Winter Heat For Battery Bank
- Thread starter LanduytG
- Start date
Subsequent to my purchase of my warmer components, I had the idea of leaving my inverter on all the time. It puts off enough heat that if I sealed up the compartment, it just might keep it warm enough in there to keep the batteries happy.
You or someone else posted the suggestion to use the reptile heater. As I recall, I looked into that and didn't like it. I'm not sure why. It might have been that the reptile heater used a higher temperature than I was comfortable with. Or, the amperage draw was too high.
You or someone else posted the suggestion to use the reptile heater. As I recall, I looked into that and didn't like it. I'm not sure why. It might have been that the reptile heater used a higher temperature than I was comfortable with. Or, the amperage draw was too high.
Sipma02
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Assuming the reptile heater uses a resistive heating element, I think that could effectively be used with 12v as well as 120v? I could definitely be mistaken on that. You could also use a 3D printer heater control/thermostat to control the heat. I used this: https://www.amazon.com/gp/product/B01LVXEU3M/ref=ppx_yo_dt_b_asin_title_o06_s01?ie=UTF8&psc=1
It basically just turns the relay (and therefore heating pad) on and off on whatever cycle you specify. I have mine set to 10 sec on, 15 sec off. You can set it to whatever delay cycle you want—and therefore regulate heat output.
It basically just turns the relay (and therefore heating pad) on and off on whatever cycle you specify. I have mine set to 10 sec on, 15 sec off. You can set it to whatever delay cycle you want—and therefore regulate heat output.
The big question I have is how to measure the temperature. Warming pads on the side of the battery will warm the internals of the battery much more than the ambient air. At least that's my theory. A temperature probe that simply measures ambient temperature isn't really reading what the battery is at. If the probe isn't sitting right on top of the battery then the readings are almost useless.
An uninsulated battery would be even worse because the top of the battery could have air movement over it.
A temperature probe that is stuck between the two center cells would be ideal, in my opinion. The probe for my Victron BMV-712 is attached to a cell post. The probe for the BMS is taped to the top of the battery bank. It's going to be interesting to see what temperatures these probes report.
An uninsulated battery would be even worse because the top of the battery could have air movement over it.
A temperature probe that is stuck between the two center cells would be ideal, in my opinion. The probe for my Victron BMV-712 is attached to a cell post. The probe for the BMS is taped to the top of the battery bank. It's going to be interesting to see what temperatures these probes report.
Sipma02
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Keep us updated. I'm interested in the results.
Samsonite801
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In my opinion, the temperature measurement is relative to some extent, proper calibration of the thermo-switch on/off points is more relevant, syncing the set-points so they are relational to the actual battery temperature at the locations of the coolest points on the bank.
Are the temperature set-points for on-off, user adjustable? When calibrating, you may have to take temperature samples at various points around the bank to make sure you're never getting too close to the minimum desired temperature at any location on the bank prior to the heat kicking on, to make sure the kick-on point allows for the time it takes from heat-on engagement, to recover the temperature readings throughout the entire bank. I would consider placing the temp probe against one of the batteries farthest away from the heat source, and put on several layers of tape or insulating material to cover it against the battery case, it might allow for it to read-inwards more accurately.
In any closed-loop feedback system, it's important to keep all parts of the circle involved in the feedback loop for best results of it actually being accurate. If the temperature probe is too close to the heat source, it will only be feeding back a smaller area in the circle and ignoring the rest of the mass it is intended to include in the feedback. Since the heat spreads away from the heat source to the farthest reaches (and cooling temperature penetrates from the outside-inward), then you would want to sample the temperature at the farthest reaches, which will mean it will take longer for the off cycle to occur (and on cycle would be more accurate), as it takes more time for the heat to reach the edges (and less time for the cooler temp to reach the sensor and trigger on cycle).
Also, if you don't set the low limit to too close to the critical operating threshold, you may use more energy, but also have more wiggle-room for potential error, and as time goes on, you can dial it in closer to the critical threshold to improve electrical efficiency.
