Lithium batteries, solar and winter layup.

[berni109]

Everything I have read so far says do NOT charge lithium batteries at or below 0°C. but there are odd days in a UK winter when it's that temperature and there is enough sun for the panels to be trying to put some amps into the battery.
Most (if not all) lithium batteries come with some form of BMS that should stop the battery accepting a charge when the temperature is 0°C.

I have seen it suggested that relying on the BMS for this function is not a particularly good idea?

Lithium batteries have a very low internal discharge rate so leaving a fully charged battery disconnected for 5 or 6 months should not cause it any problems?

Is it better to disconnect the fully charged lithium battery completely from the solar controller?
Or rely on the BMS doing its job on the very few days that conditions would enable the controller to be trying to push some amps into the battery?
TIA. bern

 

[Westbarn1]

Im not charging my lithium batteries, just keeping an occasional eye on voltage, have aded a separate cable connection directly to the engine battery and keep that on a motorcycle charger/ conditioner permanently, which only puts out o.8 amp at maximum, just to keep up with the discharge from the alarm/tracker.

 

[Raul]

How do you know if your bms it has temperature protection? Have you tested the battery if it takes charge below 4deg C? Mine does. I have tested by overiding the charger settings. You need a charger that has that function: not to charge on low temperature, like victron.

 

[Robert Clark]

I relied on the BMS with our batteries and never had a problem.

 

[Westbarn1]

How do you know if your bms it has temperature protection? Have you tested the battery if it takes charge below 4deg C? Mine does. I have tested by overiding the charger settings. You need a charger that has that function: not to charge on low temperature, like victron.

Sorry, have't a clue, its the OE Hymer set up. Though Im thinking that question is for Berni.

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[Raul]

I relied on the BMS with our batteries and never had a problem.

I would check if it has the temp protection before I would rely on it blind. The worst you can do is to whack some amps on sub zero temperatures. Li plating and dendrites then internal short:

 

[paddymcc]

Don't know about the BMS aspect but you could just remove the fuse for the solar panel when you know a cold snap is coming. On my van it's rare for the internal temperature to get below zero unless it is cold for several days.
My B2B has a temp sensor to attach to a lithium battery to prevent charging if too cold, do solar controller s with a lithium setting have similar?

 

[Zepp]

We had ours installed into a internal heated locker

You can also buy 12v heat pads but they are not cheap

 

[Raul]

Guys not all bms have temp cut off incorporated. Maybe the more expensive once have but not all.
Simple to check: a thermometer taped on the battery case to see the battery temp. If the charger does charge under 3-4degC , it means the battery does not have that kind of protection, and you have to provide such condition via the charger. The victron chargers have this built in, it reads the temp of charger or even better a blue tooth temp sens stuck on the battery, that report to the charger via victron Bluetooth network. That way the charger receives the right info and in the settings comes as default not to charge below 4 deg. You can adjust that or override. Some batteries have this built in the bms, or have heating pad; lots of money.

 

[Two on Tour]

My B2B has a temp sensor to attach to a lithium battery to prevent charging if too cold, do solar controller s with a lithium setting have similar?

If it's a Sterling B2B you have, then check, as I though they only have over temperature sensors not low temperature sensors.

I use a temperature controlled heat mat for my lithium.

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[paddymcc]

)If it's a Sterling B2B you have, then check, as I though they only have over temperature sensors not low temperature sensors.

I use a temperature controlled heat mat for my lithium.

Hi , Two on Tour mine is the Votronic 1215 which I think isn't like the Sterling. As I don't have lithium ( yet ) it is used to just enable the b2b to supply a higher voltage to the lead acid batteries when cold. It definitely does this as I have checked the voltages.

