Battery disconnects

[marshman]

You have to be very careful here there is a massive difference between a DC Isolator Switch and a DC breaker.

An isolator is only designed to be turned on or off with the current effectively at zero to literally isolate a supply. The current ratings for an isolator will just be for the current that they can safely pass on a continuous or intermittent basis.

A DC breaker on the other hand will be rated for the current it can safely "interrupt", and can be assumed to be able to safely disconnect the circuit even with the full load current flowing.

Also worth noting a lot of marine "stuff" is only rated at 12 or 24V.

[Caesium]

A DC breaker on the other hand will be rated for the current it can safely "interrupt", and can be assumed to be able to safely disconnect the circuit even with the full load current flowing.

The problem is finding a DC breaker you can trust? A lot of them don't seem to be worth the paper their spec sheet is written on and separating the wheat from the chaff is a problem. That's kind of led me down the path of ignoring DC breakers entirely and just going with a decent isolator and a decent fuse.

Which does kind of leave me with no way to safely break a large DC current (but not emergency-situation-large, that would just blow the fuse), other than pulling an NH00 fused disconnect. They're pretty meaty so I'd feel confident doing that.

It seems to be a bit of a minefield

[Stinsy]

It seems to be a bit of a minefield

That’s the problem with physics! To break a high-current DC connection under load is very difficult indeed. Most isolators are rated to carry the current, not break it.

[AlBargey]

I think like most things, there are disreputable sellers, fakes and poor designs not fit for purpose, but there are also good designs that work to spec. I've been using Tomzn DC Circuit Breakers, which seem pretty good, Schneider also do decent DC breakers but there are a lot of fakes. TBF though, I've used the DC breakers on solar circuits, and still use the 58v Mega Fuse (Not the standard 32v ones!) for (48v) battery connections.

The previous video showing unknown breakers catching fire, well they wired them the wrong way around!? The arc suppression on the proper dc breakers uses magnets inside and is polarity sensitive. You can check for the magnets with your screwdriver tip.

I did once buy some cheap Schnieder breakers, which turned out to be fakes and didn't have the magnets. I'm pretty sure the real ones will have been designed and tested to spec properly though, and probably why they're also quite expensive.

Interesting inside view of a Tomzn DC breaker:

[Jinx]

Schneider do plenty. All the commercial UPS systems will break the DC at minimum voltage (max current), from 30kVA to several MW, using a undervoltage trip.

[Caesium]

and still use the 58v Mega Fuse (Not the standard 32v ones!) for (48v) battery connections.

Oooh this is a good point, I must check if mine are 58v rated

The previous video showing unknown breakers catching fire, well they wired them the wrong way around!? The arc suppression on the proper dc breakers uses magnets inside and is polarity sensitive. You can check for the magnets with your screwdriver tip.

Yeah they did intentionally wire it the wrong way round, but that was the point though - because current can flow both ways if you put these breakers between an all-in-one inverter and a battery. So the current flow changes direction depending on if its charging or discharging, so it has to be going the wrong way some of the time, right? That's my understanding of it and why I'm wary of using these in that situation. For a solar cutoff I've no worries at all.

Off to watch the video, bigclive is always excellent