Winter Heat For Battery Bank

[LanduytG]

Going to be putting 8 280ah cells at 4S2P in my semi so I can run my Espar bunk heater and Espar engine/fuel heater and will run my 7500btu a/c in the summer. I'm getting regular empty battery case to put the cells in. I've been think of ways to heat the cells for winter charging. Thought about the regular 12v silicon heat pads but they get really hot. Not sure till I get the empty case just how much room I'll have. I will insulate the aluminium battery box on the truck but just not sure if to put the heat inside the battery case the cells go into or try to heat the the aluminum battery box. Any ideas?

Greg

 

[snoobler]

8*3.2*280*.8 = 5.7kWh

That should run an A/C unit for 10-ish hours. I know, not your question, but I had to check.

These have their own thermostat and use 65W each:

Amazon.com

 

[HRTKD]

Your battery box will be located outside of the cab? No chance to put them inside the cab?

An RV tank heater seems to be a fairly safe way to go. If it doesn't get so hot that it will melt the plastic of a water tank, you would hope it would do OK against an aluminum battery. But turning on at 45° F and off at 68° F seems a bit high to me. I would rather have it come on at 35° F and off at 40° F. Or something like that.

I'm considering a similar install for my RV trailer for when it's at the storage lot. Though my batteries will be inside the trailer, they will still get exposed to temperatures below 32° F.

 

[rbreding]

I also have 8 of the 280ah batteries. My solution in our trailer was a couple of those motorcycle handle heating wraps. They are flat, use about 7w ea @12v. Size wize they would cover two cells each if you wanted to hit each cell. Control them from a 12v thermostat.

 

[HRTKD]

I happen to have two sets of motorcycle handle wraps. But they are intended for my snowblower. Maybe the snowblower will have to wait.

 

[hour]

I built a false floor in a box (ammo can lined with thin roll insulation-not reflectix) and stuck a silicone heat pad to the bottom of the floor which is made of thick aluminum sheet. A silicone baking mat sits on top of the aluminum plate and the cells on top of that.

A 3d printer heater control operates the heat pad and never exceeds 50w draw, I guess kind of like dimming a light bulb. It can get scary hot if you don't do this. I made the mistake of plugging in the control pin to the wrong spot on my microcontroller and smelled... hot hot hot... 30 seconds later. Glad I noticed. The floor is never allowed to exceed 90*F measured at the pad itself. This is fairly well distributed through the thick aluminum and radiates in to the rest of the box+is absorbed by the cells bottom to top. The target temperature is the average of a probe on top of the cells and one in the middle of the cells. I played around with PID control and trying to supply the perfect wattage to the pad at the right time to reach and maintain a temperature, i.e. cruising on 5w or something once it's up to temperature. I abandoned this for reasons forgotten and opted to just flip it on and off @ a static wattage.

This setup worked all of last winter with the battery in the bed of my truck and days (on end) where the high temp was barely above 0*F. It also worked when a foot of snow sat on top of my 200w of panels for days at a time. Those days I would have been better off just disabling heat since solar collection wasn't going to happen anyway. I don't try to keep my battery at its happiest temperature, I just want it above 45*F or so to satisfy my MPPT & BMS low temp cutoffs.

I also screwed around with trying to heat at say 4am so by sunrise-ish I'd be warmed up enough to accept charge. This worked but I didn't really want to push my luck. I wasn't consuming enough power to even think about, even with aforementioned low/no charge days.

I tried motorcycle grips and they burned and wrinkled almost immediately with a 12.00v power supply. I also tried a 12v heater with PC fan, looks like a computer heatsink but blows heat. May have been labeled as an incubator heater. Did not trust that at all and hard to get meaningful readings with probes at the cells/between the cells blowing hot air at them. Everything in the path of the fan became a billion degrees while the cells remained a cold block. The silicone heating pad was by far the most solid feeling product I evaluated for this use.

TL;DR heat from below with thick aluminum to disperse heat. Silicone heat pads are reliable and work fine while sipping power. Design your box to allow for something more than cardboard box-thickness insulation like I had to use. Can't wait to replicate this heating system in a much larger future off-grid project.

 

[LanduytG]

I built a false floor in a box (ammo can lined with thin roll insulation-not reflectix) and stuck a silicone heat pad to the bottom of the floor which is made of thick aluminum sheet. A silicone baking mat sits on top of the aluminum plate and the cells on top of that.

