33 replies to this topic

[Vic Harder]

That would work, but automation is a wonderful thing.  Right now my batteries are at -1*C.  If I use my remote starter on the truck I will be feeding 30A into the batteries, which is not good.  It would be wonderful if the truck started, and the charge current went into a heating pad for the batteries until they were +3*C. 

[PaulT]

I have a small 700 watt electric oil-filled space heater. It has a simple thermostat.  I set the temp to keep the camper about 35-40 degrees F and leave it plugged into the internal AC outlet. I open the battery compartment and those doors where water pipes are located.  I leave it on with the camper plugged into shore power. This to ensure that my Battleborne batteries remain in the chargeable range. With the main power switch off, the Iota will not be used to charge the Battleborne batteries.

 

With the top down, there is only a small space to heat. The oil filled heater never gets all that hot so no fire hazard. If the camper is moving, I need to keep the heater from falling over so I use a large milk crate and place th heater within the crate. A couple of blocks of wood keep the heater from wobbling.

 

Most of the big box stores or local Ace HW or other HW stores carry these heaters.  The price of the smaller units is usually well under $100US. The heat will also protect your plumbing in case you didn't get all the water out.

 

Paul

[Happyjax]

Can't you take the fuse out of the charging circuit and throw a small solar panel on them? A couple amps should not damage them at 32ish degrees. Sorry I'm only good at …fahrenheit

[rando]

I was concerned about the low temperature charging when I first designed/installed my LiFePO4 battery.    I added a thermal switch that would shunt the power from the solar panels into a battery heater, until the temperature was above 5C, then switch the solar panels back to the solar controller.    In the end, I never ended up using it, so I eventually removed it to reduce complexity.  However  I did leave the heaters installed with a simple standalone thermostat if I ever wanted to use them. 

 

As with most things, it turns out that the issues with low temperature charging of lithium is a continuum, based on the temperature and the rate of charge.  It is not like everything is great when the temperature is > 0C and goes to pot when the temperature is < 0C.  At low charge rates (< 0.1C) and with a lower charge voltage (less than 3.5V per cell or 14V per pack) there is insignificant harm done charging down to at least -10C.   

 

For my setup, I have my BMS set to stop charging at -5C, my maximum charge rate is 0.1C and I only ever charge to 13.8V.   I leave the battery connected all winter (in CO day time winter highs are usually ~5C, but we will have weeks with highs below -5C), and the battery seems to stay around 80% SOC and I have not seen any capacity fade over 3 years.  

 

For colder locations (ie Vic out on the frozen prairies) then either disconnect the battery to keep it about full or if you expect some warmer days, just rely on the BMS to stop charging when it is too cold. 

[Vic Harder]

I was concerned about the low temperature charging when I first designed/installed my LiFePO4 battery.    I added a thermal switch that would shunt the power from the solar panels into a battery heater, until the temperature was above 5C, then switch the solar panels back to the solar controller.    In the end, I never ended up using it, so I eventually removed it to reduce complexity.  However  I did leave the heaters installed with a simple standalone thermostat if I ever wanted to use them. 

 

Can you share a few more details on this thermal switch and how you had it wired in?

[PokyBro]

The question I have wondered about is, would it be best to have the lithium battery charged up, then remove it from the camper and bring indoors to store over the cold months, since it’s said that lithium batteries will keep a charge for a very long time? Or is it okay to leave them outdoors, but prevent any charging that might go on in very cold weather below freezing?

[rando]

It was this:

https://smile.amazon...r/dp/B079CBXJVN

 

Take the +ve wire from your solar panels and wire that to the common terminal.  Then wire the NO terminal to the +ve solar input of your solar controller and the NC to the heater on the batteries.  The other end of the battery heater goes to the -ve solar panel output, in parallel with the solar controller.    When the battery temperature is lower than the set point (say 0 C), then the power from your solar panels is going into the battery heater.   When the temperature gets to a degree or two above 0C, the thermostat switches, returning the power to your solar controller.    While a bit clunky, I liked that one because it uses no power and the contacts are rated at 16A.  

[rando]

The question I have wondered about is, would it be best to have the lithium battery charged up, then remove it from the camper and bring indoors to store over the cold months, since it’s said that lithium batteries will keep a charge for a very long time? Or is it okay to leave them outdoors, but prevent any charging that might go on in very cold weather below freezing?

 

Most drop in LiFePO4 batteries and stand alone BMS already have a low temperature charge protection function built into the battery.  They won't accept a charge if the temperature is too low, and they won't be damaged.   There is no reason to bring them inside.

[rando]

To add, I installed 2 heaters similar to these on an aluminium plate that my battery sits on:

 

https://smile.amazon...m/dp/B082Z3HKDY

[Vic Harder]

It was this:

https://smile.amazon...r/dp/B079CBXJVN

 

Take the +ve wire from your solar panels and wire that to the common terminal.  Then wire the NO terminal to the +ve solar input of your solar controller and the NC to the heater on the batteries.  The other end of the battery heater goes to the -ve solar panel output, in parallel with the solar controller.    When the battery temperature is lower than the set point (say 0 C), then the power from your solar panels is going into the battery heater.   When the temperature gets to a degree or two above 0C, the thermostat switches, returning the power to your solar controller.    While a bit clunky, I liked that one because it uses no power and the contacts are rated at 16A.  

thanks for that rando.  I wonder if this would work:

 

1) Since I have an all Victron setup, I am inclined to use the relay output on the BMV712, which uses the temperature probe already installed onto the +ve terminal of the battery bank. 

 

2) That relay would fire a SPDT 80A relay I have on hand - to do the heavy lifting.  It would sit between the positive terminal of the battery bank and all the various charge sources... DC-DC charger, MPPT output, Victron AC/DC shore power charger.

 

I'm wondering about surges that might happen during switching from "run the battery warmer" to "charge the batteries".  Do we need to worry about that?