question

I came here to ask much the same question - and it appears your post has pretty much answered it!

Firstly, I deliberately chose a BMS without low temperature cut-off because I still want to draw power when the battery is cold, I just don't want to charge it.

I am building what looks like much the same system in my trailer - I already have the Victron MPPT solar and wall charger and I'm about to install the LiFePO4's, so I need the 12/12-18 Orion (although I am still considering running power from the battery in the car rather than using the tow cable and then using a 12/12-30 Orion instead). Either way, I need to make sure that the Orion doesn't try to charge the battery when the battery temperature (as measured by the smart shunt) is below zero. There appear to be two problems:

1. The Orion would be powered down most of the time, so if it were possible to set a low temperature alarm somewhere, that would need to be checked as it powered on, and
2. As you say, looking at the demo product in the Victron app, there doesn't seem to be a way to set shutoff based on temperature.

However, I'm planning on installing a Raspberry Pi running Venus OS and I seem to remember reading something about that acting as a controller and sending enable/disable commands to other connected devices. Unfortunately, I can't find anything that says which devices have what functionality available (and even if it were possible, would point (1), above apply?).

The other problem I have is that I still want the fridge to run even if the batteries don't charge and they're both fed from the same cable. I guess I could do something funky and power the fridge from the permanent live controlled by a relay on the ignition-switched live. That would also give me the advantage of having more power I can feed into the batteries.

I guess the other option is that I pre-heat the batteries using one of those 12v silicone pad heaters meant for fuel tanks.

I guess I should just buy the Orion and try it out.

You may want to use a Smart Battery Disconnect to manage the charge from the Orion 12/12-30. It can be wired to still feed power to loads but not charge the battery.

I am in almost the same scenario. Was all looking good until I discovered the Orion cant join a VE.Smart network to ensure non charging occurs when the battery is cold. Alas, makes the whole Victron 'smart' setup a bit useless.

I didn't even check to see whether the Orion had a VE.D port before I ordered one - I just assumed that it would. It arrived yesterday and that's when I realised it didn't. More fool me for not checking.

@arghhh40k suggested using a Smart Battery Disconnect (SBD) as a remote switch, but this won't work for me as it's going to be fed from what is essentially a switched supply - when the car ignition is off, the Orion won't output anything and so the SBD will be turned off - this means it can't be remotely turned off or on until the car ignition is turned on.

For me, I think the simplest solution is to build a little ESP8266 device that subscribes to MQTT on the the RPi/Venus (I've yet to play with this, so I'm not sure what is and what is not available here) and switches a relay on/off when the temperature is high/low. If I power this from the vehicle ignition (i.e. on the input side of the Orion) and have it normally open, this is probably the safest and easiest way of guaranteeing that the Orion can't turn on unless the temperature is above a threshold. Powering it from the vehicle ignition also ensures that it's not draining power when the car's not connected.

*EDIT* Actually, after thinking about this, it may be a good idea to put two relays on the board - that way one can switch a heating pad on/off in the battery compartment. Then I could add some LEDs to show status, then... Oh feature creep, don't you love it.

I better understand now what you want.

I was able to find some 12v powered heating thermostat relays for a low price. It's a relay with a thermistor and setpoints. Basically if temp goes below a certain point the relay closes and when it rises above a certain point it opens. My original intent was to power a heating pad under the pack but it would also work to stop charging for external devices via a remote port. If you wired the ignition and low temp relay in series both would need to be closed to allow it to work.

There is a few ways to split your bus to allow power to devices and not to batteries but it starts to get complex

If you have a BMV712 with temp sensor, then what you can do is wire the relay comm and NC to the remote on off port on the Orion. Then set the BMV relay to open when the temp is whatever you set (I do 42f). This will turn off the orion when the it hits that temp. You can set the recovery temp to +5f over your set point to turn the charger back on.