OpenEnergyMonitor Community

Recommended products to disconnect battery using the relay

Hi, I’ve seen this asked and answered before but since I’m relatively new to all this and after hours of searching and coming up with nothing I’ll ask…

What are people using to disconnect the battery if a cell goes over/under voltage in the bank? I would prefer a latching relay connected to the diybms relay but can’t find one to handle the current I need that is relatively cheap. (Also I’m not 100% confident in what exactly I need)

Any other options for a 48v battery and 100 amps+. Anyone using something they are happy with that doesn’t cost a fortune?

Thanks for any help

Mosfets to do the switching

This is also something I am looking for. Without endorsing any specific company, Shallco makes bistable (latching) relays in 12v and 24v that can handle 200-300 amps, but they are approximately $65 USD each. Add on shipping, and it is close to $100 each. Everything else I have found is at least triple that price.

I’ve looked at SSRs in the past for other projects, but haven’t seen any latching ones that don’t use any power in a energized state, and haven’t seen any in the 100+ amp range either. Don’t MOSFETs use some power in their energized state? You also need to be careful with SSRs, there are a lot of inferior fakes. I bought some “brand name” ones that turned out to be fake, they melted down at 20A despite being rated for 40A!

I’m also curious what other people are using. I can’t imagine most installations just skip a disconnect relay, that seems very risky.

Not cheap but up to 48 volts there are the Victron BatteryProtect units, they go up to 200amps. You can use them as a remote controlled switch or as under voltage disconnecting switch.

I’m working on something that can switch 60 amps at 100 volt. But it seems more difficult as expected. Making it is easy but making it safe is something different.

IGBT’s look interesting. I’ve used MOSFETs and transistors but never used one of these. Someone told me IGBTs are used in electric vehicle drives, low frequency, around 1kHz switching.

They can handle big amps it seems.

(not exactly a product, but interesting…)

Use the relay to control a contactor? Or a DC rated breaker with a shunt trip or UVR?

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This is where the DIYBMS lacks in my opinion. Its cheap until you need to find a solution to this problem. If you only need a single BMS then this is not the product to save on costs. Works out more expensive when I add the circuit breaker with shunt trip than an off the shelf solution.

However I needed a modular type BMS that could continue to change configurations while testing different batteries and pack sizes, so in my case the DIYBMS was much cheaper than buying multiple off the shelf BMS’s for my different configurations.