question

The MPPT can have low temp charge protection enabled or disabled. It is important that the MPPT receive temp data from a BMV, smartshunt or a smart battery sense connected through a VE.Smart network. If you have a GX device, then the BMV or smartshunt can feed temp data to the system through VE.Direct.

If enabled, the MPPT will clearly not charge until the temperature raises, so you would have to disable MPPT low temp charge protection to be able to heat from solar.

Some BMS do not have low temp charge protection. You need to determine that for yourself.

You would need to devise your own control circuit and heating system to accomplish your goal.

Ok thanks. I've been trying to figure out a Victron solution but there doesn't seem to be a workable design. I've seen a lot of research into water heater power sinks but those are typically after fully charging batteries and using AC power. I think a resistive radiator powered straight from the panels + a DC power contactor to switch it off once it's warm enough for the batteries to charge might work.

What I would consider doing is insulating the heck out of your battery box, then adding a little thermostatically controlled heating to the box. Just enough to keep it at, say, 10C. Given 5cm or so off polystyrene, it shouldn’t take much to keep your batteries warm enough. There are heating pads out there that are gentle enough so as to not cook the batteries.

Use L2 output switched based on temperature.

Yes, this is a feature request!

I just found this thread because I'm looking for the exact same thing: Use the load output to drive a heater. When it's so cold the battery charging is disabled, but the sun is up, take the energy from the solar input and send it directly to the load (heater) instead. Yes it'd be basically the thermostatic heater already described, but with the additional knowledge of when the sun is up, so it'd never drain the batteries into the heater -- only solar energy could be used for heating.

The SmartSolar load output functions (streetlighting, user configurable, etc) are already wonderful and they're a major selling point for me, but adding a low-temp and sun-up function would make them even more useful. (Also, letting the Tx port have a separate config from the Load port, so two separate functions could drive the two outputs.) Then I could use the Load terminals for the battery heater, and the Tx port to signal my BatteryProtect which handles the larger loads.

Like nbezanson, I found this for the same need.

I'd like to be able to use all victron for charging and 'BMS' duties with the need to heat up the battery box if it's too cold to charge. Otherwise I have to put this all on the battery with a separate BMS and disable the low temp charging protections.


It would be nice to have the MPPT go into 'low output mode' or 'matched output' and instead of outputting at charge current, read the battery volts at the terminals and then output at .1v higher than that. That way you'd never try to charge but you'd be able to power your heater from solar. Trigger a smart relay to 'on' during this time and have the heater on that relay.

Dittos on the MPPT feature request!

Since LiFePO4 batteries have their own BMS, you can connect your loads directly to the battery. The BMS will handle low voltage and temperature cutouts.

This frees up the Load terminals to run the heater. Here's the logic needed:

1. Temperature is less than 40°F (adjustable) and
2. Voltage is at or near setpoint. This indicates that either the battery isn't charging, or that there is extra power available to heat the battery.

Last night, the temperature dropped into the 20's. Here's a voltage chart from one site without a heated battery:

-Around 04:30, the BMS switched off charge capability. The battery voltage dropped due to the insertion of an outbound diode.
-Around 07:30, the sun came up. The voltage immediately popped up to setpoint. This is when the heater should be switched on.
-Around 11:00, the battery warmed up enough to begin charging. This is when the heater should be switched off.