Boondocking an Electric Heater

[Buggeee]

Ok Peeps, by Boondocking I am meaning Dry Camping, by which I simply mean not plugging in to anything. I don't mean full timing, or any length of timing for that matter. Just not connecting for some period. I'm going to be using, gulp, an electric heater. I am expecting to exhaust my batteries by the end of the trip, and recharch them at home on the grid. I am not expecting to be self sufficient or successfully off grid for more that, let's say, 3 full days at a given time. Going mountain biking for the weekend, that sort of thing. Not expecting comfort, looking for enjoyable adventure. This egg is so small it reminds ds me if a tent so I think this is possible.

So you know, I am at risk of totally hijacking a pour soul's thread over at owner's helping owner's, where she was asking about heating while driving, which is a different issue than what I'm tangenting on. Here is a link to Nancy's thread on that issue in the event you want to talk about Nancy's question instead of the nonsense I'm going to get into in this one - http://www.fiberglassrv.com/forums/f...ing-82227.html. Ok that was Nancy's question not mine. I'm not heating while driving. I'm just heating with electric off my batteries.

So as to not step on my fellow Egger's toes, and hoping I don't get banned for life by some unintended forum faux pas or another, I am going to copy my post over to here, by quoting it.

Then I'm going to copy over a very useful reply, by quoting that as well. Then I will expect you all to either laugh at me for dreaming of what is as silly as the ever elusive perpetual motion machine, or chime in with some thoughts about moving the pipe dream forward a bit.

So... Here goes...

Originally Posted by Buggeee

Because I'm ridiculous, I have been on a quest to do an electric heating solution so I don't have any propane inside my small Playpac camper.

What makes this ridiculous is... I'm going to boondock this solution off of my battery bank for short trips (which I call a 3 full day weekend). Can't be done? Tell the Wright brothers, I'm not listening.

I'll litter this thread with a little info I have so far in the event anyone ever finds it useful.

I'm running a 2000w peak pure sine inverter to get 120vac household current from a battery bank. At the time of this test I had half my bank in place, meaning I tried this on only two 100 amp hour SLA (valve regulated really, they all are) 12v batteries for a total of 200 amp hour bank for the test.

I'm playing with an electric "kickspace" heater, used for under kitchen cabinets and toll booths. My rig is smaller than a toll booth. It's called: Broan 112 Kickspace Fan-Forced Wall Heater with Built-In Thermostat, White. Here's the link to it: https://www.amazon.com/Broan-112-Kic...ckspace+heater

It can be internally modified, by instructions from the factory, to run at 240vac/1500watt or 120vac1500watt or 120vac/750watt. On 120vac/1500watt it pulls 12 amps. On 120vac/750watt it pulls 6 amps.

I have it knocked all the way down, running it at 120vac/750watt and it pulls 6 amps.

It's like a luke warm hair dryer.

But... it runs. It will immediately force a low voltage light on the inverter (meaning its pulling almost everything the batteries can offer at any given time while its running).

If I also click on the chest freezer (120vac at 1 amp when running) I'll step into the next level of alarm, meaning I'll be getting a low voltage beeping from the inverter in addition to the light (meaning "I'm givin' 'er all she's got Capt'n, there aint no more!). Even then, though, I'm not tripping a low voltage shut down, so I have found the edge of the cliff for my rig without quite going over it.

[Edit: The low voltage warnings here do not mean that the batteries are exhausted. It just means that the inverter "sees" lower voltage for the moment because the deep cycle batteries can't stream out electrons with as much volume (amps) at a time as a car battery does. Here, all of the volume that can be streamed out of the deep cycle batteries at a given moment is being demanded so the inverter thinks there is low voltage. Don't rely on me for the formula stuff because I may have it expressed inaccurately. It has to do with the math of amps and watts and volts but I'm not good at math so I just run experiments and see how far I can push it. The next step is to see how long it lasts.]

That's as far as I've gotten. This was just a "will it start?" stage of development. I let it run for about 10 or 15 minutes in mid 50s weather and the cabin warmed up just fine. Then I shut it off. No appreciable loss to the state of charge on the multimeter, but then I wouldn't have expected to see one as the batteries were excited by the test.

The goal is modest. I've experienced what a small candle can do while tent camping (don't go to sleep!) just to take the edge off. Then the body heat really keeps things moving. So here, I'm looking to just hit this thing once in a while to get things started, or to take the bite out if I wake up in the middle of the night.

I use sleeping bags by the way.

Later peeps.

