Can a furnace run all night on a fully charged battery?

[Alluminati]

Originally Posted by OTRA15

Did you ever sit for more than 48 hours, for instance, and have your batteries stay above 50% with the many uses you have listed? It would be good to have some parameters sketched out so that everyone can gauge their intended uses, and battery configurations, against some real figures IMO.

Excellent questions. I wish I knew all the answers. We made no attempt to measure battery capacity related to normal usage.

Our first night out (though we soon learned that we were operating on 12.5% capacity with one dead battery, and one at 25%), the furnace ran intermittently through the night as needed to keep the temp about 65. Outside temp maybe 50? Calm winds. The second night when the furnace kicked on, the fridge died. Not enough juice to run the furnace, and keep the electric controls running on the fridge. Fortunately we were able to find a place to plug in.

I too want to know some legitimate parameters to know the realistic capacity for off grid camping. We have never boondocked (call it what you want, you know what I mean) more than 48 hours in one place. At that time we were not using the furnace. Since installing the new batteries, never more than 24 hrs. One night in Ennis, Montana the low temp was about 28, and there was a brisk wind. We kept the trailer at 68 overnight. I don’t recall checking battery status in the morning.

We did, however, measure our water usage. I filled the fresh water tank before leaving home, and we were able to enjoy 6 hot showers before the tank ran dry, and the grey tank full (SOOOO thankful for our enormous grey tank!) I supposed we would be close to a source of water about the time we ran out. Being out of water is inconvenient. Out of electric, and you’re dead. Perhaps sometime we may try staying in a campground and remain unplugged until the batteries are dead. But I don’t fancy killing my fridge in the process. Considering we made it through one cool night at 12.5% capacity, I’m pretty confident we can boondock for a lot longer than 48 hours if we don’t use the furnace much.

[OTRA15]

Thanks for the details. You should endeavor not to let your batteries get below 12 volts, as you start to do real damage at that point, at least for standard flooded cell batteries. This is about 50% of capacity. It is considered a good practice to monitor battery voltage often, as charging really should begin if possible when the voltage gets under 12.5 volts according to some.

Your 24-hour stint in the cold weather is a good starting gauge IMO. Curious what the battery voltage was that morning.

Thanks again for the details.

Peter

PS the following resource is a good overview of RV battery practice IMO:

http://www.marxrv.com/12volt/12volt.htm#batchart

Voltage chart: http://www.marxrv.com/12volt/voltchart1.gif

[Alluminati]

I just checked with my wife. Unbeknownst to me, she was checking the batteries every morning. We don’t have a meter or gauge on our control panel; just idiot lights. There are four or five LEDs that indicate “Poor, Fair, Good, Very Good, Excellent”, or whatever, I don’t recall offhand. She said the only morning that showed any drop in battery power at all, was our coldest night when we were below freezing.


Based on her observations, we are obviously in no danger of running our batteries dead by using our furnace on the coldest night. Perhaps we could go a week off grid if we don’t use the furnace too many nights. But if it’s that cold, I’ll probably hitch up the truck and move to a warmer location anyway.

[wcs]

When I first started boondocking off-road three fully charged rv/marine batteries would last approx. two days. The 7 amp furnace fan was able to operate two days where the batteries became pretty much drained on the third. The RV also has a water pump that pumps water when using the sinks and toilet.

A larger problem is on the 3rd day the gas refrigerator requiring 12 volts to operate would shut down.

I've since purchased a catalytic heater that only requires lpg gas to operate.

Depending on your battery bank size and type, normally expect at least one to two days with non conservative rv normal use. Larger banks with true deep cycle batteries usually do better.

If you have ample sun properly sized solar panel(s) can bring a bank back in approx. one day. If not enough sun then your refrigerator and furnace will potentially keep operating but your battery bank will start to fall to around 50 percent. Once it goes under 50 percent then it's difficult to charge them back without enough time with full sun, generator or shore power.

[Boxite]

Originally Posted by Naper

The trailer will only draw power when the truck engine is running.
This is on a Ford not sure about other brands

My Ram 7-way plug provides power continuously, engine running or not.
The hazard of running the TV to provide power to the trailer is CO poisoning from the TV exhaust directed near the front of the trailer.

[daboyce49]

Just saw this thread. I know it’s been dead for awhile but I have an similar question. We’re picking up our new 25’ Flying Cloud this weekend. Picking it up in Seattle and driving it back to our home in Northwestern Wisconsin. We were thinking we would pull into truck stops on the way home for sleep time. Would be on the road home the rest of the time. So, am I safe to assume that being on the road at least 10 hours a day (possibly longer) the batteries (new, obviously) should be able to handle the task of the furnace for each of two/three nights? We typically set our thermostat at anywheres from 60-62 at night. Clearly it’ll be charging during the day while it’s connected to TV, correct?

Do the units come with a battery monitor with a readout that provides a state of battery charge?

Thanks in advance for any info.

[daboyce49]

Please ignore my above post - I see there’s been a number of other threads that have pretty well beat this dog to death. Believe they’ll have provided me with an answer.

