T-Class AND manual disconnect breaker?

[chicagoandy]

Designing an 8S 24V with MB31s. It will have a T-Class fuse.
My question is I also need additional disconnect, and what that will be?

Let's assume a JK Inverter BMS, which will have a BMS switch. It seems like adding breakers, to be used as switches, is also common. It does feel helpful to be able to internally disconnect the battery terminals for maintenance.

Discharge: 250 amps
Charge: 100 amps

Questions.
1. Is the BMS switch sufficient to safely isolate the battery for maintenance? (I am thinking: No)
2. If not, what is the proper MCB?

 

[sunshine_eggo]

Amazon.com

 

[chicagoandy]

Can anyone recommend an MCB?

 

[justchillin]

Amazon.com

I am looking for battery disconnects, specifically Blue Sea 9003e.
It shows as 48v max. I assume that would be a nominal 48v..... meaning it should be fine at 51.2v.
Thoughts?
Blue Sea doesn't seem to show me this and Amazon's Q&A doesn't exactly instill confidence.

 

[chicagoandy]

I am looking for battery disconnects, specifically Blue Sea 9003e.
It shows as 48v max. I assume that would be a nominal 48v..... meaning it should be fine at 51.2v.
Thoughts?
Blue Sea doesn't seem to show me this and Amazon's Q&A doesn't exactly instill confidence.

No, 48V is max voltage and is not nominal. A lot of BlueSea components are intended for marine 12V & 24V use.

Victron does make a good 48V nominal disconnect, max voltage is 60v.

Battery Switch ON/OFF 275A - Victron Energy

The Battery Switch ON/OFF 275A is suitable for battery systems up to 48V. It has a unique ergonomic and aesthetic knob design.

www.victronenergy.com

Nobody can recommend MCBs ?

 

[SparkyJJO]

I don't know if a MCB can do that much amperage. You can get MCCBs that can (the big boys).

What cells are you using that you're going to be dumping that much charge current into them? Most LFP cells for our application are rated at 0.5C continuous, you can do 1C but not sustained without risking damaging stuff as far as I know.

 

[agtcovert]

Can anyone recommend an MCB?

I'm using these: C125 MCB. I go from MCB -> T-Class on bus bar -> inverters (high level).

These are the highest amp MCB I could find. With 5 batteries in my battery bank and the C trip curve, I haven't had any issues with these. The entire system has peaked close to 400 ADC and I've had no issues. Under a heavy load or charging, they've gotten lukewarm; I check them frequently. If all the current is only going through 1 or 2 batteries, these may not be a great choice.

For me -- my DIY batteries didn't come with a built-in breaker. I wanted a way to isolate each battery but leave the BMS on. I don't have these in place or depend on them for overcurrent protection, that's what the T-class fuses are for.

I went back and forth on this versus MCCBs (the big breakers). I think if I was doing it over, I'd probably do the MCCB route. They have equivalent or higher AIC with a bit less complexity/wiring. Just a matter of personal preference / space you have.

 

[sunshine_eggo]

I'm using these: C125 MCB. I go from MCB -> T-Class on bus bar -> inverters (high level).

6K Icu means it's unlikely to prevent a short circuit unless you KNOW your total system resistance is HIGHER than 8mΩ.

 

[agtcovert]

6K Icu means it's unlikely to prevent a short circuit unless you KNOW your total system resistance is HIGHER than 8mΩ.

They're strictly for manual disconnect in my application. For DIY battery cases that come with a breakers, they're similar if not identical. I assume most of these MCBs are made in the same place. Since the question was about MCBs and the OP is also using T-class fuses I shared what I'm doing. I don't have expectation that these provide protection. I expect the T-class fuse, BMS, and fuse inside the battery (as a last line of defense) to provide the protection.

And to be more clear:

Each battery -> Pos & Negative terminals to MCB -> then MCB -> Lynx Power In T-class -> Lynx Distributor
None of my pack is connected electrically together, they all go to the power-in / bus.

If there's another / better way, I'd appreciate the feedback. I wanted a means to isolate a pack without turning the BMS off.

 

[chicagoandy]

What cells are you using that you're going to be dumping that much charge current into them? Most LFP cells for our application are rated at 0.5C continuous, you can do 1C but not sustained without risking damaging stuff as far as I know.

250 is definitely oversized, 150 continual will be the norm, but I am oversizing to be able to remove one of two parallel batteries and still be within wide margins.

150 may be the right way to go as that seems to have better component availability.

 

[chicagoandy]

Each battery -> Pos & Negative terminals to MCB -> then MCB -> Lynx Power In T-class -> Lynx Distributor
None of my pack is connected electrically together, they all go to the power-in / bus.

Also my plan.