Author Topic: Battery bus design  (Read 10616 times)

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Offline ChrisOlson

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Re: Battery bus design
« Reply #30 on: May 02, 2012, 11:13:56 PM »
I believe most battery posts are lead.  So you set up a galvanic couple using aluminum on lead posts.  The most common metals used for sacrificial anode are zinc, magnesium and aluminum.  It's not surprising that aluminum did work well for battery interconnects, ran warm and kept coming loose.

ASTM B 236-07 outlines the requirements for aluminum bus bars made of 1350-H19, or 6101/6061 alloys.  Aluminum is used in the electrical industry quite regularly for bus bars, and should not be a problem.  Chances are the main electrical panel in your house, if bought commercially, has aluminum bus bars in it.  SquareD, Allen-Bradley, you name it from all the big names in electrical panels, use aluminum bus bars.

Is copper better than aluminum?  Yes, because it has lower resistivity.  But aluminum is perfectly fine if sized properly for an off-grid DC main power bus.
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Offline rossw

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Re: Battery bus design
« Reply #31 on: May 02, 2012, 11:22:33 PM »
Chances are the main electrical panel in your house, if bought commercially, has aluminum bus bars in it.  SquareD, Allen-Bradley, you name it from all the big names in electrical panels, use aluminum bus bars.

Might be where you are, Chris, but not here.

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Offline birdhouse

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Re: Battery bus design
« Reply #32 on: May 03, 2012, 12:02:26 AM »
i don't know chris, siemens panels at home depot here have copper busses, or atleast copper cladded busses.  they're in line with pricing with square-d ect. 

they're my personal favorite, as even if the buss isn't pure copper, at least it has copper where the breakers connect!

adam

Offline Wolvenar

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Re: Battery bus design
« Reply #33 on: May 03, 2012, 01:34:37 AM »
I believe Siemens use full copper.
My local electrician friend speaks highly of them, and says many of the commercial jobs he works on are starting to use them exclusively on any new construction.

The main Square D fuse/disconnect box I have on my setup has a tinned copper bus in it (yup I checked it really is not aluminum).
Though my smaller one for the solar panels are aluminum.

All I can say for sure about the debate is everything I see in the manuals I have with the inverter, controller, and solar panels say all wire and connections must be copper.

I might use aluminum on my future longish run to where the solar trackers will be, because the cost vs loss when at higher voltages.
I would never used aluminum on the batteries, that's just asking for trouble.


--Edit, I just went out to watch natures little light show we have here tonight (storm)
So I decided to check on the little panel, it is actually standard copper (not tinned) instead of the aluminum I wrongly thought it was.
It must be the newer box I have future plans for.
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Offline rossw

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Re: Battery bus design
« Reply #34 on: May 03, 2012, 01:44:48 AM »
I believe they are full copper.

Oddly, pure copper connectors here are quite rare.
Probably because of coppers tendency to oxidise quickly.
The *vast* majority here are Brass. (I think Brass is also harder than Copper - so the screws are less likely to strip)

Offline Wolvenar

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Re: Battery bus design
« Reply #35 on: May 03, 2012, 02:35:54 AM »
smaller box
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Offline Wolvenar

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Re: Battery bus design
« Reply #36 on: May 03, 2012, 02:49:17 AM »
I little research just to be sure on the Siemens products

Quote
Bussing — Busbars and breaker branch
bus is tin-finished aluminum per UL 67
unless otherwise stated. See panel
submittals for optional call outs. Copper
bus is available as an option.

From the manual describing their panels.
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Offline ChrisOlson

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Re: Battery bus design
« Reply #37 on: May 03, 2012, 09:55:03 AM »
I think SquareD has copper as an option for some panels too.  But the aluminum ones are a lot more common these days.  Knife-type contacts in disconnects and so on are usually some sort of copper alloy.  Like Ross said, pure copper would be very rare as it turns green quite fast when exposed to air and moisture.

