Keeping LiFePO4 Battery Banks cool in Australia

[mcart117]

Being that my battery is in a box I have installed a mini refrigeration unit and digital thermostat. It runs off it's own dedicated 12 volt panel and battery. I only run it in the hot summer months and it does help keep the batteries cooler than ambient outside air temp. There's no chance of getting the batteries too cold being that this tiny unit isn't that powerful, plus the programable thermostat works really well. I did have to create a drain chute to get the dripping condensation out of the enclosure.

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This is the sort of solution I have been looking for and had been completely unable to find anything in that price range, so thanks for the post.

 

[octal_ip]

I have a similar problem to deal with. My batteries will be located in workshop that's exposed to pretty high temperatures. I've picked up a large aluminum toolbox that I'll line with fireproof blankets as thermal insulation and a safety measure. I'm hoping to pick up an office style water cooler with built-in refrigeration circuit that I can adapt to cool the interior of the box.
Still on the drawing board, but as my cells arrived today I'd better get to work on it soon. I'll post my experience and results.

Just an update on this - I think it's important to discuss our successes as well as failures, and this one was definitely a fail.

I bought an old office style water cooler for spare change and stripped the compressor and refrigeration loop out of it. On its own it was able to cool the 2L water reservoir down to 20°C below room temperature, even creating some ice along the liner. This didn't scale well though - I then increased the reservoir size to 20L in a large, well insulated container, and the compressor ran continuously and was only able to reduce the water temperature by about 5°C after several hours. This was with negligible external heat load, so it was pretty clear that it wouldn't be able to cool the whole battery box.
The compressor used about 60W while running and the refrigerant circuit was charged with 40g of R134a, so it's a tiny system.

I've since decided to air condition the whole workshop as it's reasonably insulated and I make a massive excess of solar power during the summer that I could use to power the AC during the hottest parts of the day. It would have been nice to have made a smaller refrigerated cooler for the battery box by itself - maybe just an old chest freezer with a modified thermostat would have been a better approach.

 

[mcart117]

By way of an update, I have been using the cooler for about 4 months now. No sign of any corrosion, but the main problem is how feeble the cooling is.

The physics of evaporative cooling is too complicated to waste a lot of time with, but the bottom line is that the best my cooler will achieve is 5 degrees below the ambient temperature, when the humidity of the surrounding air is very low.

And because air is light and the battery is heavy, it won't cool the battery if it gets too hot. Essentially all it can do is slow the rate at which the battery warms up on a hot day.



I have put a couple of plywood panels either side of the battery to improve the air flow. I turn the cooler on first thing in the morning, when the ambient temperatures is 20º or below, and I leave it on until about 9 pm. The water hopper only contains enough to last 4 hours, so I can't leave it on over night, and when I am away during the day, it is again unusable.

Bottom line, if I am home on a 38º day I can run the cooler and keep the battery below 35º until it is fully charged, but on a 40º day my over temperature protection will kick in and the battery will stop charging at that point and for the rest of the day.

For the number of times that happens, I am not sure it is worth spending a fortune on cooling just to achieve a few extra amp hours. Rather I am more inclined to buy more second hand solar panels to charge the battery faster while it is still cool in the morning.

 

[TorC]

Just coming into this somewhat late, but for LFP batteries, what about putting them underground? How far down do you need to go to get to, say 72°F/22°C or whatever your mean ground temperature is, and put them in a sealed, thermally conductive box? With the round-trip efficiency of LFP, it seems it should be pretty hard to overload the thermal dissipation of earth.

 

[mcart117]

Interesting idea, but I think I’ll build myself a wine cellar before I start excavating for a battery!

 

[zorlig]

Good call to use mechanical air conditioning. The battery spec sheets seem to be ok with 90% humidity, but you'd want to check all your components to use a system like that long term. Better to build an insulated box and air condition it with a simple window unit. I'd use foam board and be sure to tape it well to create an air seal.

Or just move it inside conditioned space.

 

[Ellcon123]

I am not so concerned with the LFP temp but the overall shed temp, what with the inverter and charge controllers in the same space. If it looks like being high then my plan is to draw cooler air from under the house through the inverter and also through the shed. I've yet to see any trips due to temp at this stage though.

 

[RV10flyer]

A small mini split a/c, heat pump or window banger in an insulated room/shed, with all electronics and battery inside works best. Mine stays between 10-25C year around. Your expensive system will stay drier, cooler and last much longer. Keeping those electronics below 30C ambient with clean cooling air is more important than the LFP cells.

 

[octal_ip]

A small mini split a/c, heat pump or window banger in an insulated room/shed, with all electronics and battery inside works best. Mine stays between 10-25C year around. Your expensive system will stay drier, cooler and last much longer.

Agreed, @mcart117 might be better off replacing the evaporative cooler with an old window air conditioner. They can be bought for less than $200 second hand and would do a far better job, with the added benefit of removing some humidity. It'd use a lot more power, though would only have to run for short bursts to deliver much better overall results.

 

[yabert]

Do everyone overthink this? Why not simply let the cells at 35-40°C?
From specs, those cells are rated to be discharge at up to 55° or even 65°C, so why bother?
Do anyone have visual/technical proof that cycling LFP cells part of the year at high temperature will drastically reduce their life?

 

[yabert]

View attachment 119490

Is not compressing the cells is worst than let them live their life at 40°?

 

[RCinFLA]

What is your relative humidity?

 

[wattmatters]

What is your relative humidity?

OP previously mentioned this:

I would be exaggerating to say we are on the edge of the Great Sandy Desert, but it is usually pretty dry here.

Sometimes we get a “heat trough” over us, and my intention is not to attempt cooling in those conditions, but rather to turn everything off until the weather improves.

 

[mcart117]

I am not so concerned with the LFP temp but the overall shed temp, what with the inverter and charge controllers in the same space.

It is a large shed with an open wall on one side. It gets hot, but not because of the inverter - because of the sun beating down on the tin roof. The battery is set to switch off at 36º, but with the cooler in place, it rarely gets there.

 

[time2roll]

Consider increasing the surface area of the cells to shed heat better. An aluminum sheet between the cells that extends into the airflow may help. Need to cut or twist the edges to allow airflow. Or create a box to direct air up or down over the fins.

Fan running on low for a couple hours before sunrise would give a head start on the day. No water, just fan if needed.

 

[mcart117]

What is your relative humidity?

 

[mcart117]

Consider increasing the surface area of the cells to shed heat better. An aluminum sheet between the cells that extends into the airflow may help. Need to cut or twist the edges to allow airflow. Or create a box to direct air up or down over the fins.

The ambient temperature goes over 40º on hot days. I'd worry about making the cells hotter, faster.

Fan running on low for a couple hours before sunrise would give a head start on the day. No water, just fan if needed.

This is a good strategy. The night time temperature might drop close to 10º, so I do run the fan from first thing in the morning to keep the battery as cool as possible for as long as possible.

And I am starting to install a third row of solar panels, with the idea of fully charging the battery in the morning, and then turning everything off until the sun goes down.

 

[mcart117]

Or just move it inside conditioned space.

Under Australian law, what they call Tier 3 batteries aren't allowed anywhere near a dwelling or place where people sleep.

 

[time2roll]

I thought the equipment was adding heat. May need a system to have the fan or cooling on only when the equipment is warmer than ambient. Not sure how to implement that.

Maybe more shade or insulation to reject the heat of the day.

 

[mcart117]

I thought the equipment was adding heat.

Not really measurable. The inverter is off during the day, and the battery doesn't seem to generate much heat while charging. I am just mitigating the external effect of the hottest days, without spending a fortune.