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12V circuit breakers |
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bitSmasher 
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Joined: 23 June 2012 Location: Melbourne Status: Offline Points: 2295 |
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 Topic: 12V circuit breakersPosted: 07 April 2014 at 12:24am |
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I'm planning a battery box with 2x 100Ah SLAs, a 400w inverter built in and a few 50A andersons to run to amps/etc
Might scale back to 1x battery per box if it's too heavy/cumbersome Fusing it will be a necessity, and I like Phil B's suggestion from another thread:
What would be the best breaker to look at using? I really like this style of DIN Rail Mount, I can keep everything neat and cables hidden The other that I've seen is Automotive surface mount which is a bit clunky in mounting Also worth asking, is there any chance household 240v AC breakers are usable in a 12v DC application? This looks like it could be a costly exercise, any advise I should take in as to products and purchasing? |
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amlu
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Joined: 30 November 2009 Location: london Status: Offline Points: 740 |
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Posted: 07 April 2014 at 12:38am |
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big car audio 30a fuse on the big wire connected to battery terminal.
keep one spare and dont make mistakes ;-) can add somewhat 12v distro to it, use a auxillary car fuse box, was getting them in uk for like £10 each in cpc shop... can dig up the link if needed. you load it up with car type blade fuses. |
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studio45
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Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3864 |
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Posted: 07 April 2014 at 1:20am |
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I wouldn't use car style blade fuses as they can melt under sustained high current especially the larger ratings. Check out AGU and ANL fuses for better designs. I do like the idea of an electromagnetic breaker though, as that Jaycar page says they offer lower voltage drop compared to a fuse and sometimes in a 12v system every 0.1v counts! For my application I would need like a 45 amp breaker though, a 70A wouldn't really give me the protection I need, I'd have to put ludicrously over-sized wires on my battery harness.
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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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Phil B
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Joined: 21 November 2004 Location: Melbourne Status: Offline Points: 2328 |
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Posted: 07 April 2014 at 11:02am |
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I only have my phone right now so can't find the links. I found some 63a dc din rail mounted 2-pole breakers in Melbourne for a reasonable price and used them for Wind / Solar. Then some Jaycar 150/250a blade fuses ..they bolt into a carrier...for positive and negative sends to main busbar and the inverter.
Mounted everything on wooden panels in the trailer and also din rail mounted the 240v breaker/ rcds... I'll try upload some fotos from my fone ! P |
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tomr_29
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Joined: 23 February 2009 Location: West Midlands Status: Offline Points: 540 |
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Posted: 07 April 2014 at 11:19am |
Yes you can use a normal household MCB if you want. Its the current which trips the breaker and they will work at any voltage up to their rated spec (note that usually the maximum DC voltage is lower than the maximum AC voltage). One thing to watch out for is household MCBs are usually B-curve which means they won't take large short-term current spikes the way a traditional fuse would. If you're using a low-cost power inverter without any current smoothing you'd probably need a C-curve minimum to prevent nuisance tripping. Edit: How much current are you expecting to pull? 400W @ 12V is just over 33A, not taking into account losses. Edited by tomr_29 - 07 April 2014 at 11:22am |
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bitSmasher
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Joined: 23 June 2012 Location: Melbourne Status: Offline Points: 2295 |
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Posted: 08 April 2014 at 2:40am |
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Did some browsing of forums to find that household AC breakers aren't appropriate - mainly due to the way they struggle to extinguish an arc from high current DC
Makes sense to me (given that I know little about them) and explains the cost difference between AC and DC breakers Was thinking of a few ~20A breakers for my Anderson outs, and a 30A or more for the inverter But given how expensive they are, might just look at one 50-60A breaker for the whole lot - Phil I'd be interested in seeing what you bought and where from Internal wiring will be thick cable, have a few jumper leads salvaged for that. Have considered fuses as well but they're not as straightforward and idiot-proof Goal is to stop any major issues from gear failure/shorts etc, being wary of what could go wrong at an outdoor party - don't want to have the battery power weld/burn things! |
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studio45
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Posted: 08 April 2014 at 3:54am |
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As an MCB is effectively an automatic relay, I suppose the usual down-rating applies when using for DC. Forum member DJLeco posted a video a while back showing (in Romanian, though the video was quite clear anyway) the difference between breaking AC and DC current with a 10A relay. DC was easily able to arc and weld the contacts compared to the same voltage and current of AC. In fact it pretty much destroyed the relay.
