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Battery Charging issues.

We just returned home from MOT (1000 miles) with our 'new to us' U295.  Coach is in good shape and came with 10 years of service records - all from MOT.  The entire way home the dash Volt meter was showing around 11.9 volts.  I contacted MOT and was told to drive with Gen on and Boost switch On - that would ensure the gen set charges the engine batteries.  The engine CPU needs to see a certain amount of voltage to avoid a shutdown.  We had no issues, but the volt meter only got to 12 v.
 At home, with the engine at idle, I tested the  Bat 1, Bat2  and Alternator stud located on the Issolator (under bed in engine bay).  The reading were consistent on all 3 studs - about 14.1 volts.  The studs were clean - I cleaned them again anyway.
I then tested the Trombeta that connects to the Battery 1 & 2 stud on the Issolator - it also was around 14 volts.  I am parked at home and on shore power - with the Boost Switch ON.  The three starting batteries are reading 12.7 volts.  Running the engine at idle - the dash volt gauge is only around 12.1 volts.
The posts have been cleaned on the starting batteries.

Is the U295 is set up to charge both sets of batteries at the same time on Shore power or with engine running.  If not, how can I address that.

As to the Dash Volt Gauge - is it maybe in error or do I have some other issues.  Greatly appreciate everyone's thought.

2002 U295
Build  # 5989
Former:  Alpine Apex (2006 Prototype), Fleetwood Discovery LXE, Berkshire 40 XL

Re: Battery Charging issues.

Reply #1 –
My dash voltmeter has always read at least .6th of a volt below the actual voltage.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Battery Charging issues.

Reply #2 –
You can check the wiring starting at the voltage gauge and follow it all the way to the batteries. You should see it increase in voltage at every connection. You can clean the connection points and that should help. I bet your mulitmeter matches the gauge if you check the wires at the back of the gauge. You are seeing the voltage drop from all the wire and connections between the gauge and the batteries. The readings you took at the isolator and batteries is good. Your gauge is just seeing the voltage drop.

My monitor system and gauge are reading low like that too, but it's just the wiring.

Your engine ECM will run down to 6v ish, You have a long way to go before you would get there.
1991 U300 Side Aisle 6V92 Silver #3897
2004 U320 40' #6246

Re: Battery Charging issues.

Reply #3 –
Engine alternator charges both chassis and house battery banks.

OE was for shore power/generator to only charge the house bank.  Many owners have added a device (several different kinds) to charge the chassis bank.

With a diode-based battery isolator, the center lug from the alternator B+ terminal should read around .7 VAC HIGHER than the outer lugs that go to the batteries, as that .7 VDC is lost to heat in the isolator.  That is why the large surface area of aluminum fins to dissipate the heat.

Important thing here is for you to determine if this is a gauge issue or actual charging issue.

Compare readings from your digital voltmeter at the batteries and then at the dash with engine off, engine on at 1,100 RPM or so, shore power or generator off and then with  it on.

Let us know all your readings.
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: Battery Charging issues.

Reply #4 –
The only way to remotely read battery voltage is to have a dedicated wire almost of any size from battery to meter. Anytime there are other loads on a voltage meter wire, the reading will be inconsistent and low.

Re: Battery Charging issues.

Reply #5 –
By chance were you running with the headlights on?  Towing anything?  I notice that when towing my trailer and running all the lights, output drops about .5V-.6V at the dash readout.
Keith
2003 U320 38' #6197

Re: Battery Charging issues.

Reply #6 –
Quote from: WS6_Keith –
By chance were you running with the headlights on?  Towing anything?  I notice that when towing my trailer and running all the lights, output drops about .5V-.6V at the dash readout.

Re-verify ground for the dash.

A loose or poor ground will cause dash gauges to read "differently" with different 12 VDC loads.
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: Battery Charging issues.

Reply #7 –
Thanks to all for your help.  Based on the various answers, it would appear that my charging system and batteries are just fine.  With shore power off - my batteries tested at 12.7 volts.  On our other coaches (and cars) I was used to seeing dash voltage readings anywhere from 13 to 14 - depending on load.
Yes, we were towing a car and using the Blue Ox cable that feeds juice to the car for brake and turn lights.

I am leaning towards a dash gauge (or its wiring) issue.  Least now I know what I am looking for.  Thanks again to everyone.
2002 U295
Build  # 5989
Former:  Alpine Apex (2006 Prototype), Fleetwood Discovery LXE, Berkshire 40 XL

Re: Battery Charging issues.

Reply #8 –
Forgot to add - when on shore power, the Magnum inverter is showing 13.1 volts on Float Charging.
2002 U295
Build  # 5989
Former:  Alpine Apex (2006 Prototype), Fleetwood Discovery LXE, Berkshire 40 XL

Re: Battery Charging issues.

Reply #9 –
13.1 VDC is OK in hot temperatures, but a little low a temps drop.

Be sure the inverter/charger is properly programmed for:

Battery technology (wet cell, gel, AGM and if newer one it may include a separate setting for Li batteries)
Battery size (in amp hours)
Temperature (unless temp sensor installed)
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: Battery Charging issues.

Reply #10 –
Just put your handheld voltmeter right on the posts of your coaches voltmeter and that will tell
you if the coaches voltmeter is right or not and how much it is out.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Battery Charging issues.

Reply #11 –
Quote from: wolfe10 –
Re-verify ground for the dash.
A loose or poor ground will cause dash gauges to read "differently" with different 12 VDC loads.
Same thing shows in the VMSpc from the ECM.
Keith
2003 U320 38' #6197

Re: Battery Charging issues.

Reply #12 –
My Silverleaf was giving me the the wrong voltage about the same as the gauge I now have
the Silverleaf adjusted correctly.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Battery Charging issues.

Reply #13 –
Totally depends on where the Silverleaf is getting its voltage reading.

Reading at the batteries can be quite different "many marginal connections and small gauge wire" later.

Often, cleaning all connections starting at the batteries (both positive and ground) and the grounds at the dash can have a significant effect on voltage difference between battery and the dash area.
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: Battery Charging issues.

Reply #14 –
On my 1999 U295 the dashboard gauge reads 1 volt lower than my Silver leaf or a hand held volt meter at the battery and if I drive with the lights on it drops an other half a volt on the dashboard but is OK on the silver leaf    on the silver leaf with no lights on or lights on it run around 14 volt it jumps back and forth 13.9  Volts to 14.3 volts  but most time 14 volts on silver leaf the gauge on the dash is out by one volt and 1.5 volt with lights on this has been since I owned it 4 years now

Rick & Hilda looking forward to full- timing one day for now couple of months at a time
1999 U270 3602
Built number  5530.  Feb 1999            Motorcade  number 18438
8.3 Cummins Allison six speed with brake  retarder
Purchased Nov 28 2019
 

Re: Battery Charging issues.

Reply #15 –
When dash voltmeter reads lower with headlights on, check dash gauge ground.  Don't hesitate to add an additional one.
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