[PKI]

You are to be commended on doing your own research. It's a great way to expand your knowledge and make better decisions. Well done!

Welcome to the forum. Hope to see you down the road in a shiny with a smile. Pat

[DBinSD]

Originally Posted by daboyce49

Please ignore my above post - I see there’s been a number of other threads that have pretty well beat this dog to death. Believe they’ll have provided me with an answer.

Search in different ways.

There is a plethora of info here. Albeit sometimes difficult to find the answers you need.

Good luck in your search.

[kkdesigns]

We are currently in Grand Tetons and it is getting down in the mid 30's at night. We set the furnace at about about 68 to warm the trailer before bed with the generator and then lower to 64 or so before lights out. If I charge the batteries (2 AGM 6 volts) with the generator before bed to a full charge (12.7), the batteries will be down to about 12.2 or 12.3 by morning. I know the furnace is running more throughout the night. I've also been turning off the pump at night as well as the hot water heater if it's not dipping below freezing to help with the battery life. I will leave the solar panel out and it helps start recharging the batteries once the sun comes up.

The lower the temp, the less the furnace cycles, the longer the batteries will last.

[mpsgolf]

Heres a possibly useful chart. As someone said dont dizcharge a lead acid battery to less than 50% or it will at least shorten its life if not damage it. The more times you discharge to min volts the shorter your battery life will be.

I have a Trimetric battery monitor. I can read volts and % discharged. If you boondock much could be worthwhile. I think monitor and shunt together about $200. I installed myself, fairly simple.

[rmkrum]

Originally Posted by kkdesigns

------------snip------------------

The lower the THERMOSTAT set temp, the less the furnace cycles, the longer the batteries will last.

Just to make this really clear...edit in bold

[Mike S.]

Daboyce 49, One other thing to look out for is the fact that batteries tend to get used up sitting on the dealer lot. They get drained with no chance of being charged, which hurts their lifetime. You can see the manufacture date on the top of the batteries. Just something to consider. Hate for you to need them and not have them. Mike

[PKI]

A whopping 22 F and the battery read 12.0. However after dropping the loads it read 12.4 volt. So it is important to normalize the batteries before you go ballistic. At about 3am I thought we we were toast. By the time we got up, I was smiling again. Note that generator time is 8-8 and we wanted to leave at 7. Worry, worry, worry. Learning how your rig responds in different conditions reduces worry. Pat.

[pteck]

For those that have 6V batts, there is real beauty in these batts.

12V and 50% depletion is not necessarily always the magic number. Part of the reason to upgrade to golf cart batts is because they are true and legitimate deep cycle batts. Not just in branding.

You can go as low as 80% (~11.7V), and still have comparable cycle life to a 12V batt that is regularly discharged to only 50%. If you babied them and only ever depleted the 6V batts to no more than 50%, you'll see something like 2.5 times the cycle life of 12V batt.

Here’s the other great feature of lead acid relative to say lithium batts. If you consider the full capacity of the lead acid bank (2x 6V @ 225Ah) vs a 100Ah Battle Born lithium. If one were using the furnace at night, and get close to 50% usage of the lead acid, your furnace will continue running! You can discretionarily use more capacity, or looked at another way, always have margin on tap should you choose to use it. With a BB batt, if you ran out, you are cutoff. Going to have to go out in the cold to fire up the genny in the middle of the freezing night (hopefully you have one).

So a 100Ah BB, is not really 100Ah usable, as you NEVER want to go anywhere near that less you get cut-off. Versus a 2x 6V bank, that encourages you to use as much as you wish, and replace easily and cheaply if you so choose to abuse it. 180Ah regularly if you choose, with margin beyond that as a safety net.

That’s the beauty of 6V batts, with safety margin beyond. It would take $2000 sunk into 2x BB lithium batts, to have comparable usable capacity.

[GOUSC]

I posted in the 2018 Globetrotter Forum about my experience in this area on a 5-week trip we recently had. http://www.airforums.com/forums/f543...ew-188569.html

Below are the parts applicable to this issue;

“We have 2 Lifeline AGM’s and factory solar. Our experience from all 4 trips boondocking is that if you use refrigerator / propane water heater / normal lights / water pump/ stove top and have full sunlight then you can go endlessly without having to use a generator or some alternative source to charge your batteries. However, if you are in the mountains with shade or little sunlight or a rainy day we only get 1 – 1 ½ days without having to recharge with a generator.

The factors we found that affected battery life the most with our set up were the furnace and inverter.

Our trip was planned for warm weather so we had no warm clothes or pajamas. We stopped by a Columbia Outlet in Oklahoma City and picked up a few items but we weren’t fully prepared for some of the cold weather we had. We had a 27-degree night at Monarch Nat’l Forest. Our batteries were 90% when we went to bed at 10. I set the furnace at 54 degrees. I woke up at 1:00am to check on them. The batteries were at 35% and 12.1V. I think you want to keep your batteries above 50% and 12V so I shut the furnace off. Our inside temp when we woke up was 39 degrees and used my generator to heat things up.

