Protecting LiFeP04 Batteries from the Cold.

[Rock-N-Ruth]

As you should know if you are using LiFeP04 or LFP batteries, it is bad news to charge them if the battery is at or below 32 degrees Fahrenheit. This can damage the batteries and really reduce their usable life. Some commercially available batteries may have low temperature sensors to shut off charging when cold, and some even claim to have a battery heater.

What do you do if you have a DIY battery or your off the shelf battery doesn't have cold protection? The solution is simple, cost effective, and doesn't require a lot of energy.

Our battery bank is made up of 6 BYD 24V LFP batteries. Each battery weighs in at about 120 pounds. And the footprint of the battery bank is about 2'x3'. We set our batteries under our bed, on a sheet of 2" thick XPS insulation board. Under the batteries is a single 18" x 60" underfloor heat mat. This runs about 80W when energised. We surrounded the batteries with 2" XPS foam board, and left the top opened.

The heat mat is controlled by a simple inkbird thermal controller you can buy on Amazon for about 15 bucks. We set the controller at 65 degrees fahrenheit and let it run all winter long. This prevents the batteries from ever reaching freezing and has the side effect of heating the bed from underneath.

The nearly 800 pounds of batteries absorb heat until they become a thermal mass storage device, radiating heat into the living space. Its better than and electric blanket and insures our batteries never get damaged by charging when cold.

[Dbacks2k4]

Originally Posted by Rock-N-Ruth

As you should know if you are using LiFeP04 or LFP batteries, it is bad news to charge them if the battery is at or below 32 degrees Fahrenheit. This can damage the batteries and really reduce their usable life. Some commercially available batteries may have low temperature sensors to shut off charging when cold, and some even claim to have a battery heater.

What do you do if you have a DIY battery or your off the shelf battery doesn't have cold protection? The solution is simple, cost effective, and doesn't require a lot of energy.

Our battery bank is made up of 6 BYD 24V LFP batteries. Each battery weighs in at about 120 pounds. And the footprint of the battery bank is about 2'x3'. We set our batteries under our bed, on a sheet of 2" thick XPS insulation board. Under the batteries is a single 18" x 60" underfloor heat mat. This runs about 80W when energised. We surrounded the batteries with 2" XPS foam board, and left the top opened.

The heat mat is controlled by a simple inkbird thermal controller you can buy on Amazon for about 15 bucks. We set the controller at 65 degrees fahrenheit and let it run all winter long. This prevents the batteries from ever reaching freezing and has the side effect of heating the bed from underneath.

The nearly 800 pounds of batteries absorb heat until they become a thermal mass storage device, radiating heat into the living space. Its better than and electric blanket and insures our batteries never get damaged by charging when cold.

I was under the impression the BMS on those batteries wouldn't allow them to charge if the temp was too low? Could be wrong on that?

The heat mat is a great idea. Chuck Casady just talked about that on a video last week about winter-proofing the build with the same suggestion. He also had a couple other good ones for plumbing systems.

https://www.youtube.com/watch?v=OIe7tIJKo5A

[indigo_k]

The thing I'm confused about here, is that I assumed that having the batteries inside the living space would be protection enough from the cold. I mean, presuming that your living space is insulated and heated in some way. A heating pad for external batteries is a great suggestion, but is it necessary if the batteries are 'indoors'?

[kazetsukai]

I use RV tank heater pads and a little heater in my battery compartment. Failing that, the BMS will disallow charge once it gets near freezing temps.

[Rock-N-Ruth]

Originally Posted by Dbacks2k4

I was under the impression the BMS on those batteries wouldn't allow them to charge if the temp was too low? Could be wrong on that?

The heat mat is a great idea. Chuck Casady just talked about that on a video last week about winter-proofing the build with the same suggestion. He also had a couple other good ones for plumbing systems.

We bought these batteries used out of solar farm use. No battery management system. Our charge controllers deal with preventing overcharging. Our inverters deal with preventing over discharge. I manually check for cell voltage drift from time to time. No apparent drift over three years.

[Rock-N-Ruth]

Originally Posted by indigo_k

The thing I'm confused about here, is that I assumed that having the batteries inside the living space would be protection enough from the cold. I mean, presuming that your living space is insulated and heated in some way. A heating pad for external batteries is a great suggestion, but is it necessary if the batteries are 'indoors'?

