What do Your Set Your Low Temperature Cutoff to for Lithium Batteries?

[chrisski]

What do Your Set Your Low Temperature Cutoff to for Lithium Batteries? Any reasoning to would be nice. I’m thinking of having the SCCs shutoff charging at 35, and the BMS shutoff charging at 32.

I used to think this was an easy question with the battery spec sheet saying 32 F; however, the software on my BMS although adjustable came programmed higher, I think 40 F, so perhaps my temps are too low.

I also want to have two steps. The first cutofff would be from a higher temp that shuts off charging from the Victron SCC by a Victron Battery Montitor that is networked together, and the second step would kick in from the BMS at a lower temp. In theory, it the BMS kicked in at 32, then the SCCs should be sending no current to it anyway.

 

[RandR]

I will tell you about my recent experience with my Victron SCC, 500A Shunt, and 30A AC charger. I was thinking like you, the factory setting of 5C* was awfully conservative, so to to stagger them and create a safety buffer. Ha! Mine were not happy until I set all 3 at 5C*. might have been something I did but nothing would work until I set them back to the factory temp settings.

 

[eXodus]

Measuring temperature is an actual science.
Took a full college class about it.

Depending where you mount your temperature probe makes more. The BMS maker don't know where the probe will end up. So they assume bad placement.

Cells are probably warmer at the terminal then at the ends. So some part of the cell will be colder then others.

Don't assume that one temperature from the SCC and the BMS match. Only if the communication between them uses the same probe..if they are different sensor. Temperature reading can be quiet different at the same ambient.

 

[chrisski]

I will tell you about my recent experience with my Victron SCC, 500A Shunt, and 30A AC charger. I was thinking like you, the factory setting of 5C* was awfully conservative, so to to stagger them and create a safety buffer. Ha! Mine were not happy until I set all 3 at 5C*. might have been something I did but nothing would work until I set them back to the factory temp settings.

I appreciate the response. Normally not an issue, but today had freeze warning and this is the first time I’m taking it out.

 

[Sojourner1]

Are your batteries the same temp as the outside ambient temps? Where are the mounted in the trailer?

 

[chrisski]

Are your batteries the same temp as the outside ambient temps? Where are the mounted in the trailer?

I don’t have good data yet. They are not outside temp, but they are mounted in the pass through RV storage. I’m taking it out for a week today and I’ll find out for sure.

I think for this trip they will be fine. Nightly lows are expected to be 33, so this keeps them above freezing kept in the pass through storage, I think. The next trip could be colder.

 

[Diesel Pro]

You could try one of those home weather stations with a remote outdoor sensor and just keep an eye on things.

I was wondering same thing. Strap to a battery case or just let it float and read air temp. In my case the cabin has a heater, but the pilot can sometimes go out so having protect is a necessity. I'm thinking the air temp will drop much more quickly than the cell temp.

 

[Hedges]

Although I'm not using lithium (except for power tools, at least some of which wait for cells to warm or cool to appropriate temperature) ...
My thought is determine max charge rate your system can deliver,
then set low temperature charge cutoff to a battery temperature where that charge current would do no harm.

Lithium accepts its maximum charge rate, typically around 0.5C, in the vicinity of ambient 25 degrees C.
Down near freezing, max rate for no accelerated degradation is greatly reduced.

 

[Sojourner1]

I don’t have good data yet. They are not outside temp, but they are mounted in the pass through RV storage. I’m taking it out for a week today and I’ll find out for sure.

I think for this trip they will be fine. Nightly lows are expected to be 33, so this keeps them above freezing kept in the pass through storage, I think. The next trip could be colder.

If they're heated basements you should be fine as long as you use the furnace. I use wireless remote temperature sensors, 1 in the front compartment, 1 outside besides all my cells have individual temp readings.

