should alternator keep up with furnace?

[red_ranger]

Last feb i was travelling with the furnace running and the coach batteries ran down. had to start the genny to run things.

I have since checked the coach disconnect and isolator relays and both seem to have the right volts on both sides with the engine running. the furnace and fridge are on a 15 amp fuse. it would seem to me that i couldn't have been drawing enough of the alt. charging current that the coach batteries would not stay charged

what can i be missing ?

thanks

[pianotuna]

Hi,

There may be a 60 amp fuse that has failed. It is in the engine compartment fuse box. I replaced the fuse with a 50 amp auto reset circuit breaker, after I had replaced it 3 times in a year.

My OEM relay lasted less than 18 months. The contacts had burned.

[red_ranger]

thanks for the replies. rig is a 2004 coachmen. turns out it's not a relay, but a 3 terminal solenoid. i found a replacement for $18 so i went ahead and ordered it.
i don't think for that kind of $$ the contacts are designed to last forever.

[JimM68]

Those isolator relays do go bad.
The contacts corrode and they just won't pull any load, won't pass enough current anymore. (Even though they still act like they are working, and will even pass a low load test)

I had to take mine apart and clean it last year, recently it failed again and I just replaced it with a trombetta 200 amp "big boy" relay. I don't think I'll ever have trouble with it again.

[diveman52]

Your furnace only draws about 8 amps. If your alternator can't keep up with that additional draw I'd have it checked.
I run down the road with my 1800 watt inverter running all the time. Powering the Frig., Laptop computer and sometimes the MV and sometime the heater if it really cold.
It would be nice if you we knew what your rig is???

[eHoefler]

Chassis lights, ignition, heater on the chassis, computers (engine, transmission, brakes, etc.. )for the running of the coach, radio, etc... size of the charge line between coach and chassis. In other words, NO. The alternator is sized to run the chassis engine and related components, not huge draw accessories a body builder hangs on the chassis.

[wa8yxm]

Furnace is a fairly big load but well within what the alternator can provide,, What else was pulling 12 volts?

If the alternator is not keeping up.. On a motor home, I'd check the isolator relay and all the wiring for bad contacts/connections.

IF the RV is a trailer.. The wire between isolator and trailer is too small.

[teddyu]

More info on the coach would be helpful. If your unit is equipped with a BIRD, the chassis and coach batteries will isolate if the alternator is not putting out sufficient voltage. My alternator will provide >13.6VDC when on the road and running my heavy DC loads. The BIRD will typically isolate around 12.8VDC. The alternator may be good enough to keep the chassis loads powered, but not the coach loads. JM2¢...

[pianotuna]

Hi,

There may be too long a run on the charging path causing voltage drop. If there is a diode type isolator that may contribute to the drop.

[MrWizard]

Yes it should be enough, as long as the fridge is on propane

If fridge has a 12v / D.C. option it will pull 20 amps just for the fridge heating element
The furnace will pull at least 10 amps main valve and the blower motor

You could have some bad connections some place, possibly in the battery negative/frame grounding or the main positive cables at the batteries
The isolator can check good but the power may not be getting to the batteries and into the house circuits, meaning you draw the power from the batteries

[KD4UPL]

It should have worked fine. Did you have the refrigerator on LP or 12v? Even if on 12v it should have worked.
What voltage do you have at your coach batteries with the engine running? It should be around 14 volts or higher.

[whem2fish]

yes