But back to the debate - I really see no problem with aluminum bus bars.  The SquareD box I bought for my bus was used and is probably 20 years old.  It was a bus box at one time for a huge industrial DC motor setup of some sort.  The bus bars in it are just soft 6061 aluminum and not the T6 tempered stuff that's more common.  T6 tempered aluminum will break when you bend it and the bus bars in my box are made of the same stuff that lots of aluminum wire is made of.  It's a just a soft 6061 alloy.

In corrosive environments like marine or salt air, or directly on the batteries, I think you'd want to use a different material - and copper alloys would probably be better there.

My bus is central to my DC system.  The batteries feed the bus with six positive and six negative leads, with a 200 amp ANL fuse on each positive lead from the bank.  The inverters are fed from the bus with 4/0 cables going to each inverter.  All incoming power from turbines and solar goes into the bus.  I got a 200 amp DC service plug wired into the bus for a DC generator in the event I ever decided to buy one.

The inverters are fed off the end of the bus bars because there's big screw lugs there that accept 4/0 cable.  Three feed wires from the bank go to each bus bar (four bars), and I got jumpers between the two positive bars and the two negative bars in the bus (dual inverters require a common bank).  At 700 amps to the inverters I only get .3 volts drop between the bank and the inverter studs - and that's in the wiring not the bus.

I'll see if I can take a photo of it at noon when I go in for lunch.  It's padlocked shut because a 1,200 amp DC bus is one dangerous SOB to be fiddling around in when it's live**.

** I would like to put out a caution for folks aspiring to build or install a high amperage DC bus.  They are dangerous.  Very dangerous.

Back when we had our 12 volt system I had a homemade bus in the basement (that also had aluminum bars).  I was working in there one day and had laid a steel handled Craftsman claw hammer on top of the (hot) bus box.  I bumped the hammer and do not know how it did it.  But I think the claw on the hammer caught the top of the bus box and it flipped and went inside the box and came in contact with two of the bars in there.  The explosion was about like a M80 going off in front of your face.  Part of the head on that hammer INSTANTLY vaporized and sprayed me in the face and arms with molten metal.

And that was just a 12 volt bus.  Since then I have great respect for what a big bank of batteries with big wires feeding a bus can deliver.  I had 24 Group 29 marine deep cycle batteries @ 125 ah each.  Each one of those batteries can deliver 700 cranking amps.  With 12 4/0 cables feeding that bus, and no fuses at the bank, I'm sure the surge that vaporized that hammer was over well over 3,000 amps.

That was back when I was young, dumb and full of vinegar.  I learned that you ALWAYS fuse your bank and you NEVER work on a hot DC bus.
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Chris

Offline RichHagen

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Re: Battery bus design
« Reply #38 on: May 04, 2012, 01:06:30 AM »
To clarify, my bus bar of aluminum is not battery interconnects, it is a DC distribution bus kind of like what Chris described for his system, only smaller.  For batteries I would want the least active metal I could find for the interconnects, or lead itself.   Aluminum, because of its rapid corrosion in acids and its much larger potential difference with lead, would not be among my first choices, in fact it would be one of my last.  I think lead tinned copper interconnects would be my first choice for battery interconnects for batteries with lead terminals.  I've seen brass marine terminals partly eaten away by corrosion, and I would expect aluminum to fare much worse in that application.   I do use Aluminum interconnects on my ultra capacitor banks, but, the terminals of those capacitors are of aluminum alloy.  Again, with greased connections, I have had no problems with those as well.  Unless there is a reason to do otherwise, I would use the metals with the closest electrical oxidation potential for junctions to avoid galvanic corrosion.  I heard somewhere that a general rule of thumb is not to join metals together in exposed joints if the oxidation potential between them was greater than .5 volts, and it seems like a basically reasonable guide.  Junctions of metal where the oxidation potentials exceed that would have to have protection from the environment in order to avoid galvanic corrosion because any of the more noble metal oxidized would likely be reduced in favor of oxidation of the more active metal at the junction if a galvanic cell were to form, such as condensation, rain, or such.  This is the idea behind sacrificial anodes, often made of magnesium or aluminum, which are used on pipelines and in some hot water tanks.  Most Junctions with Aluminum would require protection from the environment.  In my case I used anti-oxidation grease made for such a purpose.

