Furnace and single battery

[Jollero]

Okay, so i am back at this camping thing. First my question, if we don't use the lights in the pop up dry camping, so assuming just the LP detecter is running, how long could we run the furnace for until the battery starts running low. The Jayco pop up manual shows 12 amps is what the furnace uses. I used to own a large travel trailer but storage and expense was too much, back to where i started with a pop up, after years of no camping with the kids, i miss it and want them back into it. I really don't have the space or want to run two batteries, wondering what one battery is really going to get me. thanks

[Jollero]

So i took it out this weekend and one of you were right, it was doable without the furnace. it dropped into the high 30's at night, however, once bundled up, we slept thought the night with all 3 kids no heater. in the morning, i turned the heater on and got some warmth. So we did not need to run it at night, good thing because it was loud and the smoke alarm went off the first morning from the new furnace being burned the first time, that would of been annoying the first night. The poor battery did not have enough juice to lower the pop up evenly one of the front sides would not go down, i started freaking out, however, once i hooked the generator up and got it going, all went down fine, so it must have been not enough power or the right kind of power

[red31]

teejaywhy wrote:

Jollero wrote:

The Jayco pop up manual shows 12 amps is what the furnace uses...

I question the 12A number if indeed you have a Jayco popup. Can you tell us the make and model of the furnace to double check that figure?

Maybe you have a big highwall unit with a bigger furnace? My Baja uses the Atwood 7916-II (very typical popup furnace) which is rated at 3.5A. Basically the DC draw is from the fan motor.

Agreed, I use 4A to estimate. A healthy group 24 has ~80 ah (20 hr rate) to ~100 ah (1A rate). I divide 80 by 2 and get 40 ah usable.

40 / 4 = 10 hrs of furnace run time to use. That could be 1 day if it is cold and windy or many days if the furnace doesn't run much.

[Serenlyretired]

Never got over 3 nights with my Jayco 10X battery in California's Mountains.

[JLTN_James]

Replacing the mechanical thermostat with a digital programmable one is worth it! I replaced mine and it has kept the temperatures very stable. I also like that it turns way down at night to reduce battery & propane use (we have good sleeping bags), then comes back up in the morning BEFORE I need to get up. Here's a link to how I did my replacement: Thermostat Replacement.

One thing I haven't seen mentioned yet is that the furnace blower needs to run at a fairly high speed (i.e. needs higher voltage) before the safety interlocks allow the gas to turn on and ignite. The furnace not igniting is usually the first sign of a weak battery. It will blow cold air for a little while then shut off. My experience is that it does this a littel before the battery hits 50% SOC. So when the furnace doesn't light, it's time to recharge; unless it's 3AM AND we're in a campground. If boondocking, the generator fires up whenever I need it to!

[Jollero]

I will have to look at the furnace when i pull it out. I got that number out of the owners manual i downloaded from the internet. We will find out this weekend, what i don't want is the middle of the night the battery to run low and the dumb LP detector starts beeping. Then i wake up the whole family going outside to unplug a battery!!!!!

[teejaywhy]

Jollero wrote:

The Jayco pop up manual shows 12 amps is what the furnace uses...

I question the 12A number if indeed you have a Jayco popup. Can you tell us the make and model of the furnace to double check that figure?

Maybe you have a big highwall unit with a bigger furnace? My Baja uses the Atwood 7916-II (very typical popup furnace) which is rated at 3.5A. Basically the DC draw is from the fan motor.

How long the battery will last depends on:
- Battery capacity and health
- How cold it is outside
- How warm you want it inside.

Best case scenerio:
- Get the largest capacity true deep cycle battery and maintain it rigorously.
- Use reflectix window inserts and PUG bunk end covers
- Use the furnace conservatively - warm it up at bedtime then cut the thermostat back to 55 or so. Use warm sleeping bags or blankets. A digital thermostat will help with more precise temp control.

For a real world example, we spent four nights at 9000' in the mountains of Colorado. Overnight lows were in the low 40's / upper 30's. We used the furnace conservatively as described above (no reflectix or PUGs) and still had >50% state of charge on departure day. Battery was a Trojan SCS225 (130Ah).

[Bmach]

If you have a way to recharge your battery in the morning you should be fine. Make sure you have a deep cycle battery, they are designed to be discharged over and over. They can be drawn down by as much as 70-80%, then recharged. Hence the term deep cycle.

Try running the furnace while at home and monitor the battery. That way you will have a good idea before you go camping.

