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herringcove
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# Posted: 9 Dec 2013 20:20 - Edited by: herringcove
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Hi,
Things haven't gone exactly to plan so I need a 12v heat mat with a thermostat. Ill put it in my insulated battery box under the stair and leave them powering it, hope they will last. 4xL600 6v. Anyone have any ideas on what to use for this, all I can think of is a lizard mat from a pet shop but I think something much simpler must be available. What might I use?
Thanks.
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MtnDon
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# Posted: 9 Dec 2013 20:43
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You don't say what the time frame for the required heating is. I do not think there is any 12 volt solution for heating batteries if you mean the batteries will be powering the heating device. For a very short time, yes, but nothing for an extended period.
A fully charged lead acid battery will not freeze until the temperature drops to something like -90 F. It doesn't take much to keep a battery fully charged if there are no loads being run. What's the difficulty??? I have kept 4 golf cart batteries from being run down over a winter with as little as 30 watts worth of PV.
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herringcove
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# Posted: 9 Dec 2013 21:51
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The time frame is between 4 days on a good week or 2+ weeks if weather makes it inaccessible for a few weekends. Our panels will be covered in snow as they are still flat on the deck. But there is an existing 30watt panel on the wall which we could hook up to the batteries. We have built an insulated box to house the batteries under the stairs with 1" Styrofoam. I had it in my head the batteries have to be in room temperature or at least above 0°. So am I worrying for nothing? Can I leave the batteries charged by the 30 watt panel over winter?
Thanks!
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MtnDon
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# Posted: 9 Dec 2013 22:01
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Quoting: herringcove Can I leave the batteries charged by the 30 watt panel over winter?
If you start off with the batteries fully charged the 30 watts should maintain the charge over the winter. I had a small cheapy charge controller though with the limited hours of winter sunshine filtered by trees it probably would have been safe w/o one. I would be sure the water level was up and the charge full, then leave. They sat for two winters from early to mid December through to April-May. They were fine when I checked in spring. I still have 2 of the original four, re-purposed to another task where they are still doing fine... the other two I sold off.
We also have 12 other batteries that winter over with no intervention on my part. They are hooked to the PV array via an Outback FM60. The data log shows they get a brief bulk charge whenever the day is sunny, followed by a short absorb and hours of float. No issues at all with water usage even with us snow shoeing in once a month for a few days. I've got to where if the lights come on when I turn the inverter on I don't even look at them until spring warms up.
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MtnDon
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# Posted: 9 Dec 2013 22:04
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Quoting: herringcove I had it in my head the batteries have to be in room temperature or at least above 0°.
The batteries perform better when warm. Cold really hampers their ability to supply current. Capacity will be down by 42% at zero F and by 55% at -20 F. OTOH batteries enjoy a longer life in the cold, all else being equal and no abuse.
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groingo
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# Posted: 9 Dec 2013 22:20 - Edited by: groingo
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I actually placed the batteries in an insulated box next to my cabin then ran a 2 inch pipe from one to the other and then used a small computer fan to draw warm air from the house into the battery box
(fan drew 1/4 amp)....couldn't really tell if it helped but hey.
Ultimately it may just be better to keep them in an explosion proof insulated container in the house and just vent to the outside.
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Truecabin
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# Posted: 9 Dec 2013 22:50
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if the heater drains your batteries they will freeze
why dont you lean the panels up against the house
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toofewweekends
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# Posted: 10 Dec 2013 00:41
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we leave a couple of 12v marine batteries untended for several weeks thru the winter at our Alaska cabin. Temps often are below zero, and there's been no issue. Now, I make almost no demand of them -- they just run a small sink pump in the summer and some LED lights in the winter. So hard working batteries may show some decline. But still, these never freeze and I forget to get them fully charged probably half the time.
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MtnDon
Member
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# Posted: 10 Dec 2013 01:08
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75% charge 1.225 sp gr -55 F
50% 1.190 -34 F
25% 1.155 -16 F
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creeky
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# Posted: 10 Dec 2013 07:14
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Like MtnDon I've left my batteries for two winters while I vacationed in the glorious south.
There was no problem. I got home. Turned on the inverter and away i went. I did leave them hooked up to the Morningstar controller and panels. With no load they didn't use any water.
Now I'm here full time.
Last year I just let the batteries get cold (-17 was the recorded low). This year however I'm putting a gas heater in the solar shed (I have an 8x8 shed for my batteries, controllers with panels mounted on the roof). The shed is insulated to about R25.
With the fridge I'm putting more demand on the batteries and I want to keep the charge levels up.
Anyone have any ideas for heating my shed other than a propane heater? I'm thinking the 8k homcomfort as it has a thermostat.
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MtnDon
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# Posted: 10 Dec 2013 09:59 - Edited by: MtnDon
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I know someone who has done just that; a small shed to house batteries and for toilet composting. I hope you have done a better job at sealing against air infiltration. R25 sounds good; more would be nicer. What about the floor?
I am blessed with many sunny days, 300 or so a year. I would make / install a solar collector system. Either air or liquid as the medium for getting solar heat inside. I favor liquid but that is more complicated, more parts and requires antifreeze. And lots of mass inside. The batteries themselves have good mass but more if possible; concrete works well, tanks of water / antifreeze also. And then an 8K propane as backup to cover the cloudy days.