[Buggeee]

And here is the very useful reply from Jon that made me realize I needed to start my own thread, and that it probably needed to be over here with you solar folks who are good at math...

Originally Posted by Jon Vermilye

While running an experiment to see if it is possible sounds interesting, some thoughts:

With 200 amp hours of battery, common usage says you can expect to get 1/2 that or 100 amp hours before the batteries are drawn down to the point where long term damage starts to occur.

A 6 amp, 120V load will draw at least 60 amps from the batteries; more if you consider losses, and if the input voltage to the inverter drops below 12V - most inverters draw what ever current it takes to produce 120V output, and watts out = watts in.

At best, I suspect you could get a very optimistic 20 - 30 minutes of run time. How are your going to recharge the batteries for the next round of usage? Putting back 40 - 50 amp hours without a generator (and even with one) is a difficult project.

I run a 1000 watt sine wave inverter, combined with a pair of 6V, 232 amp hour batteries & have 355 watts of solar to recharge them. I find that if I go over 40 amp hours of usage during the winter when the sun is at a low angle (195 watts of the solar panels are on the trailer roof) it will be unlikely that I will completely refill the batteries, even on a cloudless day in the Arizona desert.

[Buggeee]

Ok. So now that I'm up and running, I have a place to post the results of any further experiments and, hopefully, get some good advice or sound thumping. Either way is fine.

Next on my list is to run the heater until I empty my battery bank, or at least for sufficient lenghth of time to make rough predictions on run time in minutes.

By empty I mean 12.0v. Where 12.8 (resting) is full and 10.2 is dead meat, 50% or 12.0v is where I stop abusing my battery bank. At that point I shut it down until I'm back on the grid for a full recharge.

I occasionally have opportunity to supplement with 100 watt or 200 watt worth of solar cells to extend life or just ease the abuse while camping - but not always. So I'm interested in the edge of the spectrum where I fully charge the bank before leaving, and then draw from it until it's empty (With batteries that means half empty as mentioned) like you would with a fresh water tank or a bottle of propane.

That is my quest. And blue is my favorite color... No, green... Uh oh.

[Jon Vermilye]

One of the reasons for propane furnaces in trailers is the amount of BTUs they produce. A 1500 watt electric heater produces around 5100 BTUs per hour. A typical RV propane furnace produces between 10,000 & 40,000 BTU per hour, with 12,000 typical for fiberglass trailers.

I've found that a 1500 watt electric heater (in my case a Pelonis Disk Furnace) is capable of keeping my Escape 21 comfortable at temperatures down to 32°F. Luckly, I haven't had the chance to see how much lower it can go.

The Pelonis is a variable wattage/fan speed heater that lets you set a temperature. Once it reaches the set temperature, the wattage turns down as does the fan speed. I've seen it go as low as 200 watts, and a fan speed you can't hear across the trailer.

I really like the Pelonis for sites that have hookups. It won't work on a dry site on the inverter, because it always starts at the full wattage (more than my inverter) before turning down.

[Buggeee]

The bank I'll be camping with is 400 amp hours worth of SLA batteries (4 batteries of 100 amp hours each). They are not really sealed lead acid batteries you know. They are valve regulated absorbed glass mat.

Anyway, I'm trying these out because my bank of four 6v golf cart batteries from my long long trailer (similar sized at 430 amp hours when run 2x2 in a series) is about 5 years old and way too heavy for the tongue of my little egg. Those flooded lead acid cells can't go inside because they spew poison gas when they are charging. The valve regulated AGMs only spew poison gas in extreme situations rather than all the time so I am mounting them inside over the axle and sealing them in a box with a vent to the outside at the bottom and another vent to the outside at the top. (I will need some vent at some time for sure because I am not always considerate of my batteries' sensitivities and they will be abused here and there).

[Buggeee]

Sounds like a nice heater John. Although I have knocked mine down to 750 watts, when I take the missus and am plugged into a serviced site I figure I'll be able to let it run forever for her on the shore power.

When I'm dry camping, however, the heater will not automatically lower it's wattage or the speed of the blower. It has a non-numbered dial thermostat. But... I won't be letting thermostat decide how to waste my electrons. I prefer to manually spend them.

So the solution I've come up with is a wall mounted timer switch. It is used for powerful bathroom exhaust fans and has ample 120vac amp ratings to handle a 6amp 120vac draw from this heater. It is a - Maxxima 1800 Watt 7 Button Countdown Timer Switch. It has timer settings from one minute to one hour. What I'll do is hit it for 10 minutes, or whatever, of heater when I climb in the cabin to bust the chill. And hit it again now and again as needed, or as battery consumption permits.