We are full timers with a huge solar array on the roof. It's a school bus. We did little to insulate the floor and don't always run heat. If it gets to be -20F outside and we are off visiting friends or for whatever reason not home it can get pretty cold on the floor where the batteries are.

The thing about temperature protection on your indoor batteries is that you have a lot of money sunk into them and all it takes is a one off, where they are too cold and your solar system charges them. Then you may end up with seriously degraded batteries.

Much better safe then sorry. Besides if you keep them warm during the cold season they act as a thermal mass and augment your heating system.

[Rock-N-Ruth]

Originally Posted by kazetsukai

I use RV tank heater pads and a little heater in my battery compartment. Failing that, the BMS will disallow charge once it gets near freezing temps.

Good plan. Batteries are costly. Best to protect them.

In our situation we don't ever want to miss out on free energy from the sky, so we make sure they are always up to temp. Winter is the time of reduced sunshine so we really need to optimize our solar harvest especially on cloudy days when the sun is way down south.

[cadillackid]

I thought a good external BMS could low current pulse the batteries till they warmed up to safe charging temps? what do EVs do? when i had a chevy volt asnd left it outside in super cold temps id plug it in and it would charge.. did it likely heat the batteries first? or are EVs a different type of battery?

[Rucker]

Regarding EVs, it seems there's a separate mechanism to keep the batteries above freezing, alluded to here:
https://www.sciencedirect.com/scienc...60128519301169

To state what may be well known already: no LiFePo battery will charge without damage if its internal temperature is below freezing, and no LiFePo battery will discharge without damage if its internal temperature is below zero Fahrenheit. If you anticipate very low temps, both charging and discharging protections for LiFePo batteries matter. I live in a mild climate and freezing temps are uncommon, so it's less of an concern for me.

There are at least a handful of 100A LiFePo batteries out there now with integrated heating elements that work with their internal BMS to warm the battery. For buslife, unless your LiFePo battery specifically states it 'contains a heater element' or such, a separate system is probably needed. Even then, I'm not sure you can 'set it and forget it', as even Will Prowse seems to indicate.

For DIY LiFePo batteries with an external BMS like Daly, there's usually a thermal probe option that can be programmed to safeguard against charging (and discharging) at low temps. I wouldn't say they manage charging at low temp like a solar charge controller though. They just gives a fault alarm and turn off the connection. Maybe that's a distinction without a difference, by my recent BMS experiences don't leave me with a lot of confidence in the state of BMS technology, Daly or any of the others. I do have the BMS probe set up and programmed, but I feel more comfortable knowing the solar charge controller's thermal probe is also in operation to prevent charging at low temps.

In addition, I've added a couple of RV tank heater pads, though I haven't connected them up yet. They have no controls of their own, and I don't like the idea of slapping them on and leaving them connected on their own. I'm thinking of putting the heaters on a temp switch so they only work between, say, +5 to +40 F, the temperature range that heating may be needed and can be applied without discharge damage.

Bonus build point: The RV heater element should be connected after the BMS to prevent very low temp discharge damage, and the BMS needs to be programmed appropriately-no discharge below zero F.

[dbsoundman]

All of this basically reinforces my decision to go AGM. I hate the fact that I can't really discharge them below 50%, but they are far more temperature tolerant and cheaper to purchase.

[kazetsukai]

Originally Posted by Rucker

For DIY LiFePo batteries with an external BMS like Daly, there's usually a thermal probe option that can be programmed to safeguard against charging (and discharging) at low temps. I wouldn't say they manage charging at low temp like a solar charge controller though. They just gives a fault alarm and turn off the connection. Maybe that's a distinction without a difference, by my recent BMS experiences don't leave me with a lot of confidence in the state of BMS technology, Daly or any of the others. I do have the BMS probe set up and programmed, but I feel more comfortable knowing the solar charge controller's thermal probe is also in operation to prevent charging at low temps.

Yeah, the BMS temp sensor is just a last-last-last resort. My Daly's kicked in a few times before I had the bank box heated, so it does work. Whew. But you need safeguards aside from the BMS.


I wouldn't use LFP for everything (I use AGM for the water pumps on the property), but the drawbacks here don't dissuade me from LFP in the bus. The performance and capabilities are more than worth it for me.... You just need a system designed to fail gracefully in these scenarios.

