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Old 07-08-2014, 09:36 PM   #1
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Chassis battery discharging

Hi all
I have 2012 Greyhawk 31fs, the chassis battery goes dead after a few days when ever the coach battery is connected. When the coach battery is disconnected with the battery disconnect switch the chassis battery stays
charged and there are no issues. this seems to happen eveytime I take the motorhome camping, or parked in the yard with the coach battery on, the chassis battery will go dead.
Even when I plug the unit into shore power if the coach battery is on the chassis battery still goes dead.

any thoughts, thanks Raff
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Old 07-10-2014, 02:12 PM   #2
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Raff, I've seen the same problem on 2 out of the 3 RVs that I've owned. I suspect that it's often related to the power step, but I've never managed to completely trace it down myself.

On our current RV, I simply keep it connected to a battery maintainer for the chassis battery. My prior RV, Holiday Rambler, there was a large marine disconnect switch to easily isolate the coach battery, which is another option.

If you want to trace it, you can via an amp meter and start pulling fuses... But the fact that it's associated with your coach battery means that it's likely something that is associated with both power systems (like an electric step).

It's common in RVs and I'd just say that you find a way to easily disconnect.. Or expect to spend hours chasing it.
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Old 07-10-2014, 08:19 PM   #3
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Thanks CB1000rider, Ill enable the coach battery and then pull the fuses for the electric step. I see when I crawled under the coach there were 2, so there fairly easy to get at.
Ill let you know the outcome in a few days as I plan on plugging the unit in this weekend to see if this helps.
One other thing I noticed is I pulled the chassis battery cable off of my battery isolator and I still had 1.5 volts coming from the coach battery, I would think this would be zero as the isolator was open from shutting off the key and opening the door.

Thanks again for your help.
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Old 07-11-2014, 02:03 PM   #4
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Note, I'm guessing on the step. It'll be something that interacts with both power supplies. Other guesses could be an auto-leveling system, outlet relay (no power while driving) or who knows what else.

3 day draw down is not acceptable. I have an amp meter, so that's how I measure the draw. You need to disconnect one cable, put the amp meter in the middle and see how much power she's drawing.

The truck will *always* draw some power. Stuff like keeping the radio memory, clocks, etc - the same sort of thing that's in your car. I'd expect that draw to be .01-.1 amps, at most... Anything that measures in the single digits (amps) is too much.

I'd put an amp meter on it and start disconnecting stuff.. That's the easiest way I know to chase it down.

Or again, Keep It Simple and install a disconnect... :-)
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Old 07-15-2014, 08:42 PM   #5
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Well I finally got around to looking at the draw again and since I didn't have a amp meter
I used a 12 volt test light, the amp meter I had read 4.5 amps when I hooked it inline before the 2 amp fuse that protects it blew. well then onto the test light it was very bright so I unplugged the step and no change I also unplugged the isolator and no change I then unplugged everything in the fuse block and only the radio fuse and the cluster fuse changed the light to slightly dimm, I proceeded to unplug the radio and it made no difference, Ill need a ford wiring diagram for the radio and cluster circuit to
figure this out. hope to find a diagram before the next camping trip.
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Old 07-16-2014, 10:47 AM   #6
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The test light will always light up. There is *some* parasitic drain on modern vehicles - just the clock on the radio, at a minimum. The brightness of the light won't matter.

4.5 amps is way too much... Way too much.

I'd recommend a 20A amp meter, should be relatively inexpensive via Amazon.

Get it situated and then unplug one side of the house batteries (shouldn't make a difference) - but humor me. If it does make a difference, let us know.

And remember, most of these vehicles have 2-3 fuse blocks on the chassis alone. Along with a series of fuses installed in various places for things like steps that may not be obvious.
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Old 07-16-2014, 08:51 PM   #7
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There is a switch to pull power from the coach battery to start the engine if the chassis battery is dead. Could the switch have failed and is always on?
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2012 Greyhawk 31 FK
Flat towing a 2008 Miata.
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Old 07-16-2014, 09:18 PM   #8
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That's possible, but I don't think it's likely. If that was the case, you'd find that all the batteries were dead... Or at least near-dead.
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Old 07-21-2014, 07:46 PM   #9
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One other thing I found out this weekend is according to the Jayco owners manual the
generator is suppose to charge both the house and the chassis batteries but when I run the generator the house battery is the only one getting charged, the chassis battery isn't getting charged according to my volt meter. Haven't had time to work on it yet but I will keep everyone informed of the outcome of the chassis battery discharging issue. Camped this weekend and chassis battery went dead again. I'm sure Ill be putting a chassis battery in soon at this rate.
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Old 07-21-2014, 07:52 PM   #10
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Breakaway Switch

Check to see if someone has stole your Breakaway Switch pin. I fought the "mystery load" until I hitched it up to take it to my RV guy and noticed I someone stole my hitch pin (that's what I call it).

Excessive load was coming from the brake mags.

Marlin
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