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Mostly repeating post #2. May not work for everybody due to size, but automatic on/off built in:
All good points! Many of which I have thought about but haven't written down until now. The temperature controller in the warming pad kit is not adjustable. That right there may push me to go with a separate controller. But I'm going to wait and see how this plays out.
My Victron solar charge controllers (through the Victron BMV-712) as well as the BMS can decide if the battery temperature is OK for charging. I'll set this value a bit higher than the threshold for the warming pad controller. The warming pad controller is on at 35° F and off at 45° F. If I set the solar charge controllers and the BMS to only charge at say 40° F, that should give the warming pads time to get heat throughout the battery.
I'm throwing out 40° F as an arbitrary number at this point. I haven't given it too much thought. If I set it too high (like 45° F), it's possible that the battery post that the BMV-712 is using would never get to 45° F.
The warming pad controller provides no indication that it's working (not that I would see it with the insulation on top of everything, but still). The geek in me doesn't like that, but I'll get the ammeter connected downstream of the warming pad controller to see how many amps are being pulled. That should be a good enough indicator.
Ultra Heat produces RV tank heaters just like that. They steered me away from that type, recommending an independent thermostat instead.
I really didn't want to adhere the warming pad directly to my battery. Then I thought about what circumstances would prompt me to disassemble the cells from the battery. The cells are well balanced and functioning great. I figured it would be 10 years before I pulled that battery out. A replacement set of pads after 10 years is no big deal.
Samsonite801
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The great news is you have the Victron BMV solution which has the final say, so not as critical about how well the heat pad works (or even if it's working), maybe the Victron has the ability to push notification or email you if/when it stops charging, to let you know so you can always know all is well or not (before batteries could ever discharge very much)...
I did purchase a Victron remote temp BT sensor setup to use on mine, but have no idea yet how it looks to the user (in regards to notification settings) since my system isn't deployed yet (getting there soon)...
As far as the battery post temp probe, maybe you could put some non-electrically-conductive insulation or covering around and over the post/sensor to kind of seal it in towards the battery (if you thought the temp reading might be a little too ambient from the compartment).. Honestly though, it looks like your compartment is fairly small and not really susceptible to winds or drafts, so the reading from there seems like it should be ok to probe there. I suppose the bottom of the box could be slightly cooler than the top of box, but if insulated well it shouldn't really matter...
I might recommend to take some time this winter to establish some baselines about how the actual temperatures may vary in different parts of the battery/compartment using a handheld IR thermometer, and compare the various values to the Victron temperature reading, so in your mind you know at what reported temperatures relate to temperatures at different points inside the compartment, or on different cells, both close to the probe and far away from it.
Samsonite801
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My plan is to do what I read from another thread here, where you get like a 1/4" thick aluminum plate that is the L x W dimension of all the cell's footprint, set all the batteries on top of that, and stick the heat pad onto the bottom of the plate. Of course some spacers to hold the plate up a bit since the heat pad is stuck up underneath it. But the idea is, the plate allows the heat to distribute out evenly, but also the particular heat pad I chose, some had said it can get very hot and could melt the cell plastic case or something, so the heat pad in my case is 150w, 4"x4" in size, while the aluminum plate is much larger. I guess we'll see how it works, none of this has been assembled yet, but I have all the parts, it is all theoretical that this will work for me at this point, hehe...
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My Victron component's only access to the Internet is through my phone. So no notifications there.
The warming pad controller sits about 5" from the post where the BMV-712 temperature probe is attached. Both will be within the insulated "zone" of the top of the battery. I'm expecting very little difference between the two.
I specifically chose to put pads on the sides because the compartment the batteries are in limited the height. I subsequently took the floor paneling off the closet that the compartment is under and raised the height of the compartment by 3/4". The 2" foam insulation (on top of the batteries) blew that restriction, so now I need to go back and raise the floor of the closet again. Had I known that the height of the compartment was going to change, I might have used a single warming pad that wrapped both sides and the bottom.
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