12 volt voltage sag

bruceh · 12-10-2007, 10:51 AM

My gas heater problem has morphed into a 12-volt voltage sag problem.

When I turn on every light in the motor home and turn on the inverter and both televisions, the voltage reported by the monitor panel meter is 11.2 volts. The solar panel controller meter (wired right to the battery) reports 12.5 volts. I have verified the battery voltage with a separate DVM. This is on battery only and the fuse to the solar panel removed.

I am trying to figure out if this is normal behavior for this coach. Could someone else try this and let me know the results. I am wondering if the wires are too small (too long) to handle this much current.

I have cleaned up the grounding stud on the chassis, which did improve things a little (it was showing 11.2 volts before) and the heater works unless I have absolutely everything else turned on. I also cleaned up the battery cable connections. I have four 6-volt golf cart batteries driving this. They are new and fully charged.

If this is not normal, the suspects are:

Bad or corroded connection(s) between the power solenoid and the monitor panel
High resistance in the circuit breaker to the monitor panel
High resistance in the power solenoid
Something else?

Thanks for any help or information

bruceh · 12-10-2007, 10:51 AM

My gas heater problem has morphed into a 12-volt voltage sag problem.

When I turn on every light in the motor home and turn on the inverter and both televisions, the voltage reported by the monitor panel meter is 11.2 volts. The solar panel controller meter (wired right to the battery) reports 12.5 volts. I have verified the battery voltage with a separate DVM. This is on battery only and the fuse to the solar panel removed.

I am trying to figure out if this is normal behavior for this coach. Could someone else try this and let me know the results. I am wondering if the wires are too small (too long) to handle this much current.

I have cleaned up the grounding stud on the chassis, which did improve things a little (it was showing 11.2 volts before) and the heater works unless I have absolutely everything else turned on. I also cleaned up the battery cable connections. I have four 6-volt golf cart batteries driving this. They are new and fully charged.

If this is not normal, the suspects are:

Bad or corroded connection(s) between the power solenoid and the monitor panel
High resistance in the circuit breaker to the monitor panel
High resistance in the power solenoid
Something else?

Thanks for any help or information

SCVJeff · 12-10-2007, 08:02 PM

Reading this on the surface it sounds like you're pushing your loads to unrealistic limits. EVERY light in the coach, AND the heater? That has to be pushing 40A, if not more. Off the top of my head I have 23 incandescent lamps @ 1.34A ea.) in the coach. That's over 30 Amps just for the lights! PLUS the heater? Yikes!

John_Canfield · 12-11-2007, 05:12 AM

Hmmmm... I've never tried to turn on all 12V devices in the coach. My expectation is that the wiring is designed for a maximum load scenario as a matter of engineering best practices.

Assuming the wiring is engineered for maximum load, you are on the right track with your troubleshooting. I would definitely examine the solenoid connections. Look at your wiring diagram and try to inspect every connection point. You could have bad solenoid contacts - you could bypass the terminals with heavy gauge wire or move one wire to the opposite post and see what you get.

Have you tried to bridge the house/chassis battery banks with the "Boost" switch?

I'll try to test my coach today - the results will be interesting.

John Hilley · 12-11-2007, 05:24 AM

I would measure the voltage at power solenoid in and out terminals, that will tell you the voltage drop across the solenoid, which I suspect is the largest voltage drop. There is also probably quite a voltage drop across the long cable from the battery to the power solenoid and back to the coach if it is mounted under the hood like mine, if yours is under the step there shouldn't be much loss there. If under the hood at that load there would be about .5 volt drop across the cable.

bruceh · 12-11-2007, 09:14 AM

Thanks for the replies. I will try to reply to all in order.

I am turning on everything mostly as a diagnostic. Since my batteries are full charged, it is hard to duplicate partially depleted batteries. The breaker for the coach is 55 amps, so the Winnebago folks must have anticipated this. My real concern is the voltage drop across the internal distribution. If we are doing something moderate (TV, some lights) and I turn the heater on, I want it to work.

There is a sub issue. The inverter for the TV shuts down at about 11.3 volts. The batteries will show over 12. This annoys my wife no end.

I haven't tried the battery boost and I don't think that the battery is the issue as it displays good voltage at all times. Moving a wire is a good idea and will try that.

My solenoid is quite close to the batteries (about 2 feet). The batteries are under my step and the solenoid is right behind the step. I will try to measure the voltage drop across the solenoid. I am a little paranoid about working in there as there isn't a lot of clearance and a slip up with this amount of current would not be good.

bruceh · 12-11-2007, 10:27 AM

A further data point, I just measured across the solenoid at full load and the voltage drop was 0.04. Quite negligable.

SCVJeff · 12-11-2007, 08:36 PM

I forgot all your volts are pretty localized. The Meridian's contactor is in the front of the coach, batteries in the rear, and the house panel about 1/2 way back. It's a b-i-g loop.

Take off all watches, rings, and look across all terminals, lugs, etc. starting at the battery. In the News ENG vans, those contactors get resistive all the time, so that wouldn't be a shocker to me (no pun). If I was smart I'd carry a spare knowing their track record.

John Hilley · 12-12-2007, 04:55 AM

Since you don't have any loss across the power solenoid it's down the line. Check the input connection to the DC distribution panel.

bruceh · 12-12-2007, 08:50 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by John Hilley:
Since you don't have any loss across the power solenoid it's down the line. Check the input connection to the DC distribution panel. </div></BLOCKQUOTE>

Is the DC distribution panel behind the DC circuit breakers? In my case, this is above the microwave.

I have been looking at the Winnebago wiring diagrams and a couple of things are vague.

1.) Where the heck is the ˜feed through stud'?
2.) Is the ˜upper bus bar' the same as the distribution panel?
3.) I found some grounds (4) on the grounding stud on the frame. Where physically are the rest of them? I am always suspicious of flaky or high resistance grounds.

Thanks for any input. I appreciate the chance to bounce ideas around.