Custom battery box design

[vtx1029]

Started working on a design for a custom battery box to fit my needs. The goal will be to 3d print the final parts. I will be using it in a mobile application and being it can get very cold where I'm at I plan to have both active cooling and heating of the battery. I don't have my cells yet so i won't be printing anything until all parts are obtained including my BMS. My design isn't locked in stone by any means and I'm sure will change several ways before its actually built.

Currently working on the lower half being that it will be pretty simple compared to the top of the box.

Air will be blown around the sides and at least part of the top or bottom. Fan and Heater will be thermostatically controlled (green boxes)

 

[johntaves]

Started working on a design for a custom battery box to fit my needs. The goal will be to 3d print the final parts. I will be using it in a mobile application and being it can get very cold where I'm at I plan to have both active cooling and heating of the battery.

The cells will not need any heating or cooling unless you are drawing or charging with a high amperage (like an active tesla car). They will need heating or cooling when the ambient is hot or cold, but in that case the fans will be rather useless.

 

[vtx1029]

The cells will not need any heating or cooling unless you are drawing or charging with a high amperage (like an active tesla car). They will need heating or cooling when the ambient is hot or cold, but in that case the fans will be rather useless.

I'm aware. I probably would not use cooling very much at all, Heating on the other hand I could see using much more. I'm out when its below zero often and want to charge at sub zero temps so that's the reason for it. Will it work, maybe maybe not. In the grand scheme of things its not very expensive so why not.

 

[Deleted member 4428]

Maybe design heat/cool channels into the floor and/or side walls of the battery box and tap into the engine coolant.

 

[Heap64]

I would be interested in seeing a cross section to get a better picture of your airflow.

 

[Heap64]

Maybe design heat/cool channels into the floor and/or side walls of the battery box and tap into the engine coolant.

Similar to Chevy Volt ?

 

[Deleted member 4428]

I keep seeing in my minds eye a exo-skeleton that capturers the cells by the corners only, not the top and bottom. Like a CD rack where the cells slide in.

 

[vtx1029]

I would be interested in seeing a cross section to get a better picture of your airflow.

kinda hard to tell right now but flow will be like this

Maybe design heat/cool channels into the floor and/or side walls of the battery box and tap into the engine coolant.

My use is in a trailer so no coolant to use.

 

[johntaves]

Maybe design heat/cool channels into the floor and/or side walls of the battery box and tap into the engine coolant.

180 degree F engine coolant? I think not.

Use glycol (or whatever is used in engine coolant) as the transmission medium of the heat? Sure, but how is that heat added or pumped away?

 

[johntaves]

I'm aware. I probably would not use cooling very much at all, Heating on the other hand I could see using much more. I'm out when its below zero often and want to charge at sub zero temps so that's the reason for it. Will it work, maybe maybe not. In the grand scheme of things its not very expensive so why not.

OK, but that still begs the question of what that heat source is. Fans are nice, but not a heat source. If I used a X watt electric heater that was designed as a fan, then OK, we need to blow that through the batteries. On the other hand, why not use an electric blanket and stick it on the bottom of an insulated box that has the batteries in it? That way we don't waste energy blowing air around.

But, I rather hoped to hear that since you are doing a 3-d print, you would have some heating elements in mind and a way to position them between the batteries and measure the temp and regulate that heater.

 

[Deleted member 4428]

180 degree F engine coolant? I think not.

Use glycol (or whatever is used in engine coolant) as the transmission medium of the heat? Sure, but how is that heat added or pumped away?

It wouldn't be 180F by the time the coolant got to the cells. But, OP said no coolant so I don,t want to go off topic.

Edit: But you are spot on about the source of heat.

 

[vtx1029]

OK, but that still begs the question of what that heat source is. Fans are nice, but not a heat source. If I used a X watt electric heater that was designed as a fan, then OK, we need to blow that through the batteries. On the other hand, why not use an electric blanket and stick it on the bottom of an insulated box that has the batteries in it? That way we don't waste energy blowing air around.

But, I rather hoped to hear that since you are doing a 3-d print, you would have some heating elements in mind and a way to position them between the batteries and measure the temp and regulate that heater.

Yes heater elements are in my plan using heat sinks that the fan blows over that are temp controlled. A sealed box with a heater on the bottom would be much more effective but you run into having to use much more complicated and expensive controls and run the risk of overheating them (most of the heaters I'm looking at are thin film heaters that a capable of 150*c) . And you have to get more complicated in your cooling process if you seal the box.

