12v battery system - capacity question.

[Element89]

I'm working to setup a 12v battery system for using my 13' trillium dry most weekends.

As we plan to use the trailer mostly in the winter for skiing, and as much as I would love a solar system, I don't think it would be viable as we'll be leaving the trailer parked during the week (we wouldn't be able to clear snow from the panels) and it gets pretty dark up here in BC during the winter !

What we're thinking is to have a 12v battery that we charge up at home during the week and bring up to the trailer for the weekend (generally Friday night or Saturday morning), and bring it home with us to recharge after a weekend of skiing.

I've been reading lots of forums and trying to work out the battery capacity I would need, but am still a bit lost / would love someone to check my logic / math. Apologies as I'm sure this has been covered over the years.

In terms of loads, we plan to install a a few (2-3) low power LED lights and to install 2 usb ports to charge our phones. Under typical usage, I could see us getting to the trailer Friday night and using the lights for a few hours, plugging our phones in for about an hour. Saturday, might use the lights in the morning for an hour max (often its bright enough to not need them in the morning, but trying to be conservative), then turn lights on again when returning to the trailer around 5pm. In an extreme case, we might keep the lights on until 1am, and again possibly topping up the phone charge for an hour or two each. We might use the lights in the morning on Sunday again, and typically would head home after skiing. The exception would be for long weekends or if we take an extra day, when we might want another nights worth of light. Noting this we also have the ability to charge our phones from our car on the way to the hill, bit depending on where we're setup, it may not be for long. FYI we'll be using propane for heat/cooking.

So - if we assume the loads for worst case scenario as:

LED LIGHTS:
= 3 lights x 10W x (4 hrs Friday + 8 hrs Saturday + 8hrs Sunday)
= 30W x 20hrs
= 600W•hrs

Dividing this by 12V to determine amperage:

600W•hrs / 12V
= 50A•hrs


PHONE CHARGING:
2 phones x 2A draw(?) x 2 hrs / day x 2 days
= 4A x 4hrs
= 16 A•hrs

TOTAL LOAD:
= 66 A•hrs

Does this make sense? Am I over / underestimating the loads?

If that makes sense - then comes battery selection. I'm slightly confused about deep-cycle batteries, as I've read that these shouldn't be depleted below 50% capacity to maximize their usable life. Does this mean I should be looking for an ~120 A•hr battery based on my calculations? From someone that doesn't know a lot about battery's, this sounds overkill! Are there alternatives to deep cycle batteries for my typical usage? Am I just way off in my assumptions/ methods ?

Finally, as I am open to a solar system eventually (will use it in the summer too, but I tend to do most of my summer camping / hiking in tents), can I use a generic 12v battery as a part of a solar system?

Thanks a lot for you help!
-SB

[ckayaker]

A couple of quick thoughts. First I think you are over-estimating the power consumption of the LED lights which typically run at less that a watt each. The second thought is why not go solar and mount your panels vertically? Given the low winter sun angle, you won’t lose much given the camper isn’t used during the week. I suspect by the end of the week, the battery will be fully charged and ready to go.

[k0wtz]

I don't want to step on anyones toes here I use the kiss principle works for me! Your idea of a fully charged battery makes sense to me if your battery runs down get a set of jumper cables and recharge it or for 100bux get another battery to install if you need it.

solar and all the other stuff means a lot of fiddling and other stuff I want to have fun, do other things!

Does this mean I am opposed to any other ideas absolutely not but I run things simple this works for me! by the way while your car is running charging the battery you can charge you phones in the car if needed!

or you can turn the phones on and off to save charge!

bob

[Franswa]

I will assume that your propane heater will NOT be the usual conventional RV heater commonly installed at the factory (with a blower)....if it is you might as well give up now because those are power hogs...chances are your single battery will be dead the first morning

"fiddling" with solar is a worthwhile endeavor and a satisfying hobby for a lot of us...depending on where you park and given the angle of the sun in the winter in these parts a near vertical mount is a very good idea and will work

LED lights consume so little power you can almost delete them from your calculations compared to everything else like exhaust fans, pumps and stuff like recharging laptops (surprised me!)....my phone takes a LONG time to recharge on my 12V system

the reason you buy a deep cycle battery is they are made to handle the type of use you will put them through (as opposed to "car" batteries that are designed for quick, heavy power draws followed by immediate recharges) the deep cycle will last longer before you will need to replace it...they cost more money for a reason

[Joe Romas]

Originally Posted by Franswa

...my phone takes a LONG time to recharge on my 12V system

If your charging your "smart" phone off one of those plug in adapters that go into a lighter outlet and it's slow you most likely don't have a "smart" capable adapter.