Here are the different potentials of some common metals relative to the oxidation of hydrogen from my chemical dictionary:

Magnesium   -2.38 Volts
Aluminum     -1.66 Volts
Zinc     -.763 Volts
Iron (2+)  -.409 Volts
Nickel -.250 Volts
Lead  -.126 Volts
Copper +.34 Volts
Iron (+3) .771 Volts
Silver +.799 Volts
Platinum +1.2 Volts
Gold  +1.489 Volts

I'm not certain, but I would guess that the Iron would break down at the lower voltage listed for the plus 2 (Ferrous) oxidation state first, so that is what I would use to gauge, as I know that if you join iron plumbing to copper without a dielectric, in general your iron pipe will corrode away.  I seem to recall a historical article where the Brits built a copper sheathed boat in the age of wooden warships, but ran into a problem where all of the iron nails used to hold it together corroded away within weeks in sea water.   
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Offline tomw

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Re: Battery bus design
« Reply #39 on: May 04, 2012, 08:46:25 AM »
One reason I like copper so much is the hundreds of cathedrals, etc in Europe with original copper roofs that are centuries old. I know it is not electrical in nature but sheets of material that last that long on a roof has to be tough and resistant to decay.

Plus, every plumber I know tells me to use copper if I want it to last.

Just sayin...

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Offline bj

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Re: Battery bus design
« Reply #40 on: May 04, 2012, 09:30:41 AM »
  Kind of where my thinking goes as well Tom.  Now if I could just figure out what I did with that nice piece of
tinned bussbar I've been saving.  :(
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Offline bj

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Re: Battery bus design
« Reply #41 on: May 08, 2012, 07:31:38 AM »
    I like copper, but I sure wish somebody else was paying for it.   Couldn't find my prized piece, so, had to go to the big city to
pick up my ammeters and bought another chunk.  My, My, copper has gone up. :o  Only money ;D
    Makes me glad I hoarded all that copper wire.
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Offline ghurd

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Re: Battery bus design
« Reply #42 on: May 14, 2012, 10:17:08 AM »
I stumbled on this today.
Midnite Solar bus bar, "Four 1/0 & eleven #6 useable wire slots. Comes with two sizes of 10-32 screws. 4.63" UL and CSA recognized, Made in USA.... Remove the plastic insulators for ground bus applications."
Comes (insulators) in Red, Black, or White.
~$15.

G-

Offline ksouers

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Re: Battery bus design
« Reply #43 on: May 14, 2012, 05:24:03 PM »
Thanks G.
That sounds like these, I think.  http://www.solar-electric.com/mntb.html

I've got couple of these in my combiner box. Still seem a little small to me for a battery bus. They are only about a 1/2 inch by 3/8 inch (uncalibrated eyeball method).
The web where they drilled the holes is a little on the thin side. Fine for the combiner but I don't think it'll take a high-amp hit from an inverter if a couple motors start up at the same time.

No matter how distasteful I find it I may end up using aluminum for the bus. Copper is going to cost almost $100 just for a .375 x 1.25 x 2 foot piece. Brass isn't going to be too much cheaper, maybe $20.

Thinking I should have put my money into copper instead of Apple stock...


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Offline Dave

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Re: Battery bus design
« Reply #44 on: May 14, 2012, 07:08:30 PM »

Hey Kevin,

Are you being over charged?

3/8"x1-1/4"x 24" C110 (standard buss grade) $47.80 + $10.57 shipping for me.

http://www.onlinemetals.com/merchant.cfm?id=87&step=2&top_cat=87

Could save a bit more going with 1/4" thickness... Made several buys through these folks with good service. :D

Cheers Dave