Suburban LP Furnace

[richard5933]

I've been searching for a 12v power feed to the Suburban LP furnace in our 4108a. So far, all I've seen is the 120v feed. Really looks like the original owner was either on generator or shore power at all times.

I'm working to install a house battery bank of about 550ah. Should be enough to power the LP furnace blower for a night. Problem is that I think the furnace is 120v only.

Anyone see a problem if I install a properly-sized inverter and use it to power the furnace while boondocking? I'll install a small manual transfer switch to switch the feed to the furnace from genset/shore power to inverter.

Richard

[chessie4905]

I thought they all were 12/110 volt. Maybe they never connected the lower voltage part.

[richard5933]

According to the manual they made 12v only, 120v only, and a 12v/120v version of the model in the bus. Problem is that the unit is tucked in so tightly that I can't access the model number to confirm which version was installed, and I am having difficulty getting to the wiring box as well. Since there is no switch on the 12v panel for the furnace and just the one on the 120v panel I'm going to assume that I have a 120v version. Hence the desire to run it off the inverter.

Richard
1974 GMC P8M4108A-125 (Current bus)
1964 GM PD4106-2412 (totalled Sept 2017)
Located in beautiful Wisconsin
KD9GRB

[RichardEntrekin]

Don't know if it will work in this case, but I  stole a trick from the kids, and often use the phone to snag a picture of a tight access nameplate.

[TomC]

My Atwood 40,000btu furnace pulls about 10 amps at 12v when running. That's about 120watts-which would be easy for an inverter. If you don't have an inverter already, you should get an inverter/charger. Switches between inverter and power pole automatically. Good Luck, TomC

[chessie4905]

Yeah, if it is 120 volt only, fewer issues over time and inverters are available now and relatively inexpensive. We used a Suburban propane furnace in our 4104 for several years with few  problems, Upgraded to electronic ignition unit after about 10 years of use. We used the coach 8 D's for our house batteries also. The furnace drew significent power in a day's time, if it was pretty cold out,so we'd run 12 kw Kohler diesel generator during day to recharge batteries. If the batteries were too low to start coach, there was almost always enough juice left to start generator.

[TomC]

I always believe in separate house batteries. I have 2-31 starting batteries and 2-8D deep cycle Lifeline AGM. House batteries are wired to the inverter/charger. I have a 300amp mechanical jumper relay to connect the two sets together to be able to charge going down the road, or charge the starting batteries when sitting, or jump the bus with AGM batteries if need be. Always good to have two sets of everything. (2-10gal water heaters, 2-waterpump, 2- refrigerators, 2-TV's, etc). Good Luck, TomC

[chessie4905]

Back in the 80s, separate sets in conversions weren't common like they are now.

[richard5933]

Back in the 80s, separate sets in conversions weren't common like they are now.

I know what you mean. Right now, with only the original conversion pieces in place, there is really no house battery bank at all. There is a single 8D 12v battery which serves to both start the generator and supply 12v to the few items in the coach which run on 12v. There is a bank of two 8D batteries in a 24v configuration which start the bus engine and power the few 24v interior lights in place. There is also a pair of dinosaur-sized Constavolt chargers to keep the batteries charged when on shore or generator power. That's really it for now.

My plan is to add a proper house battery bank with four Trojan 6v batteries to create a 12v bank. Not sure if I'll use the T145 or the L16 batteries, but either way I'll combine it with a Progressive Dynamics 9270-amp converter charger. Eventually I'll also add 960 watts of solar to the roof to charge the house battery bank, but that will probably have to wait a bit due to all the expenses of having a new bus unexpectedly. For space savings, I'll also add a separate 24v Progressive Dynamics charger to keep the starting batteries charged while plugged in. Not sure how I'll charge the house batteries while on the road, but I'm leaning towards using a Vanner 70-60 Equalizer (if I can figure out where to order one from.)

I want to incorporate a power inverter as well, but right now I'm torn on the best way to do that. It will be used to power the furnace and a few outlets for entertainment items like flat screen TV, Blue Ray, music, etc. I've got a small propane burner for cooking while on battery. The current microwave is a monster and not suitable for inverter use. Eventually we might change it out, but for now we can live without it when on batteries.

Ideally I'd bring a 30-amp 120v supply line to the inverter from the main 120v panel and let the inverter automatically switch between shore/genset and inverter. However, there are problems with that plan - main problem is that there are no spaces in the existing breaker panel to add anything, let alone a 30-amp breaker for a subpanel/inverter. Secondly, the way the 120v system is wired with absolutely no wiggle room at all in the harness, it will be an act of utter frustration at every step.

So, my plan for now is to add a small subpanel that will be powered by the inverter with just a few 120v breakers as a stand-alone system. I'll add a constant-duty solenoid to remotely turn the inverter on/off so it won't drain the batteries when not in use. There are unused toggle switches in the main power control center above the driver and it will be easy to designate one to turn the inverter on/off. I'll add a small manual transfer switch to connect the furnace to either the main power panel or the inverter. Along with the hard-wired connection to the furnace, I'll install a few outlets (in the front lounge, kitchen, and bedroom) so that we can plug in devices as needed. While not the most convenient way to do this, it seems the most simple and straightforward way.

I know that there advantages to using an inverter/charger instead, but it seemed like no matter which way I connect that it will busy up the installation and create the possibility for problems. If I keep the inverter as a stand-alone system I think it will be pretty easy to explain to my faithful co-pilot how to activate the marked outlets when they are needed.

I'd love to hear your thoughts on this to see if I'm missing something in my plans. Also would love to hear other ideas for charging 12v house batteries from the 24v alternator on the bus engine.

Thanks!