What I'll be trying to figure out in further study is how many total minutes I have to work with so I can ration it properly during the trip.

[Buggeee]

With 200 amp hours (half my bank installed on a maiden Labor Day voyage). I went three days running the fridge (120vac chest freezer on a fridge thermostat that pulls 1 amp when the motor is ruunning), and a Maxx Air fan vent (that I used a low setting intermittently), and blowing up a bunch of inflatable air mattresses (that's gotta be expensive), and recharging my phone a few times, and recharging a set of 4 AA batteries (for the fun of it), and the led cabin lights. I figured another 100 amp hour battery would suffice for the water pump that I'm putting in plus surplus. The surplus from that plus a fourth 100 amp hour battery is what I have to play with in the bank for this heater. That's 240 pounds of batteries over the right wheel. There's 250 pounds of fresh water capacity (30 gallon) over the left wheel so that's it for battery weight.

I know, I know, somewhere someone's head is hurting because of the way I'm discussing this but I'm not good at math so I'm picturing a savings bank that I fill with electrons that I can spend in 3 days.

[Buggeee]

And... Lastly if this doesn't work and I run the heater when I am connected to shore power it's not the end of the world. Most places we camp are serviced with at least electric. I just want to see what Boondocking might be made possible with some thoughtful rationing and low expectations. Extending the opening and closing of the 3 seasons or just having a couple hits off this thing on a cold night would be pretty cool (no pun intended but I'll take it)

[John in Michigan]

Buggeee, Jon figured that considering losses you could probably run your heater at 750 watts for 20 to 30 minutes before the two 100 amp hour batteries would be 50% discharged (i.e., 100 amp hours expended).

Even with perfect efficiency through the inverter, etc, your 120vac 6 amp heater will consume 60 amps at 12vdc. So that's 60 amp hours per hour, and with perfect efficiency your available 100 amp hours would be used up in 1 hour and 40 minutes.

[John in Michigan]

A 12vdc heater would work much better because you wouldn't have to deal with the inefficiency of the inverter. The lower wattage 12vdc heater the better. There are 12vdc 150 watt heaters with fans on Amazon.

On the other hand, we often do without heat when boondocking. Just making coffee on the propane stove in the morning heats up the camper sufficiently. Also, there is the tiny Mr Heater Little Buddy heater that uses 1 lb propane canisters. That would heat up a small camper quickly.

[Buggeee]

Raspy had a great reply over on Nancy's thread while I was busy setting this one up so here is that one as it pertains to this study

Originally Posted by Raspy

Buggeee,

I know it's fun to experiment. Go for it. But while you're doing it keep the basic physics and battery protocol in mind.

The most basic rules are: Only discharge batteries to 50% of their rated amp hours. Inverters draw about eleven times the amperage on 12 volts that they deliver on 120 volts. So, 7 amps at 120 volts requires about 77 amps from the battery.

With a battery bank rated for 200 amp hours, you'll get less than three hours from a fully charged battery bank. Then you have to re-charge them. Any other loads will educe it further.

Jon explained it well, and you can take it up with the Wright Brothers too. Physics is physics so I won't be the one to tell you you can't do something. Of course you can, but specifically what, is the real question. Let us know how it goes.

So... If I'm reading this right I'm thinking that a 6 amp 120vac draw through an inverter will burn through my allocated 12v capacity for this use in 82 minutes. (180 amp hours allocated ÷ 2 because it's a battery ÷ 66 amps per hour × 60 minutes in an hour = 82 minutes of run time) That's 8 hits at 10 minutes each. Very interesting.

Thank you very much for the coaching...

[John in Michigan]

One particular 12vdc 150 watt heater on Amazon lists the input current at 12.5 amps (sounds about right). Doing the math, this unit would consume 100 amp hours in 8 hours.

[Buggeee]

Originally Posted by John in Michigan

One particular 12vdc 150 watt heater on Amazon lists the input current at 12.5 amps (sounds about right). Doing the math, this unit would consume 100 amp hours in 8 hours.

Dang that's a long time John. Maybe I should consider kicking my 120vac unit back up to 1500 watts/12 amps and just using it on the shore, having this little 12v 150 watt for the boondock stupidity I have in mind. I'll check it out.

[Jon Vermilye]

That 150 watt heater (it doesn't matter whether it is running on 12v or 120v, it is the wattage that converts to BTUs) will only produce around 512 BTUs. While that is heat, it isn't much.

