DC breaker panels

My PV/Wind array is outgrowing the simple fuse system currently in use, so I'd like to install a breaker panel for the power inputs, between panel (actually charge controllers) or turbine and batteries.
Getting information on DC-rated equipment is difficult.
Everything's 24VDC.
Can I use a standard breaker panel?
If so, who makes DC-rated breakers for these panels, or are standard AC breakers usable (perhaps at some de-rated current)? -- derek

Derek Broughton wrote:

My PV/Wind array is outgrowing the simple fuse system currently in use, so I'd like to install a breaker panel for the power inputs, between panel (actually charge controllers) or turbine and batteries.
Getting information on DC-rated equipment is difficult.
Everything's 24VDC.
Can I use a standard breaker panel?
If so, who makes DC-rated breakers for these panels, or are standard AC breakers usable (perhaps at some de-rated current)?

You could. SquareD is DC rated, and I'm told CutlerHammer is as well. De-rating is tricky, I'd avoid it if you can.
But what kind of DC disconnect do you have? Or have you got one? You can get breakers that plug into the Xantrex and Outback ones for pretty much the same price as conventional AC breakers.
DJ

-- derek

Derek Broughton wrote:

My PV/Wind array is outgrowing the simple fuse system currently in use, so I'd like to install a breaker panel for the power inputs, between panel (actually charge controllers) or turbine and batteries.
Getting information on DC-rated equipment is difficult.
Everything's 24VDC.
Can I use a standard breaker panel?
If so, who makes DC-rated breakers for these panels, or are standard AC breakers usable (perhaps at some de-rated current)?

AC is a sine wave. Voltage and current both cross through zero amps and zero volts. This is helpful in extinguishing an arc across the contacts. DC can be like the drummin' bunny. If an arc starts it doesn't return to zero volts or zero amps to help extinguish the arc.
GIYF: http://www.mrsharkey.com/busbarn/electrics/chapt9.htm
-- www.synapticsparks.com

Dale Eastman wrote:

Getting information on DC-rated equipment is difficult.

http://www.magnecraft.com/products/e104_sec3_pg04-06_w199.pdf#search=%22magnetic%20blowout%20DC%20arc%22

Everything's 24VDC.
Can I use a standard breaker panel?
If so, who makes DC-rated breakers for these panels, or are standard AC breakers usable (perhaps at some de-rated current)?
AC is a sine wave. Voltage and current both cross through zero amps and zero volts. This is helpful in extinguishing an arc across the contacts. DC can be like the drummin' bunny. If an arc starts it doesn't return to zero volts or zero amps to help extinguish the arc.
GIYF: http://www.mrsharkey.com/busbarn/electrics/chapt9.htm

-- www.synapticsparks.com

To use any AC switching device on DC you would have to derate it lots. With a current over protection device this is obviously self defeating. The danger is that the points weld together so preventing the thing from operating. That is if it doesn't burn out after only a few operations. The best thing you can do is go down the car breakers yard (auto wreckers in your parlance I think ) and get a fuse board from there. You can then use cheap and easily available automobile fuses that are intended for DC. I don't believe you'll get a panel with DC circuit breakers. (Except maybe from a submarine:-) Be aware that AC "cartridge" fuses are also unsuitable for DC
Derek Broughton wrote:

My PV/Wind array is outgrowing the simple fuse system currently in use, so I'd like to install a breaker panel for the power inputs, between panel (actually charge controllers) or turbine and batteries.
Getting information on DC-rated equipment is difficult.
Everything's 24VDC.
Can I use a standard breaker panel?
If so, who makes DC-rated breakers for these panels, or are standard AC breakers usable (perhaps at some de-rated current)? -- derek

Dale Eastman wrote:

AC is a sine wave. Voltage and current both cross through zero amps and zero volts. This is helpful in extinguishing an arc across the contacts. DC can be like the drummin' bunny. If an arc starts it doesn't return to zero volts or zero amps to help extinguish the arc.

Was there a point to this? I don't need the lecture on how AC & DC electricity differ, I'm asking for specific advice on breaker panels.