As long as the outside temp was 45 degrees or above we could sleep comfortably without the furnace and that was most times. On those nights our batteries would generally be 60-70% when we woke up. When we turned the furnace on in the morning they would immediately drop to 50% and then 45%, etc.

My potential solutions to both of these are 1) Mr. Heater portable propane heater to knock the chill of in the mornings to save my batteries when I can’t use my generator due to weather. 2) Goal Zero 1000 lithium battery generator to carry along for coffee, wife’s hair dryer, generator use when it is quiet time a parks and other situations for travel and home. This would basically be like me adding a 3rd battery to my system. 3) I don’t want to go totally solar spend $$$$$’s for that but I figure a call to AM Solar couldn’t hurt to get their suggestions. 4) Always bring warm clothes just in case.”


Since this post I did put in a call to AM Solar. Their suggestion was to;

Put in a MPPT controller to replace the PWM one / New combiner box / 2 addt’l 90W solar panels to integrate with the existing ones / upgrade the wire size / 30 Amp Core / New Battery Monitor and continue to use my same batteries. This would cost $3,700 - $4,000.

They stated my current 160Wsolar is probably delivering 30-36-amp hours a day. He derived this by saying they were delivering 90% of their potential X 160W X 25% = 36. I’m can’t remember what the 25% represented. If I am using 36 amp and they replenish these 36 amps my batteries are not getting charged by the solar and these upgrades would address that.

I’m sure this would upgrade my current system. However; except for the furnace and coffee pot issues, I’m satisfied with the way my current set up works and don’t think $4k is worth it for me. We won’t get caught short w/o warm clothes / blankets in the future and the Mr. Heater will knock off the chill in the morning when we wake for <$100.

I’m leaning toward the Goal Zero 1000 option to improve a situation that isn’t really a bad one for me. If that doesn’t work I would consider adding a Zamp portable 160W briefcase system to double my solar capacity for <$800. The attraction to these options is that I can use them at home and on the road. However, I think the Goal Zero will be enough for our use.

[pteck]

Originally Posted by GOUSC

“We have 2 Lifeline AGM’s and factory solar. Our experience from all 4 trips boondocking is that if you use refrigerator / propane water heater / normal lights / water pump/ stove top and have full sunlight then you can go endlessly without having to use a generator or some alternative source to charge your batteries. However, if you are in the mountains with shade or little sunlight or a rainy day we only get 1 – 1 ½ days without having to recharge with a generator.

<snip>

I woke up at 1:00am to check on them. The batteries were at 35% and 12.1V. I think you want to keep your batteries above 50% and 12V so I shut the furnace off. Our inside temp when we woke up was 39 degrees and used my generator to heat things up.

<snip>

You are already well prepared and geared up without further investment.

As you have Lifeline AGM's, they are a quality deep cycle battery that can support more reserve utilization than you're giving them credit for. As I like car analogies, you bought a corvette, and are driving it like a camry.

Similar to flooded 6V golf cart batts, 50% and 12V are not necessarily the magic numbers. Even deep cycling them regularly to something like 80% (~11.8V), will still result in great usable life. On occasion, it'll simply shrug it off. And you should easily still get 5++ years out of them with casual use.

Normal 12V batts only last something like 300 50% cycles. Lifeline AGM's will do 1000 50% depth of discharge cycles. At 80%, you'll still do better than your typical 12V battery at some 550 cycles. Refer to the graph for more data points.




Also, know that you likely didn't discharge them as deep as you thought on that night. In order to take an accurate reading, you have to remove the load from the batt. So an instantaneous reading of 12.1V, is likely something more like 12.3V with the load taken off. Still plenty of reserve capacity!

[GOUSC]

Ptek,

To follow up - when I use my 1000W inverter to power our 500W coffee maker the battery% draws down to 25% for the 5 min or so it takes to make our 4 cups of coffee. Per your graph I would get 600 recycles before the batteries would crash. We only did this about 3 times on our trip and then ended up boiling water and pouring it over the grounds when my generator wasn't available due to weather. So that should be no big deal either as the batteries do recover once the load is off.

I don't feel like the batteries would've have held up all night with the furnace in those temps but this was an unusual situation for us with that cold of temp.

Otherwise our habits are not energy use crazy so we just use the batteries and quit worrying about isolated incidents and enjoy ourselves as these batteries should hold up.

Thanks for the info!

[pteck]

I see a little confusion. While the battery is being loaded (e.g. 500W coffee maker), the voltage droop (drop) is interesting, but does not mean it’s being down to that level. The voltage reading after it recovers (without it being charged) is the what tells you the depth of discharge.

For example, on a freshly charged batt, it might read 12.7V (100% remaining capacity). When using the coffee maker, it might droop to 12.3V (interesting, but not a particularly useful number). After done brewing coffee, it recovers and reads 12.5V. The useful number is the 12.5V, which suggests 80% remaining capacity, or a 20% depth of discharge.

I hope that helps. You have great batteries. Feel free to use them. They would have held up great that night when you read 12.1V. Cold affects battery readings too. It’s likely they easily still had 60% (40% usable) capacity left.