Diy lithium. Does a lthium battery need heating from solar?

[Derekoak]

I was sure that my underslung diy lithium from Chinese cells needed heating when being charged from the alternator. We came to Spain in winter with the heaters not working and often had to go out of our way to warm places to get the battery to charge. Now our heaters are working from alternator/sb charging and that it's fine. I have been looking to test whether my solar charging is advantageous to have heating from solar if we are not driving.
Yesterday I got an opportunity. We were leaving the camper for 2 days running over la Maroma in Andalucia . I parked the camper at 1100m in an area recreativa facing south with a reasonable arc of clear sky. The weather forecast was for 2 similar sunny days of about 6 hours of sun with some cloud. The car outdoor temperature dropped to -1C. I used the battery to warm itself to charging temperature which took about 3ah or 40 watt.h of energy . We left the camper at 9 am day 1 on our return at 3pm the day after the first day had a record 580 watt.h nearly all bulk charging. The 2nd day had no bulk charging and a poor amount of float. Looking at the bms the battery temperature was still at 9C. It needs to reach about 11C to reactivate the charge mosfet automatically after it has fallen below 5 C. So all the 2nd day the battery had not been charged although the solar had helped the fridge demand during the day. When I looked at the solar at 3pm the output was 15 watt. After I cleared the charge mosfets at 3.05 pm it jumped up to 90 Watts.
So it seemed I lost a solar charge day of of some 580watt hours for the cost of 40 watt hours of heating. I have worked out a circuit where the solar energy itself, if not used because the battery is cold is used to heat the battery, rather than using stored battery power, so if we are in a different environment, say cloudy Scotland. The battery energy is not wasted heating when the solar gain will not repay the heating energy used.

 

[1 Cup]

Some days we at a loss.

 

[Nabsim]

Are you actually getting harmful current from solar while the temperatures are low? I know in the two years I have had my Lifepo4 fitted I haven’t had a problem, mine are mounted inside not outside though

 

[Derekoak]

No I have no problems as it is. I just think I have missed opportunities for the sake of a switch and a relay. It may well be that this is only to do with underslung batteries or campers that are not heated or always occupied. We sometimes go off tent camping., so our camper counts. I cannot deal with a manual solution as we are not always there.

 

[Derekoak]

Clearly at significant altitude in southern Spain where there are often clear skies through out the year whilst still cold at night, is very different to England and Scotland

 

[QFour]

Some lithium batteries have a low temp cut off to stop charging if the temp is to low. Also seen some with internal heating but you would need plenty of insulation round the battery to keep the heat in.

 

[Derekoak]

I think all lithium batteries need a low temperature cut off to charging. Unless they are guaranteed to be kept above 5C anyway. My bms has that low temp cut off set to 5C. I added 4 heat pads between each pair of cells. (8cells total). They take about 12 amp of current when heating. I have a little insulation around the cells but so far if the nights are cold, there is no charging until daytime so one heating to 11C before we drive has been enough, there must be a little heat from the charging and the day warms up.
If the battery did cool below 5C again, the heater would come on again, if there was any charging.

 

[wildebus]

You mentioned about cloudy Scotland ... I am guessing the theory there was because of the clouds, the temperature does not drop so much overnight? This might interest you? my Battery Temp from the start of the Winter (i.e. 1st Dec 2021) to now....

For a great deal of the time, the battery is below 10C and for a significant period (maybe half?) it is below 5C. So if this were a standard (i.e. No Heater) Lithium battery at this temp, and the alogorithm was no charge if drops below 5C, and then only restart at 10C (which I think is a common setup? you actually have 11C on yours), this battery would have got a charge maybe 3 days out of the last 120!
My Lithium Battery is actually right next to this Lead Battery that the Sensor is attached to, but has internal Preheaters so will "charge" as long as it doesn't get lower than -20C (I say "charge" - the current is diverted to the heater at below 0C until it gets to 5C (from memory) and then actual charging will occur), so at no time did I have no charging possible.
But I think - IMO - the above graph does illustrate how important low-temp cutoff is to Lithium, and how advantageous Heating (be it built in, or added) can be for Lithium Setup.