GIYF: http://www.mrsharkey.com/busbarn/electrics/chapt9.htm

That's about as useful as the general run of advice I've been able to find. It doesn't give any actual suggestions for solving the DC overload protection system. I'm reduced to asking on Usenet because even licensed electricians seem woefully ignorant of DC. -- derek

DJ wrote:

Derek Broughton wrote: My PV/Wind array is outgrowing the simple fuse system currently in use, so I'd like to install a breaker panel for the power inputs, between panel (actually charge controllers) or turbine and batteries.
Getting information on DC-rated equipment is difficult.
Everything's 24VDC.
Can I use a standard breaker panel?
If so, who makes DC-rated breakers for these panels, or are standard AC breakers usable (perhaps at some de-rated current)?
You could. SquareD is DC rated, and I'm told CutlerHammer is as well. De-rating is tricky, I'd avoid it if you can.
But what kind of DC disconnect do you have? Or have you got one?

Not as such. The turbine has a stop switch & fuse. The PV panels have a removable fuse.

You can get breakers that plug into the Xantrex and Outback ones for pretty much the same price as conventional AC breakers.

Pretty much the same for the breakers, perhaps - but that Outback disconnect is about $400!
If I can put in a SquareD load centre with DC rated breakers, it sounds good to me. -- derek

Derek Broughton wrote:

GIYF: http://www.mrsharkey.com/busbarn/electrics/chapt9.htm

That's about as useful as the general run of advice I've been able to find. It doesn't give any actual suggestions for solving the DC overload protection system. I'm reduced to asking on Usenet because even licensed electricians seem woefully ignorant of DC.

Dual-Rated Circuit Breakers The Square D line of QO breakers and QO load centers are rated for 120/240 Volts AC, and they also have a lower voltage DC rating. When used in DC branch circuits (circuits from the battery to the load) they can be used on 12 and 24 Volt battery systems. Although rated for 48 Volts DC, the higher battery voltages (above 48 Volts) in normal charging and during equalizing pose stresses on these breakers and they should not be used in 48 Volt battery systems. In PV source circuits there is the potential for higher than nominal voltages. A 24 Volt system with crystalline silicon modules may have an open-circuit voltage above 48 Volts. Because of this consideration, Square D QO breakers and load centers should be used only on 12 Volt PV systems. http://www.nmsu.edu/~tdi/pdf-resources/cc68.pdf#search=%22DC%20RATED%20BREAKERS%22
Access DC rated, UL listed fuses are made by Littlefuse, Power Fuse Division, 800 E. Northwest Highway, Des Plaines, IL 60016. CALL 1-800-TEC-FUSE for the name of the nearest power fuse stocking distributor. Use midget type KLKD for array wiring and to protect electronic devices. Use FLN-R type for branch wiring as well as battery to inverter fuse. Marathon Special Products, PO Box 468, Bowling Green, OH 43402 makes fuse holders and power distribution blocks. Call 419-352-8441 for a catalog and the name of the nearest distributor. http://www.nmsu.edu/~tdi/pdf-resources/cc16.pdf#search=%22DC%20RATED%20BREAKERS%22
MODEL: Single Pole SD-15 - 15 amp DC rated breaker SD-20 - 20 amp DC rated breaker SD-30 - 30 amp DC rated breaker SD-40 - 40 amp DC rated breaker SD-60 - 60 amp DC rated breaker
Double Pole SD-15D - 15 amp DC rated breaker SD-20D - 20 amp DC rated breaker SD-30D - 30 amp DC rated breaker SD-40D - 40 amp DC rated breaker SD-60D - 60 amp DC rated breaker http://www.spsenergy.com/pages/products/distributingWiring/wiringSafety.htm
CF125 Circuit Breakers, DC rated for 125 volts. They are UL Listed for up to 48 volt systems, but they can be used for 12 or 24 VDC nominal systems as well as AC systems. They have lugs at both ends which accept up to 1/0 cable. If you look at the picture you will see that they can be mounted in one of two ways. You can attach them using # 6-32 mounting screws to the face of the breaker. They can also be placed on a vertical flat surface with mounting screws or bolts going through the "U" shaped tabs on the top and bottom.
125 vdc breakers These can also be used in the Trace DC Disconnect. PRICE: A) CF125 - 1 amp circuit breaker ( CF125 - 1 ) $ 19.00 each Currently we have 6 in stock.
B) CF125 - 5 amp circuit breaker ( CF125 - 5 ) $ 19.00 each Currently we have 10 in stock.
C) CF125 - 10 amp circuit breaker ( CF125 - 10 ) Currently we have NONE in stock.
D) CF125 - 15 amp circuit breaker ( CF125 - 15 ) $ 19.00 each Currently we have 7 in stock.
E) CF125 - 20 amp circuit breaker ( CF125 - 20 ) $ 19.00 each Currently we have 3 in stock.
F) CF125 - 30 amp circuit breaker ( CF125 - 30 ) $ 19.00 each Currently we have 3 in stock. http://www.solarseller.com/dc_circuit_breakers__dc_circuit_breaker_ul_listed_to_125_volts_dc.htm
GIYF. Have a nice life.