 

[Robert Clark]

I would check if it has the temp protection before I would rely on it blind. The worst you can do is to whack some amps on sub zero temperatures. Li plating and dendrites then internal short:

I did check and it did have low temperature protection thanks

 

[Two on Tour]

Hi , Two on Tour mine is the Votronic 1215 which I think isn't like the Sterling. As I don't have lithium ( yet ) it is used to just enable the b2b to supply a higher voltage to the lead acid batteries when cold. It definitely does this as I have checked the voltages.

Your Votronic 1215 appears to be a mains (EHU) battery charger, not a B2B and does not look to have a charging program for lithium either ?

 

[berni109]

Note to self RTFM! (Sorry MO read the ****ing manual).
I have a 'MPP 350 duo' solar controller that with tha addition of a temp sensor cable will ensure that the charging is cut when temp gets to 0°C.

All is well and I can safely fly away on holiday (if only) in the depths winter and not have to worry about needing a new battery on return.

Now does anyone have a temperature sensor cable they want to sell for a votronic controller?

 

[funflair]

I don't think that our solar charger "Votronic MPP" will charge LiFePO4 below 0 deg as long as the temperature sensor is connected of course.

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[SandraL]

"Now does anyone have a temperature sensor cable they want to sell for a votronic controller?"

I suspect it is just a thermister. So if you could get someone to check its resistance at 0 deg c and 25 deg c you could then fit a cheap standard thermistor at circa 50p ?
I did this with the fiat external temp sensor usually found in wing mirror.

 

[Googlebot]

"Now does anyone have a temperature sensor cable they want to sell for a votronic controller?"

I suspect it is just a thermister. So if you could get someone to check its resistance at 0 deg c and 25 deg c you could then fit a cheap standard thermistor at circa 50p ?
I did this with the fiat external temp sensor usually found in wing mirror.

Give me 10 minutes and I will let you know.

I have one waiting to install.

 

[Googlebot]

1.76 at 7 degrees.

1.9 at about 20 degrees.

Does this mean I could have saved the £35 I paid for two?

 

[SandraL]

Are you reading straight ohms across the sensor with it disconnected, apart from the meter?
Is it Kohms or ohms?

 

[Googlebot]

Are you reading straight ohms across the sensor with it disconnected, apart from the meter?
Is it Kohms or ohms?

Disconnected and no idea. Have a photo, sorry, I am a bit green when it comes to resistance. Says 1.87 when on this setting.

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[SandraL]

That is 1870 ohms, or 1.87k ohms at 20deg c
And 1760 ohms or 1.76k ohms at 7deg c.

So resistance is getting higher as temp rises, so IF a thermister a ptc type.
Usually temp sensing is done using a ntc thermister, ie resistance falls as temp rise.

Sorry cant find a cheap solution.

 

[Googlebot]

That is 1870 ohms, or 1.87k ohms at 20deg c
And 1760 ohms or 1.76k ohms at 7deg c.

So resistance is getting higher as temp rises, so IF a thermister a ptc type.
Usually temp sensing is done using a ntc thermister, ie resistance falls as temp rise.

Sorry cant find a cheap solution.

Thanks for the info, every day is a school day.

 

[BigDean]

Guys not all bms have temp cut off incorporated. Maybe the more expensive once have but not all.
Simple to check: a thermometer taped on the battery case to see the battery temp. If the charger does charge under 3-4degC , it means the battery does not have that kind of protection, and you have to provide such condition via the charger. The victron chargers have this built in, it reads the temp of charger or even better a blue tooth temp sens stuck on the battery, that report to the charger via victron Bluetooth network. That way the charger receives the right info and in the settings comes as default not to charge below 4 deg. You can adjust that or override. Some batteries have this built in the bms, or have heating pad; lots of money.

I know this is probably a silly question, but.... if an internal BMS is supposed to cut off at 0, why would it NOT charge at 3-4 degrees?