[HamSkoolie]

We're just putting ours inside so that they will always be above 50F and below 90F even when we aren't in the rig. Our solar and inverter will always be on so if we leave for an extended period a small electric heater (750W with thermostat) will keep the closed up bus warm enough in winter and the main mini split will keep it cool enough in summer.
If that plan doesn't work, a small heating pad for winter and a small fan for summer should be sufficient while drawing even less power from the battery bank.
Once we're on the road, we'll see if any adjustments are made for real life conditions.

[Rock-N-Ruth]

Originally Posted by dbsoundman

All of this basically reinforces my decision to go AGM. I hate the fact that I can't really discharge them below 50%, but they are far more temperature tolerant and cheaper to purchase.

We started out years ago with lead acid RE batteries from Trojan. When that bank required replacement we went AGM to get away from the need to maintain the batteries. Our battery bank was huge. We had 8 200ah AGM batteries in a 2S4P configuration. Each battery weighed 98 lbs.

At the time we were running just one 5500BTU window air conditioner, a 10 cubic foot deep freezer, and a 10 cu foot refrigerator, along with lights an tv. If we wanted to get 8 hours out of the air conditioner after dark we had to turn off the fridge and freezer every night.

Then one day we got the opportunity to buy a pair of used BYD 24V 220ah LFP batteries. Our plan was to build an LFP system in addition to the AGM system, but for the time being, we just swapped a them out.

The difference in energy density was apparent. We didn't have to turn anything off at night and still had capacity left when the sun came up and started charging the batteries.
That was the first thing we noticed. Then it became clear that the LFP batteries could charge faster than the AGM batteries and not get hot.

The AGM batteries weighed 784 pounds. The LFP batteries weighed 324 pounds. Though in theory we had 400ah of usable AGM (50% of 800ah) and only 352ah (80% of 440) of usable LFP, the real world results were that for half the weight amp hour for amp hour the LFP batteries perform twice plus as well as the AGM batteries.

We don't use a BMS. Solar controller is set to prevent overcharging. Our inverters cut out long before over discharge and our hillbilly thermal protection has worked flawlessly for years now. A temperature controller like the one below, and a 80w heating pad keep our (now 6) 220Ah 24V BYD batteries within acceptable operating temperature. It's no hassle.

We have been off grid for decades an using LFP batteries since 2018. We will never go back to lead acid chemistry.

"Amazon.com: Inkbird Dual Stage DV 12V Digital Temperature Controller Fahrenheit Thermostat Heating and Cooling for Homebrewing Brew Fermenter Fridge Incubator Greenhouse : Industrial & Scientific" https://www.amazon.com/Inkbird-Temperature-Controller-Fahrenheit-Thermostat/dp/B019I3YCFS/ref=sxts_rp_s_a_1_0?content-id=amzn1.sym.baab4206-64c6-4030-8499-88f2f76870e3%3Aamzn1.sym.baab4206-64c6-4030-8499-88f2f76870e3&crid=1K7QPF4L4SQ2U&cv_ct_cx=temperatu re+controller&keywords=temperature+controller&pd_r d_i=B019I3YCFS&pd_rd_r=0c32b9e0-3ce2-4a02-a218-57f6c5082260&pd_rd_w=dVMay&pd_rd_wg=KHJnN&pf_rd_p= baab4206-64c6-4030-8499-88f2f76870e3&pf_rd_r=6EJT1EK9NSTXQVQMVCX8&qid=1671 736970&sprefix=Temperature%2Caps%2C251&sr=1-1-5985efba-8948-4f09-9122-d605505c9d1e

[HamSkoolie]

Like Rock-N-Ruth said....Lithium is KING. Yes the upfront cost is expensive but they last and you have far more useable energy than traditional lead acid technology whether it's flooded, sealed, glass mat, or gel.


