I just learned that you can charge lifepo4 batteries in cold weather, just currents have to be low. Anyone tested this with Gerbo, is it possible to program to do it automatically? So MPPT and Multiplus II for example would charge with lower amps when freezing?
From the net...cant remember where but your choice...
If you have a Lithium (LiFePO4) battery, there are some things to consider when charging under extreme temperature conditions.
Lithium battery manufacturers often state an operational temperature range of -30°C to +80°C / -22°F to +176°F and an optimal temperature range of -10°C to +50°C / 14°F to 122°F (this varies depending on brand and model, consult your manufacturer). This is often misconstrued as a safe temperature range for both charging and discharging, this is not the case. The operational temperature range is referring to discharging the battery only.
Charging a Lithium battery in ambient temperatures below 0°C / 32°F must be avoided. The reason for this is it may potentially damage the battery and / or reduce its lifespan.
The optimum ambient temperature for charging a Lithium battery is +5°C to +45°C / 41°F to 113°F.
When attempting to charge a Lithium battery below 0°C / 32°F a chemical reaction referred to as “Lithium Plating” occurs. Lithium plating is caused by the charge current forcing the lithium ions to move at a faster reaction rate and accumulate on the surface of the anode.
When this chemical reaction occurs, the internal resistance of the battery increases and reduces the rate of chemical metabolism. This chemical reaction causes a permanent reduction of the battery’s capacity and will continue to reduce its capacity each time this reaction occurs.
If you plan on using a Lithium battery in a location that may drop below 0°C / 32°F, you must be cautious as to when you attempt to charge the battery. Simply waiting for the temperature to raise during the day is a simple solution.
Having the batteries mounted in a location that will have a higher ambient temperature than outside temperature is also advisable.
Having a battery management system that can monitor the batteries temperature will be beneficial and convenient.
With the touch of a button you can see what the standing temperature of the battery is and therefore whether it is safe to charge.
The point is to charge with low amps in order to not force battery to take in what it cannot. So far I've seen a BYD manual state -10 Celsius and another -20 if I remember correctly.
That's correct, it's possible to charge LFP below 0C (actually, even +5C, see below) but only at reduced current, and the manufacturers rarely supply any information about what this should be. IIRC the BYD batteries allow full-rate charging (1C?) above 5C and at reduced rate (0.1C?) down to -10C, but this is all controlled by the internal BMS for which the user has no access to or control over the charging settings.
I know that some time after the LVL batteries were released BYD updated the charging firmware to enable charging below 0C following demand from cold-climate customers. But the point is that they are 100% in control of low-temperature charging, not the user.
If you're building your own system, doing anything like this is at your own risk, you're unlikely to get any support from the cell/battery supplier.
Like i said your choice
This is often misconstrued as a safe temperature range for both charging and discharging, this is not the case. The operational temperature range is referring to discharging the battery only.
The process of heating and charging is automatically controlled by the BMS and the heating element embedded within the battery and takes roughly 40 minutes to change the temperature from -20°C to +5°C. Once the battery temperature reaches +5°C the charging starts immediately and once the temperature rises to +10°C the heating element stops and continues with the charging.
When you charge a lithium ion cell in below freezing temperatures, most of the lithium ions fail to intercalate into the graphite anode. Instead, they plate the anode with metallic lithium, just like electroplating an anode coin with a cathode precious metal. So charging will electroplate the anode with lithium rather than recharging it. Some of the ions do intercalate into the anode, and some of the atoms in the metal plating will intercalate later over 20+ hours if the cell is allowed to rest, but most will not. That is the source of the capacity reduction, increased internal resistance, and also the danger.
This lithium plating of the anode isn’t nice and smooth and even – it forms in dendrites, little sharp tendrils of lithium metal growing on the anode.
As with the other failure mechanisms, which likewise are due to metallic lithium plating of the anode, these dendrites can put unexpected pressure on the separating membrane as the anode expands and forces the membrane to one day fail unexpectedly – ie a short circuit / dead cell.