I imagine that when on my driveway that my battery could easily be down at 3 degrees but unlikely to go down to zero. I have not tested this but want to make sure I understand the theory before doing my experiments

thanks

 

[Nasher]

A big thanks to this thread, I was toying with fitting Lithium, but if it won't charge it if it's a bit chilly, I'll carry on with lead acid

I can see the advantages of Lithium, but I'll wait until the technology improves and I know it will

 

[BigDean]

A big thanks to this thread, I was toying with fitting Lithium, but if it won't charge it if it's a bit chilly, I'll carry on with lead acid

I can see the advantages of Lithium, but I'll wait until the technology improves and I know it will

I am beginning to think the same.

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[Googlebot]

A big thanks to this thread, I was toying with fitting Lithium, but if it won't charge it if it's a bit chilly, I'll carry on with lead acid

I can see the advantages of Lithium, but I'll wait until the technology improves and I know it will

Are your batteries in a heated compartment? If so, I wouldn’t have thought it would matter? If not, then yes, it would be an issue.

 

[Raul]

BigDean
The 4deg is a conservative figure adopted by victron, and others. You can change that to suit any battery spec. Some do not want to be charged, way before 0 threshold. In the early days the bms did not had sub zero protection and was left with the charger to do that right from the source, and it makes sense. I would rather have the charger stop the charge but still have the battery connected for the charger, rather than battery to disconnect and leave the charger open with the panels live in it. Very bad. The more advanced bms, communicates with the charging source and load control. Any 48v bank has that and dictates how much it charges, discharges, cell balancing, cell level voltage protection etc. The recent 12v mono blocks that have the bms incorporated, it relies on relays to disconnect, but no coms. Except for victron smart batteries with external bms. That is a more advanced system with bms communication for load and charge.
I have mine set at 3 deg and I can manually override if necessary. I would not go down to 0. Charging at 0 or below, it does irreversible damage. You can not recover that back, and reduce capacity every time it does it, until to much lithium plating will create dendrites that will pierce the membrane insulation and short the cell inside. The electrolyte is a paste semi liquid that will become to viscous on low temps and ions migration will be slowed down.
The same thing applies when you heavy discharge towards 0 state of charge. The current should be very low until the battery is about 10-15% charged, then full current can resume. You will damage it if you give a high rate at low SOC.

 

[wfdTamar]

Lithium are best long term stored at 50% charge, so for over wintering you would think you'd be ok to fully charge them (or close to) then disconnect them.

 

[Nasher]

Are your batteries in a heated compartment? If so, I wouldn’t have thought it would matter? If not, then yes, it would be an issue.

Sadly no, it's under the drivers seat and as a Snowboarder, the van spends time in the cold - not this season obviously

 

[BigDean]

BigDean
The 4deg is a conservative figure adopted by victron, and others. You can change that to suit any battery spec. Some do not want to be charged, way before 0 threshold. In the early days the bms did not had sub zero protection and was left with the charger to do that right from the source, and it makes sense. I would rather have the charger stop the charge but still have the battery connected for the charger, rather than battery to disconnect and leave the charger open with the panels live in it. Very bad. The more advanced bms, communicates with the charging source and load control. Any 48v bank has that and dictates how much it charges, discharges, cell balancing, cell level voltage protection etc. The recent 12v mono blocks that have the bms incorporated, it relies on relays to disconnect, but no coms. Except for victron smart batteries with external bms. That is a more advanced system with bms communication for load and charge.
I have mine set at 3 deg and I can manually override if necessary. I would not go down to 0. Charging at 0 or below, it does irreversible damage. You can not recover that back, and reduce capacity every time it does it, until to much lithium plating will create dendrites that will pierce the membrane insulation and short the cell inside. The electrolyte is a paste semi liquid that will become to viscous on low temps and ions migration will be slowed down.
The same thing applies when you heavy discharge towards 0 state of charge. The current should be very low until the battery is about 10-15% charged, then full current can resume. You will damage it if you give a high rate at low SOC.

Thanks for that.
Maybe the marketing for Lithium them should be useable to 5 degrees rather than zero. Will design systems sound the latter.
Thanks again.

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