 

[vtx1029]

Redesigned how I was going to do the heating. Went with more of a modular approach. Heater assy will now bolt onto the side. You can see it here transparent. The two green control boards will be temp controllers. One will be the main heat and fan controller, the other will be an overtemp fail safe controller.



Also did some work on the top case half, still in progress...

 

[johntaves]

I don't see the point of fans. Why not put the batteries in a very well insulated box, with a heating blanket at the bottom and a temp regulator? The fans seem like a waste of power.

Unless you are going to draw a lot of amps (high C), then these batteries will not generate any heat. Thus the only worry is the cold, and when it is cold, solar is usually at a premium so energy wasted on a fan is not good. Its cold, so insulation is key, and a fan represents a hole in that insulation. In addition, if they get below freezing, you have to know the internal temperature of the cells, not the temp of the air blowing past them.

If the concern is ambient heat, for example, you live in some place that is freaking hot, and does not cool in the night, then you need a heat pump. If it does cool in the night then a well insulated box will ensure that the batteries experience the average temp between day and night.

 

[vtx1029]

I don't see the point of fans. Why not put the batteries in a very well insulated box, with a heating blanket at the bottom and a temp regulator? The fans seem like a waste of power.

Unless you are going to draw a lot of amps (high C), then these batteries will not generate any heat. Thus the only worry is the cold, and when it is cold, solar is usually at a premium so energy wasted on a fan is not good. Its cold, so insulation is key, and a fan represents a hole in that insulation. In addition, if they get below freezing, you have to know the internal temperature of the cells, not the temp of the air blowing past them.

If the concern is ambient heat, for example, you live in some place that is freaking hot, and does not cool in the night, then you need a heat pump. If it does cool in the night then a well insulated box will ensure that the batteries experience the average temp between day and night.

Yes you are correct the most efficient way to heat the cells would be in an insulated box with a heater surrounding them. Going with that approach means a total redesign of my design, and the box will exceed my 3d printers envelope. The goals of this battery box is for me to be able to build it myself (especially now with $ lost due to covid), Secure and hold the battery in a mobile environment. And fit my needs.

I'm not worried about cooling the cells, I won't ever pull over 1C so I will only be heating.
I do not have solar right now, and when its cold here there's minimal sunlight (around 3 hours of peak sunlight)

There is only one fan, its there to blow over the heat sinks to warm the air, then blow around the cells to warm them. The fan draws 1.2 watts, the heaters themselves will draw 7w each x2 so a total of 15.2 watts. So Pretty minimal power to operate. I will pull off the grid most of the time and only the battery when I'm traveling.

 

[Engineer34]

Hey there can you update what you did ?
I am also planning a few sealed battery with a heated pad in the bottom. Planning to use Ceremic wool around the battery.

I hope ceramic will help pad to heat cells at more distributed temperature below freezing. But also if the batteries will have fire , thermal runway ceramic will protect the house.

I have a question ;when pad heat the cells above 0 degree celcius and stopped. BMS will start charging it with normal rate. But in a few minutes ambient temperature will again try to freeze cells. But cells started charging so it is heating itself and will never need external heating again till next charging day will begin.

Hope i am clear what i am asking about. By the way i will only use good quality Lifepo4 and yes i will never use 18650 Lion anymore.

 

[Haugen]

Have you considered using TECs?
A Thermoelectric Cooler works both ways. Depending upon which polarity you apply the power, it will transfer heat either direction. You'll need more heat sink though.
You could probably use the TEC and run your fan across the heat sink to distribute it to the cells.
I would design to thermally bond one to each of your cells and use a heat sink (or your trailer frame) to transfer heat to/from

 

[Haugen]

Here's a very reasonable one.

Thermoelectric Cooling Module, 127 couple, 12VDC

127 couple, edge sealed Peltier cooling modules optimized for 12VDC. ~90 BTU heat pumping possible. 6A max, 16V max, Draws 4.4A@ 12VDC. 10in. Leads.

www.mpja.com

 

[Engineer34]

I heard Peltier element is good for heating but not for cooling.
They are not efficient or not reliable in long term. What do you know ?

 

[Haugen]

I know that we used them in ruggedized military applications to maintain the temperatures of electronics built to operate at extreme temperatures
I know that most ice-free coolers on the market use them to cool and heat.
I know that I built a system for an amateur jeweler that will draw the heat out of a ring to prevent the stones from being damaged while heating the shank to the melting point of silver.
I also know that they are a simple heat transfer device. They always move the heat from one side to the other. Efficiency is the same both directions. The effectiveness depends heavily on the design. The thermal mass needs to be calculated and the right amount of energy transfer has to be done.
The great thing about this application is that it will be that its only really needed to bring the temperature above freezing.