Advice for lifepo4 in very hot temperatures.

[BlitzSSS]

Hey all

My CALB 100ah cells are going to be used for a 12v battery backup system where they will spend most of their time on float charge via the grid. As they are for a backup system I don't expect them to actually see much use.

Unfortunately they will also be in a very hot shed over an Aussie summer which will regularly reach 40C (104F) but also anything upto 50C (138F) on occasion.
The shed is NOT insulated however I will be doing my best to insulate radiant heat off the tin walls. Air conditioning or anything like that is NOT an option for me, I wish it was but it is what it is.

-What CAN I do to maximise the life of my cells?

-Should these cells not see float charge for most of their life or at the very least during our hot summer days make sure they are not seeing any charge at all;

-Should I even discharge them slightly and if so, to what voltage?

-Do I need to apply some compression in their casings?

-Should I keep the cells as seperate as possible to allow for as much cooling?

-Would a fan or any kind of passive cooling be worth the while or not really?

Has anyone seen any simple watercooling based set-ups? I don't want anything too extravagant however perhaps some waterblocks under/between the cells (I understand uniformity of the cooling will also be very important here) or a box which is entirely water-cooled?

Any tips very much appreciated.

Thanks

 

[softdown]

That is unacceptably hot for decent longevity. Can you dig a hole to a cooler depth?

What is the night time temps?

 

[gnubie]

Would it be practical to have the batteries in an insulated cabinet that has fan forced ventilation to outside the shed, ie inlet and exhaust are to the outside?

 

[RCinFLA]

Heat is the biggest accelerant to degradation. It speeds up the degrading side chemical reactions that decomposes electrolyte and consumes Lithium in non-reversible chemical reactions. Results is less capacity due to Lithium reduction, higher equivalent cell impedance, and greater cell self leakage rate. Above 35 degs C starts to get bad, above 50 degs C is very bad.

If you couple this with maintaining high state of charge the degradation rate is even higher rate. If you are going to continuously float charge cells do it at about 3.35vdc per cell. You will still achieve 85% capacity from cells. A resistor dump BMS that triggers above 3.4vdc is not going to help keep cell leakage variance under control. A BMS with active balancer would help on this.

Try to find a way to get battery temp down. If you have cool ground you may be able to keep batteries in ground or cool down a tank of water and use a small pump into a water jacket around battery during the hottest portion of day.

 

[Kesa32]

Being an Aussie too l know what your up against ,,,, a shed will need lots of ventilation ,, even then it'll be still around ambient temperature,,,,,,,,, maybe a water bath setup with a small pump driven by a small panel / your batteries linked to a nearby water tank for cooler mass water .... cheapest thing l can think of (( if you have a tank within range of course ) ,,,, you'd have to bury / insulate the piping a fair bit too otherwise you'd be pumping hot water

 

[BlitzSSS]

That is unacceptably hot for decent longevity. Can you dig a hole to a cooler depth?

What is the night time temps?

Digging a hole is unfortunately not feasible, concrete slab. Night time temps could drop into the 20's but also stay into the 30's (Celsius)

Would it be practical to have the batteries in an insulated cabinet that has fan forced ventilation to outside the shed, ie inlet and exhaust are to the outside?

Hmmm that's not a bad idea, simple to setup but I would need to put holes in my shed. Will keep this idea in mind.

Heat is the biggest accelerant to degradation. It speeds up the degrading side chemical reactions that decomposes electrolyte and consumes Lithium in non-reversible chemical reactions. Results is less capacity due to Lithium reduction, higher equivalent cell impedance, and greater cell self leakage rate. Above 35 degs C starts to get bad, above 50 degs C is very bad.

If you couple this with maintaining high state of charge the degradation rate is even higher rate. If you are going to continuously float charge cells do it at about 3.35vdc per cell. You will still achieve 85% capacity from cells. A resistor dump BMS that triggers above 3.4vdc is not going to help keep cell leakage variance under control. A BMS with active balancer would help on this.