There are two things to consider when using batteries. The first is easy to calculate - how many amp hours you have vs how many you can safely use.

The second consideration is how are you going to put back into the batteries what you take out? If you are only going to boondocks for a day or two, you can ignore the problem & just plug in the trailer when you get home. If, however you want extended stays, you really need to consider this.

The charging characteristics for the various types of lead acid batteries are different, with the AGM allowing for the fastest recharging, but in all cases you can only put so much current into the batteries, more when they are very low, less as they reach a full charge.

In general, the batteries will take lots of current until they reach about 80% of full, but at that point, only charge very slowly. Trying to push more current into them than they will take will only cause outgassing. This is why good converters & battery chargers are 3 stage (4 if you add equalization). The bulk is the charging cycle that dumps as much current into the batteries as they can take. This is where you need lots of amps, something that solar doesn't do well unless you have lots of it. This is why those with limited solar often run their generator in the morning - it provides bulk charging through the RV's converter, then the solar takes over during the day to provide the absorption cycle.

At around 80%, the charger switches to Absorption, where the voltage is limited so that the battery charges without outgassing or overheating. Once the battery is fully charged, it switched to the float cycle, which keeps the battery topped off & powers your RV.

Probably more than you want to know, but if you are going to boondocks any length of time, you do need to consider how you are going to refill the batteries.

While many have no problems with a 60 - 100 watt solar panel keeping their battery reasonably charged, in the case of taking the battery down to 1/2 capacity, it is going to take a lot of solar or a large converter plugged into a pedestal to refill the batteries before you need the power again.

[Buggeee]

Excellent place for the information Jon and more is better not only for me, but for whoever stumbles on this thread. I'm familiar with the charge stages but had never put together that generators were running in the morning for bulk, allowing the solar to serve as top-off during the day. Thank you.

I use a 60 amp Progressive Dynamics Intelipower converter with a charge wizard dongle. I had used it in my long long trailer to fill golf cart batteries. It's a smart charger that follows the bulk, top-off and float stages you describe artfully here. It also throws a desulfation stage of 15 minutes at 14.3v or so every third day to shake up the lead plates when it senses long term storage so they don't get crusty with... We'll sulfates I guess. That desulfation stage has me scratching my head on these AGM batts because they do not like higher voltages (you can't add water if you boil them into venting out the off gassing, ordinarily the gas is reabsorbed in these so no water loss occurs) but the manual says it is compatible with AGM.

I'm looking to see if I can squeeze a 3 day weekend out of the bank and then recharging on the grid at home. But this info is great because I could add a generator to the mix if some crazy winter trip presents itself and now I know where it would fit in.

I had 200 watts of rooftop solar that rolled away with the long long trailer. Right now I have a 100 watt panel that I will have available as a portable to set out in the sun if opportunity arises. Even If I doubled that to 200 watts I'd guess 5 to 7 amps of solar input given I'm in Ohio, not the sun belt really. So lets say 4 or 5 hours of usable sun could return 25 or 30 amp hours in a day.

[Raspy]

Originally Posted by Buggeee

Dang that's a long time John. Maybe I should consider kicking my 120vac unit back up to 1500 watts/12 amps and just using it on the shore, having this little 12v 150 watt for the boondock stupidity I have in mind. I'll check it out.

If you want to know how much a 150 watt heater will do, or what 150 watts feels like, get yourself a 150 watt incandescent light bulb (old school light bulb, not LED) and turn it on. Two 75 watt bulbs will do the same thing.

Since 150 watts is 150 watts, either with 12 volts or 120 volts, a standard 150 watt / 120 volt light bulb will give you a good test to feel how much heat that represents. An old lamp or a clamp on reflector fixture from Home Depot would work fine. Just put your bulb in, plug it in and turn it on. Will it heat your trailer if left on overnight? No.

Remember: volts X amps = watts, which is the same as: amps = watts divided by volts. This simple equation is very useful and can be manipulated as in a normal math problem. Watts is an indirect measure of heat, as far as heaters go. Heat is expressed in BTUs. 1000 watts = 3412 Btus. So a 1000 watt, 120 volt heater produces 3412 BTUs while drawing 8.3 amps. An equivalent 12 volt heater would draw (8.3 X 10) 83 amps. Through an inverter it would be 8.3 X 11 or 91.3 amps. In order to get the same number of watts from a 12 volt circuit as from a 120 volt circuit, you must have 10 times the amps.

You know that you can only draw batteries down to 50% of their rated capacity. A 200 amp battery bank rating (total amp rating) means 100 amps are available.

