Battery Heater

[bdosborn]

I bought a heating pad from Amazon to try and build a battery heater. Its a 25W heater, about the size of a playing cad. Pretty sure I'm not going to use this one:

Anybody have some suggestions for a heating pad that won't burn everything down?

Bruce

[saltydawg]

I am using 2 12 watt bee hive heating pads, one for each 60 ah lifepo4 battery they are almost the perfect size for the battery. Also they say they have a max temp of 85F iirc. I also have a 10 buck amazon thermostat with the sensor between the two batteries. The thermostat also activates a relay that cuts off the charging current.

When its cold I turn on the switch, one led on the switch lights, letting me know its on. The thermostat controls the heaters and the relay as well as lights the other led on the switch so I know the batteries are too cold to charge. When the switch is off, the charging current just goes thru the relay and charges like normal.

[saltydawg]

just looked them up they state a max temp of 60C, what ever that is. But my thermostat turns them off at 40-42 F.
https://www.amazon.com/GAOHOU-Electric- ... NrPXRydWU=

[bdosborn]

Thanks for the link, got one on the way.
Bruce

[saltydawg]

Thanks for the link, got one on the way.
Bruce

How big is your battery, as I said I have 2 one for each battery. The size is almost perfect for the bottom of my battery

[bdosborn]

About this big:



Bruce

[saltydawg]

About this big:



Bruce

You might want 2.

Show off

[John61CT]

The Chinese eBay sellers of those silicone pads let you order custom sizes and temps, with integrated thermostat, can specify a low-temp startup or a high-temp cutoff.

I chose the latter, and put in a dedicated circuit for the latter.

About $20 for once-off, in quantity down to under $5, maybe a month turnaround.

[nbcarey]

Wouldn't you just buy a battery blanket, and wrap it around the battery like pretty much everybody in Minnesota and rest of the upper Midwest?

This is a GMC OEM part: https://www.amazon.com/gp/product/B000FE7IIS/

And there's this one.

https://www.amazon.com/gp/product/B002UNASS4/

[saltydawg]

Wouldn't you just buy a battery blanket, and wrap it around the battery like pretty much everybody in Minnesota and rest of the upper Midwest?

This is a GMC OEM part: https://www.amazon.com/gp/product/B000FE7IIS/

And there's this one.

https://www.amazon.com/gp/product/B002UNASS4/

Because they are 120 volt. Most guys are trying to avoid shore power or plan just dont have it. So for the most part we are using 12 volts.

[bdosborn]

Wouldn't you just buy a battery blanket, and wrap it around the battery like pretty much everybody in Minnesota and rest of the upper Midwest?

I think there are two scenarios for LiFePo4 battery heating:

1. Off grid and wanting to keep the batteries above 32F. You can't charge a LiFEPo4 battery below 32F without damaging it. In this scenario a 12V, small heater with good temperature control would work best to keep the energy use as low as possible. All though I wonder how often I would let the camper get below 32F while camping since the water supply would freeze.
2. Long term storage while on shore power. The 120V battery heater would be great for this, We recently got down to -12F, which is lower than LiFEPo4 batteries are rated for storage. In this scenario, the 120V heater would keep me from having to bring the batteries into the garage. I need to look at the battery blanket and see if it is self liming or if I should add thermostatic control.

Thanks for the link!

Bruce

[bdosborn]

Doh!
Guess it's a no-go on the battery blanket:

Notice: This product is NOT recommended for use with lithium ion batteries, nickel cadmium batteries or with battery case material ABS

Bruce

[Cosmo]

Thanks for diving into the search for a solution.

From a numbers perspective a 60 amp hour battery at 12V = 720 watt hours. Ignoring cost
AGM 120 amp hour at 50% useable power = 720 watt hours. Ignoring weight.

12 Watt heating pad will consume 288 watts in 24 hours or 24 amps running continuously. Major assumption here based on nothing - If the heater runs s 50% with a thermostat in 24 hours it would consume 144 watts or 12 amps. leaving 576 watts or 48 amps of power for consumption.

