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What options to build a low temperature cut off?

lupo

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Jun 10, 2021
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Austria/Netherlands
I am using a daly bms without low temperature cut off. The victron charge controller has a built in temp. sensor but I would like to have an external sensor option. The victron bluetooth temp. sensor is quite expensive and I do not trust bluetooth that much for such a crucial function. Do you have any recommendation for an (inexpensive) low temp. cut off for a ~100A system?
 
The victron charge controller has a built in temp. sensor
This internal sensor cannot be programmed as a low temperature disable.

You need additional components like the Smart Batter Sense as suggested, or the BMV712 or Smart shunt with sensor.

As a fail safe I used a low temperature mechanical thermostat connected to the Victron solar controller via VE port.
frost thermostat
A similar product should be available in your location.

Mike
 
if you want really reliable they make things called "thermostat snap switches"...about as simple as it gets and you can use it to switch anything you want.
 
you are right, it is not that expensive. It just looks expensive if you compare it to a simple temp sensor on a cable for 5$. For my use case I would like to have a bullet proof solution as at it up on the mountain and it could happen that there won't be anyone for weeks or months. As a software developer I like solutions with as little software as possible ;) and I do not know how reliable bluetooth is for this crucial low temp cut off functionality. I can understand that bluetooth is convenient when the battery is far away but for a lot of use cases a simple temp sensor on a cable would be quite useful and less error prone I guess.

This internal sensor cannot be programmed as a low temperature disable.

oh thanks, that is good to know as I haven't tried it yet. I have the smart victron mptt which no longer has a VE port, so I would prefer a really simple solution like the mechanical thermostat or bi metal you proposed. I could disconnect the solar panel with such a switch as it is quite difficult to find a temp switch that can handle 100A of the battery...
 
The Victron default LiFePo4 profile has a low temp cutoff of 5 Celsius. The sensor is not on the battery so will be less accurate - perhaps why the cut off is set so high.
 
The Victron default LiFePo4 profile has a low temp cutoff of 5 Celsius. The sensor is not on the battery so will be less accurate - perhaps why the cut off is set so high.

thanks for the hint. so the internal sensor can be used for that? I will try it out and test it...because this would be sufficient for my use case I guess.
 
thanks for the hint. so the internal sensor can be used for that? I will try it out and test it...because this would be sufficient for my use case I guess.

Yes, it will work. I have the Victron BMV-712 connected to my two Victron 100/50 MPPT solar charge controllers. Once that Bluetooth connection is made, the solar charge controllers get the temperature from the BMV-712's probe and - as near as I can tell - ignore their internal sensor. A few months ago I tried to see what the "ambient" temperature was by looking at the solar charge controller. But it was showing a temperature that had to be from the probe on the battery.
 
Yes, it will work. I have the Victron BMV-712 connected to my two Victron 100/50 MPPT solar charge controllers. Once that Bluetooth connection is made, the solar charge controllers get the temperature from the BMV-712's probe and - as near as I can tell - ignore their internal sensor. A few months ago I tried to see what the "ambient" temperature was by looking at the solar charge controller. But it was showing a temperature that had to be from the probe on the battery.

thanks. that would be even better, to have the bluetooth sensor and the internal one as a fallback in case the bluetooth connection fails.
 
I believe the reason for the 5c setting is the scenario where your batteries are getting colder than 0c at night and remain so longer than the ambient air around the controller.
 
The Victron default LiFePo4 profile has a low temp cutoff of 5 Celsius. The sensor is not on the battery so will be less accurate - perhaps why the cut off is set so high.
have you ever tried it, because the internal sensor of the Victron MPPT is not used, at least I couldn't trigger it. See also my test in
 
internal one as a fallback
The internal sensor on the Victron controller will not cause low temp shutdown on its own. It need info from the system.
This is clearly stated in Victron literature.

Mike
 
The internal sensor on the Victron controller will not cause low temp shutdown on its own. It need info from the system.
This is clearly stated in Victron literature.
unfortunately, do you know why? I think it would be quite useful to use it as well. Of course the temp sensor can't be super accurate as the controller also emits heat, but it could turn off at e.g. 5 degrees.
 
If you’re going to use a temp sensor to trigger a relay between the SCC and the battery, I’d be careful in the choice of a relay. I have a different Victron SCCs that charge at 15 amps, 30 amps, and 50 amps. I would need a relay that could work at DC amps. On one system I have three SCCs, a 50 amp and two 30 amps, so the temp sensor would need to trigger all three.

When I looked at doing this, some of the relays I looked at were not easily labeled for AC current, which is safer to work with then DC current. The DC relays I looked at were also more expensive than an AC counterpart.

Since I already had the VIctron BM-712 with external sensor and Victron Blue Tooth SCCs, I gave up my search and used the Victron Bluetooth to shut off the SCCs When it gets too cold. When I did that, I had to put the Victron Cutoff voltages above the Overkill BMS voltages so this would be primary.
 
If you’re going to use a temp sensor to trigger a relay between the SCC and the battery, I’d be careful in the choice of a relay. I have a different Victron SCCs that charge at 15 amps, 30 amps, and 50 amps. I would need a relay that could work at DC amps. On one system I have three SCCs, a 50 amp and two 30 amps, so the temp sensor would need to trigger all three.

When I looked at doing this, some of the relays I looked at were not easily labeled for AC current, which is safer to work with then DC current. The DC relays I looked at were also more expensive than an AC counterpart.

Since I already had the VIctron BM-712 with external sensor and Victron Blue Tooth SCCs, I gave up my search and used the Victron Bluetooth to shut off the SCCs When it gets too cold. When I did that, I had to put the Victron Cutoff voltages above the Overkill BMS voltages so this would be primary.
thanks for all the details. I also think that a dedicated relay introduced also new problems and is also not that cheap, I guess the bluetooth sensor might be the better solution then.
 
Here are the settings for the VIctron BMS as primary cutoff and what I set the BMS to a lower setting:
35947466-4A4B-4C20-8FF7-4ECCBF1BBF7B.png
 
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