Then I'd think about the trade offs between the standing pilot on the housewarmer and electrical use on a spark ignition model. Use purchased propane or "free" electricity?
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MtnDon
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# Posted: 10 Dec 2013 10:45 - Edited by: MtnDon
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Sometimes I don't connect all the dots at once.  But eventually I do, most the time. I'm planning a cargo trailer to camper conversion and I have what I believe to be the ideal heater for that small space. A Propex. They are very small, very efficient. Use propane and 12 VDC. They are a tad costly at $700 and up.
Another vehicle type of heater is Webasto. Like Propex they are from Europe. Unlike Propex no USA distributor. Webasto uses diesel. And even more expensive. I've seen them on ebay UK.
Both are direct vent types.
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sparky1
Member
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# Posted: 10 Dec 2013 13:32
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New Rv Camper Trailer Marine Holding Tank Pipe Heater Pad 12 volt | Add to watch list
Seller :tristatesurplusllc (23335 ) 99.7% Positive feedbackSave this seller | See other items | Visit store: Tri State Surplus LLC
Item InformationItem condition:New other (see details)
Quantity: 3 available / 9 sold
Price:US $24.95
,,,
here's a idea.
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Truecabin
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# Posted: 10 Dec 2013 13:36 - Edited by: Truecabin
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a heat pad might be good to get more power out of your cold batteries if you have extra sunlight
but if you are not using the batteries just hoping they survive the winter it is the wrong way it will drain your batteries then they freeze
the right way to go is to keep them full charged you can put a solar panel under the eaves it wont get snow and it will add a little each day for what was lost
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MtnDon
Member
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# Posted: 10 Dec 2013 13:39
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Quoting: sparky1 New Rv Camper Trailer Marine Holding Tank Pipe Heater Pad 12 volt | Add to watch list
As truecabin said... trying to heat batteries with the batteries own power is a death sentence. And it would not take long. Those 12 VDC heating devices are meant to brief use or use while driving with the tow vehicle pumping power into the batteries.
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creeky
Member
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# Posted: 10 Dec 2013 14:12
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That propex heater is pricey. But nice features. No wasted space inside has to be the biggest feature. Plus "forced air".
Sadly I have to have more than a solar furnace as we get very cloudy here in Nov/Dec. I'm currently looking at 2 solid weeks without a full sunny day. So . I'll see. I'm building one this winter for my "outhouse."
I figure the propane pilot light is a source of heat in itself. so it doesn't cost that much. I was told 1 lb of propane lights the pilot for 40 days (and 40 nights).
My solar shack has an R30ish insulated floor and I've got the batteries in an additional xps insulation box during the winter. it does help the batteries conserve the heat they create working/charging. air sealing is fairly good. there is a gap under the door which I just noticed.
truth be told I hadn't thought of heating the batteries. But with recent explorations in "hybrid" solutions. Most notably my excellent experience with adding a propane furnace (as so many have done, thank you to the many for the idea).
I began to think about my batteries and the decrease in available amperage as they cool (as MtnDon has posted). i need my electric. so why not heat the batteries with propane? heck I could store paint and other cold sensitive sundries in there as well.
thoughts?
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MtnDon
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# Posted: 10 Dec 2013 15:53 - Edited by: MtnDon
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Quoting: creeky I was told 1 lb of propane lights the pilot for 40 days (and 40 nights).
I believe that is grossly inaccurate although the amount of propane used by a pilot flame varies widely between devices. I did a test about three years ago. The device was my Suburban brand RV water heater; 6 gallon with pilot light.
I am not saying that is correct for every propane appliance. But that is what I got on that one device and that one test.
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creeky
Member
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# Posted: 10 Dec 2013 16:54 - Edited by: creeky
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ya. i thought the 40 day thing sounded like bull. i am recovering some of the heat tho.
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herringcove
Member
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# Posted: 10 Dec 2013 19:19
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Thanks so much guys looks like I was barking up the wrong tree. I knew the deficit in power due to cold temps but somehow also thought that if they get below zero celcius they would be damaged. I will stand my three 250watt panels and fix them vertically and leave the house to get cold during the week. When I visit I will warm up the house anyway, but in any case they are only powering cfl and shurflo water pump.
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toyota_mdt_tech
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# Posted: 10 Dec 2013 20:09 - Edited by: toyota_mdt_tech
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Quoting: MtnDon I'm planning a cargo trailer to camper conversion...
Interesting Don, I did just that in 04.
I kept it simple, ie still a cargo trailer, able to haul the dirt bikes and quads, but comfy for that overnight stay(s)  Sorry to hijack the thread, I'd of PM'd ya, but no good on this forum.
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MtnDon
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# Posted: 10 Dec 2013 20:23
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Quoting: toyota_mdt_tech Sorry to hijack the thread, I'd of PM'd ya, but no good on this forum.
I just started a whole new topic to get your attention on something.... look for propane ... fittings....
It's a 6x12 with a deep v-nose, single axle, should have it by mid January. It will not be overly fancy, mainly a base camp on wheels, but with a shower!!!
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herringcove
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# Posted: 12 Dec 2013 19:48
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Quoting: creeky I was told 1 lb of propane lights the pilot for 40 days (and 40 nights).
The guy's name wasn't Noah was it?
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creeky
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# Posted: 13 Dec 2013 07:45
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i think it was Muddy Waters
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