Overcharging Issues- HELP!!

[fire94sfd]

NEED HELP!!  Sorry for the long post.

I few days ago I started my coach (2002 Monaco Dynasty, Leese Neville Duvac) to take for a drive just to make sure everything was operating like it should.  Engine turned over fast and started fine.  About a mile down the road I noticed that the volt meter on the dash was only reading around 11 volts.  I turned around and came back to my shop.  I left the Coach running and checked voltage at the house batteries.  They were reading 18 volts at the battery bank.  Went directly to the rear run panel and checked voltage on all 3 lugs of the battery isolator.  Chassis batteries showed 11.4 volts, house batteries showed 18 volts, alternator lug showed 18v.   Killed the engine and rechecked.  Chassis read the same, house read 15.4 volts, alternator lug read 7.2 volts(fluctuated up and down by a few tenths).  Tried to restart the engine but wouldn’t start.  I let it set for probably around 30 minutes and rechecked chassis batteries.  Now they were back to 12.5 volts and the coach started fine.

 

I figured I might be having trouble with the voltage regulator in the alternator so I removed the alternator and took it to a local alternator repair/rebuild shop.  The shop seemed to be familiar with this alternator and the Duvac system.  They called me a little later and said that the alternator was fine and was putting out 13.9-14 volts consistently.  

 

I’m at a loss as to what could cause the increase in voltage but at the same time cause the dash voltage gauge to show low voltage?  Could the battery isolator be the problem?  I am prepared to switch to the newer style isolator system and Delco alternator in order to move away from the Duvac system.  I just would like to know that it will fix my problem before I do.

 

A little past history: While on a trip last summer, my inverter caught fire. The batteries over-charged causing battery failure of all 4 house batteries. The alternator shut itself off,as intended, due to the extremely low voltage.  I was able to bypass the inverter, charge the batteries enough to get the alternator to kick in, and go on with our trip.  I tied the house battery cables to the chassis batteries and used an automotive style charger on the chassis batteries to provide 12v power to the house.  Other than a few things that quit working (refrigerator, trip tek, bathroom vent fan,due to the high voltage spike, everything seemed to work fine and we continued on with our 3 week trip.  I attributed this to the inverter burning up but now I wonder if something else caused the inverter failure??

 

I’d appreciate any suggestions or ideas on where to go from here.

Thanks!!!

Edited April 28, 2023 by fire94sfd

[Ivan K]

My first thought is if the duvac terminal on alternator is getting correct reference voltage from the batteries. There should be an inline fuse for it, possibly in the battery compartment?

[jacwjames]

On my chassis wiring diagram it shows that the dash voltmeter gets its feed from a 10 amp fuse in my #2 Monaco box in the front drivers side run bay, the fuse is also for the dash gauges.   The label on the #2 box doesn't have a label for voltmeter but does have one for "Dash/Fuel Sender", not sure if that is the correct one but the only other 10 amp fuse is for the Park Bell.  There is also an Ignition relay in the box.  Might check the connections there.

I have a separate Duvac fuse in my passenger side rear electrical bay in a separate fuse holder. 

 

My house/chassis charging system was different, I had the BIRD/Lambert system to maintain the batteries.  Started having trouble with min in 2021 and installed the Bluesea MLACR.  Easy change for me and it works great. 

[fire94sfd]

9 hours ago, Ivan K said:

My first thought is if the duvac terminal on alternator is getting correct reference voltage from the batteries. There should be an inline fuse for it, possibly in the battery compartment?

Thanks,  I’ll check my wiring diagram for the fuse location.  Do you know if this wire should show the battery voltage if checked while disconnected from alternator?

3 hours ago, jacwjames said:

On my chassis wiring diagram it shows that the dash voltmeter gets its feed from a 10 amp fuse in my #2 Monaco box in the front drivers side run bay, the fuse is also for the dash gauges.   The label on the #2 box doesn't have a label for voltmeter but does have one for "Dash/Fuel Sender", not sure if that is the correct one but the only other 10 amp fuse is for the Park Bell.  There is also an Ignition relay in the box.  Might check the connections there.

I have a separate Duvac fuse in my passenger side rear electrical bay in a separate fuse holder. 

 

My house/chassis charging system was different, I had the BIRD/Lambert system to maintain the batteries.  Started having trouble with min in 2021 and installed the Bluesea MLACR.  Easy change for me and it works great. 

I don’t think my gauge has a fuse problem because it is working, it just reads low voltage.  I will definitely double check though.  I think I will switch to the Bluesea MLACR as well.  Thanks!

