Discussion of DC Breakers

[jim]

Hello, I have a sbms120 I want to set up.  I've been searching for proper DC breakers, which are not cheap in the US.  I wasn't wanting to necessarily purchase the cheapest DC breakers I find on ebay or aliexpress.  Mouser and Digikey seem to have some options, but the least expensive option I found was some phoenix DC breakers starting around $16 and go up.  

Alternatively, how would a blade fuse box work for my purposes?  For now I'm just wanting to get things set up to charge and test some batteries I have.  I read Dacian mention two 60 cell panels could wired up together, and then four panels could eventually go to a single 63A DC breaker.  I may go that route anyway on the PV side, but how about the breakers needed for all the DC devices I would be using like lights, computers, etc?  Could it work decently well with the below photo?  It seems to provide a common negative that appropriate things can attach to which I would need anyway.  Right now I would not have an inverter (but will eventually add one).  I assume this is often what is done for mobile projects like RVs and vans and marine.  It seems most of these fuse blocks go to 32V (, and they usually are around 75A to 100A rated, which seems to be about right for the battery side of things (especially as I'm only going to have at most 10x250w panels for now).  I'm less clear if this could/should be done on the PV input side (and removing all these fuses would be more annoying than switching a breaker, which I've read is one purpose of the breaker on the PV side. 

I believe Dacian mentioned he had trouble with the fuses integrated in to the MC4 connector and eventually switched.

I'd be open to other suppliers.  I did find a place somewhat near me that may have $8-9 DC breakers, but having a lot of 3A lines on the battery side would really add up in price quickly.  I know fuse has to do with protecting based on wire size, so what are people using for these?  I was assuming a 10A circuit would allow 25v x 10A max, so allow up to 250w on that circuit?  Do people make a lot of smaller circuits so the lights may only be on a 3a or 5a circuit? (I realize people probably do all kinds of things, my experience is limited to AC home breakers and circuits generally)

My assumption is these fuse blocks could maybe work for a portable unit, or an offgrid cabin.  No inspector would allow this in a US home?  Perhaps my "offgrid" non-electrical detached garage, maybe they wouldn't know or care if I'm not hooked up to the power system.

For testing, two of these are $35...  but I don't want to be unsafe obviously.  I tried searching but didn't come up with much.  I believe one company in the US has breakers for DC and AC, but I was leaning towards the mini din rail breakers more typically seen in places like New Zealand and Europe.  Many thanks for any comments.

https://www.amazon.com/Circuit-Waterproof-Indicator-Protection-Automotive/dp/B07NZSJDY7/ref=sr_1_32?dchild=1&keywords=12+way&qid=1597159928&sr=8-32

[Demosthien]

Just for some extra info and a layout for you to ponder... I'm using DC MCBs in my build - 24V 280A LiFePO4 in a motorhome.

I'm in the UK so I'm looking at Schneider DC MCBs but I've also seen TOMZN branded ones from AliExpress recommended by people in different forums.

https://docs.google.com/viewer?a=v&pid=forums&srcid=MDEzMTk3MjE1MjIwMTk4NjAzOTABMDE5ODg0NTMxNjM3MDQ1NjgzNTgBYnFTdkhxaDFDUUFKATAuMQEBdjI&authuser=0

[Dacian Todea]

Jim,

What you are protecting with either circuit breakers or fuses is the cables.

Not sure what you will have as loads in your garage but say you want to have 6x 10W LED lights (DC 24V LED lights) then each LED light may need around 400mA so all 6 of them will need 2.4A and maybe you will want to add more of them in the future. All you need is a single circuit with say a 10A fuse or breaker and 14 AWG wire to supply all this LED's and maybe add a few more in the future you do not need individual wires and fuses for each LED light.

Maybe I mentioned before but I use this type of DC breakers and they are $11 on amazon and fairly decent quality with both fast electromagnetic protection and slower bimetal overtemperature protection.

https://www.amazon.com/dp/B06XDYZCPZ/ref=twister_B06XDJNP82

For two parallel PV panels connected with 10AWG wires you will want a 32A breaker. This are also bidirectional breakers fairly unusual for DC breakers but a great future.

While you will find even lower cost breakers this are very good quality and you should not need that many but I do not know what your application is.

[jim]

Perhaps you did and my searching was a failure.  I didn't see too much discussion, but makes me feel better those Tomzn being an option.  I'm less nervous about trying those out.  I mean, I've seen $50-100 or over from some companies as well.  I figured $16-18 minimum at mouser was more than I was looking to spend.

I believe someone had old stock midnite solar DC breakers, some for 63a, that were maybe $8 in bulk (if others are looking).

Still not sure how local codes would even accommodate 24v DC lines in new construction.  I can get away with a large system in my non-electrified garage if I keep it separate.

I did realize I do not need a fuse for each "thing" I hook up, but I would need one for each circuit I as you say (and it may have four or five separate leds).  I thought one of these 6 or 12 way fuse blocks at $12-18 may allow a lot of experimentation without a lot of additional cost.  Those fuses are cheap and locally available.  I just wasn't sure if they were bad for some reason.  In theory, I should be well below the wire limits anyway.

Many Thanks for the quick replies!

[Casey & Gina]

Not sure if this is of interest to you, but these are what I use for DC power distribution to lower-amperage devices: https://www.amazon.com/dp/B074QMRBPB/ref=cm_sw_r_cp_api_i_i60mFb239XCVP

A little more costly and requires you to buy Anderson Power Pole connectors as well, but makes for a very safe way to distribute power with no exposed live power points.

[Chris Cord]

Square d QO series have dc ratings and are sold at Home Depot. But only the Qo line have dc info in the specs

[michael clark]

i bought Square d 20amp QO breakers and 100 amp 8 slot outdoor rated load center enclosures. i hope to employ these for the breakers to the 250 watt  60 cells solar panels .they will not work for high voltage dc but should be great for the 24-volt system the electrodacus uses. still working on it waiting for lifepo4 batteries and some pieces and parts. i hope!

[Dacian Todea]

Michael,

You mean this breakers ?  They are only rated 120Vac so not sure if they will be capable of 40Vdc needed for 60 cell panels.