For reasons I won't get into for a smart phone capable of fast charging needs a adapter that is also smart that has the SND and REC pins, the two center ones, connected. This tells a fast charge capable device it's connected to a fast charger. (if you want a long discussion, google it)

They cost no more also. Here's two for under $5 that I can verify do fast charge capable devices.
2Pcs Universal USB Car Charger Power Adapter Adapter for Smart Mobile Cell Phone | eBay

[John Linck]

I too think you are overestimating your power needs. I expect you could go for a week or more on a Group 24 battery with such tiny loads, even in cold weather.

John

[Glenn Baglo]

This LED lamp will run continuously for 30 days on low, powered by three D-cells. Probably can use your vehicle to charge phones.
Can be set on table with globe or hung from a hook, without.
Available at Mountain Equipment Coop.

[TimR]

I think it's a good idea you have to take out the batteries and charge them at home. Not sure how cold it will be during the week where you keep your trailer, but it might kill the batteries regardless. Or at the very least lessen their lifespan.

[FRL001]

First, if you do end trucking the battery back and forth each week for charging, consider getting a semi-sealed AGM battery rather than a standard lead acid. Less chance of acid spills when you're moving it around and they have higher capacity for the same physical size. The downside is that an AGM deep cycle battery is more expensive....

Second, for propane heat I'm assuming you will use a radiant heater that does not require electricity to run? It will require some ventilation in the trailer and the wall mounted units are safer than portables. There are usually some for sale on Amazon and eBay.

Finally, have you already tried camping out in the Boler on a cold frosty night somewhere with heat running? You may be surprised at how much condensation you will get in an uninsulated unit plus you're going to burn quite a bit of propane to keep warm if you're parked at altitude. Something just to try out before you spend too much money on the project.

Good luck! I'm sure with trial and error you'll have a lot of fun.

[k0wtz]

I put a phone charger in mine it has a dropping resistor to drop it to 5v any voltage past that and I think you could blow up your battery then your smart phone.

I wouldn't risk much!

bob

[k0wtz]

I consider agm batteries a waste of money I know you are sold on them that's fine. I boonedocked for 30 days in Feb. we never recharged the battery once we were never on electricity. Walmarts will furnish you a place to park but no utilities!

we do not run a furnace off a battery we run a wave 3 off propane. it puts out more than enough enough in an Aliner way more than we need in the Scamp!

I know you must vent a non-vented heater! How do we do that? We crack a window and one roof vent to pull in fresh air as it is burned. we do not open windows all the way what is the point!

Condensation yes in an A-Liner because there is lots of al. trim and that made it worse not terrible with a huge wind and 20d wx snow and ice!

[Byron Kinnaman]

I think there's a lot of misconception about power needs I'll tell you how I manage 30+ days stay in one place. My battery gets pretty well charged when towing so the state of battery charge only matters with stays longer than 4 days in cold weather and 2 weeks or more in warm weather.
What draws power in my trailer?
1. The biggest draw is the furnace at measured 3.1 amps. If it ran for an hour that would be 3.1 amp hours (my Marine/RV deep cycle batter is rated at 74 amp hours with 37 amp hour usable.)
2. If was to turn on every light in my trailer that would be 1.5amp measured. All lights on for 1 hour would be 1.5 amp hours.
If I was to run the furnace for 1 hour and all lights for 1 hour that would be 4.6 amp hours. Therefore 1 hour of maximum use would deplete the battery by 4.6/37 * 100 = 12.4% of my battery capacity was used.
There's something wrong with this picture. !. My furnace never runs for 1 hour a day. I'm guessing 20 minutes when it really cold. 2. I have several lights and 3 kinds of lights. The .02 amp light gets used the most. So my daily usage is a lot less than 10% of capacity.
I use a solar panel that puts out a little over 4 amps, which charges the battery at 4 amp hours per hour(if the battery is discharged enough). Batteries draw less current the closer they get to fully charged.