Not sure how easy they are to get apart, but one way might be to take a 100A or 3 phase big-man DIN breaker and rewind or replace the coil so it trips at 50A or whatever instead. The contacts should be big enough to break the DC. Depends how good your hacking ninja skills are :)
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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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bitSmasher
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Posted: 08 April 2014 at 4:05am |
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I do enjoy dismantling things. Not so good at reassembly though!
Have read about polarised breakers too, and how they can catch on fire if wired the wrong way. Eek! Definitely don't want to chance a fire, will just pay the money and get the right thing done properly once |
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Phil B
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Posted: 09 April 2014 at 11:59pm |
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Mr Studio is correct...you CANNOT use AC designed breakers for DC. The arcing will reduce them to molten slag pretty quickly at larger DC currents.
So these bolt down fuses from Jaycar for the pos and neg ends of the batt bank... Then a bunch of spare fuses ( just in case of a short somewhere!) http://www.jaycar.com.au/productView.asp?ID=SF1984
Then these for our din rail 24v DC stuff... Along with the 240v RCD outlet ended up with this rough start...  And then the first fix of stuff into the trailer....  I haven`t got a decent foto of the finished article yet.... it was all tidied up and the 240v was seperated out on the din rail and covered with a plastic box ( to keep it away from the 24v dc !) . But now everything can be accessed easily, the big switch is a three phase stop switch for the wind turbine , and what`s not in the picture is the old wi-fi router that connects to the midnite cc and means we can log in remotely and access info on the state of the batt bank ( as well as see exactly what the wind turbine is doing !) The old wind controller to the very left is now just acting as 3 phase switch for the wind dump load which operates off 2 x aux outlet of the midnite cc ( it is a v.clever box !) .p.
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bitSmasher
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Posted: 10 April 2014 at 2:12am |
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Informative as always Phil, thanks for your response!
I love looking at how it's done "properly", learning from that and scale it back for my own purpose Good to know the Noark breakers are worth buying, was eyeing them off earlier Does it make sense to have one master breaker (I've been called worse  ) - ie the 63A as linked above - with a couple of smaller breakers downs from thatDon't want total load to get near 60A, and having that as a maximum limit will keep my system design sensible Then a breaker on each Anderson, would be ~16A and is to protect the "circuit" without taking out other items Ie, if I'm powering lights on one Anderson and someone shorts them it won't take out the projector which is running from inverter... but if something goes horribly wrong the 63A breaker will shut down the whole thing Also with a short thick cable run from battery to big breaker, would I need to worry about fuses as well? If so, I have a big in-line housing that can be added too - The hassle would be that if it's inside a screwed together box it couldn't be swapped out in situ Will build a plywood box with handles, recess a panel for the breakers and sockets For distributing internally, was thinking of eye terminals bolted together on a piece of perspex that's mounted on standoffs inside the box. Cover the terminals and bolts in paint-on insulation just to be safe. Worst case scenarios come to mind, ie being outdoors in the rain for days on end... also I'll be using it in public spaces so I want everything to look "legit", no wires strewn everywhere or the like... Should be a pretty good start to a larger system to come! |
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Phil B
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Posted: 10 April 2014 at 6:57am |
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I would always recommend fuses on the main posi and neg sides of the batt bank? If there is a major short you know the fuses will pop and protect stuff from melting / vaporizing / self-combusting !
If you run to a main busbar with thick cabling and say a 63a din rail breaker inline that should then give you ample protection further down the line. We have a small car type fuse holder as well which distributes 24v dc from the bus bar to odd things like the old wind controller and charger. This has 20a or 40a car type blade fuses which are ample to protect smaller stuff I would say you should go with something like that to run to lights & projector ....just to keep costs down? Busbar on Aus ebay... .p.
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bitSmasher
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Posted: 17 April 2014 at 2:13am |
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Have the breakers, DIN rail and a whole bunch of Anderson connectors. Ammeter/Voltmeter arrived from China - cheapo ebay thing. Wary of installing them but will give them a go, see if they melt...
Also bought chunky D handles for the box, and have the ply on hand No excuse to not get this done over the next fortnight! Was going to draw up wiring diagram but CBF, instead here's a good video highlighting possible issue with polarised breakers (also I imagine AC breakers would do similar with DC load) |
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Phil B wrote: