Community Forums

billiam · 02-07-2011, 09:39 AM

88 Winnebago Superchief-Chevy P30/454
The engine battery won't switch off power to the coach. Even with the
coach batteries and shore pwr unhooked I still have power w/the engine off. It keeps draining the engine battery. Can anyone direct me to the problem switch? Thanks

wildtoad · 02-07-2011, 10:10 AM

I have a switch on my Superchief that is marked "Dual MOM". Have you have/tried that one? I don't have an owners manual so I've had to do a lot of trial and error testing.

billiam · 02-07-2011, 10:40 AM

I tried that switch yesterday while doing some trial and error of my own. (mostly error I think) The solenoid under the hood was clicking when my wife pushed the "MOM" side of the switch. I can only assume that meant it was working. Once I discovered that I unhooked all of the wires from the right of the solenoid leaving only the 2 wires on the left which are engine battery and then to the starter. To my surprise I STILL had power in the coach. Now I'm stumped. I thought that cable only ran to the starter.

wildtoad · 02-07-2011, 10:52 AM

I went outside and did as you did and unplugged. Verified the coach lights worked and then disconnected the house batteries. No lights. So on mine it appears things are working as expected. Could someone have run a feed from the engine battery to where the house batteries connect?

billiam · 02-07-2011, 11:08 AM

Well, I don't think so because everything was working fine before. I've had the MH for about 3 years now. A few weird things happened on our last camping trip back in the fall. We were plugged in at a campground, My daughter put some popcorn in the microwave to pop. I pulled it out and realized that it haden't popped but a few pieces. Then I found that my house batteries had been drained all the way down. They were fully charged before. Also, my headlights are so dim now that you can barely see the road. I don't know if these things are related or not but I have a feeling they are. It was after that trip that I first noticed that the interor lights were working off of the engine battery. I appreciate your help by the way Tom. This is frustrating as camping season begins next month!!!

wildtoad · 02-07-2011, 06:21 PM

Well good luck with this. Sounds like something got fried but what is the question.... Here's hoping someone with more knowledge chimes in...

Does everything work correctly when the house batteries are connected? Plugged in? If you are plugged in and start the engine are the headlights normal? House batteries being charged ? So what happens if you disconnect the engine battery? Do you still have house lights?

deandec · 02-08-2011, 11:22 AM

On my rig the alternator power runs to an isolator and from it on to the engine battery and house battery. Both batteries are charged by the alternator.

I am not knowledgeable enough to know how that isolator might act when it fails.

But, it seems it could fail and allow the engine battery to back feed through the isolator and into the house battery?

Mine is located on the outside of the battery trays compartment.

If the house battery shut down switch has failed and the alternator current isolator has failed you might get your symptoms?

TQ60 · 02-08-2011, 11:46 AM

Ok,
You have tried a lot of things and made some guesses, and you are getting nowhere slowly.

This is a long one...

We should assume that the batteries are good, the charging system checked and all is in clean working order.

I suspect you may have something wrong with the isolator or another common connection between batteries, but that is a GUESS.

First thing is to purchase a voltmeter with an amp function that can read up to 10 amps.

They are less than $10.00 at harbor freight, so make a trip and get one, then learn how to use it.

Next, when making connections sometimes there are sparks, these sometimes are normal due to filter capacitors in some devices, so be carefull as sometimes these can damage the amp meter if it is not in the 10 amp range, so ALWAYS start in the 10 amp range.

Have some 10 amp fuses handy.

Next, ALWAYS remove the leads or check them before starting, the amp meter functions inside the meter result in a direct short between the 2 leads, this is what you want for amp readings, but in a voltmeter function it is a bad idea.

Now that you are ready, turn everything OFF and remove all wires from the positive post of all batteries and unplug shore power.

Next verify voltages, set meter to DC Volts, connect black to ground and touch every wire, should read 0, and batteries should read 12 or so.

If you have a stand alone charger you can attach it to the battery to charge it as an option.

Now switch to AMPS and switch range to 10 AMPS and place the red wire on the positive post.

Before checking a wire "flash" it on the battery, this will charge any filter devices, if you get a large spark do it a second time, if you get a large spark again something is turned on, leave the wire attached and locate what is running, if nothing seems to be operating then this may be what is draining the battery.

If the spark seemed large, place one of the 10 amp fuses between the wire and the battery, this is done to insure it will not damage the amp meter, if the fuse does not blow then use the meter and measure the amperage.

Write down all measurements and add them up, this will tell you the total load on the battery as well as any that seem too high, if everything is off then they should be close to zero on all wires except for those with things like clocks or memory.

After this, connect all wires to one battery and re-measure at the other, the readings should not change, then reverse and remeasure, this will insure that something is not being turned on by one battery and causing a load on the other.

If you have a wire with a load that you want to investigate then you may need to follow it to where it goes, take notes and describe it in the notes, it helps down the road.

Another tip is to locate any fuse boxes, while the wire is connected remove the fuses to see which one causes the load to change.

You may also want to check at the fuse box, with all wires connected at the batteries you can remove the fuses and use the amp meter to confirm current in each circuit.

So if you measure a 5 amp load, in one hour you will have a 5 amp hour drain on the battery, if the battery is a 100 amp hour installed capacity then it would take 20 hours (100/5=20) to drain the battery.

If you have no adnormal loads and the calculation above indicate the battery should be good for a longer period of time than they are, then the battery is bad or not getting completely charged.

You may want to lag the wires as you go, handy later.

THere are a lot of things to do here, you will find the problem and will also know what every wire does, it is upto you to determine if you want to continue after you find the problem.

Let us know what you find, good luck!

pwf16129 · 02-08-2011, 07:45 PM

don't know specifics on your coach mine uses solenoid to separate the batteries had a starter duty solenoid installed when i bought it that melted internally and killed both my batteries. got a constant duty solenoid on it now, read as way more expense initially but will live in this situation for long time

leadman · 02-12-2011, 10:21 PM

Yes, check for a constant duty solenoid. This is what the switch on the dash controls. My batteries sre in the compartment by the door. The solenoid is on the frame rail behind the batteries.
The coach batteries are also in this compartment so is it possible a wire shorted across or was hooked up wrong?
If a diode in the alternator goes back it will drain the engine battery, but should not drain the coach batteries unless the switch on the dash is pushed to "both".