 

[Derekoak]

You mentioned about cloudy Scotland ... I am guessing the theory there was because of the clouds, the temperature does not drop so much overnight? This might interest you? my Battery Temp from the start of the Winter (i.e. 1st Dec 2021) to now....
View attachment 106829

For a great deal of the time, the battery is below 10C and for a significant period (maybe half?) it is below 5C. So if this were a standard (i.e. No Heater) Lithium battery at this temp, and the alogorithm was no charge if drops below 5C, and then only restart at 10C (which I think is a common setup? you actually have 11C on yours), this battery would have got a charge maybe 3 days out of the last 120!
My Lithium Battery is actually right next to this Lead Battery that the Sensor is attached to, but has internal Preheaters so will "charge" as long as it doesn't get lower than -20C (I say "charge" - the current is diverted to the heater at below 0C until it gets to 5C (from memory) and then actual charging will occur), so at no time did I have no charging possible.
But I think - IMO - the above graph does illustrate how important low-temp cutoff is to Lithium, and how advantageous Heating (be it built in, or added) can be for Lithium Setup.

When I mentioned Scotland I was thinking of a previous conversation with you. You suggested that although you agreed that lithium needed heating you were unsure if solar charging needed heating as in Scotland the cold days are without significant sun.
On that basis I did the easy thing and got heating working from the battery before or during driving but left heating from solar to see if it was needed, by experiment. Now that I have a victron mppt (thanks) I have a working solution to heating using the solar energy until it can be diverted to solar charging.
I think you are correct for the uk, but my experiment shows at altitude in Spain is a different environment. You often get blue skies after a below 5C night and for many months of the year. As you say cloudless nights are often cold.

 

[Nabsim]

You battery’s could well be different but mine without heaters can charge below 5 degrees just at lower rates. The reason I asked what current you were getting was because if it’s at a safe level you can still be charging okay. Is the 5 degrees your own self imposed minimum or did your cell manufacturers state that? If it’s your self imposed min8mum the that’s fine it’s your choice but needent apply to others

 

[wildebus]

You battery’s could well be different but mine without heaters can charge below 5 degrees just at lower rates. The reason I asked what current you were getting was because if it’s at a safe level you can still be charging okay. Is the 5 degrees your own self imposed minimum or did your cell manufacturers state that? If it’s your self imposed min8mum the that’s fine it’s your choice but needent apply to others

I think the better BMSes (often spec'ed by the big Commerical battery makers as opposed to the DIY market) have more advanced features like permitting lower charge rates at lower temps and heater diversion built in. The basic ones just have the direct on/off cut-off (and sometimes not even that!)

 

[Derekoak]

I set 5C because it was always safe. My bms either switches charging on or off there is no, on only for low charge rate setting. I have no problem with that with heaters installed.
The thing I find annoying is my bms can set the switch off heating temperature but has no way that I can find to switch on again until the temperature rises to about 5 degrees C higher so off at 5C and on again at 10 or 11C the 2 battery sensors seem a little different, and I have to ensure both switch on again.

 

[Nabsim]

I think the better BMSes (often spec'ed by the big Commerical battery makers as opposed to the DIY market) have more advanced features like lower charge rates at lower temps and heater diversion built in. The basic ones just have the direct on/off cut-off (and sometimes not even that!)

