What does The Dual/MOM switch do?

[Oldbag373861]

Sent: 6/7/2005 8:57 PM

OK, here I am again asking for some knowledge. I attempting to get my Brave started in the campground the other day I recalled that when I used to have a Jamboree class C which I could start even with a depleted coach battery by toggling a switch to the ignition battery. In looking for an analogous switch in the Winnie, I tried this "DUAL/MOM" switch, but to no effect. It stays on the dual side, but when I toggle it to MOM, it lights up instrument lights and the fan will blow if turned on. I suspect the MOM means momentary, no? But what does this switch really do anyway?



From: Boise_Chief1
Sent: 6/7/2005 9:43 PM

It sends out a signal to the nearest Super Mom and she'll come jump start you.  
It really momentarily connects coach and starter battery so hopefully you'll have enough juice to start your motor.  You have to hold down the MOM button while you try to start your motor.

Sean



From: denison
Sent: 6/7/2005 10:09 PM

The switch shouldnt be needed for starting of course. If you ran your RVs dashboard radio all night, or left something else on that was powered by the engine battery drawing current (via the cigarette lighter socket for example) , it might discharge the engine battery enough so it wouldnt start.
In my Winny that switch is able to energize the solenoid that connects the two batteries together, ONLY WHEN the ignition switch is turned on; because it gets its power from the ignition or accessory circuit, not from the coach battery.
In such a case it would be simplest for me to access the battery tray and swap the positive battery cables, from one battery to the other, then start the engine. Then I would connect the two batteries, either with that -dual- switch, or a piece of wire, to let the running engine charge up the discharged battery.
I expect there will be cases of people who used an inverter plugged into the cigarette lighter all evening, to power a laptop or t.v. or whatever, and find out in the morning they have taken a lot of charge out of the battery.



From: wendell
Sent: 6/8/2005 1:12 PM

When you put the switch in the "Dual" position, it puts the batteries together in parralel, but only if the ignition switch is on as Denison says.  This is used to enable you to charge the coach battery with the alternator while you are driving down the road.  You can release the switch and it will stay in the "Dual" position.

When it's in the MOM (momentary) position, it does the same thing, but as you no doubt discovered, when you release the switch it goes back to the "normal" position.  This is used to enable you to borrow a little more amperage from the coach battery to help start the engine in the event the chassis battery is a little low or it's cold or something and you need a little more boost to get the engie to turn over and start.

Never run the generator (if you have one) and the engine at the same time with the switch in the DUAL position.  This can blow the diodes in your alternator.

All of this is true if the wiring is still the way it came from the factory.  As I found out the hard way, sometimes previous owners take liberties with this arrangement and don't hook things back up properly as they made modifications over the last 30 years.  I'd get a wiring diagram and make sure things are the way they belong or you may have dead batteries and blown alternators to contend with.   



From: Oldbag373861
Sent: 6/9/2005 10:59 AM

Thanks gentlemen, for all the info. Now I am DUALly educated on this switch and don't have to call on MOM for help.

I put in a new coach battery, as the old one was, well, pretty old, and Fred Meyer was having a sale. My ammeter is shot on the Old Bag, so I don't know what she's charging at.

Wendell, do you see any corelation here between my generator problem and my charging problem?



From: OldEdBrady
Sent: 6/9/2005 9:57 PM

J. C. Whitney has ammeters.  With a chrome bezel, it's only $5.99, plus shipping.  With a black bezel, it's $14.99 (according to their latest catalogue, which may be a misprint--I'm not sure).



From: wendell
Sent: 6/13/2005 6:20 PM

Could be.  Like I said in my earlier post, if you run the genset and the engine at the same time with the DUAL/MOM switch in the DUAL position, you have a good chance of damaging the alternator.  It could be that this has happened.

You really need a good voltmeter to be able to tell what's happening here.  You can pretty easily see if the alternator is charging by connecting a volt meter across the battery terminals with the engine running.  You should read 14.5 volts or so there.  If it's down in the 12-13 range, your alternator is probably not working for one reason or another. 

I would check the wiring of the solenoid that the DUAL/MOM switch controls to make sure it is wired properly.  It should be located in or very near the battery compartment.  My alternator worked fine, but my batteries kept discharging at much too high a rate.  I was working around the solenoid one day and discovered that it was warm and figured out that the way it was wired, it was always activated and was continually drawing the battery down.  I bought a new one just to be safe and re-wired it all.  No more dead batteries.   



From: famecity
Sent: 11/13/2005 8:47 PM

Why does my radio only work when I hold down the MOM button? Is there a wire crossed somewhere?



From: daved27c
Sent: 11/14/2005 10:24 PM

Vince;

Looking at your other posts and this one, I would have to say that someone has crosssed a few wires under the dash of your Winne. I would start by checking all of the ground wires, making sure all of the connections are good. Most of us could spend a lifetime trying to undo the wiring of the previous owners. As for the radio, I would find the power supply for it and wire it to the coach battery(so you can listen to it when the rig is off), or to the Ign if you only want it when going down the road.

Dave



From: firebug9-1-1
Sent: 11/16/2005 11:26 PM

I have an isolator hooked up to my alternator to charge both of my batteries when the engine is running.  I also run down the hi-way with the generator running , if I need the air on in the back.  What I have determined is that the alternator charge rate drops when I fire up the generator as it is sharing the electrical load with the converter... I have about 3000 miles with this setup and no problems yet. I also have a small inverter, and If I am riding down the highway and the generator is not needed, the kids plug there playstation and TV into this and the engine alternator will charge the coach battery (it is evident by my ampmeter) where the inverter is hooked with no problem... as of yet anyways!!!!   I still have the dual/ mom switch but only use it to boost off in really cold weather or if I run the truck battery down for some reason