A 3d printer heater control operates the heat pad and never exceeds 50w draw, I guess kind of like dimming a light bulb. It can get scary hot if you don't do this. I made the mistake of plugging in the control pin to the wrong spot on my microcontroller and smelled... hot hot hot... 30 seconds later. Glad I noticed. The floor is never allowed to exceed 90*F measured at the pad itself. This is fairly well distributed through the thick aluminum and radiates in to the rest of the box+is absorbed by the cells bottom to top. The target temperature is the average of a probe on top of the cells and one in the middle of the cells. I played around with PID control and trying to supply the perfect wattage to the pad at the right time to reach and maintain a temperature, i.e. cruising on 5w or something once it's up to temperature. I abandoned this for reasons forgotten and opted to just flip it on and off @ a static wattage.

This setup worked all of last winter with the battery in the bed of my truck and days (on end) where the high temp was barely above 0*F. It also worked when a foot of snow sat on top of my 200w of panels for days at a time. Those days I would have been better off just disabling heat since solar collection wasn't going to happen anyway. I don't try to keep my battery at its happiest temperature, I just want it above 45*F or so to satisfy my MPPT & BMS low temp cutoffs.

I also screwed around with trying to heat at say 4am so by sunrise-ish I'd be warmed up enough to accept charge. This worked but I didn't really want to push my luck. I wasn't consuming enough power to even think about, even with aforementioned low/no charge days.

I tried motorcycle grips and they burned and wrinkled almost immediately with a 12.00v power supply. I also tried a 12v heater with PC fan, looks like a computer heatsink but blows heat. May have been labeled as an incubator heater. Did not trust that at all and hard to get meaningful readings with probes at the cells/between the cells blowing hot air at them. Everything in the path of the fan became a billion degrees while the cells remained a cold block. The silicone heating pad was by far the most solid feeling product I evaluated for this use.

TL;DR heat from below with thick aluminum to disperse heat. Silicone heat pads are reliable and work fine while sipping power. Design your box to allow for something more than cardboard box-thickness insulation like I had to use. Can't wait to replicate this heating system in a much larger future off-grid project.

Was thinking about doing something similar with false floor. I have a couple of 120 watt pads but as you stated they get scary hot. But mounted on a aluminum plate would help distribute the heat. Have already figured on insulating and I have a few options for that. But I think the pads on the aluminum plate with a temp probe on the plate to control the temp of the plate is the safest way.

Greg

 

[rbreding]

Was thinking about doing something similar with false floor. I have a couple of 120 watt pads but as you stated they get scary hot. But mounted on a aluminum plate would help distribute the heat. Have already figured on insulating and I have a few options for that. But I think the pads on the aluminum plate with a temp probe on the plate to control the temp of the plate is the safest way.

Greg

Exactly. Whatever you use it needs to be mounted to a plate to dissapate heat more evenly.

 

[LanduytG]

I think I've come up with a plan. Will use a PID controller and SSR to control this pad on a aluminum plate which will be a false bottom in the battery box. The heat pad is self stick with a thermistor sensor wire coming out but that can't be hooked up to the PID. Will use this PID and this SSR. Maybe use 2 pads for better heat distribution. Will be a lot of current to start but the once up to temp the PID will manage them nicely. I figure regulate temp to about 100 deg that should be enough even in the coldest days I see which might be 10-15 below. Of course batteries will have insulation around them to help keep the heat in.

Greg

 

[Freep]

I'm considering a similar install for my RV trailer for when it's at the storage lot. Though my batteries will be inside the trailer, they will still get exposed to temperatures below 32° F.

I'm just pulling my battery when I put the camper in storage for the winter.

 

[LanduytG]

This is for my semi so I can't do that.

Greg

 

[Freep]

This is for my semi so I can't do that.

Greg

I'm assuming you're replying to my reply to HRTKD. If you put your semi in storage for the winter you could.

I will do some winter camping and I'm planning on using an RV tank heater for my battery. They're already designed to not overheat and I'd hate to burn my rig to the ground because of a dumb mistake on my part.

 

[HRTKD]

Have you found a tank heater that fits a 4s battery? I switched from 2p4s to 4s2p and the batteries are now separated. I thought I had found a tank heater that fit the 2p4s, but of course that's not going to work for the changed configuration.

 

[Freep]

Have you found a tank heater that fits a 4s battery? I switched from 2p4s to 4s2p and the batteries are now separated. I thought I had found a tank heater that fit the 2p4s, but of course that's not going to work for the changed configuration.

You don't have to fit the battery so much as fit the compartment it's in. There are elbow heaters that are pretty small. I even contemplated using a small incandescent light in the compartment.

I have a Koi pond and for years I used a 25w bulb inside an overturned tub about the size of a litter box to keep a small hole in the ice to vent methane. So as long as you have a confined space, the heat builds pretty quickly.