Ah so it would be a decision due to the type of bms rather than a limit on the cells the self? I know you are aware but I suppose I should have stated mine are commercial battery’s rather than diy

I keep thinking I may at some point add some diy battery’s on my van but it’s still very much undecided, especially as commercial battery’s are dropping all the time

 

[wildebus]

Ah so it would be a decision due to the type of bms rather than a limit on the cells the self? I know you are aware but I suppose I should have stated mine are commercial battery’s rather than diy

I keep thinking I may at some point add some diy battery’s on my van but it’s still very much undecided, especially as commercial battery’s are dropping all the time

I am pretty sure that it is a limit of general lithium technology that means they get seriously damaged when charging under 0C, so the BMS is there as a protection. Some people decide to "self-manage" with no BMS setup at all

 

[Derekoak]

Ah so it would be a decision due to the type of bms rather than a limit on the cells the self? I know you are aware but I suppose I should have stated mine are commercial battery’s rather than diy

I keep thinking I may at some point add some diy battery’s on my van but it’s still very much undecided, especially as commercial battery’s are dropping all the time

Yes the bms dictates but must follow the chemistry a little. To my reading low temperature AND a high SOC can still plate a battery slowly even at low current
I got a good deal at the time, diy v commercial lithium with heating built in, but things change all the time and I don't follow prices anymore.

 

[Stanski]

Very interesting reading.
Without being too nosey, roughly how much have you spent on the setup.
Victron mppt + Solars + Lithiums + wiring ?
Chap I bought leisure batteries from in Jan said he had bought 4x lithium, whole system costing 2.5K.
Allowed him & partner to run 2 Laptops and Network for work purposes, as well as entertainment.
Curious if prices are falling.

 

[Derekoak]

I already had the solar panels 5 year old semiflexible 2 x 80 watt photonic universe. I can't remember their price. The mppt was around 100 pounds 75/15 victron smart. I think the 8 x 100 ah cells were around 400 pounds and the 2 bms 100a daly Bluetooth were around 100,, that was over a year ago, they took 3 months overland to arrive. The victron lict smart voltage sensitive relay for lithium was 80. I have to guess over cables, polycarbonate and steel to make the underslung battery case, relays, switches heater pads and aluminium heat spreaders to make them the right size, say 150 pounds. So add that up I guess 1000 pounds.
The system allows us to sit still in Europe for weeks in the summer, in the UK in winter we would have to drive for 3 hours every 5 days I guess. We run a 75litre fridge, 2 phones 2 x 10 inch tablets, a propex, recharge cameras, led lights, a 19 inch 12v TV, a 350watt inverter.

 

[Stanski]

I already had the solar panels 5 year old semiflexible 2 x 80 watt photonic universe. I can't remember their price. The mppt was around 100 pounds 75/15 victron smart. I think the 8 x 100 ah cells were around 400 pounds and the 2 bms 100a daly Bluetooth were around 100,, that was over a year ago, they took 3 months overland to arrive. The victron lict smart voltage sensitive relay for lithium was 80. I have to guess over cables, polycarbonate and steel to make the underslung battery case, relays, switches heater pads and aluminium heat spreaders to make them the right size, say 150 pounds. So add that up I guess 1000 pounds.
The system allows us to sit still in Europe for weeks in the summer, in the UK in winter we would have to drive for 3 hours every 5 days I guess. We run a 75litre fridge, 2 phones 2 x 10 inch tablets, a propex, recharge cameras, led lights, a 19 inch 12v TV, a 350watt inverter.

The 100A, daly Bluetooth is what for exactly - daly is?
The Victron lict smart voltage sensitive relay - lict is ?, and how used?

 

[wildebus]

Very interesting reading.
Without being too nosey, roughly how much have you spent on the setup.
Victron mppt + Solars + Lithiums + wiring ?
Chap I bought leisure batteries from in Jan said he had bought 4x lithium, whole system costing 2.5K.
Allowed him & partner to run 2 Laptops and Network for work purposes, as well as entertainment.
Curious if prices are falling.

Prices are actually increasing generally at the moment unfortunately
Hard to say if his system at £2.5k was ok, cheap or pricey... What did it include and how much battery capacity?

 

[Derekoak]

Daly I'd a trade name for a well used cheap Bms. It would have been cheaper to havev4 bigger cells and one bigger Bms, but I would loose redundancy. This way if a bms or cell breaks I have still 100ah battery working.
The victron lict recommended by admin Phil allows the alternator to charge my lithium at 40 to 70 amps, a clever split charge relay with voltages set for lithium.