DC Disconnector vs Breaker

[aaron_c]

I saw a youtube video recently where the guy suggested that a battery bank should have what I think is a disconnector or a breaker placed on I think the negative pole of the battery bank. In other words, there should be a switch I can throw to cut the current to the whole thing so that I can monkey around with things without having to remove the outgoing wire from the negative terminal manually (and perhaps risk sparks? I'm not clear on this, he showed sparks but I'm not clear what situations create sparks and when that's dangerous).

In terms of placement I think it would go like this: Battery Bank --> BMS --> Disconnector or Breaker --> Shunt-Based Battery Monitor --> Fuse Boxes (I'll have 24 V and 12 V fuse boxes because the system is 24 V but a few small things will run 12 V) & inverter/charger. Right?

So obviously I'm a bit wobbly on all this would love some feedback on pretty much anything I just mentioned.

But also I'm wondering whether there's a reason I'd get a disconnector and a fuse vs getting a 300 A breaker (which I understand basically encompasses both the "disconnection" and "fuse" functions...I think). And I see some automotive breakers at that size selling for $20 or so.

 

[John Frum]

The orthodox setup is to have the breaker as close as possible to positive terminal of the battery.
This minimizes the possibility of a short upstream.
It also leaves your grounding intact.
By convention we ground the negative and because of this we fuse the positive.

 

[John Frum]

As far as I know quality thermal breakers only range up to 200 amps.

 

[John Frum]

I would be very skeptical of a 20 dollar 300 amp thermal breaker.
Link please.

 

[aaron_c]

Link please.

Good to know. Here's what I saw when doing a quick google.

 

[gnubie]

Search results - everything reputable, hundreds of dollars; everything crap, tens of dollars.

 

[aaron_c]

Glad I've got yall here to set me straight. I'm just a babe in the woods, don't know nothing about nothin.

 

[aaron_c]

So now that yall have made me paranoid... Here's a 300 A disconnector. Is it alright?

 

[John Frum]

So now that yall have made me paranoid... Here's a 300 A disconnector. Is it alright?

Yes

 

[Zil]

You can not do better than Blue Sea dc switches. I use a DPST to disconnect my solar panes and battery from the charge controller. Blue Sea M-6010. I also used a singe to disconnect the negative when I had my large lead acid bank. With batteries, it is good practice to disconnect negative first and reconnect negative last.
If you want dc circuit breaker look at Blue Sea for those as well. I prefer fuses.

 

[aaron_c]

Thanks for the recommendation @Zil

Can you explain the benefit of using a DPST vs a SPST circuit breaker in your situation? Or is it even something that I should be worrying about at this point?

 

[Zil]

Not a circuit breaker. I use fuses. Don't worry. Do it your way. It is fine. I have a double pole single throw switch. That is a switch that connects or discontents two separate circuits with one action. With one turn I can disconnect the panels from the CC at the same time, with the same turn, disconnects the battery from the CC. I'm an old lazy bastard that don't want to use any excess movements that don't get me happy ending.