Battery heating, yes, I read the threads

[JeffreyD]

I recently installed 4 SOK 206ah batteries in my motorhome. They all fit on the original slide out tray. I insulated the compartment on all walls exposed to the outside with 1 inch foil backed rigid foam. I have seen about a 10 degree benefit using my Victron battery temp monitor. I don't feel that this will be sufficient when temps dip into teens

I have read the threads on using rv tank heaters and the need for heat sinks and such. The SOKs have a steel box and the tray is steel that they sit on with a plastic liner in it. I only anticipate needing heat down to 15 degrees a handful of days each year. What are your thoughts on mounting the tank heaters to the bottom of the battery tray versus direct to the batteries. The heat given off should heat the compartment with radiant heat while not overheating the batteries. I am a novice at this so likely am missing something that will result in an agonizing death....

 

[kenryan]

If you keep your RV heated, you might consider using a small computer type of fan to continuously blow the warm air directly into the battery compartment (when needed).

 

[JeffreyD]

Thank you. I have considered that, but location of battery compartment under a slide doesn't give me any easy options. For the immediate term, I have a small 500w heater with a thermal cube that I can power from inverter or generator.

 

[Horsefly]

You didn't say, but I assume your 4 SOK batteries are in parallel, so you have a 12V bank, and your intent is to use that to heat the batteries, not 120VAC from shore power or an inverter. So that says you need a heater and a thermostat. I don't much care for the tank heaters with a built in thermostat that you can't see or set. But that is up to you.

From what you described, if the heat pad is under the battery tray, the batteries will be sitting on a "plastic liner" inside the tray. How thick is the plastic? The steel tray will act as a sort of heat spreader (which is good) to make the heat be more uniform. The steel is probably pretty thin, which means it won't do a really good job at spreading the heat, but you are right that it is better than putting the pad directly on the batteries. The plastic might be a bit of a complication. If it is thick it will be a thermal insulator that will make it harder for the heat to get up to the batteries. I'm hoping it is not thick.

If you've read the threads then you know most people (including me) have used small silicone heating pads rather than the tank heaters. They don't use much power (you want to heat slowly), and you need to add a separate thermostat to it to control when it heats and when it doesn't. That adds complication, but also adds control. I'll tag @HRTKD here, because he did use a tank heater and had a really nice solution. However, it wasn't a tank heater like you can buy on Amazon that has a built in thermostat.

 

[kenryan]

That seems like a pretty good solution. You could install heating pads, but if it is only for a few days a year, is it really worth the cost and effort? If your pads are used in an insulated box, they should be effective no matter where you put them. They would not be in direct contact with the cells, so I don't think there would be much of a chance of dangerously overheating the battery as long as you don't go crazy with wattage.

 

[JeffreyD]

Thank you both. Yes a 12v parallel system, and only desiring to keep the batteries warm enough to accept charging. The plastic liner was there solely as a corrosion barrier, so maybe 1/8 inch in total. I said tank heater, but did like the silicon pads with separate thermostat with the remote probe (was likely the route I would go). The size and output flexibility of silicone would have many benefits.

 

[Bobert]

I recently installed 4 SOK 206ah batteries in my motorhome. They all fit on the original slide out tray. I insulated the compartment on all walls exposed to the outside with 1 inch foil backed rigid foam. I have seen about a 10 degree benefit using my Victron battery temp monitor. I don't feel that this will be sufficient when temps dip into teens

I have read the threads on using rv tank heaters and the need for heat sinks and such. The SOKs have a steel box and the tray is steel that they sit on with a plastic liner in it. I only anticipate needing heat down to 15 degrees a handful of days each year. What are your thoughts on mounting the tank heaters to the bottom of the battery tray versus direct to the batteries. The heat given off should heat the compartment with radiant heat while not overheating the batteries. I am a novice at this so likely am missing something that will result in an agonizing death....

If your battery box is insulated (especially the floor and sealed you probably won’t need heat. It takes a long time to cool down a small space with any kind of thermal mass inside it. If it was me I would set up what I have as an emergency heater and test it under real world conditions. You may find that you don’t get anywhere near freezing.

 

[time2roll]

The tank heaters on the tray should work well. I assume they have a built in thermostat.

My Ultraheat.com pads have worked well on my water tanks.

 

[JeffreyD]

@Bobertthat is my intention for now. I have the small heater in a pinch, so was going to monitor temps as we head North. But want to be ready in case the need arises. I am not happy that despite the insulation the spread is only 10 degrees, so don’t want to be caught flat footed

 

[Bobert]

@Bobertthat is my intention for now. I have the small heater in a pinch, so was going to monitor temps as we head North. But want to be ready in case the need arises. I am not happy that despite the insulation the spread is only 10 degrees, so don’t want to be caught flat footed

The SOK batteries that I am seeing have low temperature protection so In theory they will continue to work with no trouble at 15 degrees the just won’t take charge. So regardless you shouldn’t be able to damage the batteries.

