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24v heating pads on 4s battery packs?

ericfx1984

ericfx1984

Solar Enthusiast
Joined
Oct 10, 2021
Messages
784
A While back I bought a whole bunch of 24 volt battery packs off the battery hookup for super cheap

I have a pretty large 4S battery bank and it's pretty cold right now

I did go ahead and test by hooking up to a car battery... And the results are that the heating pad draws about 3.6 to 3.8 amps. He gets really hot... So much so that you don't want to keep your fingers touching it for two terribly long... It looks like overall that's about 50 watts...

Is there any potential issue that you can think of with running a 24 volt heating element on a 12 volt power source?
 
Partimewages said:
If it's just resistance heat then you get 25 watts. That might still be to much. Two in series would cut it down more.
Click to expand...
Okay it looks like we get about 2.65 amps with a pair of them in series... They don't put out nearly as much heat but that's about 35 or so watts
 
Also the heating element in bare air will warm up much faster than if it were directly contacting cold cells.

Is there a thermostat built into the element or are you relying on the BMS or other external control mechanism.
 
The seller suggests a pair of them in series of you run them at 48v

So why would I run them in series at 12v if they are designed for 24v?

Is it a current issue or a heat issue?
 
740GLE said:
Also the heating element in bare air will warm up much faster than if it were directly contacting cold cells.

Is there a thermostat built into the element or are you relying on the BMS or other external control mechanism.
Click to expand...
I don't this the tstat is built it... They never seem to shut down
 
740GLE said:
Maybe that’s why battery hook up was selling them ?
Click to expand...
Actually just talked to the manufacturer... They say that it does have a high temperature shut off switch built in

He also made sure to mention that it's pretty important to have this properly adhered to the battery otherwise the heat transfer will not be enough and it could potentially burn the unit out... Though he says typically they don't build these with high temperature shut off switches, that's somewhat of a unique addition... And he says that should help to keep it protected
 
ericfx1984 said:
Actually just talked to the manufacturer... They say that it does have a high temperature shut off switch built in

He also made sure to mention that it's pretty important to have this properly adhered to the battery otherwise the heat transfer will not be enough and it could potentially burn the unit out... Though he says typically they don't build these with high temperature shut off switches, that's somewhat of a unique addition... And he says that should help to keep it protected
Click to expand...
??

I really worry about my batteries in this last cold snap, -14F. I went out and checked on them from time to time, and while not "warm" they are not freezing, so I think that is good.

Well insulated to keep the heat in I think goes a real long way.

Personally I would want to make sure they have a high temp cutoff.
 
Heat should be mild running at half voltage. Two in series is even less.
I run my small 12v heat pads as two in series for less heat. Works perfect. I use a temperature controlled relay to keep the battery 40 to 44 degrees.

Get them connected and monitor temperature every 20 minutes until the effect is known.
 
ericfx1984 said:
Actually just talked to the manufacturer... They say that it does have a high temperature shut off switch built in

He also made sure to mention that it's pretty important to have this properly adhered to the battery otherwise the heat transfer will not be enough and it could potentially burn the unit out... Though he says typically they don't build these with high temperature shut off switches, that's somewhat of a unique addition... And he says that should help to keep it protected
Click to expand...

Are these the heating pads? What temperature did the manufacturer say high temp shutoff is activated? Did they suggest how to adhere them to the batteries? Any other info they provided? I’m new here, and also toying with these.
 
yoopNreb said:

Are these the heating pads? What temperature did the manufacturer say high temp shutoff is activated? Did they suggest how to adhere them to the batteries? Any other info they provided? I’m new here, and also toying with these.
Click to expand...

I will have to look at home to see what mine are, but those are not it.

IIRC mine shutoff at 40-something. I know just yesterday I put my hand on the pads and they are cool to the touch. It was mid 70's yesterday. This morning it is 20F so I bet they kicked on again.

Stupid weather.
 
fpgt72 said:
I will have to look at home to see what mine are, but those are not it.

IIRC mine shutoff at 40-something. I know just yesterday I put my hand on the pads and they are cool to the touch. It was mid 70's yesterday. This morning it is 20F so I bet they kicked on again.

Stupid weather.
Click to expand...
Did you ever find out what your heating pads were?

I am building some 24V batteries for my RV and need some 24V heating pads for when it is in storage. My JK BMS has a heating pad relay that turns on when the low temp cutoff is tripped.