In doing our battery bank calculations, to get 10kWh usable (20kWh needed with lead/acid tech) we found that we would need 16ea, 6v, 205ah deep cycle batteries at 70 pounds each for a total of 1120 pounds without accounting for the weight all the interconnection cables, the mounting tray, etc.
Used and checked by the manufacturer we could (3 years ago) get them for $60 ea + $20 core so $80ea of $1,280 for all 16. After all the cables, lugs, mounting trays and securing devices, we figured it was going to be AT LEAST $2,000, a PITA, take up a LOT of room, AND require maintenance to keep the water levels correct. And they'd last MAYBE 3-4 years.
Our 10kWh useable of lithium weighs 202 pounds consisting of just TWO batteries. They are approximately 19w x 20d x 6.1h for a total of about 20x20x12.5. The rack they mount it will take two more batteries if we find we need more storage and the inverter will mount above that heavy steel rack that will contain the batteries even in a crash as long as we mount it securely. AND they are guaranteed for 7,000 cycles (19.5 YEARS) to have 80% capacity remaining. Cost, just $3500 and we could have gone with the standard versions (no lcd screen on the battery) for just $3000.
So for us, the up front cost wasn't very much more than for lead acid deep cycles but the advantages blew away the lead acid and it wasn't even a consideration after the research.

[cadillackid]

reading this makes me want to change to Lithium.. i have 4 AGM 100AH group 31's.. and am thinking I could really increase my capacity by going lithium.. right now i just assume that i dont A/C my bus when parked for very long just because its 1000 watts to run my portable AC on high.. (I have engine air for the road)..



my bus is often parked on shore power when im home so I could have a heating mat to keep the bats warm.. if i am parked in super cold weather then ill be drawing from and not charging the batteries..



so what is the upper limit on temperature.. being I dont live in my bus it gets parked outside in summer where it can get 110+ inside.. im guessing I shouldnt charge them that hot..


when im travelling I rely on alternator charging as my main method although I do have a portable 200 watt panel that has its own controller (you program it for the battery type) which I can set up to keep batteries topped off..



one thing i do is charge via the alternator.. so im sure id need a DC-DC charge controller so I could limit the amount of current and have correct voltage...

[dbsoundman]

Originally Posted by cadillackid

reading this makes me want to change to Lithium.. i have 4 AGM 100AH group 31's.. and am thinking I could really increase my capacity by going lithium.. right now i just assume that i dont A/C my bus when parked for very long just because its 1000 watts to run my portable AC on high.. (I have engine air for the road)..



my bus is often parked on shore power when im home so I could have a heating mat to keep the bats warm.. if i am parked in super cold weather then ill be drawing from and not charging the batteries..



so what is the upper limit on temperature.. being I dont live in my bus it gets parked outside in summer where it can get 110+ inside.. im guessing I shouldnt charge them that hot..


when im travelling I rely on alternator charging as my main method although I do have a portable 200 watt panel that has its own controller (you program it for the battery type) which I can set up to keep batteries topped off..



one thing i do is charge via the alternator.. so im sure id need a DC-DC charge controller so I could limit the amount of current and have correct voltage...

I'm in the same boat. I started out thinking AGM was the wiser choice but I'm running into a lot of issues with my batteries getting too close to 50% charge in a fairly short amount of time just running interior LED lights, diesel heater, and an inverter just for the mini fridge. 8-10 hours with that load from a full 100% charge is about all I can get from my "400 AH" of AGM batteries. And they take FOREVERRRRR to recharge from 50% with my 30 amp solar charger (running from shore because I don't have solar panels yet).

[Rock-N-Ruth]

Originally Posted by cadillackid

reading this makes me want to change to Lithium.. i have 4 AGM 100AH group 31's.. and am thinking I could really increase my capacity by going lithium.. right now i just assume that i dont A/C my bus when parked for very long just because its 1000 watts to run my portable AC on high.. (I have engine air for the road)..



my bus is often parked on shore power when im home so I could have a heating mat to keep the bats warm.. if i am parked in super cold weather then ill be drawing from and not charging the batteries..



so what is the upper limit on temperature.. being I dont live in my bus it gets parked outside in summer where it can get 110+ inside.. im guessing I shouldnt charge them that hot..


when im travelling I rely on alternator charging as my main method although I do have a portable 200 watt panel that has its own controller (you program it for the battery type) which I can set up to keep batteries topped off..



one thing i do is charge via the alternator.. so im sure id need a DC-DC charge controller so I could limit the amount of current and have correct voltage...

Lots of good questions that can help you to be really blessed by a long fruitful relationship with LFP batteries.

The upper temperature limit for charging LFP cells is 55C (131F). Also realize that if the ambient temperature is 110 degrees it will take some time for the batteries to reach that temperature. They will heat up a little when you charge them but unless you are charging at more than 1C they won't heat up much as a result of charging.

If your batteries are being stored on a battery maintainer and used infrequently, you can extend the life of your batters by maintaining the at 80% SOC rather than 100%.

