So I go out to crank my motorhome. Batteries are fine. House power is fine. Everything works on the house side. But I have no voltage to the power distribution box located under the driver area. Consequently, nothing related to dash features shows any signs of life. Turn the ignition key, nothing. No gauges come to life, no buzzers, no power to the radio. Nada, zip, nothing. We have had this coach for over a decade. We have had many little glitches to work through. But this one is a first. Anyone out there have an idea?Coach: 2006 Forest River CharlestonChassis: Feightliner

You do realize that there IS a separate "chassis" battery?That battery operates all engine/chassis/headlights items and does not get charged from the house battery side.So, if the MH has been plugged in to shore power and you have not run the engine for a few months, you have a dead chassis battery.Find the chassis battery (which most likely is in the engine compartment and put a charger on it (not a "smart" charger, they will not start charging a totally dead battery)..

Dead starting battery or batteries?

What is missing is exactly what Gdetrailer and Beemerphile pointed out...The CHASSIS battery...How is the voltage at the chassis battery lead posts? Not the clamps that bolt on, the lead that sticks up from inside the battery.If a meter reading shows there is voltage around 12.6 volts at the post, you have a VERY bad connection OR a burned out chassis fusible link.Measure chassis battery voltage and report back, por favor :)

Joeycockerspaniel wrote:So I go out to crank my motorhome. Batteries are fine. House power is fine. Define "Fine"How have you checked both house and engine batteries? What are their voltages at rest and when you turn the key?How long has it been sitting? Sometimes converter/charger can't charge the engine battery due to isolator circuit failure or other things.More often than not, if someone says "fine" instead of a measurement, there is something to be learned about testing for failures- which help now and in the future. We've all been there ;)

OK, here is what has apparently happened. My coach has a battery isolator solenoid. That solenoid should charge both house and chassis sets of batteries when either set require it. The coach has been plugged in all winter to the in-house float charging system. For ten years, that has kept both sets charged while the coach has not been in use. I replaced all my batteries a little over a year ago. The chassis batteries were almost completely discharged, even while the coach has been plugged in. I highly suspect that the battery isolator unit has gone bad. It no longer charges both sets of batteries, house and chassis, only the house batteries. So now, if recharging the chassis batteries does not work, I will not only have to replace the isolotor solenoid, but also two year-old chassis batteries. Here is the unit I just ordered. https://pdxrvwholesale.com/products/battery-boost-solenoid-1500-amps-intermittent-duty Thanks for the help. Hopefully this will remedy the problem.

No Power to Dash/Chassis | Good Sam Community

DiskDoctr
Explorer
Jan 23, 2018
Gdetrailer wrote:
DiskDoctr wrote:
Gdetrailer wrote:
Why don't you simply buy a "battery maintainer"?

An isolator is designed to allow charge to flow from alternator or converter/charger (later powered by shore power or generator) to BOTH the motor battery and the house battery.

But it also allows ONLY the house battery to flow back to power the "RV parts" thereby leaving the motor battery to start the motorhome- even when the house battery is dead.

Sometimes there is a "combine" switch to allow house battery to aid in boosting the motor battery to start in the event of emergency (dead battery).

If the isolator was bad, the converter/charger cannot charge the motor battery, allowing it to slowly lose its charge to parasitic or standby losses.

Wrong.

There are TWO "types" of isolators..

Smart and non-smart.

Non-smart are the STANDARD ISSUE version which allows the vehicles alternator to charge both the starting battery AND the house battery. Acts like a one way valve and does not allow the house converter or batteries to "charge" the starting battery.

DOES NOT PROVIDE EMERGENCY START OR COMBINE OF THE BATTERIES.

Smart isolators on the other hand, can allow the house battery/converter to trickle charge the vehicle battery.

Also provides EMERGENCY STARTING WHICH COMBINES BATTERIES FOR A FEW SECONDS.

The OP obviously does not have a smart isolator or they could have simply pushed the EMERGENCY COMBINE BUTTON to get the engine started.

It's quite obvious which one I described. I've also seen diodes added to simple isolators to allow charging from the genny/converter.

BTW, starting a post with "Wrong" is not only combative, in this case it is also incorrect ;)
MEXICOWANDERER
Explorer
Jan 23, 2018
I tried to find one that looks like this that is considered "continuous duty" but failed. I have to assssssume the one pictured is a starter motor use relay. Maybe 1.2 ohms resistance across the magnetic coil.

If this rig is a pusher diesel with larger than a seven liter diesel engine, it would require an expensive relay like this to power the jump start which can range to 500+ amps and even more than that in cold weather.

This is an image of a 200-amp bi-directional SMART relay which would pass the power of all but the largest alternators.

With a 7.0+ liter diesel engine I would not elect to use the "feature" of this smart relay to jump start from bank to bank. I would retain the relay what is featured in this thread. Two relays each best suited for it's purpose.

By selecting the BI-Directional model relay the relay will operate and pass current no matter which direction the power is coming from -- alternator or converter. This keeps chassis and hotel batteries happy.

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