How did you handle your overcurrent protection for DC cabins?

Started by NM_Shooter, September 27, 2011, 09:29:58 AM

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NM_Shooter

I'm running all 12V DC in my cabin.  My electrical system is in need of completion, and I am considering overcurrent protection schemes.  Looks like the dc breakers are a bit expensive, so I'm thinking about just using fuses.  Heck... I am surprised at the cost of fuses at Affordable Solar too.  

My DC loads will be well controlled.  It's not like I have outlets that I am going to plug appliances of varying requirements.  All my circuits have known maximum loads.  So using fuses should be fine.... I'll only pop one if something goes seriously wrong.  I'm planning on 15 amps protection for each circuit.

I need to protect 6 circuits.  

Any ideas for cost efficiency?

Thanks....
"Officium Vacuus Auctorita"

NM_Shooter

"Officium Vacuus Auctorita"


MountainDon

Just because something has been done and has not failed, doesn't mean it is good design.

MountainDon

Looks like their selection is rather meager right now. Stock comes and goes. I bought my HD DC breakers from them (inverter values)




I guess Square D QO or QOC series boxes and breakers are pricey too once all is added up. Okay for low voltage DC.
Just because something has been done and has not failed, doesn't mean it is good design.

UK4X4

This website is more for vehicle wiring -but still modular and aplicable to solar

They have auto shut off protectors and also fuse/ distribution panels
based on anderson connectors
http://www.powerwerx.com/powerpole-power-distribution/rigrunner-4008.html

Also used in the offroad comunity alot are these
http://bluesea.com/category/5/21/productline/126

price for a 12 way hard wired fuse board-$52

http://www.sierraexpeditions.com/index.php?l=product_detail&p=550


considerations

"Any ideas for cost efficiency?


Buy someone else's miscalculation.

I had to upgrade from a 30amp DC breaker to a 60amp...so I still have this one.





She's brand new just been sitting. If you can use this let me know. I would make it easy for you.

TheWire

I used the Square D QO Series for my DC overcurrent protection which are widely available and rated for DC up to 20A & 24VDC.  A 6 slot breaker box is about $25 and the single pole breakers are about $6 each.  The box is well suited for housing the wiring and the breakers provide easy on/off control also.

As an aside, I have a 120VAC 2KW inverter and the main cabin lights are 120VAC CFs & LEDs.  However for nightime, I installed 12VDC LED fixtures (Actually waterproof license plate lights) that consume about .04 A each and easily light a stair well or 10x10 foot area brighter than most night lites.  


To wire these, I used 20 gauge thermostat wire.  Because of the small gauge wire, I fed the 20 gauge to the lights from a block of 2A fuses from one of my 15A 12VDC breakers.  I put these little but bright LED lights in the stairwell, over the wood stove, in the hall, in the bathroom and on the porch.  I leave them on all night with minimal battery discharge and they are bright enough to stoke the fire, use the bathroom, etc without switching on the 120VAC lights which fires up the inverter.  The lights are available at: http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Fspecs%2FLPC.htm#photos


MountainDon

As a note to the Square D QO, I should have added there is a couple of things to watch for if the NEC rules/inspections are to be followed.

While the QO is rated to 24 VDC under NEC there can be a problem. All 24 VDC battery system undergo periods where the actual voltage is higher; charging, equalizing. In those situations the voltage applied to the batteries is actually greater than 24. So technically that places the breaker outside the parameters of the NEC approval.

A second issue is the AIR rating of the QO breaker. It is not high enough for safety especially when there is a large battery bank involved. A dead short could conceivably overheat a smallish diameter wire and the breaker might not trip fast enough to prevent that. A good DC rated fuse with high AIR rating should be placed in the positive line, after the battery and before the QO breaker. Sorry, just off hand I forget the AIR values involved.
Just because something has been done and has not failed, doesn't mean it is good design.