What all this means in the practical world is that my 65 Watt portable solar panel used about every 4th day in full sun will do more than enough to keep my trailer powered.

Those that camp only on week-ends need not do anything or buy any thing.

[Ed Harris]

I actually agree with Byron....... no excuse either other than common sense this time?

LED bulb replacements just make sense overall and require so little power is is hard to accept,I don't run them all around as they seem to interfere with the TV in my trailer so I leave a few incandescent bulbs in place in case I really need light and TV at the same time.

Your battery should be fine installed all the time and Solar will only help guarantee that this is the case even if sun exposure is not optimal at all times.

The entire point for me of Solar is also to keep things more simple not the other way around and once setup and running the Solar requires no real intervention at all as opposed to the odd comments about keeping things simple and avoiding letting Solar provide a more worry free time.

Really!

Unless you have tried it how can you knock it?

73

[k0wtz]

Some people like to tinker I do not if you like solar go for it. If my battery runs down I turn the car around put the jumper cables on it and recharge the battery.

I also have my car fixed now so it charges the Scamper battery along with the car battery. It never gets low enough to need much we go camping we don't take tvs dvd players anything not needed we use our lights sparenly we don't have a b/r or a shower to suck juice out of our battery. Again if that is your life style go for it.

We spend our time traveling by 8pm we are ready for bed and up at 6 the next am.

I put this battery thing along with trailer tires, towing all sorts of things camping as the arguments can get heated I don't know why. I have my ways of camping they may not be your ways and viceversa. I am not going to try to change your theories I just make suggestions for considerations!

Its really no big deal!!

bob

[itlives]

I find some of these threads strange. The OP does their thing. The peeps respond. The OP is never seen again....

Good answers. Good thoughts.

[Joe Romas]

It lives

That seems to happen more times then not

Joe

[Element89]

Thanks everyone for your input and suggestions! Appologies for not responding sooner, trailer work has been keeping us busy.

We have gone with a 72A-hr deep cycle battery (on sale at Canadian Tire!) and have wired in two LED dome lights, two LED strip lights for under the kitchen cabinets/above sink/stove, a fuse box, and a dual USB charger / voltmeter.

The dome lights run at about 0.1A each, and the strip lights run at about 0.2A each, and each single light is quite bright despite their size. We're quite interested in solar, but for now it wasn't in the budget. Ideally we'll get that set-up in the spring when we strip and repaint the exterior... For now we've gone with a battery charger and I think that will work well for us for the winter ski season!

We also are using a fanless Mr. Buddy portable propane heater, and have run a line in from the main 20lb tank (bypassing the regulator for the stove), so that won't be a drain on the battery. These aren't designed for indoor use, but we will be ensuring air flow and definitely won't leave it running overnight. It does have a low oxygen and tip-over auto shut-off, and we have purchased CO/smoke detector and a fire extinguisher. We'll be able to keep it in the cupboard, run it to warm up the trailer when we arrive and when wake up - it doesnt take long! We also have -7 C sleeping bags so we'll be all set.

Anyway, I'll be posting progress to our project thread here with photos as the trailer evolves, so take a look if you're interested.

Thanks again!

[John Linck]

Sounds like a sensible plan Scott. Good luck.

John

Pic in Yosemite Valley

[k0wtz]

you have great ideas myself I don't care about solar but I respect the ones that do for one I don't like to tinker! You have figured out a battery aint going to hack it running a furnace fan all night unless you want a huge bank then that has to be recharged! Where do you put all this weight?

I looked at mr buddy heaters before settling on the wave 3 I still look at the mr buddy heaters and wonder. I think they have better output but a little more expensive to run.

we took a 4 week trip to Texas in Feb. used the Waver 3 down to 20d at night. This was in a drafty A-Liner I am hoping the little 13f will be easier to heat. we will see!

Just do you ventilation and you will be fine!! By the way I like beneficial debate!

bob