These... https://www.amazon.com/AcuRite-0109...80856317&psc=1&ref_=d6k_applink_bb_dls_failed

Edit: My cell cut off from charging is 32f. I use solar 99% of the time, before adding the extra insulation in the front compartment the cells would get down near 32f but that's when the outside temp was near single digits with daytime not getting above mid twenties. I never worried about the amps going in even at those temps because the amount of solar is minimal that early in the morning and if need be I would take the small 120v heater and run it off the generator for 1/2 hour and that would raise the compartment and the cell temps by 15-20f degrees.

 

[OffGridInTheCity]

From a practical standpoint - I have my lithium-ion (18650) powerwall under the house where it bottoms out at 48F/9C in the cold, cinder-block/concrete corner. It was about 26F/-3C ambient last night....


No problems charge or discharge so far and this is the 3'rd winter.

 

[HRTKD]

On one of my batteries (the one closest to the exterior wall) I have three temperature probes. These are for the Victron BMV-712, Overkill 4s 120 amp BMS and the thermostat for the warming pads. The probe for the BMV-712 is on the positive post of the battery. The other two probes are taped to the top of the battery between cells two and three, with a bit of insulation over them to shield them from the ambient air.

When I checked on a cold day last winter, all three probes were within .2° F as I recall. It was such a small difference that I was impressed and called the placement good enough.

As for temperature settings, the warming pads are set to 35° F to 45° F. The BMS cuts off at 32° F and I think I set the Victron 100/50 solar charge controller to be one degree lower than that, but I haven't looked at the settings in a year.

I would argue that the solar charge controller should have a lower cutoff than the BMS. In my system, that would allow the heating pads to get power from the solar charge controller instead of the battery. If you have no warming system then I would set the solar charge controller to be one degree higher than the BMS.

 

[OffGridInTheCity]

I would argue that the solar charge controller should have a lower cutoff than the BMS. In my system, that would allow the heating pads to get power from the solar charge controller instead of the battery. If you have no warming system then I would set the solar charge controller to be one degree higher than the BMS.

I can see that because charge min temp is higher than discharge min.

I did a little research into my Midnite Classic owner's manual because it has battery temp probes as part of it's feature set. However, these are for lead acid voltage compensation and no option for low temp disconnect. Its a shame because the basics are there - e.g. temp probe and charge shut-off. It does have hi temp shut-off capability.

I stumbled across this while googling:


I use Batrium BMS, which has separate temp control options for charge / discharge. I don't have it 'active' because its not needed.

 

[chrisski]

First night out with the batteries and I set the BMS cut off to be 1 C off and then 3 C back on. Fare higher was not an option. That comes out to 33.8 F off and 37.4 F on. The Victron, which is my main shut off device is set to 39 F off.

My five temp sensors are off by about 1.5 F and they seemed to be within 6 degrees of the outside temp all day long. This is one of the measuremensts at 5 PM:

Outside Temp. Victron Temp. BMS 1 Sensor 1 BMS 1 Sensor 2 BMS2 Sensor 1 BMS 2 Sensor 2
==========….========….. ======…………======………….=====…………======
52 F…………57 F……………….56.3 F…………..57.6 F…………….56.5 F…………57.7 F

Coldest it got here last night was 44 F. The batteries were 48 F.

I would argue that the solar charge controller should have a lower cutoff than the BMS. In my system, that would allow the heating pads to get power from the solar charge controller instead of the battery. If you have no warming system then I would set the solar charge controller to be one degree higher than the BMS.

I like the thinking there. Although low temps won’t happen much here, I can see my next project is temp management. Whether that means move the battery and inverter inside, which would be good for 115 F summer temps, or put a heating pad in, that remains to be seen.

 

[Diesel Pro]

Midnite is planning a firmware update that should provide low temp charge cutoff.

"Unfortunately the Classic does not have a low batt temp shutoff feature. We plan to incorporate that in the next firmware release, which may be a few months down the road."

 

[gray webber]

Midnite is planning a firmware update that should provide low temp charge cutoff.

"Unfortunately the Classic does not have a low batt temp shutoff feature. We plan to incorporate that in the next firmware release, which may be a few months down the road."

Can an existing Midnite Classic be upgraded when the low temp shut off software becomes available? I and my nieghbor both have a need.
Thanks