For comparison a 120AH AGM would provide 60AH of usable power. Both the AGM and Lithium will loose efficiency in cold weather. I am guessing the AGM will loose 1/3 capacity which brings available power down to 40 amps or 480 watts. Not sure about the Lithium. The difference under these extreme conditions might be 8 amps or 96 watts of extra power from the Lithium. When the cost per watt of the gain is calculated its expensive. Of course the rest of the year in friendly temperatures it’s a different story and lithium wins. There are other factors both pro and con for both batteries.

I am sure my calculations are embedded with errors and I am missing a lot of considerations. My intent is to learn more.

Thanks for your help and research
=Cosmo

[saltydawg]

From a numbers perspective a 60 amp hour battery at 12V = 720 watt hours. Ignoring cost
AGM 120 amp hour at 50% useable power = 720 watt hours. Ignoring weight.

You are ignoring some important info. the 60 amp lithium will be 1/2 the size and 1/4 the weight. Cost you could diy a 60 amp lithium for under 200 with out much trouble, but 300 if you buy one. A good name brand agm is close to 200 last time I looked. Sure there are some cheaper.

12 Watt heating pad will consume 288 watts in 24 hours or 24 amps running continuously ( my edit, unless you total for the day, which I think you do ) . Major assumption here based on nothing - If the heater runs s 50% with a thermostat in 24 hours it would consume 144 watts or 12 amps. leaving 576 watts or 48 amps of power for consumption.

Your math is off, a 12 watt heating pad will consume 1 amp an hour, or 24 ah in a day. if it runs 50 % your down to 12 ah. I think more realistic is the heater running 10 to 25% of the time, as you would not due this with out insulating the battery ( if you where smart ) even just a layer of 1 inch foam tapped on it ( now it is larger )

For comparison a 120AH AGM would provide 60AH of usable power. Both the AGM and Lithium will loose efficiency in cold weather. I am guessing the AGM will loose 1/3 capacity which brings available power down to 40 amps or 480 watts. Not sure about the Lithium. The difference under these extreme conditions might be 8 amps or 96 watts of extra power from the Lithium. When the cost per watt of the gain is calculated its expensive. Of course the rest of the year in friendly temperatures it’s a different story and lithium wins. There are other factors both pro and con for both batteries.

Lithium looses about 15%, but if your eating it then the loss is even less, but made up for by whats used to heat it. read the article at the end battle born only got 8.1 % out of the lead acid in a high drain test 15 % in a low draw test

I am sure my calculations are embedded with errors and I am missing a lot of considerations. My intent is to learn more.

Thanks for your help and research
=Cosmo

https://mortonsonthemove.com/lithium-ba ... d-weather/

[bdosborn]

Cosmo,

I don't quite follow what you are calculating and I think your situation is different from mine. I'll be using 4 bee heaters so the total load is 28 watts or 28W/13.2V = 2 amp-hr load. I used 13.2V for my voltage because LiFePo4 battery voltage is much more stable and the capacity doesn't change much with temperature compared to lead acid batteries. So it's 24 amp-hr of usage assuming they run continuously all night. My LiFePo4 battery has 400 amp-hrs total capacity, 320 amp-hr usable at 80% discharge. So a single night of heating represents 7.5% battery usage. The PV panels should easily be able to replace that, even in winter months. I can start the engine to charge if the panels aren't harvesting.

I think the water get muddy when you look at how you camp. I won't be camping an extended time in the snow like you do, we quit camping in the winter. So it's only the shoulder months that I'll need heat and we'll also be running a diesel heater when it gets chilly (the batteries will be inside the camper). I doubt I'll have to run the battery heater at all when we're camping. The only reason I'm adding a heater to the batteries is because they will be going into a camping van that will be parked outside and they can't go below -10F temperature.

The situation is much different with a lead acid battery. Battery capacity drops by 50% for every 10C below 25C so it makes sense to keep them warm. Unfortunately, most LA batteries don't have enough capacity to make heating them worth it, IMHO. I'd try and move the batteries inside the trailer before I tried heating them.
Bruce