[SteveAE]

I suspect that, unless your children have a medical condition that requires they sleep in a warm environment, they will be very content as long as you are happy. I suggest forgetting about the furnace other than maybe to take the chill off in the morning before the kids get up...for you. Just have a campfire at night (I am generally not a campfire person)and then go to bed with lots of covers.

Just my thoughts....having snow camped (in tents and snow caves) since a child.

Winter camping is great. Have fun.
Steve

[Jollero]

Ouch, i did not want to go back the route of 6 volt batteries again, they cost me a big chunk of change before. Half the time we have hookups, the other half, we are in yosemite and normally don't use a heater in the summer and really have no use for a battery since my kids go to bed at sunset. But dry camping for a weekend at the beach in the winter like next weekend, might not work well. Weather is supposed to be 40 degrees at night plus wind, i will need that furnace for the little guys, one battery is not going to cut it, in fact two 12volt deep cycles might not even cut it, i do have a generator i could recharge each day though.

[SteveAE]

Jollero,

Take the amp-hr rating of your battery (for easy math, lets just say it's 100 Amp-hrs.
Divide by your power usage .... 12 Amps (you can ignore the CO detector for now because it represents so little of your total usage).
This yields a result of 8.3 hours.
This means that if you run your furnace constantly, a new, fully charged 100 Amp-Hr battery will be completely depleted in 8.3 hours.
Fortunately, it is likely that your finance doesn't run constantly, and perhaps is only on about 20% of the time. So dividing 8.3 hours by 20% (0.25) you get 41.5 hours.
While this initially sounds great, something to keep in mind is that your battery will last much longer before it needs to be replaced if you don't use more than about 1/2 of it's total capacity before recharging.
Hence, multiplying 41.5 hours by 50% (0.5) gives you 20.8 hours.
So, with a single 100 Amp-Hr battery running only your 12 amp furnace, you are likely to have to recharge at least once every ~24 hours to maintain good battery health. This seems to agree with the rule of thumb of "one battery per day".

I hope you or someone else finds this useful,
Steve

After posting, I see others are able to type faster than I and have also answered your question. O-well. 🙂

[skipnchar]

Too many variables to make a prediction. Depends on temp outside, wind conditions and insulation factor in the rv. All of these will effect the run cycle of the furnace. Add too that a factor for how warm you try to keep it. My 4-season trailer would struggle too make it one night with your battery with temps of 30 degree and 60--degree temp setting but I suspect the furnace is larger also.

[RoyB]

JOLLERO - Just for comparison as to what MARKW8 says above..

My three batteries gives me 255AH capacity. I have a good DC BATTERY MONITOR panel that monitors both 12VDC from the two battery bank setup and a 75AMP DC Current from what is being drawn from the trailer items.

I usually draw 20AMPS DC Current from 8PM to 11PM each night running all the 120VAC items from a inverter and direct connected to the 12VDC terminals. In addition to this I have a good 1-2 AMP parasitic drain from the batteries 24/7. This will drop my three batteries (255AH capacity) to around 12.0VDC at 8AM each morning which is pretty close to being a 50% battery bank charge state. This is where I must re-charge by connecting my on board PD9260C converter/charger to my 2KW Honda Generator and run it for three hours to get my three batteries back up to their 90% charge state.

Perhaps you can judge from this what you 12AMP drain from your furnace 12VDC blower is going to do to you before 8AM the next morning.

What you don't want to happen is to drain your battery down below 12.0VDC without re-charging again. This will do internal damage to your battery unless you get it charged back up.

You can look at the specs of your battery to determine how many minutes it will produce 12VDC to totally drain your battery.

consider this spec sheet for a Trojan T1275 150AH 12VDC battery


The spec sheet says you can draw 25AMPS for 280 minutes before draining down to 0% Charge rate. SO running down to just 50% it will only last for 140 minutes or just over 2 hours of use. Your 12AMP draw using this battery should last 4 hours... Then you must re-charge back up to 90% right away before doing internal damage to the battery.

All of this is not exact but sort of gives you an idea on how to determine how long you can survive with one battery.

Roy Ken

[Crazy_Ray]

Run a TEST while your still at home. JMO. I bet you have a GROUP 24 and that is near nothing to RUN DOWN.

[MARKW8]

I have a single group 31 Sears Platinum AGM in my TC. Can't remember exactly but 205-220AH. Not cheap but should do the job.

Mark