 

[JeffreyD]

The SOK batteries that I am seeing have low temperature protection so In theory they will continue to work with no trouble at 15 degrees the just won’t take charge. So regardless you shouldn’t be able to damage the batteries.

Yes, I am not very worried about discharge, just being able to charge when we are boondocking. If below 32 the battery management will not allow charge (whether solar or genset) while we are boondocking. While I will have gas furnaces on, they heat the wet bay directly but on the cargo bays indirectly (leaks in the wall dividing wet bay and cargo bay. The battery compartment is forward of that, so it gets residual heat through the top (as radiant from the floor under the drivers seat) and from the cargo bay (radiant through the wall between the cargo and battery bay). These two I left un-insulated hoping to take advantage of the residual heated spaces. The still is only going to be effective to a point, so either I start the genny in the a.m. and plug in my space heater, or I have an alternative somewhat more automated system (heat pads), so those are the debates going on in my feeble mind. Thanks again.

 

[Bobert]

Yes, I am not very worried about discharge, just being able to charge when we are boondocking. If below 32 the battery management will not allow charge (whether solar or genset) while we are boondocking. While I will have gas furnaces on, they heat the wet bay directly but on the cargo bays indirectly (leaks in the wall dividing wet bay and cargo bay. The battery compartment is forward of that, so it gets residual heat through the top (as radiant from the floor under the drivers seat) and from the cargo bay (radiant through the wall between the cargo and battery bay). These two I left un-insulated hoping to take advantage of the residual heated spaces. The still is only going to be effective to a point, so either I start the genny in the a.m. and plug in my space heater, or I have an alternative somewhat more automated system (heat pads), so those are the debates going on in my feeble mind. Thanks again.

I really doubt you will have a problem if a portion of the battery bay is surrounded by heated space as the btu output from those walls to the battery box will increase exponentially as the temperature of the box decreases. If the batteries are being used they will also emit a small amount of heat.

 

[JeffreyD]

Thanks all

 

[HRTKD]

I put my heating pads directly on the cells. I chose to NOT put them on the bottom of the battery with the thought that the weight of the battery could damage the heating pad. That may or may not be a valid concern, but it's what went into my design. I put one pad on each long side of the battery.

An off-the-shelf battery is a little more inefficient to heat since the pads won't be in direct contact with the cells.

My heating pads are self adhesive. That sounds like a bad thing for the couple reasons. First, I'm not sure how easily the pad could be transferred to a new set of cells, if at all. Given that I expect my cells to last at least eight years, I'll cross that bridge when I come to it. Second, too much heat is a bad thing. However, my pads are 12 watts each. I get low and slow heat that gives the cells enough time to spread the heat internally without ever getting too hot. Also, the pad comes with insulation on the back side that is good enough that I can't feel the heat with my hand when the pad is active. On the plus side, I didn't have to figure out a way to hold the pads against the cells.

 

[JeffreyD]

I put my heating pads directly on the cells. I chose to NOT put them on the bottom of the battery with the thought that the weight of the battery could damage the heating pad. That may or may not be a valid concern, but it's what went into my design. I put one pad on each long side of the battery.

An off-the-shelf battery is a little more inefficient to heat since the pads won't be in direct contact with the cells.

My heating pads are self adhesive. That sounds like a bad thing for the couple reasons. First, I'm not sure how easily the pad could be transferred to a new set of cells, if at all. Given that I expect my cells to last at least eight years, I'll cross that bridge when I come to it. Second, too much heat is a bad thing. However, my pads are 12 watts each. I get low and slow heat that gives the cells enough time to spread the heat internally without ever getting too hot. Also, the pad comes with insulation on the back side that is good enough that I can't feel the heat with my hand when the pad is active. On the plus side, I didn't have to figure out a way to hold the pads against the cells.

May I ask which pads you used.

 

[HRTKD]

I bought them from Ultra Heat through Annod Industries. They were custom made to my dimensions. I have full coverage of each long side of the batteries.

It wasn't cheap. I don't think I would call these tank heaters, though that's where the technology started from. Mine do not have thermostats in them. I use an external thermostat that is programmable for start and end temperatures.

 

[Neon]

I bought them from Ultra Heat through Annod Industries. They were custom made to my dimensions. I have full coverage of each long side of the batteries.

It wasn't cheap. I don't think I would call these tank heaters, though that's where the technology started from. Mine do not have thermostats in them. I use an external thermostat that is programmable for start and end temperatures.

I am wondering if your batteries have a metal or plastic casing? The pads I purchased says to apply to non-conductive surfaces. My SOK batteries have metal cases.