BMS with Temp cutoff

[Davehc130]

OK I have been racking my brains and searching the internet for about 6 months trying to get this one issue resolved...I Cant find a BMS that will cut off charging while still allowing discharge..I can find Solar chargers that do this but here is what I am building...Basically a Battle Born to go in my 4Runner...I had hoped when Will pulled apart the Battle Born he would have ID'd the BMS they use....So I have a Redarc DC-DC charger and all the rest of the components, Balancer etc and even a few BMSs but I cant find a BMS that will cut out the DC-DC and Solar when the Cells get below freezing...basically the Solar panels go through the REDARC so just need a BMS that will stop taking a charge from the REDARC below freezing....I was out a few weeks ago and it was 1 degree...that would have killed my home build Cells if I had it hooked up and the REDARC tried to charge them when I turned the 4runner on...the REDARC even allows solar to power the charger when the alt is off so I have to make sure the BMS will not allow charging below freezing....IF anyone has a suggestion please pipe up...I am sure that there are others trying to figure this out as well...thanks

 

[Johan]

I have very little experience with BMSs and I may misunderstand the problem, but recently I fully read some BMS manuals. So what is your budget? What about a €159 TinyBMS in dual port mode? From the manual, p31 (Revision A, 2018-07-30):

Condition
If one or both external temperature sensor channels are connected and in use:
Ext. Temp #1 < Low Temperature Charger Cutoff threshold or
Ext. Temp #2 < Low Temperature Charger Cutoff threshold. [...]
Action
[...] Load Switch – turned on [...]
Charger Switch – turned off.
BMS switches to sleep mode after 10 seconds time interval, if no charger, Ignition signal or ongoing UART communication connected. BMS in sleep mode on Charge Under-Temperature Warning (if no Under-Voltage Fault occurred at the same moment) measures temperature and, if the Warning condition recovers, wakes up from sleep mode and turns back on Charger Switch, if the charger was detected.

? However, depending on your case and possible other requirements, I can imagine that this BMS is overkill for "only cutting off charging below freezing". A temperature-sensor-controlled contactor may be cheaper and simpler. See for example this one on Ebay for $10 to keep a normally-open contactor closed when above freezing. The sensor is 12V, so can be powered (use a fuse) by the Battleborn. But maybe there are strong arguments not to use this design.

 

[Bob B]

I bought a Sendon battery thru Alibaba and the BMS does cut off the charge input independently of the discharge. I did a little testing by adjusting the low temp paramater to force it to cut off charging .... but didn't fully test this function. I was able to apply a load and have it work while the low temp cutoff had disabled charging. I did see an odd cycle occur. It seemed that it did allow the charge input to be used to directly supply the load and once the load was turned off ... 5 seconds later it would shut off the charge input again. I didn't continue testing because the application I am using, I don't intend to have the load and charge operating simultaneously.... hope that made a little sense.
I haven;t been able to determine the BMS part number for sure, but I think it is the same as THIS ONE being sold on Ebay based on part numbers I am seeing in the Bluetooth App. I may end up ordering one of these for testing since I may build my own battery pack for my RV.

 

[Maast]

Well, you could always use a couple of 100A schottky diodes and then have a normally closed contactor/relay bypass it with the above mentioned temperature controller opening up the circuit whenever it gets close to freezing. The diodes will need a heat sink and be electrically isolated from the chassis.

The diodes will prevent power going to the batteries and the normally closed contactor bypass will allow two-way power flow when it's not triggered.
You'd lose about a half a volt going through the diodes but it shouldnt be noticeable.

 

[israndy]

Why hasn't anyone created that as a stand-alone circuit, tested, and ready for purchase? It seems so necessary for RV battery packs that travel to the cold. Perhaps there could even be a relay or knife switch that controls when the diode is in-circuit so you don't lose the power driving thru the diode all the time. Turn it on in winter and off the rest of the year, or some such.

Come on, Victron, get to it

 

[Picasso]

Come on, Victron, get to it

Victron, couldnt even put a temp sensors on its solar charge controllers........later adding it via a bluetooth device that some times just forgets what its doing. Don't even get me started on it LoraWAN device.....