Switch or Breaker?

[geoffr]

I've been looking at a fair number of lithium system designs and a fair number have a switch or breaker right at the battery. This makes sense to me as it means you can shut everything down (BMS included).

Where I get confused is when this is a breaker as I thought that DC circuit breakers could only accept current flowing in one direction - am I wrong?

I really would like to use one of these:
https://www.bluesea.com/products/cat...ers/187-Series

It's a much nicer size that the standard switch I can find:
https://www.bluesea.com/products/cat...tches/e-Series

(In either case I'll have a fuse (ANL or T-Class) as well...)

[wholybee]

Switches and breakers are for different purposes. A fuse and a switch is what you should use.

There is a more convenient size:
https://www.bluesea.com/products/cat...tches/m-Series

[GordMay]

Many circuit breakers are rated foe “Switch Duty”.
For Instance: Blue Sea Systems ‘285-Series’ [up to 150A, 48V] & ‘187-Series’ [up to 200A] Surface [or Flush] Mount Circuit Breakers combine switching and circuit protection into a single device.

[geoffr]

Thanks, but my actual question is:

Where I get confused is when this is a breaker as I thought that DC circuit breakers could only accept current flowing in one direction - am I wrong?

[team karst]

Originally Posted by geoffr

Thanks, but my actual question is:

Where I get confused is when this is a breaker as I thought that DC circuit breakers could only accept current flowing in one direction - am I wrong?

polarity of I not an issue. It makes the same magnitude of magnetic flux to pull in the latch...

just like a magnet N pole will stick to iron same as a S pole....

[misssherry]

Originally Posted by geoffr

I've been looking at a fair number of lithium system designs and a fair number have a switch or breaker right at the battery. This makes sense to me as it means you can shut everything down (BMS included).

Where I get confused is when this is a breaker as I thought that DC circuit breakers could only accept current flowing in one direction - am I wrong?

I really would like to use one of these:
https://www.bluesea.com/products/cat...ers/187-Series

It's a much nicer size that the standard switch I can find:
https://www.bluesea.com/products/cat...tches/e-Series

(In either case I'll have a fuse (ANL or T-Class) as well...)

The switch or breaker will not turn off the BMS. It is powered by the small sense wires inside the battery. It is always on, unless the battery cells fall outside the set safety limits.

[GreenWave]

Yeh you cant turn off a battery. A switch is the best option as close as possible to the output(s) of the batteries.

[CaptainRivet]

Originally Posted by geoffr

Thanks, but my actual question is:

Where I get confused is when this is a breaker as I thought that DC circuit breakers could only accept current flowing in one direction - am I wrong?

You are wrong, a DCbreaker can accept current both ways.
What cannot accept current both ways are SSR, maybe you saw a switch that actually uses an SSR to cut off the big load.

[Pete7]

Originally Posted by CaptainRivet

You are wrong, a DC breaker can accept current both ways.
What cannot accept current both ways are SSR, maybe you saw a switch that actually uses an SSR to cut off the big load.

You have used the abbreviation "SSR" without explaining it first. The result is I am at a loss to know what you mean by SSR. Is it another name for a voltage sense relay (VSR)?

If so, are you aware that some are dual sensed and can connect power to flow either way.

Pete

[Pete7]

Originally Posted by geoffr

I've been looking at a fair number of lithium system designs and a fair number have a switch or breaker right at the battery. This makes sense to me as it means you can shut everything down (BMS included).

Where I get confused is when this is a breaker as I thought that DC circuit breakers could only accept current flowing in one direction - am I wrong?

I really would like to use one of these:
https://www.bluesea.com/products/cat...ers/187-Series

(In either case I'll have a fuse (ANL or T-Class) as well...)

Geoff we have both, a 120A Blue Sea 187 panel mount, which is about to be upgraded to 150A version. Pricey, but this is one item I want to work properly and not have to replace or have cause problems as a single point of failure. The panel mount version bolts directly to a Victron Lynx or Power In box which is handy and saves a couple of connections in a high current cable.

Note, they don't "pop" straight away, they allow a degree of over current before disconnecting. Higher current earlier pop. I only know because whilst cooking breakfast one morning on the all electric galley, I turned the electric kettle on whilst the toaster was running and the induction hobs. Way more than the inverter or Blue Sea was rated for. Anyway it managed 3 minutes before popping so cutting the power to the inverter.

This was the point I realised what I had done A simple reset and we were back to cooking breakfast.

We have a NH00 fuse as well. These are the European equivalent to a class T fuse, just a quarter of the price in the EU. Sadly more expensive than class T in the US.

Pete

[Wotname]

SSR = Solid State Relay
https://en.wikipedia.org/wiki/Solid-state_relay

[CaptainRivet]

Originally Posted by Wotname

SSR = Solid State Relay
https://en.wikipedia.org/wiki/Solid-state_relay

Thanks.
A DC breaker is generally both ways but yes you can buy special models that only work one way on purpose. As with fuses they are so many specs and use cases out there, so be careful what you buy. And there are one way DC breaker out there that effectly using a SSR inside the dc breaker enclosure to switch the high load side but also have a protection diode to protect the SSR from current the wrong way.

