Has anyone used the alarm signal from a smoke detector to automatically disconnect a large battery bank? I’m looking at how to make a diy system. I assume that a latching relay with the off signal taken from the smoke alarm would work, but I’m struggling to find such a relay that will take 500 amps at 12v. I have considered a high load relay from something like an electric winch, but this would need to be constantly energised and probably produce a fair bit of heat, whilst eating power.
It is easier to disconnect loads and chargers, that way all current movement is stopped.
The other way is the ATC and ATD connections if you battery has them.
Disconnecting a whole bank (especially underload) introduces its own hazards like arc quenching so you would need to consider one that is rated for switching load. Then you want it to be bibstable so you don’t have to be powering something to hold it latched.
It is some I have thought about and obviously products exist as evs need them and many bigger voltage batteries have this in their design with contactors for control already.
As an example here that in my wonderings found from Blue Sea. I have never used them though.
Agreed, the loads such as inverters are straightforward to stop. I was thinking more in terms of being able to isolate the bank from everything in the event of the lithium batteries off-gassing inside a sealed container. The battery bank consists of multiple LiFePO cells, where the main catastrophic failure mode is off-gassing through the pressure relief valve. There have been a number of explosive events with these cell types, where the gas is ignited by external electrical fires after various types of equipment have failed. At this point, trying to turn off a failed device, probably a dead short, isn’t likely to work, hence looking at isolating the batteries at source.
Like you, I’ve found several of these remote battery switches, but they are all far too expensive and have far too many features for the purpose I have in mind.
Obviously such a safety cut off isn’t something that will be operated regularly - hopefully never.
So the cheapest way is basically stop current movement from loads and chargers and have a en extinguisher built into the battery. There are also a bunch on the market now for that.
Manufacturers are starting to include them in the battery box.
This is an egg chicken discussion among many… What happend first cell failure or wiring/bms failure? Cell venting is usually a non event if there is no ignition source.
Venting can be brutal. Hot toxic gasses. A pouch cell can be the cause, but so can over charging. A simple BMS setting error is all you need. Or a malfunctioning BMS. Research shows that 35% of the gasses is hydrogen. Hydrogen need a certain level of oxygen to go off. It can potentially self ignite with temperatures over 500°C. Without enough oxygen it will ‘only’ burn, but not explode.
I much rather see a prismatic cell leak its electrolyte than having to witness a venting cell. Scary sh*t.
Also. I much rather shoot a bullet in a prismatic cell than to overcharge it (research shows that over charging is even more dangerous).
Hopefully nobody runs into something tragic like that. Homes, boats and vans will be lost. Still waiting on news from the last two incidents.
I’ve thought very carefully about cell choice and how to avoid dangerous situations. I’ve decided that the primary risk comes from venting gas becoming stoichiometric in an enclosed space and being ignited. You’ve probably all seen the exploding boat this summer.
My design choice given that the installation is in a boat, is to enclose the batteries in an air tight container (fire retardant grp), vented to the outside of the boat.