It is just fine when you are using your batteries to charge to 100% and discharge to 20% they don't mind the work. They do prefer to be stored between 80% SOC and 40%SOC

If you are charging from your alternator, you are correct, you really want to use a charge controller between your alternator and your LFP batteries. Without it they will draw as much current as your alternator can provide and likely reduce the life of your alternator and your batteries.

If you use a heating mat, a thermostat to bring the heat on at 40F and off at 50 or 60F will prevent crystalization.

A good source in the USA for LFP cells is 18650batterystore.com. They provide excellent customer service. They are quick to respond to pre sales questions. Shipping from Georgia is reasonable.

[HamSkoolie]

We swear by the EG4 batteries sold by Signature Solar.
5.12kWh each in a roughly 20x20x6" steel housing that fits into standard audio racks (though the rack needs to be up to holding the weight.
They're 101 pounds each and include the BMS, comm ports, etc.
At $1500 for the standard battery which is available in 12, 24, or 48 volts they are a little expensive. But they're guaranteed for a lot of cycles. Our upgraded batteries carry a 10 year 7000 cycle guarantee to retain 80% capacity at that point.
Paired with the EG4 6.5 inverter.... it's better than cooking with gas.

[Rock-N-Ruth]

Originally Posted by HamSkoolie

We swear by the EG4 batteries sold by Signature Solar.
5.12kWh each in a roughly 20x20x6" steel housing that fits into standard audio racks (though the rack needs to be up to holding the weight.
They're 101 pounds each and include the BMS, comm ports, etc.
At $1500 for the standard battery which is available in 12, 24, or 48 volts they are a little expensive. But they're guaranteed for a lot of cycles. Our upgraded batteries carry a 10 year 7000 cycle guarantee to retain 80% capacity at that point.
Paired with the EG4 6.5 inverter.... it's better than cooking with gas.

Very well built batteries, backed by a warranty. Sounds like you are going to have a very robust system. Years ago when Ruth and I first went off grid, a friend told us that we would always be making sacrifices to live on solar. While that was true for some time, eventually our solar system became robust enough that we live like we are tied to the grid by invisible wires.

[cadillackid]

Originally Posted by Rock-N-Ruth

Lots of good questions that can help you to be really blessed by a long fruitful relationship with LFP batteries.

The upper temperature limit for charging LFP cells is 55C (131F). Also realize that if the ambient temperature is 110 degrees it will take some time for the batteries to reach that temperature. They will heat up a little when you charge them but unless you are charging at more than 1C they won't heat up much as a result of charging.

If your batteries are being stored on a battery maintainer and used infrequently, you can extend the life of your batters by maintaining the at 80% SOC rather than 100%.

It is just fine when you are using your batteries to charge to 100% and discharge to 20% they don't mind the work. They do prefer to be stored between 80% SOC and 40%SOC

If you are charging from your alternator, you are correct, you really want to use a charge controller between your alternator and your LFP batteries. Without it they will draw as much current as your alternator can provide and likely reduce the life of your alternator and your batteries.

If you use a heating mat, a thermostat to bring the heat on at 40F and off at 50 or 60F will prevent crystalization.

A good source in the USA for LFP cells is 18650batterystore.com. They provide excellent customer service. They are quick to respond to pre sales questions. Shipping from Georgia is reasonable.

great info here!!! I remember reading about the 20-80% charge rule as a normal.. when i had a chevy volt, the car had a 16.2 kwh pack but only used 10.1kwh of it.. I had that car 3 years and in 3 years time and a lot of cycles my battery was still had no noticeable loss to it..



my aim is to have a battery pack that I dont deplete at each use.. which with my AGM I dont generally, however I can see myself in situations where i would.. sounds like I need a really nice charge controiller / BMS where I can set the target SOC when being charged.. and stay in that 20-80% unless I know ill be running extended in which id top em off..



when I think about my usage pattern, my most likely times to charge would be parked at "the barn" on shore power wehich is generalkly at night.. or driving with the alternator charging.. the bus is well air-conditioned when im driving.. in fact if summer temperature became an issue I could run a vent from the overhead unit to blow across the pack.. but just the fact the bus is usually nice N cool when im travelling is prob enough.. if im on shore power at night, its easy to have a heating mat keep the batteries warm..



but since im rather inexperienced I need to find something somewhat idiot proof..