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bruceh · 02-18-2008, 09:59 AM

I have been troubleshooting a weird voltage drop problem. When I turn on lots of 12 volt stuff, my coach voltmeter reports voltage much lower than the battery. The coach might show 11.5 volts while the DVM at the battery shows 12.6. If I don't have anything turned on, the voltages are within 0.1 volts of each other.

I have measured the battery disconnect relay and the battery mode solenoid and they track the battery. I had thought that I might have a high resistance relay or solenoid but that doesn't seem to be the case.

My questions are:

1.) Where physically are the grounds? The Winnebago wiring diagram shows a ground bar behind the battery box. I have found this and cleaned it up to no effect. The batteries (coach and engine) are grounded here as well as 4 14 gauge white wires coming from somewhere. The wiring diagram shows several different grounds (with as many as 12 wires going to them) but gives no clues as to their physical location. I am going after the grounds because in my experience, bad grounds cause lots of problems. It is something that I would like to eliminate as the cause of this problem. I have found one other ground for the gas heater at the back of the coach.

2.) What else should I be looking at?

Any help or ideas would be appreciated.

bruceh · 02-18-2008, 09:59 AM

I have been troubleshooting a weird voltage drop problem. When I turn on lots of 12 volt stuff, my coach voltmeter reports voltage much lower than the battery. The coach might show 11.5 volts while the DVM at the battery shows 12.6. If I don't have anything turned on, the voltages are within 0.1 volts of each other.

I have measured the battery disconnect relay and the battery mode solenoid and they track the battery. I had thought that I might have a high resistance relay or solenoid but that doesn't seem to be the case.

My questions are:

1.) Where physically are the grounds? The Winnebago wiring diagram shows a ground bar behind the battery box. I have found this and cleaned it up to no effect. The batteries (coach and engine) are grounded here as well as 4 14 gauge white wires coming from somewhere. The wiring diagram shows several different grounds (with as many as 12 wires going to them) but gives no clues as to their physical location. I am going after the grounds because in my experience, bad grounds cause lots of problems. It is something that I would like to eliminate as the cause of this problem. I have found one other ground for the gas heater at the back of the coach.

2.) What else should I be looking at?

Any help or ideas would be appreciated.

MrTransistor · 02-18-2008, 03:19 PM

Hi bruceh,

What you describe may not be a problem because of where in the coach wiring the panel meter is connected. Normal voltage drops in +12 and ground circuits under high load can easily amount to .5 volts each. Unfortunately, Winnebago's electrical design team tends to size wiring per the NEC specs. which are for 120 volts AC. A voltage drop of 1 volt at 120 volts isn't much but at 12 volts DC becomes an issue. All wiring for 12 volts DC should be 10 times the wire size to get equivalent % voltage drop. And this doesn't even consider the fact that the current is higher by X10 for the same wattage appliance.

Our panel meter also reads a similar error although not as much. I have installed an Onan AGS which has battery voltage readout and I ran separate voltage sense wires directly to the batteries just to avoid the voltage drops of the coach wiring.

bruceh · 02-19-2008, 06:54 AM

The reason that I am concerned is that my heater fires from the coach voltage. When it is low, the heater won't fire.

I suppose that I could run a wire to power the heater directly from the battery but I think of that as a last resort.

I have a similar issue with my built in inverter, when it preceives low voltage it shuts off even though the batteries are fine.

I have a Siemens solar controller that accureately reflects battery voltage so it is easy to spot the difference.

MrTransistor · 02-19-2008, 09:04 AM

Hummmm..... At that point, I would use very long meter leads to measure the voltage drops in the circuit. Go from the battery negative post to different points around the coach, both positive and negative, looking for either too low a +12 or too high a 0 volt reading. This will tell you what wire or at least which connections are too high of a resistance. I'm and X Siemens service engineer and I've used leads of up to 40 feet for some troubleshooting chores.

bruceh · 02-22-2008, 07:58 AM

Going after all of the intermediate connection points is Plan B because of difficult access. After years troubleshooting computers I learned to 'do the easy things first'.

I has thought that finding and cleaning up flaky grounds would be rather easy, maybe not. The grounds that I did find had a fair amound of rust on them and cleaned up very well.

Will resume this after a brief winter trip to Clear Lake.