Independent high voltage cutoff

[danphillips]

Looking for a device to disconnect my LifePo4 battery bank at a configurable voltage as a safety net to my BMS.
My boat has an xantrex 2012 so I can not use a Victron Battery Protect. Power can come from alternator, SCC, or the inverter charger. Having just read about a failed SSC that over injected a very high voltage into the BMS causing it to fail, and then over charging the batteries.

 

[TorC]

Have you read the thread on the SOK battery in Up in Smoke? Per HighTechLab, he's checked Victron, Outback Flexmax, and Midnite. Those companies use magnetic isolation for PV+ (not full isolation, as PV- is bonded to Batt-), so they are immune to the issue. As long as PV+ goes open circuit it's no different than normal operation with no charging happening.

 

[danphillips]

@TorC , I was not able to find your sited thread, could you provide a link?

 

[TorC]

SOK Troubles (user error)

I feel bad for this guy.

diysolarforum.com

 

[danphillips]

@TorC , thank you for the link. However is seems that most of the discussion was addressing just the SCC Issue. I need something that could sit in front of the BMS and isolate the battery from all charge sources in the event of an over charge.

One thought was to use a second BMS with more conservative settings. After reading the entire thread, seems that there is not a ‘box’ available at this time that will do what I am looking at.

 

[Don B. Cilly]

You could use a voltage controlled switch to pilot a set of big relays.
The alternator would probably be dodgy... maybe divert the charge to a decent load instead of cutting it, or have a small battery on it all the time...
-

 

[TorC]

Correct, there is not yet a box. A lot of thinking has been going into the problem in this thread: https://diysolarforum.com/threads/why-not-to-use-daly-bms-with-mppt-controllers.24922/

It seems we've got confirmation that a few of the best SCCs are designed fail-safe. If you want something else, I think the current most likely is a watchdog on the DC bus to trigger a remote trip breaker that will cut the SCC(s) if it approaches the BMS cutoff point.

 

[toms]

The GSL MIHV will do what you want, it comes with preset voltage but they will make you one with any voltage you require.

 

[TorC]

Close. The pass-through current on that is too small for most systems. That said, if it could trip a PV breaker it might work. The kicker: there's a clause "MOQ applies to other voltages."

 

[danphillips]

That is what I am looking for, only if it would support 130-200a and voltage be user adjustable. Maybe a new product idea starting to form.

 

[toms]

It might be cheaper to just get a BMS that’s capable of using the cell high voltage trigger on a contactor between charge sources and main bus bar.

 

[danphillips]

@toms , this was my first thought. Use a second BMS, however that means twice the cell wiring, and a lot of internal components, however does provide redundancy.