Air gap for heat to escape?

[Kahdeksan_minuuttia]

Would be interesting to just put the battery outside, turn on the heating function and measure energy used for a period of 8-hours, with no loads affecting the numbers.
Some 50mm polystyrene insulation would reduce the heating requirement considerably. I am working on an removable insualted box option.
I can do a more detailed test this weekend if you would like the data collection, just let me know.

I am very interested to hear the results, if you do some testing with the battery box outside in cold with energy measurements of heating energy / power. And additionally how do loads affect the need for heating.

My next step is to order some heating and cooling parts as well as fans for a "dummy" battery box to be constructed. It won't be that cold this spring anymore so the summer time tests are my focus at the moment.

Probably the heating is easier to solve than cooling especially if cooling with just fans is not enough to keep the battery temperatures at the acceptable level.

After watching some videos about terminals, busbars and connectors and possible heat produced by them it seems that the resistance over the terminals and connectors may cause lots of additional heat. So the first thing is to eliminate the need for cooling in the first place. Flir One for a phone would be nice toy, would it be useful for battery builds?

 

[OffGridForGood]

I am very interested to hear the results,

Today is a holiday, so the shop is closed and I have all day to play with solar, Bonus: it is a super sunny day, and minus 10-12c
-My Favourite for some wood processing.

... if you do some testing with the battery box outside in cold with energy measurements of heating energy / power. And additionally how do loads affect the need for heating.

I will do some playing with the LFP pack, just in it's DIY plywood box outside all day, see what we get.
I have been using the 315Ah LFP pack to run a firewood processor - we heat with firewood from the property and I like to have next winter's wood cut-split-stacked by end of April (before the bugs wake up). The processor pushes the pack to 125A current at times(in-rush), so this is a hefty load on the battery, but not sufficient to hold the cell temperatures above freezing without the heater cycling on/off in minus 10 - 15 c temps. (5 to 14 F) - This tells me the cells do not 'self-heat' sufficiently, or at least not in the plywood without better insulation, or not at the processing rate I find comfortable.

My next step is to order some heating and cooling parts as well as fans for a "dummy" battery box to be constructed. It won't be that cold this spring anymore so the summer time tests are my focus at the moment.

Probably the heating is easier to solve than cooling especially if cooling with just fans is not enough to keep the battery temperatures at the acceptable level.

I don't need cooling, but that is perhaps mostly due to what loads I run with the mobile unit each season. Not much during summer except for camping RV use or as a power source in the back of a pick-up truck.

After watching some videos about terminals, busbars and connectors and possible heat produced by them it seems that the resistance over the terminals and connectors may cause lots of additional heat. So the first thing is to eliminate the need for cooling in the first place.

I like to use oversized conductors in all the battery builds, as you say keeps things running cooler, less losses and reduce the chance of anything getting too hot. The nice thing about the digital thermostat on the battery box is it shows the internal temps of the box as well as the set point I have programed. Keep an eye on the display and know the internal temp of the box at any point during use.

I will report back tonight, which may be near your tomorrow morning, LOL.

 

[OffGridForGood]

Ok, took a few days to deal with some things, like having thirty people over and eating far too much.
I put the DIY self heating pack outside for a day - eight hours.
Temps varied from -12 to -4 then back to -10 during those 8 hours, with the peak temp of the day around five hours into the test.
The battery was just sitting on the tail gate of the truck, and it was very light wind. The truck lives in a car port area so the battery didn't have any heating effects from being in direct sun or anything else that would skew the test.
So, no load on the battery except for the heating elements. The heater control was set to +12C and the heater has 4-degree delta so cycles between 10 and 14 degrees C.
After running all day, the watt hours consumed were 156Wh
As I said earlier, the box is just plain 3/4" (19mm) Fir plywood, and an insulated box would reduce rate of heat loss.

 

[Skypower]

Well, pick up more junk to play with Lol.
Presently, I have a fan setup to blow air across the tops of two batteries that are open on top but are protected by a table top spaced over them. The fan is controlled by a smart plug that turns it on 3:30 AM and off at 10:00 AM. That’s the time that the garage is coolest to reduce the cell temperatures. It would be counterproductive to blow hot air over them just to heat them up. It’s better to just have stagnant air around them and not transfer heat into them. You can just look at the chart and see when the fan drops the temperature and how quickly. Buss bars are good at pulling the heat out of the core. The third battery is on the floor and it just being lower than the two on the shelf makes a difference so If you can you want low. I did have the fan shown mounted on the box last year to test. I blew air in on the plenum/bms end and the air went up, over the top and out the other end. I found it worked well but the cells at the far end were about 5F warmer than the ones closest to the fan. I’m thinking that it’s not as much that the air is warming as the air is becoming more laminar and not carrying heat away so I’m going to position some little turbulent walls to stir it up a bit. I had it on a battery charger and worked it manually for a few days before the cool weather came and cleared it away. Now I’ve got a 12 volt timer, 12 volt thermostat and 4 different 60 to 12 V down converters to play with. I even picked up a Peletier unit which should work good in a small confined space but given how cool it gets late at night here, I’m thinking just the fan is more efficient. The Peltier cooler draws 45 watts at 12 volts and 70 at 15. Condensation is a concern so the box would need to be well sealed to keep new air from making things worse. Not keen on wet air over my cells. I’m going to position some thermal fuses in the outlet to shut off the air incase of fire. No sense in fanning the flames