Keeping LiFePO4 Battery Banks cool in Australia

[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.

 

[ArthurEld]

I put a small window air conditioner thru the wall of my shed. I plan to put four full size solar panels on the roof. I spent more than a year thinking of ways to deal with the batteries.
It's an expensive battery enclosure but I sleep better not worrying about fires. It is cheaper and safer than the commercial battery solutions I have seen.

 

[mcart117]

It is cheaper and safer than the commercial battery solutions I have seen.

I agree with you there

 

[curiouscarbon]

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?

without any first hand experience...

it seems that 40C might reduce the calendar life of the cells by more than a few months.

here is one resource that goes into some detail

Why temperature of lithium cells is important

Temperature is an important parameter that influences the aging of a lithium battery. At 35°C a lithium cell ages twice as fast as it does at 15°C. So if the battery’s useful life is 15 years at 15°C, it will be 7.5 years at 35°C. I summarize...

diysolarforum.com

 

[Robbert]

I live on Bonaire (Dutch Caribbean) and in the garage where my inverters are, temperures go over 35 Celsius. Also the humidity here is very high.

Since I am upgrading to lifepo4 and have plenty of solar, I'll install a mini split next week to keep everything stable at 25 celcius and keep humidity low.

 

[yabert]

here is one resource that goes into some detail

Interesting, thanks to share.
Based on this, It's clear that I would never spend money, time and effort to try to save a bit of life over a long period of time.
Imagine, if you use your cells wisely and discharge them at an average of 75% you could save around 4% of capacity over 10 years. It's nothing and a cheap BMS will probably destroy it before 10 years.
Take a look at the cells available 10 years ago (price, energy density, cycle life) and try to imagine the cells available in 10 years (price↓, energy density↑, cycle life↑). You will certainly be tempted to add or replace it with a low cost/high cycle life new battery in 10 years.

And please don't tell me you are living in a place where it's temperature is always 35°C. Some place are hot, like on the edge of the Great Sandy Desert, but most of the year (night, winter), the temperature is lower. So, really, add all this stuff to save ridiculous amount of life out of the cells is way more about interesting experiments than real needs.

I'm all to extend life of things to reduce waste and be gentle on new resources extraction, but it's clearly not the case here as those mini split/evaporative cooler have their own impact (resources, energy, garbage).

 

[wopachop]

Sounds like a fun project. I mess around with DIY evaporative coolers. Theyre fun to build but never work that great.

There are smaller 12v mini split systems designed for trucker cabs. Maybe you could score a really good deal on those. Then build an enclosure from foam board.

Like others said i would be worried about moisture. You could use your existing cooler but build a different enclosure. Pretend you had 2 enclosures. The batteries and inverter on the inside. Then you cool the outer enclosure around it. The batteries would have a barrier of cooled air around them. While not getting hit with moisture.

Another cheap option is shade. If its not too ugly. Hanging a shade fabric over the shed would keep the overall temp down. Especially that morning sun. Longer you can block it the better.

 

[toms]

Interesting, thanks to share.
Based on this, It's clear that I would never spend money, time and effort to try to save a bit of life over a long period of time.
Imagine, if you use your cells wisely and discharge them at an average of 75% you could save around 4% of capacity over 10 years. It's nothing and a cheap BMS will probably destroy it before 10 years.
Take a look at the cells available 10 years ago (price, energy density, cycle life) and try to imagine the cells available in 10 years (price↓, energy density↑, cycle life↑). You will certainly be tempted to add or replace it with a low cost/high cycle life new battery in 10 years.

And please don't tell me you are living in a place where it's temperature is always 35°C. Some place are hot, like on the edge of the Great Sandy Desert, but most of the year (night, winter), the temperature is lower. So, really, add all this stuff to save ridiculous amount of life out of the cells is way more about interesting experiments than real needs.

I'm all to extend life of things to reduce waste and be gentle on new resources extraction, but it's clearly not the case here as those mini split/evaporative cooler have their own impact (resources, energy, garbage).

View attachment 140814

That’s if you believe what you read. My personal experience is that heat is a major contributor to cell degradation. I’ve seen the same installations where temp controlled cells are still going after close to a decade where neighbouring non-temp controlled cells are finished inside 5 years.

 

[curiouscarbon]

Cell degradation speed increases as temperature increases. To what degree, I cannot personally attest.
Degradation speed slows as temperature decreases. However, past a certain point, the cell can't deliver nominal capacity until warmed back up.

Each person's situation and goals/priorities are different, and engineering thermal management systems is a real extra effort.
Having the cells last a very long time is one of my goals personally. Even if new chemistries come out, I want my system to still work.

HVAC or peliter are my two preferred ways to keep LFP cells in an optimal range to reduce degradation (both calendar aging and cycle aging).

With an insulated pack, the inefficiency of peltier units does not matter as much as without insulation.

Below is one way to do it. Still designing hope this info is of some use.

 

[octal_ip]

Cell degradation speed increases as temperature increases. To what degree, I cannot personally attest.
Degradation speed slows as temperature decreases. However, past a certain point, the cell can't deliver nominal capacity until warmed back up.

Each person's situation and goals/priorities are different, and engineering thermal management systems is a real extra effort.
Having the cells last a very long time is one of my goals personally. Even if new chemistries come out, I want my system to still work.

HVAC or peliter are my two preferred ways to keep LFP cells in an optimal range to reduce degradation (both calendar aging and cycle aging).

With an insulated pack, the inefficiency of peltier units does not matter as much as without insulation.

Below is one way to do it. Still designing hope this info is of some use.

I'd be interested to hear how your experiments with peltiers go. My initial work with a small phase change refrigeration system didn't produce enough cooling to be worthwhile. I estimate that it was able to move about 100W of heat, however this wasn't enough to keep an insulated container much below ambient temperature, let alone remove the heat produced by charging/discharging batteries and the BMS.

 

[littleharbor2]

This is on a smaller scale than the other units discussed here but thought I'd mention it anyway.
I built my own cooling unit for my LiFePo4 enclosure using this 12 volt mini refer unit and digital thermostat. It gets, and stays HOT for 3 solid months here on the Baja peninsula and this thing works pretty well keeping my battery bank cool.