Try to find a way to get battery temp down. If you have cool ground you may be able to keep batteries in ground or cool down a tank of water and use a small pump into a water jacket around battery during the hottest portion of day.

Thanks for this, the BMS I will be using is the Overkill one, I think that's an active balancer can you tell me?

Being an Aussie too l know what your up against ,,,, a shed will need lots of ventilation ,, even then it'll be still around ambient temperature,,,,,,,,, maybe a water bath setup with a small pump driven by a small panel / your batteries linked to a nearby water tank for cooler mass water .... cheapest thing l can think of (( if you have a tank within range of course ) ,,,, you'd have to bury / insulate the piping a fair bit too otherwise you'd be pumping hot water

Thanks, the water jacket or water bath is an idea I like, I was also looking at some large alloy water cooling blocks and thinking of either having these mounted directly on the cells or perhaps lining a wooden box that then encloses the cells in hope that was create a bit of a cooler box.
I'll need to look into the water pumping side of these ideas now too.

Anyone got any examples of water cooling setups used for anything in a shed?

thanks for the replies.

 

[Floral_Indutries]

What's the humidity during these hot hot periods? If the humidity is low & you have a water source you could investigate an evaporative cooling system for the shed or a small enclosure around the batteries (aka "swamp cooler"here in the US).

 

[heatwave]

I live your conditions as well. These are things we do for temperature regulation for my SLA batteries to stay below 27C.
1. you could rather than burying the shed, raise the level of the earth around it. Ram packed earth in tires make an incredible insulated wall; like earthship housing.
2. Double roof over the shed. Meaning a shade over the roof that provides airflow around the main roof. It would set 6-12 inches above the shed roof.
3. I only have water that is 110F. Snaking a buried pipe(I have over 100ft) 18inches below the surface 'cools' the water, depending on time of year significantly.
4. swamp cooler has the potential to add 60-70% humidity to the shed on humid days. Though for it is the best option to cool my living house; most everyone here uses evap cooling.
5. I ended up simply putting a small AC unit from Home Depot on my shed. The shed is small so it only runs on medium to low setting even when it is 53C outside, also it is under shade. My unit is fully DC and has it's own pv system, runs 24/7 from April to October averaging about 50watts DC when operating, pump is a small bilge on a timer.
6. small computer fans that take little power always flowing air over batts is good too, like a comp server room.
7. there is flexible irrigation tube/pipe that is 6inches, this could be buried deep and connected to the the room for passive cool air flow. earthships utilize this idea for passive AC. Air is drawn in from the tube on one end, the other connected to the shed. The hot air rising out of the roof vent on the shed pulls the cooler air through the pipe from underground. This works very well the deeper you dig and cover the pipe.

Mitigating the amount of direct sunlight is always my first thought. If I cannot dig down, I raise the earth around something and work angles for shade. The pic is from before the shade structure build. The roof lifts for ventilation and access when needed.
Just some ideas. Water in the shed would require some serious thought about how to stay safe as my water will eventually eat anything away because it too highly mineralized and salty.

Hope something here might help! These conditions are where I thrive :D Good Luck!

 

[pops106]

Just a wacky idea...

Could you make something like a portable fridge, I think these have a peltier in the bottom. So insulated box with pelt in the bottom, build this box inside another box to add more shade.

Then a panel to run it.

 

[dRdoS7]

Hi,

Just a wacky idea...

Could you make something like a portable fridge, I think these have a peltier in the bottom. So insulated box with pelt in the bottom, build this box inside another box to add more shade.

Then a panel to run it.

Instead of "something like a portable fridge", just buy one, and put the battery inside it over summer. Might need one large enough to keep a slab of VB (or XXXX) in it as well, next to the battery, as a cold sink.

As suggested, put up a solar panel to supply 12v.

