LiFePO4 heating pad for cold temperatures

Short_Shot

Photon Sorcerer
View attachment 68459For a temperature controller I think an “inside the battery box” is a better way to go than an external controller, and it’s simpler. I used the following controller to turn the heater pads on and off…if I recall correctly they are about $5 a unit.

HiLetgo W1209, 12V DC Digital Temperature Controller Board Micro Digital Thermostat -50-110°C Electronic Temperature Temp Control Module Switch with 10A One-Channel Relay and Waterproof​

That's pretty much exactly what I'm using too. Just a different vendor that includes an acrylic case for an extra 2 bucks.


So back to the point, I'm really going to have to find a way to log the battery Temp in an appropriate location this winter. Heat it up to operating temp of 75F then turn off the heat and see how long before the bms cuts off.

My initial plan was to simply run the heats off the tow vehicle and hope the average consumption is low enough to get by for 24 hours, including running my diesel heater.

Now I'm thinking I might be able to tap some of the heat from said heater and pipe it to that side of the tongue box. It'll be much less efficient on fuel but use way less power.

I could probably blow the hot air right into the lid of the box. Bonus points if I can figure out a way to regulate it.
 

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Short_Shot

Photon Sorcerer
Anyone by chance know if those cheap controllers retain settings after power off?

I can try it myself later but am curious now while standing here watching it get warm.

Decided to put my switch in and turns out, at least for a few minutes, it did retain settings.
 
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Horsefly

Solar Addict
So back to the point, I'm really going to have to find a way to log the battery Temp in an appropriate location this winter. Heat it up to operating temp of 75F then turn off the heat and see how long before the bms cuts off.
Since my battery box and heating system will mostly be unattended while it is doing its job, I'll be testing it through this winter here at my home in Denver. I bought three loggers.

Two temperature loggers. I'll put one at the bottom of the box, near the aluminum heat sink, and one resting on top of the cells.

Here's the first one. I've not used this first one before, but it seems like it should do.
https://www.amazon.com/gp/product/B01MY9A0G1

Here's the second one. I've used this type before to log the temperature at our cabin through the winter.
https://www.amazon.com/gp/product/B082WV43HH

Then I have a voltage logger that will simply log the times the heating pads are on and off. I've also used one of these before.
https://www.amazon.com/gp/product/B003DS0BS2

Hopefully I'll be able to get all three datasets sync'd up time-wise, and then I'll put it into a spreadsheet and a scatterplot, It should let me see how the top and bottom of the cells differ as the heating pads are on, and how often they are on.
 

TowerCamp

New Member
I've been using Elitech data loggers for some time. I recommend spending a bit more on the Elitech loggers with PDF function. They create a PDF of dates, times and temps without the use of their clumsy software.
 

Short_Shot

Photon Sorcerer
So. It's about 7.5C tonight and I'm out here with these heater pads cranking away at full power.

60w going into the bottom of the cells and the temperature at the very bottom next to the pads is rising extremely slowly.

This suggests the heat is being transferred into/ through the cells very well.

Pads read 24C and the midpoint sensor for the bms shows 15.5C.

Top of cell shows 12C ish looking through a hole in the lid to the black plastic top of the cell.

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Screenshot_20211017-034810_xiaoxiang.jpg

Dropped the setpoint of the heater and it only overran 0.1C and started dropping within a second or two so the response time is very rapid and I won't have to worry about excessively long on-off cycles.
 

Horsefly

Solar Addict
I've been using Elitech data loggers for some time. I recommend spending a bit more on the Elitech loggers with PDF function. They create a PDF of dates, times and temps without the use of their clumsy software.
I noticed the PDF, but I want to combine the data from three different sensors so I can put them in one time plot. So I think I have to use the software. I tried it and it doesn't seem that bad.
 

Short_Shot

Photon Sorcerer
Since I can, and will use this for work I've ordered this bad boy and some type k probes.



I don't need calibration, high accuracy, or precision for what I do (for work, +/- 5F is fine) but I have needed logging for some time and the cost is low enough that I can buy it rather than having my employer pay and thus own it.

I'll use this at the pads, halfway up the cells on the opposite side of the battery, one on top of the battery, and one for ambient temp I'm thinking.

I'm thinking I can detect the pads on/off via nearby sensor, though there will be some expected latency.

My goal is to ensure bottom doesn't exceed, say, 25C while the top doesn't dip below 5C. As we discussed earlier about two thermostats I ordered an inexpensive mechanical capillary thermostat which I'll use to cut off the power to the bottom digital controller based on the top of the cell reaching, say 10C or so.

The only reason I'm cutting power to the controller instead of just interrupting the pad power is, as I mentioned before, to hopefully reduce the total on-time of the digital one since those displays and cheap components don't last forever.

I'll use the shunt to get an idea of total power used per hour at X ambient temperature and if I'm really motivated I'll repeat at a few temp ranges as it gets cooler this year.


It's also possible I'm totally wasting my time with ensuring the bottom doesn't get too hot as the cells may conduct heat quickly enough that the bottom doesn't get hot enough to worry about before the top gets up to temp.

However I also don't want a false sense of security in the the bottom might be warm but the top still too cold and then I'm damaging half the cell, though I feel that's unlikely.
 
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