Breakers for 48V lithium batteries that get up to 54V of current?

[AlaskanNoob]

I've got an MPPT that can push 200A to my 48V lithium batteries. But it will push at higher than 48V to charge the batteries, so I'm assuming the breaker between my MPPT and batteries should be rated for 60VDC? Local solar shop sold me 48V 200A breakers and I only realized it after the fact that this might be an issue.

Same with the circuit breakers they sold me that go between the batteries and the bus bar. Local shop sold me one that was rated for only 32V. I should have checked before I walked out. I need 60VDC 120-125A breakers (single pole preferably) but I'm having a tough finding one.

If anybody can recommend a 60VDC 200A breaker and a 60VDC 120-125A breaker I would be very appreciative.

 

[sunshine_eggo]

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[AHTrimble]

I've got an MPPT that can push 200A to my 48V lithium batteries. But it will push at higher than 48V to charge the batteries, so I'm assuming the breaker between my MPPT and batteries should be rated for 60VDC? Local solar shop sold me 48V 200A breakers and I only realized it after the fact that this might be an issue.

Same with the circuit breakers they sold me that go between the batteries and the bus bar. Local shop sold me one that was rated for only 32V. I should have checked before I walked out. I need 60VDC 120-125A breakers (single pole preferably) but I'm having a tough finding one.

If anybody can recommend a 60VDC 200A breaker and a 60VDC 120-125A breaker I would be very appreciative.

Breakers are usually rated for voltages "between" stated values or "up to" values. And they are usually safe to operate at a voltage above their stated "rated" voltages.
All that being said...I would return the beaker and get a better fit.
For each of my batteries I use a "

OutBack Power PNL-125-300VDC Panel Mount Circuit Breaker

 

[OffGridInTheCity]

I use these Midnite Solar 250a Panel Mount breakers between my 48v powerwall and 12,000w Inverters - https://www.solar-electric.com/mnedc250.html They go up to 120vdc. Here's a bit cheaper on AMZ - https://www.amazon.com/Midnite-Solar-MNEDC250-Panel-Breaker/dp/B007IAAETC

 

[AlaskanNoob]

I use these Midnite Solar 250a Panel Mount breakers between my 48v powerwall and 12,000w Inverters - https://www.solar-electric.com/mnedc250.html They go up to 120vdc. Here's a bit cheaper on AMZ - https://www.amazon.com/Midnite-Solar-MNEDC250-Panel-Breaker/dp/B007IAAETC

So for my 48V-54V (or whatever the MPPT puts out to charge) I could use a higher voltage DC breaker.

Perhaps this would work for my battery C/B where the wires can only handle 100A. https://www.solar-electric.com/midnite-solar-mnepv-150-volts-100-amps-array-breaker.html

And this one you use for the MPPT to bus bar, 60V & 200A: https://signaturesolar.com/nader-dc-circuit-breaker-60v-200amp/

Breakers are usually rated for voltages "between" stated values or "up to" values. And they are usually safe to operate at a voltage above their stated "rated" voltages.
All that being said...I would return the beaker and get a better fit.
For each of my batteries I use a "

OutBack Power PNL-125-300VDC Panel Mount Circuit Breaker

That's good to know, thanks for that.

 

[OffGridInTheCity]

That's good to know, thanks so much for that. So for my 48V-54V (or whatever the MPPT puts out to charge) I could use a higher voltage DC breaker.

Breakers/fuses protect the wire (not the devices). And secondarily (unlike fuses) they offer on/off switch to work on things.
If the wire is OK for 250a then yes, a 250a breaker is OK.

Midnite makes a wide range of DC breakers (5a up to 250a) that are good for 48v systems - e.g. usually rated to 150vdc. Most are UL listed.

They're high quality / top tier. They are not the only choice (not pushing them), just the choice I use, OK prices, and they've served me well for 5yrs and counting..... and a couple of them have tripped as they should have, lending confidence for me.

Perhaps this would work for my battery C/B where the wires can only handle 100A. 125V & 125A breaker: https://www.solar-electric.com/midnite-solar-mnedc125rt-remote-trip-circuit-breaker.html

If the wire can only handle 100a you want <100a breaker (not higher) - 80a is the next lower Midnite size.
The primary goal of of a breaker (or fuse) is to keep the wire from melting/burning/shorting a neighboring wire.

 

[AlaskanNoob]

If the wire can only handle 100a you want <100a breaker (not higher) - 80a is the next lower Midnite size.

The battery charge/discharge is rated at 100A. These wires are from Pylontech batteries and they actually say they are rated for 120A although there is some question about that, they're a bit troublesome (https://community.victronenergy.com/questions/41642/pylontech-battery-cable-spec.html). I want to push 100A through them at their max rating. If I get a breaker that is less than that I would lose charge ability. So I *think* a 100A breaker should work.

 

[OffGridInTheCity]

The wire's max continuous is 100A. And the battery charge/discharge is rated at 100A. These wires are from Pylontech batteries. I want to push 100A through them at their max rating. If I get a breaker that is less than that, won't I lose charge ability?

Yes, but remember that a 100a breaker won't trip immediately, the current could surge momentarily above 100a.
This is a DIY site and I don't judge - but me personally, I wouldn't put a 100a breaker on 100a max wire. If you want 100a then get bigger wire or double up the existing wire.