[Ivan K]

My duvac post on alternator is always hot, it comes directly from batteries. Only the ignition post is switched power.

[waterskier_1]

Thanks for providing the voltage reading at the Isolator Terminals.  What the dash gauge reads is not important to fixing the problem, but it is important to notify you that you do have a problem.  Since with the engine running, you are getting 18 volts out of the alternator, it is likely that the voltage regulator (VR) is running wide open (max voltage).  Since you have had the alternator checked, you know the regulator itself is likely good.  That leads to the DUVAC sense causing telling the alternator VR that the battery is discharged.  This is true, based upon your readings - the sense for the DUVAC goes on the chassis battery, which you state was reading 11.4, severely discharged.  Therefore, the chassis battery voltage is telling the alternator, through the VR, that it need maximum voltage to recharge.  The alternator responded, sending 18 volts out.  Now, the House battery is at the same voltage as the alternator output, so the isolator is supplying current (too much) to the house battery.  But, it is not getting to the Chassis battery, so I suspect your Isolator is bad.  It is not allowing the alternator to supply current to the chassis battery - likely the Diode is burnt in an Open condition, not allowing current to flow in either direction.  But, when you turn off the engine, you see voltage on the alternator terminal, which you should not.  So it is likely that the Diode for the House battery is also compromised.  In any case, the Isolator is likely toast.  

When I had this same system on my old Dynasty, I replaced the Isolator with a direct replacement, and all worked fine.  I know my problem was due to the House battery shorting out, and drawing excessive current from the alternator.  It shorted out the diode, but in my case, in a "shorted" versus "open" condition.  I was driving slowly approaching the campground office and I saw the smoke coming out from the battery bay in my side view mirror.  Back to your problem, if that happened today, I would replace the existing solid state (diode) Isolator with a Blue Sea ML-ACR Isolator.  I think Van Williams has a white paper on this in the files section.  Your DUVAC alternator will still work with this Isolator.

FIY:  The purpose of DUVAC is to allow for remote reading of the battery being charged.  If the battery is located a long distance (wire connections are long) there can be a voltage difference in what the alternator voltage is and what is actually at the battery.  With Solid State Isolators, there is between 0.3 and 0.8 volts dropped across the diode itself, meaning that if the alternator is at 14.4 volts, battery would only see 13.6 volts.  

  -Rick N.

Currently in Deming, NM

5 minutes ago, Ivan K said:

My duvac post on alternator is always hot, it comes directly from batteries. Only the ignition post is switched power.

It should be "hot" only when the engine is running.

 -Rick N.

[Ivan K]

35 minutes ago, waterskier_1 said:

 

It should be "hot" only when the engine is running.

 -Rick N.

Why would the remote sense wire only be hot when engine running? It comes directly from the batteries, in my case anyway.

[waterskier_1]

15 minutes ago, Ivan K said:

Why would the remote sense wire only be hot when engine running? It comes directly from the batteries, in my case anyway.

You are correct.  I was thinking the center post of the isolator which is connected to the alternator.  That should only show voltage when the engine is running.

  -Rick N.

[Ivan K]

9 minutes ago, waterskier_1 said:

You are correct.  I was thinking the center post of the isolator which is connected to the alternator.  That should only show voltage when the engine is running.

  -Rick N.

Yes, agreed.

[TomV48]

Well I have nothing directly to the problem, but low voltage indication often means resistance at a connection or fuse contact. 

My water pump, making wimpy noises, was the first I knew that I had a voltage problem.  We found a high resistance at the contacts to my Salesman switch, which in our 2005 Ambassador is a Latching Relay so no load from the relay itself when activated.  We found that the contacts on the side had tell tale heat and were found to have some bi-metal corrosion and were just flat NOT TIGHT so clean all the ring connectors and tighten them and bingo no more notable heat at the connections (they were hot enough to burn your fingers) and voltage back up at the water pump by over a volt and a half.  I guess that in normal use the water pump is the highest amperage item so it showed up there first.

Edited April 28, 2023 by TomV48
typo

[fire94sfd]

10 hours ago, jacwjames said:

On my chassis wiring diagram it shows that the dash voltmeter gets its feed from a 10 amp fuse in my #2 Monaco box in the front drivers side run bay, the fuse is also for the dash gauges.   The label on the #2 box doesn't have a label for voltmeter but does have one for "Dash/Fuel Sender", not sure if that is the correct one but the only other 10 amp fuse is for the Park Bell.  There is also an Ignition relay in the box.  Might check the connections there.

I have a separate Duvac fuse in my passenger side rear electrical bay in a separate fuse holder. 