With NH fuses 5 tips and facts:
1) there are printed on DC only fuses available specially speced for solar parc installs which you can also get in superfast like class T fuses are only available. They are expensive, even more then class T.
2) the standard NH AC fuses (only uses GS or GG spec type!!!) from top notch Eaton, Bussmann... are also all DC rated but not printed on and hard to find in the specs. But they are DC approved and only the short circuit current rating is 80kA for DC and 100kA for AC. That's also part of the corresponding ISO Norms and certification for grid station, which is the main use case and what they are developed for originally. They are all fast fuses in GS and GG spec.
3) there is nothing wrong with buying NH fuses used, you get a lot eg on Ebay from factories that are demolished. These factories have often a huge stock of replacement fuses never used and even if they are used they have no real wear and aging. As long as the indicator shows they are intact and the ceramic body is undamaged they are good to use. If they are black and ugly the reason is they are silver coated and oxidized (that's 95% optical as oxidizedsilver is not effecting electric conductivity), take a polish for silver cutlery and 10min later they look like new and work like new out of the box. I bought a box with around 50 fuses and 30 fuse holder for 80Euro from ebay, most where unused. A NH3 fuse holder for 250 till 630A fuses costs 300Euro new, used between 30 and 50. Its just ceramic and highest grad cooper coated in silver made to last very long.
4) in 12-48DC spec the NH GG AND gS for the constant power draws you have in your system and or constant current delivery of your bank NOT peak!
they are fast fuses and made for 24/7/365 running at 100% rating (my NH3 500A fuses is 8-10 degrees above ambient temp when pulling 500A). The superfast Class T you need to spec for peak current, they are developed for electronics to protect them from spikes like lighting. Not really the best main battery fuse. The bigger the fuse, the bigger the voltage drop=losses...NH are metricously designed to have the smallest voltage drop possible as eg losses here can cost a company 1000s of dolars a year more on their eletricity bill.
5) their are no fakes and copies out there of NH as thats a) highly controlled and b) its simply massive material used where no much space for savings, just a big chunk of ceramic and silverplated cooper...use tin or cheaper cooper and fuse will immediately heat up significantly showing you its a fake and a) will then take care of this manufacturer. Megafuse as well as ANL are a lot fakes and low quality out there that are nearly impossible to dedect as fake but when its melting down and introducing massive heat into the install its already too late.

[SOLAR SUPPORT]

Originally Posted by geoffr

I've been looking at a fair number of lithium system designs and a fair number have a switch or breaker right at the battery. This makes sense to me as it means you can shut everything down (BMS included).

Where I get confused is when this is a breaker as I thought that DC circuit breakers could only accept current flowing in one direction - am I wrong?

I really would like to use one of these:
https://www.bluesea.com/products/cat...ers/187-Series

It's a much nicer size that the standard switch I can find:
https://www.bluesea.com/products/cat...tches/e-Series

(In either case I'll have a fuse (ANL or T-Class) as well...)

DC Switch, breaker, fuse can pass current in both directions. We can also add VS battery combiners to this. VS battery combiners allow bidirectional passage of current within a certain voltage range.

Imagine drawing energy from your battery above the charging current. Let's call the direction of this current polar "+". When the devices that consume energy are turned off, the direction of the current will be polar "-" and the energy current will begin to fill the battery.

It is a dc device battery isolator that allows unidirectional current flow. They are used in two types: Argodiode or Argofet. These are battery isolators that allow current to pass in one direction.

[OS2Dude]

Originally Posted by geoffr

(In either case I'll have a fuse (ANL or T-Class) as well...)

For lithium you need a Class T fuse. Lithium batteries can produce a LOT of juice if they short. Class T can take over 20,000 amps and remain open when blown.

General Information: You can not use AC breakers on DC circuits.

If you are using the breaker as a combination fuse/switch, it needs to go at the battery end of the positive wire. If you use a separate fuse and switch, the fuse will go at the battery end of the wire and the switch can go anywhere before the distribution bus. Since you said you will have a Class T at the battery, why bother with a breaker instead of a switch?

A switch will not disconnect an internal BMS. The ABYC requirement for a switch is to have a means of shutting down the power to the system in case of an emergency such as an electrical fire. If you plan to also use it to turn off your DC devices when you leave, then you will have to bypass the disconnect for your bilge pumps, solar chargers and anything else that requires a current while you are gone, such as a radio memory.

[smacksman]

My surveyor told me that the coastguard require all positive supply leads off the battery to be fused within 6" of the terminal. When I was inspected by the Coastguard heading south they were suprised that I had complied to this rule. This inferred that many people don't.