talking apples & apples here. I uploaded the picture below

Another interesting twist, the alternator has been consistently showing 12ish volts. Now it’s showing 27.6v on the isolator center post, 11.7 on the chassis and 12.1 on the house. At the battery it’s showing 11.79 chassis and 12.03 on the house. The maintainer is showing .22 on the chassis and 12.02 on the house

Quote:

Originally Posted by SafariBen

Yes, if anything was hooked up 24V, all bets are off, take pictures before you touch anything, and measure the voltage overall and at each battery.

Agree with Twinboat, a diode battery isolator is a likely cause of this issue. IF you have a diode based battery isolator, the center post is typically the alternator, one side is chassis and one side is house battery, so easy to measure voltages right there with the engine running. Chassis should be 14V, alternator a little higher, and house is irrelevant at this point. If the alternator voltage is not getting to the chassis terminal, you can re connect the cables right there to bypass the isolator, but then your house use will drain the chassis battery also.

If you have another isolator style, post pics and whatever voltage readings you find.

A Delco 28SI will have a remote sense terminal so it will CHARGE correctly, but you'll need minor modifications to make the warning lights work correctly.

shootist · 06-20-2025, 10:38 AM

Quote:

Originally Posted by bfam2008

Pretty sure we’re talking apples & apples here. I uploaded the picture below

Another interesting twist, the alternator has been consistently showing 12ish volts. Now it’s showing 27.6v on the isolator center post, 11.7 on the chassis and 12.1 on the house. At the battery it’s showing 11.79 chassis and 12.03 on the house. The maintainer is showing .22 on the chassis and 12.02 on the house

You need to disconnect the isolator. The alternator sees the .7 volt drop through the isolator and ups the voltage accordingly. I don't think you should ever see 27 volts, sounds like bad diodes in the isolator.

bfam2008 · 06-20-2025, 11:12 AM

Quote:

Originally Posted by shootist

You need to disconnect the isolator. The alternator sees the .7 volt drop through the isolator and ups the voltage accordingly. I don't think you should ever see 27 volts, sounds like bad diodes in the isolator.

The alternator shouldn’t be putting out 27v at the center post should it?? Or does the isolator split the voltage and distribute it to each bank

shootist · 06-20-2025, 11:17 AM

Quote:

Originally Posted by bfam2008

The alternator shouldn’t be putting out 27v should it?? Or does it split the voltage and distribute it to each bank

Your alternator cannot put out 27 volts, you are looking at leaking diodes from the isolator combination of alternator and battery bank in series is my guess. Get the isolator checked, it's just an ohm meter. You need to straighten this out before you start burning stuff up. Even the sequence you hook and unhook your batteries matters, running the engine without the alternator hooked up can damage it.

bfam2008 · 06-20-2025, 12:06 PM

Quote:

Originally Posted by shootist

Your alternator cannot put out 27 volts, you are looking at leaking diodes from the isolator combination of alternator and battery bank in series is my guess. Get the isolator checked, it's just an ohm meter. You need to straighten this out before you start burning stuff up. Even the sequence you hook and unhook your batteries matters, running the engine without the alternator hooked up can damage it.

Not sure why I didn’t think of that! I’m getting closed loops from chassis to the house and when I switch the probes I get the other way too. That explains the voltage

bfam2008 · 06-20-2025, 12:45 PM

Quote:

Originally Posted by shootist

Your alternator cannot put out 27 volts, you are looking at leaking diodes from the isolator combination of alternator and battery bank in series is my guess. Get the isolator checked, it's just an ohm meter. You need to straighten this out before you start burning stuff up. Even the sequence you hook and unhook your batteries matters, running the engine without the alternator hooked up can damage it.

Not sure why I didn’t think of that! I’m getting closed loops from chassis to the house and when I switch the probes I get the other way too. That explains the voltage