Better way is to install battery heaters. Maybe add thermal insulation as well, but you're going to have to look at cooling in warmer weather if you insulate.
Battery heating works as temporary solution, or if you have long term energy for the heater, you probably can run space heating too.
FWIW...there are some people, that use heating mats, normally used in a greenhouse to keep seedlings warm (or for reptiles in a terrarium). these draw only a small amount of energy (5-50W) and are temperature controlled, hence as long as your batteries are not drained, you could use some discharge to heat these via the mats.
Best suitable/be fitted to battery modules that are placed in a Rack, like Pylontechs.
Using a smart socket, you could control these via Node-Red, even.
I don't think slow charging is the way to go. My system in winter only has small solar yield (59 degrees latitude) but I still didn't do it like that. I also cannot control mppt output remotely in vrm, maybe with a cerbo this is possible but with my globallink 520 it's not.
Use a heating pad of some kind, and a temp sensor.
My first step would be insulate the battery. I used a cooler bag for drinks and food and put some extra armaflex foam in it. This helps massively, and may already be enough for you.
I've put a ruuvi sensor in the bag, and one in the cabin for outside air temp.
I use a battery with heating elements build in. It kicks on below 5 degrees celcius, and uses solar output if available to heat. If no solar output or charge is present (at night) it won't heat. You could build a system like this yourself with a heating pad, temp sensor and controller and the mppt load output I think. But you will have no way of remotely turning it off unless you use a relay of some kind.
I also have a diesel heater that heats the room my battery is in, that I can switch on remotely. But I don't think it's needed as it only gets to -20 Celcius inside here, and the battery stays much warmer than that so far.
When I'm not at cabin, I typically have more solar yield than the system is drawing. So using it to heat the battery is fine with me. Start with a temp sensor and insulation, you may not need a heater at all. Victron Mppt has low temp cutoff so damaging your battery will not be the issue.
Yes, but it would be depending on where it is placed and how cold it is mostly. And also the mass of the cells and placement of heater pads. Mine is 100Ah Redodo, so fairly small lifepo with a heating pad above and below from the factory. Also it's placed on an insulated floor in the warmest part of the cabin. I've looked at the bag I used with an infrared camera to make it lose as little heat as possible. Where the wires poke out it still loses some, can be improved. Nothing is permanently stuck to the battery, I can just take it out of the bag in summer.
It uses 60watts in my setup, and will take a little over an hour to warm to 10C from around freezing. I've not had it much colder than that, but I've missed the beginning of winter this year as it's a new install. So I can expect to make that 60wh back from solar on most days even in winter once it begins charging.
I think you need to look at what you're trying to accomplish. For me, I always want to arrive at the cabin with a charged and working system. The system is always on, just the inverter switches off. The lifepo is pretty good at holding a charge. But if this was a house or RV I probably wouldn't need any of this to keep it warm.
How cold is your climate?
But is your state of charge dropping much when the RV is parked for a few weeks? If not you can just heat the battery with a heat pad (off the alternator even) at the beginning of the trip, and switch your gear on after the drive. The rest of the trip you'll probably be fine because your RV needs to be above freezing to use it I assume.
A ruuvi tag is really nice to start with, at least to monitor your actual battery temp and set alarms. You can use it for lots of other things too, like monitor your fridge temp or outside temp.
Are there any heating kits for batteries that don't have internal heating?
I don't think there are kits. But the way they are build is very simple. It just has a heat pad on top and below or the sides of the battery and a way of turning them on and off.
The advantage of this is that you can actually turn it all off. A build in BMS with heater you can't actually turn off. So when my cells are just above freezing I actually have to wait untill the heating cycle stops untill it stays charging.
If you're ordering this from AliExpress with long shipping times, it's probably a good idea to order one extra temp sensor/switch because the cheap ones break sometimes.
