Lifepo4 BMS without low temperature cut-off for charging, No problem with the right CC..perhaps

mcgivor

The question of finding a BMS with a low temperature cut-off is a common dilemma, whilst thinking about something entirely different, something came to light that may be of interest to others. This is something I've no need for, therefore not tested, but it probably will work, the intent is to plant the seed and hopefully someone will nuture it.

Some of the better charge controllers now have ground fault detection for the PV input, using a fuse that once blown due to a ground fault event renders the controller inactive until such time the ground fault is rectified and the fuse replaced.

The idea is to use an accurate thermal detection device (relay) preferably with an external sensor that can be placed on a cell, or cells. Using a normally closed contact of the relay, run the ground bonding for the controller through the contact, this would simulate a blown fuse when in a low temperature condition has occurred, by opening the contact, thus shutting down the controller. Multiple relays could be utilized to better cover the battery as opposed to a single sensor, all NC contacts in series 

Naturally I understand there will be questions, along with negative feedback as to the legitimacy of doing this, so for the point of discussion let's refer to this as a hack, using something for a function it wasn't initially intended for.

BB.

Midnite/Carlington Switch may have a configuration for breakers that you are looking for:

http://www.midnitesolar.com/pdfs/Carling_C_series.pdf

I think there are "shunt trip/Aux Coil" types that are available pair with standard breakers. Like the Ground Fault Breaker used to detect Ground Fauls (1 amp breaker paired with ~80 amp breaker) where a small current will trip the 1 amp breaker, which is tied to one or more parallel connected 80 amp breakers. They also have Aux coils available that use 5/12/etc. volts to trip a breaker stack.

I do not know much about the details--Contacting NAWS/Midnite/Carlington engineers/sales engineers is probably necessary to understand the acceptable configuration options.

And if I recall correctly Dave A. worked with a Lithium battery set that used a large fuse on the battery bus terminal, and had a relay that if the BMS determined there was a dangerous condition, the BMS threw a large relay across the battery bus, which then popped the battery fuse--Then required a "service person" to put the bank back in service (and inspect to ensure that the fault condition(s) were addressed and the batteries not compromised).

Using "crowbar" circuits is a time honored system to protect equipment and power sources.

Things are progressing on the Breaker Front--Some WIFI/Smart Home units are becoming available:

https://www.amazon.com/s?k=Remote+control+Circuit+Breaker&ref=nb_sb_noss_2

At the above link, many of them are for 220 VAC systems... A little few 120 VAC may be available too. Did not see any DC rated units with a quick search...

-Bill

mike95490

As long as the LVD is wired to the PV input side of the CC.   You don't want to disconnect the CC from the battery while solar is active

mcgivor

mike95490 said:

As long as the LVD is wired to the PV input side of the CC.   You don't want to disconnect the CC from the battery while solar is active

Just a clarification, the discussion is about low temperature disconnect of charging, not low voltage disconnect, a simple mistake I understand.
 
The theroy of operation is to cause an intentional fault which causes the controller to stop charging, with a Schneider MPPT 150 the ground fault method in post #1 will most likely work without disconnecting the battery.

With Morningstar the disconnection of the remote temperature sensor (RTS) by a relay contact would also have the same results ( with LFP the RTS is not required but can be used with a zero value for compensation programed with MSVIEW software ) this is confirmed by Morningstar as a suitable method to achieve PV shutdown.