Sure, from my horizon (Europe...), I have seen most the same! Most electricians don't have knowledge of DC, but thy think it is like installing a car, in other words, nothing to act seriously upon...
Myself, I have been doing major overhaul of ships' electrical systems in museum vessels. DC 120V, network supply from paralell sources, for example: One supply from grid at the dock, a motor-generator set 20 kW, one prime generator 15 kW, one spare generator 10 kW, these might all be connected in paralell (worst case). The network all the time also connected to an accumulator battery (Led-Acid, 290 Ah, 56 cells if I dont remember totaly wrong...)
To find suitable breakers was not easy at all! We finally managed to find old, slightly used switches that had both grades labelled. The clue to break DC is to combine wery distinct opening of contacts with magnetic arc blowing. The first requires good mechanics, and quite strong spring elements. To open a switch rated 100A at DC 250V requires two hands and a steady position on the floor! (In our case; rotating switches turned 90 deg to operate).
The arc-blow is part of the switch design, and must be there from factory...
In the US, DC 72 V is widely used for supply and operations at telephone network "central offices". Here, there shuld be possible to find equipment and other stuff, both new and used/old.
As goes for fuses, the advice to use Car fuse elements is far from sane! These are designed for minimum cost in a wery single application...
When you design a fuse/Circuit Breaker, there are a few things to consider, mainly: the breaking capacity of the fuse compared to the supply capacity into a short-circuit from the network. This current has nothing to do with normal operations current! For a battery, like the one mentioned above, the internal resistance is in the range of 1 milli-ohm per cell!
That gives a maximum short-circuit current in the battery mentioned above of: (I = U / R - Ohm's law) I= 2,0 x 56 / (0,001 x 56) = 2 000 A.
So: a fuse that "normally" would blow/break for lets say 10 A overload current in a line, placed close to a battery and subject to a short-circuit close by would have to be able to break 2000 A safely in order to do its job! Breaking 2 000A @ DC 120 requires a physical distance (arc length) of several Inches in free air, but there are methodes to cool the arc off enough to make it vanish. Anyhow, don't expect this to be of physical micro-size.
Design of fuses always requires identifying the maximum available short circuit current during worst case operations (several sources in paralell) and a short at the worst place. (A long cable in series with the battery reduces maximum current at the other end of the cable "a lot" due to the resistance in the cable, but protection against a short in the cable must be done somehow...)
A generator's max current is given primarilly by the internal resistance of the windings and the generated voltage. This will not last for long during a short, the machine will stop rotating quite fast from an overload, but still, at the beginning of a short, the maximum current will be observed, and the fuse should be able to breake this.
Another problem is to make sure the fuse breakes if it comes to a short at a distant point in the network! If there is to low network supply voltage compared to the resistance in a supply-line cable you can have a short at the other end of the line that causes say 25A to be drawn in the cable designed to safely carry 10A without overheating, which will not make a 10A fuse/CB to blow/trip fast enough. (A rule of thumb here: A 10 A fuse will supply 20A for 1 hour before breaking! - A CB is slightly better on this point) So, operating at low voltage is as difficult to protect as higher voltage, just slightly different. Most fuses/CB:s require a Current 10 times the rated in order to bolw/trip safely within a time of seconds.
For 12V with a 10A fuse, thus requiring 100A to blow decently fast, connected using 1,5 sqare mm of wire (about AWG 15) - standard electicians choice at 10A here - the total length of the loop may not exceed 11,7 m (35 ft) - the distance from the battery then half of this in order to close the loop. (I presume that US trucks, operating at DC 12V either have fuses protecting the rear lights far less than 10A, or are shorter than 20 ft ;-) (I know, sending the return current in the steel frame reduces resistance, but I'd say it is still really a mystery how this can be decently designed at such a low voltage - thick wires will help, but the ecconomy will not gain from it...
Myself, I often prefer regular fuses to Circuit Breakers for DC networks. Here, max. breaking current /voltage must be considered. Car equipment is low-voltage oriented, and it dosn't even do that to well... Ceramic fuse body filled with sand helps a lot, compared to air in glass-tubes. But for larger applications it often comes to "knife style" fuses (I don't know if they are available or their name in US...)
Good luck with the design! (Remember: Fuses are needed to prevent fire and injury - if you are not sure - Do hire someone properly educated and experienced for the design-task, that might be a M. Sc EE rather than an electrician)
/G�ran
Derek Broughton wrote:

Dale Eastman wrote:
AC is a sine wave. Voltage and current both cross through zero amps and zero volts. This is helpful in extinguishing an arc across the contacts. DC can be like the drummin' bunny. If an arc starts it doesn't return to zero volts or zero amps to help extinguish the arc.
Was there a point to this? I don't need the lecture on how AC & DC electricity differ, I'm asking for specific advice on breaker panels.
GIYF: http://www.mrsharkey.com/busbarn/electrics/chapt9.htm
That's about as useful as the general run of advice I've been able to find. It doesn't give any actual suggestions for solving the DC overload protection system. I'm reduced to asking on Usenet because even licensed electricians seem woefully ignorant of DC. -- derek

Dale Eastman wrote:

Derek Broughton wrote:
GIYF: http://www.mrsharkey.com/busbarn/electrics/chapt9.htm
That's about as useful as the general run of advice I've been able to find. It doesn't give any actual suggestions for solving the DC overload protection system. I'm reduced to asking on Usenet because even licensed electricians seem woefully ignorant of DC.
.... A 24 Volt system with crystalline silicon modules may have an open-circuit voltage above 48 Volts.

Not according to either the specs or actual measurements on any of mine. Nothing over 40V.
Thanks for all your links. -- derek

nnc@eta.chalmers.se wrote:

As goes for fuses, the advice to use Car fuse elements is far from sane! These are designed for minimum cost in a wery single application...

Not to mention that, even though cars do have the odd 30A fuse, the wiring all seems woefully inadequate for such a load. Trying to connect my PV/Wind wiring to auto fuse blocks would be difficult at best (and still not UL approved). Thanks.
-- derek

I think I read somewhere that the Square D QO breakers have some kind of non conducting item that slides between the contacts when the breaker is tripped to prevent arcing.
I use 2 of there panels, one on the load side (not for the inverter) lights, ham gear etc. the 2nd is for my panels. I split the feed from my 315 watts of panels into 2 seperate sets. There is a reson I did this but do not want to explain it in depth in this thread.
Joe KI4ILB

"Harry" wrote in message

The best thing you can do is go down the car breakers yard (auto wreckers in your parlance I think ) and get a fuse board from there. You can then use cheap and easily available automobile fuses that are intended for DC.

If you want to use automotive fuses, (and are using 12 V.) and your current needs are modest, check with a marine supplier such as West Marine for some nice panels. Also MFJ sells some nice panels (here is one version: http://www.mfjenterprises.com/products.php?prodid=MFJ-1126 ) Bear in mind that none of this stuff is NEC rated, meaning that it might be OK for your camper or hunting cabin, but probably not for a real residence. I keep thinking about running some 12 volt branch circuits in my home, but the cost of doing it correctly is prohibitive and it will likely never happen; even though I am a licensed electrician.
Vaughn

DC breakers are rated on the nameplate with their DC capabilities or else they are not designed to break DC current.
"Merlin-7 KI4ILB" wrote in message

I think I read somewhere that the Square D QO breakers have some kind of non conducting item that slides between the contacts when the breaker is tripped to prevent arcing.
I use 2 of there panels, one on the load side (not for the inverter) lights, ham gear etc. the 2nd is for my panels. I split the feed from my 315 watts of panels into 2 seperate sets. There is a reson I did this but do not want to explain it in depth in this thread.
Joe KI4ILB

Derek Broughton wrote:

Thanks for all your links.

You are welcome. Remember GIYF.
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