Look - wire / amps is not just about wire size but about temperature max of the coating on the wire. So I assume when you say 100a max wire, the wire may have 90C plastic coating resulting in 100a max. But 90C is REALLY HOT (194F)! I wouldn't run anything where the wires are hotter than I can hold my finger on.

What AWG is this 100a wire?

 

[AlaskanNoob]

I edited my above to be more accurate. The wires are claimed by Pylontech to handle 120A. But they're 4 AWG wires. Some claim the extra insulation makes them handle the 120A.

Pylontech battery cable spec - Victron Community

community.victronenergy.com

 

[OffGridInTheCity]

OK then, 100a breaker on 120a max wire may be perfectly OK. My 4awg fine strand wires between my Midnite Classics and battery get 55C/131F (which is OK / feels warm to the touch) at 80a inside of conduit over 15ft distance. If exposed to air, and short distances, I can see 100a being <60C / OK. I would check the temp once you get operational. You know - try it and just double-check as you operate.

Personally, I don't like things too hot to touch even if (in theory) they are specified to handle that level of heat as heat means efficiency loss!

 

[AlaskanNoob]

OK then, 100a breaker on 120a max wire may be perfectly OK. My 4awg fine strand wires between my Midnite Classics and battery get 55C/131F (which is OK / feels warm to the touch) at 80a inside of conduit over 15ft distance. If exposed to air, and short distances, I can see 100a being <60C / A-OK. I would check the temp once you get operational. You know - try it and just double-check as you operate.

Personally, I don't like things too hot to touch even if (in theory) they are specified to handle that level of heat. Heat also means efficiency loss!

I'm with you. The last thing I want is a fire since we're putting this setup in a wood shed in the middle of tens of thousands of acres of a forest tinderbox and there ain't no fire department this off grid.

The wires will be mounted on the wall, open air, and our ambient temps are 70F at the warmest and -10F at the coldest.

Guy from Victron suggests the cables are *actually* rated to handle 178A given the insulation they use, although the company advertises only 120A.

I will definitely be keeping an eye on the cables for sure and I appreciate your insight.

 

[AHTrimble]

So for my 48V-54V (or whatever the MPPT puts out to charge) I could use a higher voltage DC breaker.

Perhaps this would work for my battery C/B where the wires can only handle 100A. https://www.solar-electric.com/midnite-solar-mnepv-150-volts-100-amps-array-breaker.html

And this one you use for the MPPT to bus bar, 125V & 250A: https://www.solar-electric.com/mnedc250.html



That's good to know, thanks for that.

Remember...fuses and circuit breakers protect the wire. Size CBs according to wire size. Wire is sized according to maximum load + headroom.

 

[再生可能 エネルギー]

It is recommended to have a T-Fuse connected to the battery negative pole.

Adding a circuit breaker on the positive pole would provide a good surge protection
and also isloation between a battery and a Quick Disconnect Anderson connector.

I wonder what would be the best recommendation when using both a T-fuse and a DC circuit breaker:
- Should both devices rated for the same Amp, or should one rated larger or lower that the other one?
I mean, a fuse can be used only once but would a fuse protect faster than a circuit breaker, or is it the opposite.

 

[AlaskanNoob]

All the connections are fused in a Lynx Distributor. The circuit breakers are additional and to help with shutting off components for working on the system.

 

[12VoltInstalls]

It is recommended to have a T-Fuse connected to the battery negative pole

Why not the pos(+)?

 

[AlaskanNoob]

Why not the pos(+)?

My fuses and circuit breakers are all on the positive wires. Except for the breakers from the inverter/chargers to the bus bar, because the only circuit breaker I can find is 2 pole, so both positive and negative will go through those.

Of course that is assuming the breaker I found isn't polarity sensitive. If it is, it's back to the drawing board.

 

[12VoltInstalls]

assuming the breaker I found isn't polarity sensitive. If it is, it's back to the drawing board.

Just wire it in the right direction…

I have 125A Class T on the batt pos(+) for 100A-max lithiums and a disconnect (DC circuit breaker) planned for convenience.

 

[AlaskanNoob]

Just wire it in the right direction…

I have 125A Class T on the batt pos(+) for 100A-max lithiums and a disconnect (DC circuit breaker) planned for convenience.

The problem, I think, is that the circuit breaker between the battery and the inverter/chargers will have power going both ways. Sometimes pulling power from the battery to invert to the loads, and sometimes pushing generator power to charge the batteries. So I think a polarity sensitive breaker would result in a fire, no?

 

[AHTrimble]

T-class fuses are a requirement in my opinion. I place it between the battery BANK busbar (Victron PowerIn) and the inverter...on the positive side.
Almost all solar system circuit breakers can NOT perform anywhere near the level of a Class-T fuse for high-current protection of a battery bank.
Between the battery and the Victron PowerIn (busbar) I use a

OutBack Power PNL-125-300VDC Panel Mount Circuit Breaker

 

[12VoltInstalls]

circuit breaker between the battery and the inverter/chargers will have power going both ways

They should be fused internally for any fault there.

The problem with batteries is a gazillion amps in a few seconds can dump through an unprotected wire. I ‘knew’ that but I learned here about 20kA discharge potential and decided that my ‘casual’ habits with batteries needed amending with energy-dense lithium chemistry batteries- because lithium is not only a delicious dessert topping, it’s a floor polish, too.