 

My house/chassis charging system was different, I had the BIRD/Lambert system to maintain the batteries.  Started having trouble with min in 2021 and installed the Bluesea MLACR.  Easy change for me and it works great. 

Thanks!  I have a bunch of fuses in my battery compartment but unfortunately I don’t have a page in my wiring diagram that shows where they go.  I bet one of them is the fuse that you mentioned.  I’ll trace it down and make sure.  Thanks again for your help!

5 hours ago, waterskier_1 said:

Thanks for providing the voltage reading at the Isolator Terminals.  What the dash gauge reads is not important to fixing the problem, but it is important to notify you that you do have a problem.  Since with the engine running, you are getting 18 volts out of the alternator, it is likely that the voltage regulator (VR) is running wide open (max voltage).  Since you have had the alternator checked, you know the regulator itself is likely good.  That leads to the DUVAC sense causing telling the alternator VR that the battery is discharged.  This is true, based upon your readings - the sense for the DUVAC goes on the chassis battery, which you state was reading 11.4, severely discharged.  Therefore, the chassis battery voltage is telling the alternator, through the VR, that it need maximum voltage to recharge.  The alternator responded, sending 18 volts out.  Now, the House battery is at the same voltage as the alternator output, so the isolator is supplying current (too much) to the house battery.  But, it is not getting to the Chassis battery, so I suspect your Isolator is bad.  It is not allowing the alternator to supply current to the chassis battery - likely the Diode is burnt in an Open condition, not allowing current to flow in either direction.  But, when you turn off the engine, you see voltage on the alternator terminal, which you should not.  So it is likely that the Diode for the House battery is also compromised.  In any case, the Isolator is likely toast.  

When I had this same system on my old Dynasty, I replaced the Isolator with a direct replacement, and all worked fine.  I know my problem was due to the House battery shorting out, and drawing excessive current from the alternator.  It shorted out the diode, but in my case, in a "shorted" versus "open" condition.  I was driving slowly approaching the campground office and I saw the smoke coming out from the battery bay in my side view mirror.  Back to your problem, if that happened today, I would replace the existing solid state (diode) Isolator with a Blue Sea ML-ACR Isolator.  I think Van Williams has a white paper on this in the files section.  Your DUVAC alternator will still work with this Isolator.

FIY:  The purpose of DUVAC is to allow for remote reading of the battery being charged.  If the battery is located a long distance (wire connections are long) there can be a voltage difference in what the alternator voltage is and what is actually at the battery.  With Solid State Isolators, there is between 0.3 and 0.8 volts dropped across the diode itself, meaning that if the alternator is at 14.4 volts, battery would only see 13.6 volts.  

  -Rick N.

Currently in Deming, NM

It should be "hot" only when the engine is running.

 -Rick N.

Thanks for the great information.  I’m going out this evening to re-install the alternator and try to diagnose the things you mentioned.  After I can confirm, I’m definitely going to switch to the Blue Sea.  Then I’m going to order a new Delco alternator to carry as a spare.

[MyronTruex]

Alternator likely running full tilt because of loss of sense line voltage.

Your isolator is showing the high voltage on two posts I believe. The one from the alternator and then the one to the house batteries. This means that side of the diode setup is working.

 

What is not working is the other side of the diode isolator. Put a temporary jumper across the two outputs, that is the engine bank and the house bank.  Or stack them both on the house side of the isolator posts. This will bypass the isolator function basically and if the issue is the sense line is connected to the bad side of the isolator this should give it a proper signal to bring the voltage down to a proper level.

 

[fire94sfd]

14 minutes ago, myrontruex said:

Alternator likely running full tilt because of loss of sense line voltage.

Your isolator is showing the high voltage on two posts I believe. The one from the alternator and then the one to the house batteries. This means that side of the diode setup is working.

 

What is not working is the other side of the diode isolator. Put a temporary jumper across the two outputs, that is the engine bank and the house bank.  Or stack them both on the house side of the isolator posts. This will bypass the isolator function basically and if the issue is the sense line is connected to the bad side of the isolator this should give it a proper signal to bring the voltage down to a proper level.

 

I have already removed then isolator so I won’t be able to check it like you mentioned but I did check it with my voltmeter and it seems like you are exactly right.  Current moves from alternator post to house battery post but not from alternator post to chassis battery post.  I have ordered a new BlueSea ML-ACR.  Thanks for your help!!

[fire94sfd]

Thanks again for all the help!!  The problem was the battery isolator.  Replaced it with the BlueSea Magnetic Latching mechanism.