Why is generator tied into master battery switch

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rider1520

rider1520

Well-known member
Joined
Mar 15, 2010
Posts
258
Location
Nazareth, Pa
Here in the northeast we had a severe snow/wind storm that left many of us without power. I have my house equipped so as to properly backfeed power from the generator on my RV to the home for the basics like lights refrig & freezer. After marking the proper connections and ensure it everything was working properly, I decided to turn off the master battery switch so as to eliminate and parasitic draws on the RV batteries while parked since all I was using was the generator. When I did that the generator stopped. I turned the switch back on and was able to restart the generator. I don?t understand why the master battery switch for the RV kills the generator since it is already running.. Thanks for your responses
 
Apparently your generator uses the 12 volt RV system to power its ignition and doesn't have an internal means of doing that.
 
I think that typically in motorhomes, the generator starts from the house batteries. Mine does. If I engage the battery disconnect, my generator won't start. If my house batteries are down, I have, as I think most do, an auxiliary momentary switch to add the engine battery into the circuit to start the generator.
 
But why would it shut it down once it is running??
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A gasoline powered engine always requires 12V for the ignition etc in order to keep running. Since many generators (not all) are powered from the house batteries, turning off the master battery switch in your case removed the 12V source for that generator.
 
As Stu explained, the genset fuel pump, control board and ignition use external 12v power. In a typical motorhme wiring, that is provided via the battery bank, so the battery disconnect removes 12v power and the genset dies.  It dooesn't need to be wired that way, but that seems to be standard practice.
 
Uh
Alfa38User said:
A gasoline powered engine always requires 12V for the ignition etc in order to keep running. Since many generators (not all) are powered from the house batteries, turning off the master battery switch in your case removed the 12V source for that generator.
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Uh. not entierly true.. I have run many Gasoline engines that had NO 12 volt or other external power source. they used Magnetos.

HOWEVER... In the case of an ONAN generator.  The fuel pump is 12 volts. so.. you are correct. also some of the control ciruits in the box.
 
I thought that once started the generator would sustain its own operator, much like a starter on a car disconnects once the car is started. I did realize that an outside 12 volt power source (a house battery) would be needed to provide power to the fuel pump, even though the generator provides the charge for that battery. I was just unaware. Thanks to all who responded.
 
I thought that once started the generator would sustain its own operator, much like a starter on a car disconnects once the car is started.
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Yeah, but the starter isn't what keeps it running. Disconnect the battery and alternator and your car engine will stop dead too.

I have run many Gasoline engines that had NO 12 volt or other external power source. they used Magnetos.
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Still uses DC voltage, though. The magneto is basically just a built in DC generator that puts out pulses.
 
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