This is where it gets more tricky. The faster you draw down a battery, the less you get overall and loading it up to about 100 amps is a very big load. Next, you can't read the state of charge while under load. The batteries must be "rested" in order to get an accurate reading with voltage. So, the best you can do is guess based on your load. And then rest the batteries before taking a good voltage reading. Resting may take a couple of hours. Or you can use a hydrometer and do it chemically.

Just as a wild guess, I'd estimate that you'll only get about 40% or less at your 100 amp draw and any other loads will reduce that further. That 40% guess is the number of amps you can draw, at a large load, until the battery is at 50% charge.

So, play with it and be thoughtful of what you are doing. See results and justify what you see with real numbers. You'll see things that don't make sense at first, but you will have variables that can't be accurately measured and will have to be estimated to make your numbers work. Look at charts for flooded cell batteries with amp hour graphs. Pretty soon you'll see what the real deal is with batteries.

[Buggeee]

Excellent discussion Raspy. I'll spend the 60 bucks on dinner instead of the 12v 150watt heater and continue to play with the one I am installing as the permanent heater, which as mentioned is 120vac 750watt 6amp running through the inverter when not plugged into shore.

Our primary destinations are serviced by electric. So far I am very pleased that it will run at all on the battery bank as this will allow for some form of play time for me with the concept on my own time with the egg. Good fun.

I've now got 300 amp hours installed (3 x 100) and may try some run times this weekend on that partial bank for grins and giggles.

[Civilguy]

Originally Posted by Buggeee

That is my quest. And blue is my favorite color... No, green... Uh oh.

I normally like to be supportive when people get knuckle-headed ideas like I do all the time.

However, in this case, I think blue better be your favorite color as I think that's what you'll end up turning if you go winter camping in Ohio!

Batteries don't contain much energy. The prevalence of gasoline-fueled vehicles and recreational vehicles fitted with propane cylinders is due to the relative economy and particularly the high energy-density of these fuels.

I think other folks have been doing a good job of citing the basic math and physics involved. So I can basically coast on adding any quantitative data here. I will restate what's been said in qualitative terms.

Every time you convert energy, there is an inefficiency, which means energy lost. This occurs with solar cells, voltage inverters, converters and generators. It may be good news that this energy is generally dissipated as heat; an inefficient inverter located inside the trailer will lose energy as heat, so you are actually making out OK in that case.

One difference with the solar as a source of energy is that the source is "free", at least when available. However, the density of the energy collected is generally fairly low due to the cost of the collection systems.

If you bring a generator into play, then you are basically using the high energy-density of gasoline (or some other fuel) and converting it inefficiently to electric power. In this case, the heat caused by the inefficiency of the generator is lost outside of the trailer. At least I expect that it will be unless you have something particularly dangerous in mind.

To look at this another way, a perfectly-efficient engine would not get hot at all.

Anyway, I was just hoping to give you another perspective on this, sort of a big-picture view free of all the watts and Btu's and formulas and such.

Down bags, insulation, Clif bars, a friendly Husky, and a firm resolve will all be your friends here. And, take a tip from Jimmy Carter and wear a sweater! Good luck with your experiments and keep us posted!

[Raspy]

On my boat, I used to occasionally make coffee with an electric coffee maker while out at anchor. Rude for the batteries, but similar to what you are doing.

Get your solar fired up to try to make up some of what you are turning into heat.

Wait till you begin to use batteries to make cold in the fridge. That is a more fun problem for me. I designed a holding plate system for the boat that ran for 20 minutes once every 6 hours on 12 volts at about a 15 amp draw. It sent all of it's condenser heat to the fuel tanks. Beers were so cold they'd freeze when I popped the top.

I was able to reduce the fridge run time from about 30% of the time to about 5% of the time and control when it ran. This meant I could regulate my battery charging times to match the load. It worked out very well.

[Raspy]

Originally Posted by Civilguy

I normally like to be supportive when people get knuckle-headed ideas like I do all the time.

However, in this case, I think blue better be your favorite color as I think that's what you'll end up turning if you go winter camping in Ohio!

Down bags, insulation, Clif bars, a friendly Husky, and a firm resolve will all be your friends here. And, take a tip from Jimmy Carter and wear a sweater! Good luck with your experiments and keep us posted!

Just as a suggestion and followup to Civil's post, consider the best alternative to the down bags, huskies, etc, is probably much more likely to be a warm girlfriend. These can be very effective, but the cost may be prohibitive.