 

[HRTKD]

I haven't installed an RV tank heating pad on my RV. It came with them. I thought that it was important that the pad had direct contact, otherwise the thermostat wouldn't work properly. I'll have to read up on them again.

 

[mapguy525]

Keenovo has many, many different size and type heaters in multiple voltages.
https://keenovo.store/

Briskheat has many options, too.
https://www.briskheat.com/

 

[Freep]

I haven't installed an RV tank heating pad on my RV. It came with them. I thought that it was important that the pad had direct contact, otherwise the thermostat wouldn't work properly. I'll have to read up on them again.

You might be right about contact. I haven't installed my heaters yet. They're waiting for me at home.

But as I think about "won't work properly" I'm left to wonder what exactly that means. The ambient air temperature should also be in the same temperature range as the battery. It seems to me that a small metal plate under the battery as others have mentioned is a good place to stick the tank heater.

I will definitely report back when I'm done. I want to do some winter camping this year.

 

[HRTKD]

I've watched many of the videos that Jared has posted. I haven't watched this one yet, but it might be worthwhile for this discussion.

I will say that the four pad heaters on my tanks will suck the living daylights out of a battery. I started a drive home with at least some portions of my tanks frozen. Thinking I would be OK on power since the battery was charged, solar was producing and the truck was also contributing some amps I turned on all the pad heaters. When I got home my state of charge was down to about 55%. This was on a 225 Ah battery bank (flooded lead acid).

Turning on the pad heaters was an exercise in futility. My underbelly is exposed. The black and gray tanks have zero insulation. The 120 gallon fresh water tank is well insulated, but I had perhaps 45 gallons of very cold, if not frozen, water. Add in wind from driving and there was no way those tanks were going to thaw.

A small battery that isn't exposed to the elements though, that just might work with a pad heater

 

[HRTKD]

This thread went to eight pages and there seemed to be only one participant in the thread that actually kept batteries warm in the winter:

LiFePO4 heating pad for cold temperatures

If you are trying to use a lifepo4 battery in freezing cold temperatures, battle born just released a 12v heat pad for keeping the batteries warm without melting the case. This pad should work for any standard lifepo4 battery. Just slap it under your batteries and connect it to 12v and you are...

diysolarforum.com

 

[HRTKD]

I sent an inquiry to a company that is known for their expertise in RV tank heaters. The company is Ultraheat. Here is the response they sent.

Based on your dimensions, we have a system that would work very nice, I'll put together a quote and attach it for your review. As for using RV Tank Heaters the way you described is not recommended, they are designed for direct contact of a poly holding tank, and are not designed to be an "open air" heater. It also takes a lot more energy to heat the batteries in this way, because you are heating the air to heat the battery this method is 50% less efficient right from the start. We have made battery box heaters in the past, mostly for tractor-trailer units, they do work great however they are 120VAC for overnight when the semi is stationary. Using a tank heater attached to the battery itself is also not recommended, it produces way too much heat for the cells, possible thermal run-a-way or other damage. You can always find someone that has a work-around for something, I would prefer to lesson to the experts in what they do. Both the battery manufactures and ourselves work exclusively in what we produce, our solutions are tested by both to ensure the desired outcome.​

​

Basically there are two types of heaters that have been approved by the different lithium battery manufacturers, the first and most popular by consensus is the "wrap". It places a heating element on each side of the battery, driving heat inward towards the center. The other design is called a "shelf heater", it is by far less popular by the manufactures, as it heats the bottom of the battery by having the battery sit on top where heat can rise through the bottom. The basic consensus is that heat panels on each side, produces a more even heat throughout the cells, allowing more consistency. Whereas the bottom is more heavily insulated and thicker, thus requiring more heat and larger amp draws. Both designs are controlled by an Electronic Ambient Sensor, designed to activate once temperatures drop to 35 DegF and deactivate upon rise to 45 DegF. This sensor is normally installed within the battery storage area to measure the air around the batteries themselves. One Sensor can control normally up to three battery wraps by itself of what I'm recommending for your use. If you decide to expand your battery bank beyond three, you would have to add in a 12 Volt relay to run power through to the warmers.​

​

With our heat wraps, we give a life of the battery limited replacement warranty. The Quote is for your 2 batteries and one sensor.​

The quote is attached as a PDF. Summary: 1 wrap with temp sensor, 1 wrap without sensor =$344. My opinion: it's expensive, but these guys sound like they know what they're doing and it's not some cobbled together hack of questionable capabilities. I do like the range at which their device works. I don't see a need to get to 60° F like some pad heaters do.