Moisture might be a problem!

dRdoS7

 

[DThames]

I am working on an experiment in my spare time, so no telling when I will get results. But I have a pipe buried deep enough that in the winter the water in the pipe will be warmer than the surface air temp. In the summer the water in the pipe will be cooler than the surface air temp. If the batteries are in an insulated box and if the mass of underground water is large enough, I can bring the water into the box to carry off or deliver heat. A tiny pump with a couple of temperature dependent switched in series will only pump when needed.

 

[Maast]

Does it get cool/cold at night?

There was an article in Homepower Magazine many years ago where the guy buried 3 or 4 50 foot parallel lengths of 10" plastic pipe two feet in the ground, combined them and ran it to his house, then he took another 10" pipe - this one made of black stove pipe and ran it out the house and 25 feet in the air.
When the sun would shine on the black stove pipe it'd heat up and cause a really strong convection flow up through the pipe and draw fresh air through the buried plastic pipe which would cool the air.

I remember thinking it was really ingenious, the article said it worked really well and at night the air flow would reverse because the black pipe would get cool and the convection would go in reverse.

Change out the house with a sealed plywood box and maybe downsize the pipes to 4 inches (120mm) and bobs your uncle!

 

[BlitzSSS]

Hey all, just an update, I've decided on simply using a small 140L bar fridge to house the batteries in. I know this might not be the most efficient method however it will only be turned on for those extreme temperature days/weeks and even with the fridge off it might help to insulate the batteries on those milder days.

I've picked up a cheap second hand fridge and on its highest temperature (thermostat set on 0.5 out of a Max of 7) is around 10 degrees on a 15 degree ambient temperature day so I'll have to see how it goes during those extreme days. Also I might have been better off with a wine cooler than a fridge as most of those can be set to 18-20 degrees. (but im not certain if they are insulated as well and will cope in the extremely hot days).

My only concern now is condensation which I'm seeing a lot of now, but hopefully not as much when it's hot. The fridge has a removable freezer tray so its "all fridge" however there are obviously a lot more coolant lines at the top were there freezer section is and there's a lot of condensation forming in this section.

 

[pops106]

Hey all, just an update, I've decided on simply using a small 140L bar fridge to house the batteries in. I know this might not be the most efficient method however it will only be turned on for those extreme temperature days/weeks and even with the fridge off it might help to insulate the batteries on those milder days.

I've picked up a cheap second hand fridge and on its highest temperature (thermostat set on 0.5 out of a Max of 7) is around 10 degrees on a 15 degree ambient temperature day so I'll have to see how it goes during those extreme days. Also I might have been better off with a wine cooler than a fridge as most of those can be set to 18-20 degrees. (but im not certain if they are insulated as well and will cope in the extremely hot days).

My only concern now is condensation which I'm seeing a lot of now, but hopefully not as much when it's hot. The fridge has a removable freezer tray so its "all fridge" however there are obviously a lot more coolant lines at the top were there freezer section is and there's a lot of condensation forming in this section.

What if you stick it on a smart plug, you would need something to be able to measure the temp inside but you could turn the fridge on and off automatically if it gets to 20C.

Something like this https://www.amazon.co.uk/dp/B0813DY...9Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

Stick the probe in the fridge, wire the fridge into the smart plug and set a min and max.

 

[gnubie]

An alternate mechanical thermostat would be a better choice IMO if temperature is too low. Simple, reliable and uses no power at all. Almost all of those smart plus etc use basic capacitor dropper power supplies and cheap electrolytic capacitors behind that and die in a few years and consume a couple of watts all the time too.

 

[heatwave]

My only concern now is condensation which I'm seeing a lot of now, but hopefully not as much when it's hot. The fridge has a removable freezer tray so its "all fridge" however there are obviously a lot more coolant lines at the top were there freezer section is and there's a lot of condensation forming in this section.

I use a smart plug on my fridge/freezer. In very hot temps, it creates a great deal of moisture as it is turning on and off more; now this is also only on the walls where the coils run. Very dry and hot conditions. Winter not so much issue.