@ericfx1984 or @time2roll which ones are you using?
 
I used a silicone beehive heater (aliexpress) and separate digital thermostat. On 40F, off 45F.
The heaters are 12v and used pairs in series for 1/4 the heat. Works fine well below freezing with my 12v battery.
Used automotive high temp silicone adhesive to attach to the edge of the cell. Each cell has its own heat pad.

I would not want to wait for the low temp to trip before applying heat.

Something like this: https://www.aliexpress.us/item/3256805734623930.html?

Thermostat: https://www.mpja.com/Digital-Temperature-Controller-FAHRENHEIT/productinfo/32764+MP/
 
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time2roll said:
I used a silicone beehive heater (aliexpress) and separate digital thermostat. On 40F, off 45F.
The heaters are 12v and used pairs in series for 1/4 the heat. Works fine well below freezing with my 12v battery.
Used automotive high temp silicone adhesive to attach to the edge of the cell. Each cell has its own heat pad.

I would not want to wait for the low temp to trip before applying heat.

Something like this: https://www.aliexpress.us/item/3256805734623930.html?

Thermostat: https://www.mpja.com/Digital-Temperature-Controller-FAHRENHEIT/productinfo/32764+MP/
Click to expand...
Thanks.

So to make sure I have this correctly. If I wire two 12V heating pads in series off my JK BMS heating port on 24V batteries, that should work. Doing this will supply each pad 12V (nominal) and the 1/4 of the heat is per pad not total. Correct?

Also I was thinking of attaching the heating pads to an aluminum plate to more evenly disperse the heat and then separate the aluminum plate from the cells with either a thin layer of high temperature silicone, a very thing cutting board material, or even making a layer of Kapton tape on the cell side of the aluminum plate. Then I was going to use kapton tape to hold the aluminum plate tight to the cells inside the battery case.

I know the JK BMS heat port is only active when the low temperature cut off is triggered, but this application is for protecting the cells when the RV is in being stored for the winter.

Does that sound okay?

Edit: I believe the JK BMS can handle a maximum of 3A and 75W when directly connected to the heating pads.
 
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I also use the 12v heating pads, 12W each, wired in series to reduce the heat. I do not affix the pads directly to the cells for fear of creating hot spots on the cells. If i were to consider using an aluminum plate to help disperse the heat, I would first run a few tests to see how much dispersion actually takes place for a given plate thickness.

Two pads wired in parallel heated to 170 degrees F, vs. two pads wired in series heated to 95 degrees F; measured at the pads.
 
SoggyShoes said:
Thanks.

So to make sure I have this correctly. If I wire two 12V heating pads in series off my JK BMS heating port on 24V batteries, that should work. Doing this will supply each pad 12V (nominal) and the 1/4 of the heat is per pad not total. Correct?

Also I was thinking of attaching the heating pads to an aluminum plate to more evenly disperse the heat and then separate the aluminum plate from the cells with either a thin layer of high temperature silicone, a very thing cutting board material, or even making a layer of Kapton tape on the cell side of the aluminum plate. Then I was going to use kapton tape to hold the aluminum plate tight to the cells inside the battery case.

I know the JK BMS heat port is only active when the low temperature cut off is triggered, but this application is for protecting the cells when the RV is in being stored for the winter.

Does that sound okay?

Edit: I believe the JK BMS can handle a maximum of 3A and 75W when directly connected to the heating pads.
Click to expand...
No. Two 12v pads in series on a 24v supply will be at 100% rating. Need 3 or 4+ in series to cut the rating.

Although if going through the heat plate it might be OK to be at full rating.

May need a relay if the pads are going 3+ amps.
 
time2roll said:
No. Two 12v pads in series on a 24v supply will be at 100% rating. Need 3 or 4+ in series to cut the rating.

Although if going through the heat plate it might be OK to be at full rating.

May need a relay if the pads are going 3+ amps.
Click to expand...
Thanks.
It looks like I will have to experiment a bit. I wouldn't think that I would want anything in the battery box getting over 100°F.

The 3A is the output from the BMS port. With a 24V BMS 72W makes sense as (24V)(3A)=72W. So then does that mean as long as I keep the sum of the all the heating pads to under 72W, that will work? Like four 12V heating pads that are 15W each?
 
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