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Topic: Intermittent charging of house batteries while driving (Read 592 times) previous topic - next topic

Intermittent charging of house batteries while driving

Hello,

I could use some help on how to diagnose this charging problem.

Recently, on several occasions, the voltage of the house battery was declining while driving.

When things are working normally:
  Dash volt meter:  13.7v
  Victron battery monitor:  chassis battery 14.2v
  Victron battery monitor:  house battery 14.2v (once it's charged)

When the house battery isn't getting charged:
  Dash volt meter:  13.7v
  Victron battery monitor:  chassis battery 14.2v
  Victron battery monitor:  house battery 12.6 or below and falling

Most of the time the issue has occurred after driving for a while.

The issue has occurred from the time the engine was started.

Sometimes the issue corrects itself while driving.

Most of the time the issue continues until the engine is restarted.

If I turn on the boost switch, the house battery voltage starts climbing.  If I then turn off the boost switch the voltage starts falling again.  Cycling the boost switch repeats the behavior.

I have talked to Foretravel and they thought it was the boost solenoid and that I should try tapping on it the next time the problem happened.  I haven't had an opportunity to do that yet.  Every time it's happened has not been a good time to pull over, extend the slides, and open the hatch to get access to the boost solenoid or to take voltage readings on the battery isolator.  I don't see how the boost solenoid could cause this scenario, but when I get the the chance I'll give it a tap when the issue is occurring.  When I asked Foretravel if it could be the battery isolator, they said probably not, that if the isolator fails, it usually doesn't cause an intermittent problem.

Thanks much for any input.

Joe
2008 Nimbus

Re: Intermittent charging of house batteries while driving

Reply #1 –
You say when driving sometimes the alternator is charging sometimes it's not. One thing if that's
what's happening I would think sticking brushes in the alternator.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Intermittent charging of house batteries while driving

Reply #2 –
Joe,

If the boost switch functions when you flip the switch on the dash it is doing what it is made for. If the switch is in the normal position that would be off it is out of the picture as it is just there. Said another way it has no way to know what is going on as it is only a manual switch to control it.

The Isolator can do a lot of strange things and this could be one of them. One of the diodes can be failing causing intermittent charging. The isolator is the only place that the 2 battery banks are tied together while the engine is running unless someone has done some creative wiring in the past. Pull the wires off the isolator and give them a good cleaning along with checking the diodes to see if they are functioning properly. If the isolator looks like it has been hot and melted some of the epoxy then for sure I would bet the problem lies here.

With the battery voltage on the house batteries dropping that quick you may need to check the batteries to see if you have a failing battery or a corroded cable This could be causing the isolator to overheat and break down.

Mike
Pamela & Mike 97 U 320

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

Re: Intermittent charging of house batteries while driving

Reply #3 –
First thing I would check as well would be all connections alternator to batteries.

Does your 2008 have a diode-based battery isolator or solenoid-based isolator?
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: Intermittent charging of house batteries while driving

Reply #4 –
Quote from: wolfe10 –
Does your 2008 have a diode-based battery isolator or solenoid-based isolator?

I am going to guess diode-based like I have. 

First guess that came to mind was the isolator is going south.

Mike, coach probably has a residential refrig and the inverter is running off the house batteries while going down the road and batteries are not getting a charge from alternator. .
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Intermittent charging of house batteries while driving

Reply #5 –
Quote from: joe g –
I have talked to Foretravel and they thought it was the boost solenoid and that I should try tapping on it the next time the problem happened.
Like Mike says, your boost solenoid is working correctly.

I would avoid accepting electrical system advice from the FOT employee who told you to "try tapping on it".

Intermittent electrical problem often = bad cable or loose connection, most likely suspect the cable(s) running from isolator to house battery bank.

Do what Brett said - check cables for corrosion (swollen insulation), clean the terminal posts and cable connectors, make sure they are tightly bolted on posts.
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: Intermittent charging of house batteries while driving

Reply #6 –
Hello,

Thank you for all the feedback.

When the house battery is discharging, it's not a fast discharge.  Didn't mean to imply that.  No residential fridge.  With the inverter running and misc. 12v draws, the battery voltage drops .1volts in a couple of hours maybe.

The isolator is a diode based, 3 post, 200 amp Cole Hersee.  I don't know if it's original, but assume so.

Thanks for confirming that the boost solenoid can't be part of this issue.  I'll focus on testing the isolator and cleaning and inspecting connections and cables.

If it is the isolator, since it's an intermittent problem I feel there is a good chance the isolator will test okay.  If the isolator tests okay and I don't find any connection/cable problems, what do you think of the idea of switching the cables on the two battery posts on the isolator?  I'm thinking if I do that and then if the next time it happens the chassis battery is the one discharging, it means it's the isolator for sure.

Thanks much you guys.

