Temp sensor placement

[sunrise]

The 304ah cells and BMS both arrived so I will start to assemble my 2nd LiFePo4 battery soon. One question - where should I place the temp sensor? After watching Will's battery review videos seems making them in direct contact with the cells is not recommended? One year ago I built a 105ah battery, I taped the sensor 'tip' onto the top of the cell. Not sure if that's the right way.

BTW the BMS comes with 2 temp sensors(not including the built-in one) so from the BT app it shows 3 sensor readings.

Thanks in advance!

 

[curiouscarbon]

I'm a fan of gaffer or kapton/polyimide tape the sensor somewhere on the cell that it won't be crushed.

When I go real crazy, adding a little pad of adhesive backed neoprene afterwards to isolate it from the air.

Have got 302Ah cell and plan to place a temperature sensor between the vent and terminal.

hope this helps, and good luck on your projects!

 

[sunrise]

I'm a fan of gaffer or kapton/polyimide tape the sensor somewhere on the cell that it won't be crushed.

When I go real crazy, adding a little pad of adhesive backed neoprene afterwards to isolate it from the air.

Have got 302Ah cell and plan to place a temperature sensor between the vent and terminal.

hope this helps, and good luck on your projects!

Thanks, Kapton tape the sensor between vent and terminal was exactly what I did for my first build a year ago, somehow I am under impression that's not the right way, might when Will mention this in his review video, he meant put sensor between cells was bad idea, as they could be crushed or dent the shell.

 

[curiouscarbon]

sensor between cells was bad idea, as they could be crushed or dent the shell.

without proper precautions, yes! the small bead could easily dent the soft thin aluminum cell case. either during assembly or during normal 0.5mm per cell flex over charge discharge cycle.

if the task is to place a single sensor to best observe the entire pack cell material temperature accurately

making a simple sandwich of three spacers. all three same width/height as cell. center one has a cutout to place NTC thermristor at center.

ensuring that the center spacer is as thick as the NTC thermristor. this is to mitigate the crush issue.



there are pros and cons to this approach. i have not done it before. it would be the center of thermal mass, though and no crush hazard

maybe put silicone to seal the cable in or something.

not sure what material i would use. maybe stainless steel and have the center one laser cut. don't have the tools on hand to machine it myself.

just kinda some more temperature sensing random thoughts.

 

[curiouscarbon]

the terminals conduct heat from the inside of the cell pretty well from what i gather reading other people’s experiences

to protect most aggressively against damage to cells from too high temperature, i would place on top of cell center of pack somewhere. that would be close to terminal, perhaps biggest source of heat outside of cell.

to protect most aggressively against damage to cell from charging at too low temperature, i would place on either of the two uncompressed sides or bottom and be careful to not crush the NTC thermristor. also near center of pack.

 

[HRTKD]

I put my BMS temperature sensor on the crack between two cells and then taped the sensor down and placed some insulation over the top of it. So far, zero issues. The BMS sensor and the sensor for the BMV-712 mounted on the end cell terminal, show the same temperature, within the margin of error. I haven't checked the temperatures with the batteries under a heavy load.

 

[John Frum]

I put one sensor in free air to get ambient room temperature.
I put the other on the narrow side of the cell at the back, where it would be protected and air circulation would be lowest.
I want to see the temperature of the cell and the differential with the ambient temperature.

 

[HRTKD]

I put one sensor in free air to get ambient room temperature.
I put the other on the narrow side of the cell at the back, where it would be protected and air circulation would be lowest.
I want to see the temperature of the cell and the differential with the ambient temperature.

Ambient temperature would be handy have. My furnace duct runs through the compartment where all my components and batteries are. It would be good to know how much the compartment heats up just from the furnace duct. I know it's significant, I just don't know how much.

 

[shadowsteve]

My 4s cells are arranged as:

===|===
===|===

where === is a cell and | is the 1/4" allthread. I tucked the sensor down in the gap between the cell blocks and above the allthread. Right now it shows 8.1C

 

[HRTKD]

I have battery warmers on my cells, so I wanted the temperature sensor in direct contact with the cell. How much difference would there be between direct and possibly indirect contact? Beats me.

I'm also in a mobile environment, so having everything secured down is a good thing.

 

[John Frum]

2021-10-26 11:21:30 Low=3.313V Average=3.314V High=3.316V Delta=0.003V Balance=00000000 Cell=24.9C Ambient=24.1C SOC=84.3AH Rate=-9.3A float 04:31:04