Need help on wiring the dual battery (MOM) dash switch

Started by The_Handier_Man1, November 30, 2008, 04:41 PM

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The_Handier_Man1


From: Robert-19722  (Original Message)
Sent: 3/10/2006 8:12 PM

Have a 1972 Indian been working on the wiring. On the dash there is a rocker switch for the dual battery / single / momentary dual. The wire is missing from the lower connection. I would think it would go to a solenoid somewhere but can not find it. Can anyone help?  Robert




From: Easybago
Sent: 3/10/2006 8:26 PM

Not sure about the 72 Indian, but the one on my 78 Brave is mounted on the wall of the battery compartment.




From: LJ-TJ
Sent: 3/11/2006 1:02 AM

Mine is mounted on the left side of my battry box both in my 75 and 72.




From: Cooneytoones
Sent: 3/11/2006 8:36 AM

Robert, follow your positive cables from the battery (both cables should be hooked into a 3 pronged spitter (may look look a Ford regulator) some PO's or their mechanics used those if the original battery splitter went bad....that is the battery isolator......mine (on a '76) is just before the starter relay on the wall between the battery compartment and the starter...you have to get under the vehicle to see it. this wires into the rocker so you'll have both batteries on MOM,  for starting in case chassis battery gets low, single mode charges only the chassis battery when driving, dual mode charges both house and chassis battery, never use dual mode while parked or boondocking unless your hooked up tho shore line, or have an independant way of charging (generator etc.) ......it will deplete the charge in both batteries running the house 12v system on battery power only. When boondocking leave rocker in single mode.  Let us know how you make out....

Timmy




From: denisondc
Sent: 3/11/2006 9:15 AM

Although someone might have changed it, I think on the 72s the original battery A-to-B connection item was a solenoid, that looked like the starter solenoids that cars had in the 50s and 60s. A round can about twice the size of the container that you get 35mm film in. The two positive cables (hopefully both red) would be connected to its opposite terminals, and each of these connections would also have a cable running from it - on into the RV. One to go to the starter relay mounted on the frame rail. The other one going to the coach 12V wiring.
I believe the battery isolators are a double diode item, probably better than the older style solenoid, except I dont know how you diagnose their eventual failure.
My original solenoid takes its time to 'pull-in'. I cant use it to connect both batteries for starting, but havent really needed to.
Once the engine battery died in mid-day, when we went to restart after having lunch at a rest area. I knew the batt. had been on its last legs, so it was no surprise. I just switched the red cables between battery A and battery B, and we went on our way. (Minus the 12volts for interior lights from the coach battery - which we didnt need as it was daytime.)
I bought a replacement solenoid, one of the 'continuous duty' type, but havent gotten to installing it yet. 




From: Robert-19722
Sent: 3/12/2006 9:18 AM

Thanks I found it. Looks like the wiring goes from power on the center prong on the rocker switch. then both upper and lower prongs are spliced into one wire that turns on the solenoid. So I can run one battery solenoid off  to both batterys on all the time soleniod on.  To hold switch down soleniod on for both batterys on for extra power for starting only.  Robert 




From: Bill_Rowles
Sent: 3/14/2006 12:39 PM

I remember when I rewired my '75 Brave several years ago, the MOM contact energizes the solenoid at the battery box for jumpstart. However my Winnie has a second solenoid under the dashboard that connects the two electric systems together but also includes a circuit breaker (may be 30 amps w/auto-reset ) . This solenoid is energized by the wire from the DUAL contact of the switch.
There is evidence that a P.O. had a fire in the underdash wiring so I wonder if the circuit breaker was added to prevent over-current when operating in DUAL mode.
I test these circuits sometimes but use them seldom cause I don't like smoke and fire .
Bill




From: Slantsixness
Sent: 3/15/2006 4:16 AM

In reading through this message list, I see there is an ongoing misconception about the MOM switch.
MOM is MOMENTARY. IT IS NOT FOR STARTING YOUR WINNIE!

Let me explain:
Normal operation of the Dual/MOM switch is that you leave it in the center position, not in Dual or Mom. this keeps the two batteries as separate systems. The chassis battery charges from the Engine alternator, and the Coach battery charges from the Converter, when you have the Motorhome plugged in to shore power, or the generator is running and connected to the converter.

Dual mode explained:
The Dual mode is used to top off or refresh the chassis battery, and allows you to Charge the chassis battery from the vehicle alternator, while the vehicle is running. However, if the vehicle is NOT running, leaving the switch in the Dual position when the engine is off, the normal Philips Converter does not have the capacity to charge both chassis and coach batteries, furthermore, the chassis alternator circuit will use the converters output and "regulate" the voltage and current (this is a quirk with chrysler charging systems). What it amounts to is, the regulator will send a grounding voltage to the alternator, and with the alternator not spinning, will just create a current load for both batteries of about 2 amps. What does it mean? the charger, running at about 14.8 volts will be regulated and drain both batteries. Now as long as you're still plugged in, it shouldn't effect operation, but if you're not plugged in, you will come back to two dead batteries in about 2 days.
It's best to just leave the switch in the center position while parked and not running. Use dual, only after you have started the vehicle, and the Dash ammeter has returned to the center position (meaning the chassis battery is no longer discharged from starting) If you are in heavy traffic, and running at low RPM's or idling, leave or turn the Mom switch off. Why? At idle, the alternator does not function, and the added load just serves to drain the battery.

What is MOM for then?

Mom mode explained:
MOM stands for MOMENTARY. push and hold the switch to the MOM position, this connects bot the chassis and Coach batteries together..MOMENTARILY.
So, how do you use it and what benefit is it to you?
First,
The only reason it's there is to recharge the Chassis battery if it has been depleted for some valid reason. If the battery is actually "Bad" the "MOM" will be of no help to you. At that point, get out of the winnie and switch the Chassis and coach batteries, it's the only thing that will help at that point, or buy and install a new battery.
DO NOT TRY TO START YOUR WINNIE WITH THE MOM SWITCH HELD DOWN. (Yes it might work, but have a fire extinguisher ready, and a damn good excuse for your wife that your winnie is now on fire..)
Push and hold the Mom switch down for 30 seconds and release. This allows the chassis battery to get a booster shot of charge from the hopefully fully charged coach battery. Now try to start the Winnie.... did it start? No? Try another 30 seconds. Try it up to 5 times. Still no start? Replace your battery, or switch with the chassis battery.
Under no circumstances was the Mom switch ever intended to be held down while cranking the engine. The wires to it, the solenoid and the entire circuit was never designed to withstand 425amps of current flow. Holding it down and cranking it will potentially cause the wires to burn, and it happens all the time. MANY Winnies have had electrical problems and fires due to both improper Dual / Mom switch operation, jury rigged electrical system modifications, and ignition switch connector corrosion.

Other curious problems facing the electrical sytems in our winnies:
The dash radio.
There is a coach system 12v wire for your dash radio. Use it! Don't connect the radio to the chassis battery. That's what usually kills the chassis battery anyway. That amongst other accesories you might use while parked. That's what the coach system is for, and when driving, what the Dual mode is for!

The batteries themselves:
Do not operate your Winnie with only one battery. If you have to, connect it ONLY to the Chassis, when driving, and to the Coach when parked. Do not use the chassis battery and leave the ignition on and flip the dual switch. You'd be asking for a fire or at least melted wires.

Ok I realize this was a long post, but I hope it cleared at least something up for somebody!

Tom