Joe
2008 Nimbus

Re: Intermittent charging of house batteries while driving

Reply #7 –
To check the diode-based isolator when voltage is down:

Engine running and at around 1,100 RPM. Check between good ground and center lug (from alternator B+). Should be in the mid to high 14's.  Next, check the outer lugs (connected to the two battery banks).  The readings here should be about .7 VDC lower than the center.
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: Intermittent charging of house batteries while driving

Reply #8 –
Hello,

I did some of the testing/inspecting.  Here are the results:

Volts at the isolator:  Engine off, wires connected (not cleaned yet), generator running, inverter's charger charging:
Note:  In addition to the wire going to the chassis battery, that post also has a small wire connected to it.  Didn't trace, but assume it's the alternator sensing wire.
  Chassis battery post:  13.04v
  Alt. post:                    13.08v
  House battery post:    14.70v

Volts at the isolator:  Engine off, wires connected (not cleaned yet), generator/inverter had been off a few minutes:
  Chassis battery post:  13.04v
  Alt. post:                    12.86v
  House battery post:    12.92v

Out of curiosity, I measured Volts across isolator posts:  Engine off, wires connected (not cleaned yet), generator/inverter had been off a few minutes:
  Pos. test lead on chassis battery post, neg. test lead on alt. post                  = 0.11v
  Pos. test lead on chassis battery post, neg. test lead on house battery post = 0.16v
  Pos. test lead on alt. post, neg. test lead on house battery post                    = 0.05v

Wires disconnected and multi-meter in diode test mode:
  Pos. test lead on alt. post, neg. test lead on chassis battery post  = .435
  Pos. test lead on alt. post, neg. test lead on house battery post    = .419
  Neg. test lead on alt. post, pos. test lead on chassis battery post = no reading
  Neg. test lead on alt. post, pos. test lead on house battery post  = no reading
  No reading between ground and any of the posts when touching ground with either the neg. lead or the positive lead.

Multi-meter back in DC voltage reading mode:

Just out of curiosity, voltage of cables when disconnected:
  Chassis battery:          13.03v
  Alternator:  Started at 12.15v and dropped to .02v over the course of about 45 seconds
  House battery:            12.79v

Connections at isolator cleaned and connected:
  Chassis battery:  13.03v
  Alt.                      12.80v
  House battery:    12.79v

Engine running at 650 rpm, connections at isolator cleaned and connected:
  Chassis battery:  14.48v
  Alt.                      15.31v
  House battery:    14.46v

Engine running at 1,200 rpm, connections at isolator cleaned and connected:
  Chassis battery:  14.45v
  Alt.                      15.27v
  House battery:    14.42v

I took it on a road test the day before doing the testing, but it didn't act up.

Thanks for any input.

Joe
2008 Nimbus

Re: Intermittent charging of house batteries while driving

Reply #9 –
It doesn't seem right to me that you would have voltage at the center post of the isolator with the engine not running, but I don't know what alternator you have on your coach. I would think that if you have voltage on the center post and the house batteries go dead then it would also drag down the engine batteries. The isolator may not be the problem. You need to see why there is voltage on the center post. Has the alternator been replaced? If it has maybe a duvac alternator was not what was put on.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: Intermittent charging of house batteries while driving

Reply #10 –
I would think if there is voltage at the center post with the engine off the isolator
diode is shorted out and you need a new isolator.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Intermittent charging of house batteries while driving

Reply #11 –
Thank you for the feed back.  I'm going to order an isolator.  According to this article, there should be no voltage on the alternator post when the engine isn't running:  How To Test A Battery Isolator | RV Lifestyle  (Second to last paragraph.)

I'm confused that when the generator/charger were running (but not the engine), the alternator post voltage was the same as the chassis battery voltage, which was not being charged and thus lower than the house battery voltage.  But with the gen and the engine both off, the alternator post voltage was the same as the house battery voltage, which was then lower than the chassis battery voltage.  So the voltage I'm reading on the alternator post is the same as whichever battery has the lower voltage.  I'm no elect. eng. so I have no idea why/how a diode isolator would behave that way.  I'll just do the bad thing and "assume" it is the culprit.

Thank you everyone.

Joe
2008 Nimbus

Re: Intermittent charging of house batteries while driving

Reply #12 –
Take the alternator cable off the isolator and see if you have any voltage that way with the engine
off on the alternator post.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Intermittent charging of house batteries while driving

Reply #13 –
Good idea.
2008 Nimbus

Re: Intermittent charging of house batteries while driving

Reply #14 –
Quote from: red tractor –
It doesn't seem right to me that you would have voltage at the center post of the isolator with the engine not running,

What you're seeing here is a whole bunch of electrons trapped between the diode bridge in the alternator and the diode in the diode isolator.  There would have been nothing to see here if the original poster had used a cheap Radio Shack VOM, but all of the Volt Ohm Meters made today have high impedance inputs:  It took long enough to see for the electrons stored in that line to bleed off through the meter.  Touching a finger to the post and ground will do the same thing faster.  This is why, in some instances, I suggest using a 12v light bulb as a load on a circuit under test, as a high impedance VOM, $8 at Harbor Freight, can lead you astray.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Intermittent charging of house batteries while driving

Reply #15 –
Does it make any sense to replace it with a B2B charger instead of an isolator.  If you are considering Lifepo4 at a later date?

2000 GV320 4010 build #5712  2019-?
1999 Bounder 2000-2008
Bardstown, KY
🥃The Bourbon Capital of the World🥃
 

Re: Intermittent charging of house batteries while driving

Reply #16 –
Quote from: joe g –
According to this article, there should be no voltage on the alternator post when the engine isn't running:  How To Test A Battery Isolator | RV Lifestyle  (Second to last paragraph.)
Joe,

I encountered the exact same situation (mystery voltage on isolator center post with engine off) 8 years ago.  We had a rather lengthy (and wandering) discussion on this subject.  You may find the thread interesting.  See link below.  I eventually replaced the OEM isolator as a first step in continuous upgrades to my electrical system.  I will say, however, that I never could pinpoint any specific problem that I could attribute to the fact that my old isolator always had some voltage showing on the center lug.

I DO agree that replacing your original isolator (with something...) is a wise move at this point.

Bad Isolator?


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"