How Is There Current Flow

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arcticfox2005

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Apr 18, 2011
Posts
716
In our Winnebago class C the house batteries are under the entry step. I got rid of the two group 24's and bought two 6v golf cart batteries, which are sitting on the floor in the garage. Yesterday I was looking at the battery cables in the battery box and when I moved the positive cable it touched the side of the steel box. There was a spark. Obviously, I think, the source of the current has to be the engine battery but how? Where do these circuits share a common point? Do I have a problem?
 
It depends on the type of battery isolator you have, some can back flow current in situations like yours, alternatively if you are plugged into shore power it would be from the inverter, the other option is if you have solar panels.
 
Depending on your model and design, early Winnebago's had a switch that would combine the house batteries with the chassis battery full time and labeled AUX or something similar usually on the dash somewhere in a 2 position design. Later years they changed that switch to a momentary switch which removed the ability to connect the house and chassis full time and was designed to be used as a momentary jump start for the chassis engine or a jump start for the generator which ever was needed or available.
 
There are devices in the RV that store a small amount of power.. Often the converter.. The one I had was what is called a "Filtered" supply.. The "Filter" contains a Capacitor (also called condenser) this is two metal plates with a insulation between them in case you wonder how it's made..
Some of those can hold an amp-second or more. Major spark.

Spot welders.... Actually do much the same thing.. Charge up a capacitor than POP it to spot.
 
I think you are all over-complicating this. The OP said, …when I moved the positive cable it touched the side of the steel box. There was a spark…”

Of course there was a spark! If the POSITIVE cable touches the “…steel box…” it has touched GROUND, which is where the negative cable from the battery is connected! It has nothing to do with a back feed, the converter, the battery isolator, or anything else. This is nothing more than a simple short from the positive battery cable to ground.
 
I think you are all over-complicating this. The OP said, …when I moved the positive cable it touched the side of the steel box. There was a spark…”

Of course there was a spark! If the POSITIVE cable touches the “…steel box…” it has touched GROUND, which is where the negative cable from the battery is connected! It has nothing to do with a back feed, the converter, the battery isolator, or anything else. This is nothing more than a simple short from the positive battery cable to ground.
The batteries are not installed.
 
Oh…I didn’t read the OP that way.

As Rosanne Rosannadanna used to say, “Never mind.”

Now you know how old I am. 😉
 
As was said above, if the RV was plugged into power the converter will provide power to the positive battery cable. If the RV is unplugged, you may get one spark if it's capacitors are charged. You may also get a spark when you connect the battery as the capacitors charge up. If you get a second spark, check the solenoid that lets the house batteries boost a low starting battery.
 
There are several ways for that to happen, the most likely being what Lou described (converter on & producing 12v). Or the engine running and feeding 12v to the house side (charging). Another is an LP gas alarm with dual power source. But it's not unusual for an older RV to have been modified at some point in a way that allows power to cross over between house & chassis.
 

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