Question about laying batteries on their side for cold weather heating.

A.Justice

Swears he didn't start that fire.
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I got these Topband 25 AH LiFePo4's (metal cased) for my trailer (they are an old, undersized pack for another project). I am in the process of insulating and heating the pack for cold morning charges. The orange pad is a 15 watt silicone heating pad, and the clear box is a thermostat that is set to kick the pad on at 35 degrees, and off at 40. I will be adding a low voltage disconnect to the pad circuit as well. The pack will be insulated in non-conductive foam, and cased in Styrofoam / wood box.

Here's my question. Could the batteries be set on their side and the heating pad go underneath? The pad is a little too large to go on the bottom of the pack, but it fits almost perfectly on the side, and I think that the heat would radiate upward into the cells, especially if the thermostat is programmed to kick on BEFORE it freezes, and the sensor is far away from the pad.
 

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snoobler

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Most manufacturer's recommend prismatic cells be operated in a terminal-up position to ensure full contact between electrolyte and plates. In some cases, they permit side-operation on the SHORT side of the cells as that still allows contact with all the plates. Operation on the long side can starve some plates of electrolyte.

Personally, I would just put the pad on the bottom even if it's not a perfect fit.
 

A.Justice

Swears he didn't start that fire.
Joined
Sep 12, 2020
Messages
825
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Most manufacturer's recommend prismatic cells be operated in a terminal-up position to ensure full contact between electrolyte and plates. In some cases, they permit side-operation on the SHORT side of the cells as that still allows contact with all the plates. Operation on the long side can starve some plates of electrolyte.

Personally, I would just put the pad on the bottom even if it's not a perfect fit.
That's all I needed to hear. I'm not about risking my safety or money, and they will be going upright. I appreciate the information!
 

HRTKD

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The source of power for my warming pad system is downstream of the BMS, on the common bus bars. That way, it uses the low voltage disconnect of the BMS. If you're looking for a higher low voltage disconnect for the warming pads then you will need a secondary/dedicated low voltage disconnect.

That isn't many Ah for that pad. I have 560Ah between my two batteries and I run four pads, each rated at 1 amp. That 1 amp rating seems to be a tad bit low. Real world readings indicate it's higher than 1, but less than 2. The temperature range I use at this time is 35° F to 45° F. I'm still testing that. I'm thinking of bumping it up about 5° F to ensure that the entire cell is warm. Each battery has two pads, on the sides.
 

A.Justice

Swears he didn't start that fire.
Joined
Sep 12, 2020
Messages
825
Location
TN
If you're looking for a higher low voltage disconnect for the warming pads then you will need a secondary/dedicated low voltage disconnect.

That isn't many Ah for that pad. I have 560Ah between my two batteries and I run four pads, each rated at 1 amp. That 1 amp rating seems to be a tad bit low. Real world readings indicate it's higher than 1, but less than 2. The temperature range I use at this time is 35° F to 45° F. I'm still testing that. I'm thinking of bumping it up about 5° F to ensure that the entire cell is warm. Each battery has two pads, on the sides.
I intend to use a separate LVD to protect my batteries. I've had a LVD fail (or just not work) on a BMS before, and I'm paranoid about it happening again, so all of my systems use a secondary LVD, at least on devices that could potentially kill the battery. Everything small (lights and USB chargers) goes through the BMS.

My bench supply says that at 13.5v its pulling 1.1a. Are you saying that I should use a larger pad, or that it will be draining more than I'm aware of?
 

HRTKD

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I intend to use a separate LVD to protect my batteries. I've had a LVD fail (or just not work) on a BMS before, and I'm paranoid about it happening again, so all of my systems use a secondary LVD, at least on devices that could potentially kill the battery. Everything small (lights and USB chargers) goes through the BMS.

My bench supply says that at 13.5v its pulling 1.1a. Are you saying that I should use a larger pad, or that it will be draining more than I'm aware of?

Use two pads. One on each side.
 
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