Copper Bus Bar Design

ouelloouello Registered Users Posts: 21
I have copper bar stock and I'm a machinist so I'll finally save on something...
  • 6 UPS batteries x 50ah (not the best I know, but they were free...)
  • Max of 100A draw
  • All #2 AWG welding cable (not purchased yet) around (16" runs)

Can the bus bar be too big? Lets say I have 1" x 1" x 6"...

I'm also wondering if I should drill 5/16" (.3125") holes and a set screw on top to hold the wires in (like on cc)
This way I would save on wire connectors...
or will copper connectors give a better contact?

Can anyone share their set-up pictures?
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Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Copper Bus Bar Design

    No--Cannot be too much copper bus bar. Obviously very soft, so more thread length will help too.

    Regarding welding cable--It is usually very fine wire because it is designed to flex a lot. It makes welding cable difficult to terminate reliably. And the holes in the bus bar/copper crimp lugs need to be larger diameter because of the fine stranding (more air space in between strands).

    If you can, I would suggest crimping the welding cables with proper copper lugs--I think it will be more reliable than using set screw type clamping.

    Poster 2manytoyz has made a website with lots of pictures about his solar installation (from the beginning through several upgrades--Lots of DIY type projects).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Copper Bus Bar Design
    ouello wrote: »
    Can anyone share their set-up pictures?

    Hi, I did not use copper, but instead 6061 T6 aluminum. I just rebuild my bus - the old one was build the same way and was still working fine after 9 years. I just replaced it because we changed our system from 24 to 48 volts.

    The bolt holes in the bus bars are 5/16" NF, stainless steel bolts and every connection coated with dielectric grease to prevent corrosion.

    Attachment not found.

    --
    Chris
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Copper Bus Bar Design

    i like the set screws like on most commercial bus arrangements, but in dealing with pure copper it will tend to be too soft to maintain a tight connection. buses from commercial sources are plated and it gives them strength for set screw use.
    commercial example here,
    http://www.solar-electric.com/mnsbbn.html

    now you could increase the ampacity of a bus like this if bolted to another bus below it for pv combiner uses, but i don't foresee the need for you to go that far with your setup and it's just to easy to use commercial buses as they don't cost an arm and a leg. if you use either brass (sorry as i didn't mean to imply something leaving one s off:blush:) or stainless screws with nuts and washers the copper bus can work, but presents more work in tightening and loosening the connections. just mho.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Copper Bus Bar Design

    Chris I see you have a mix of plated and bare copper crimp-on lugs on your wires. Any comments or preferences?
     
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  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Copper Bus Bar Design

    No real preference. It's whatever I can find in my electric drawer of stuff, usually :D

    For the battery cables I got a hammer-type crimper. But on the THHN wires I crimp them on first, then solder them besides. The crimp seems to work OK on the finer stranded wire like used in battery cables. But I don't trust just a crimp on #4 THHN. For small DC circuits like relays, gauges or meters I use regular 14 gauge extension cord sections with the black as negative and the white as positive. The green is always in there if a gauge or relay box needs a separate ground too. It's not the cheapest wire to use for light duty circuits, but it sure is handy because all three wires are neatly bundled in a nice jacket.
    --
    Chris
  • ouelloouello Registered Users Posts: 21
    Re: Copper Bus Bar Design

    Thanks for your insight and resources...;)
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: Copper Bus Bar Design

    If you use the copper bus bars you should try and insulate the mid-section as much as possible. Large shrink tubing or wrap them with tape.

    The more exposed the connections for the batteries, the greater the chance for undesired excitement. Tightening down the connection bolts on the battery with a a slip of the wrench is the most likely occurance.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Copper Bus Bar Design
    RCinFLA wrote: »
    If you use the copper bus bars you should try and insulate the mid-section as much as possible. Large shrink tubing or wrap them with tape.

    The more exposed the connections for the batteries, the greater the chance for undesired excitement. Tightening down the connection bolts on the battery with a a slip of the wrench is the most likely occurance.

    i agree with rc that you do have to watch around these buses, especially with tools. some tools have insulated handles which can help too and you can probably figure other ways of protecting from accidental shorts on those buses.

    rc,
    i don't know about you as i don't get excited around buses, good or bad, but i guess some kind of precaution should be taken as i linked to a naked bus.:blush::p
  • ouelloouello Registered Users Posts: 21
    Re: Copper Bus Bar Design

    My batteries are inside an insulated "chest" with a butcher block top. I was thinking of keeping the buses inside and only come out with the connecting wires.

    I know I have to keep short equal runs. Is it the same for + vs. -
    Will a couple of inches of longer cable on the negative side throw everything of balance, or create unnecessary heat?
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: Copper Bus Bar Design

    Find some 2" round aluminum stock (6" long) laying around the shop and mill a few flats on it every 90 degrees. Drill/tap some holes on the flats. Everything can be machined from a Bridgeport mill. Afterward, use a couple conduit supports to fixture down to some plastic or even wood is fine.
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  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Copper Bus Bar Design

    Aluminum is a problematic material to work with... It forms an insulation layer (actually a very hard oxide) within seconds of being exposed to air (oxygen) and is can be very difficult to get reliable electrical connection because of this. You can use a grease made for electrical connections and star lock washers to pierce and seal the electrical contacts.

    And aluminum also cold flows (heat it up, it squeezes around like tooth paste--Contracts when cool, then again forming the oxide layers, which makes more resistive electrical connections which can heat even more, causing even more oxides to form, repeat--Until the connection fails/starts a fire).

    I would avoid aluminum bus bars unless you have no other choice.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Copper Bus Bar Design
    ouello wrote: »
    My batteries are inside an insulated "chest" with a butcher block top. I was thinking of keeping the buses inside and only come out with the connecting wires.

    I know I have to keep short equal runs. Is it the same for + vs. -
    Will a couple of inches of longer cable on the negative side throw everything of balance, or create unnecessary heat?

    There is no need to keep the + leads the same length as the - leads. What you need to do is keep the + path to one battery the same length at the + path to each of the other batteries, when putting batteries in parallel. Within a series string, keeping all of the lead lengths the same per battery also is not important. Keeping them short is, unless you are using very large wire.
    SMA SB 3000, old BP panels.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Copper Bus Bar Design
    BB. wrote: »
    Aluminum is a problematic material to work with... It forms an insulation layer (actually a very hard oxide) within seconds of being exposed to air (oxygen) and is can be very difficult to get reliable electrical connection because of this. You can use a grease made for electrical connections and star lock washers to pierce and seal the electrical contacts.

    Bare copper does the same thing. But instead of the oxide being white it's green.

    In my experience 6061 T6 works perfectly fine for DC buses - at least as good as copper, and in many cases better. Just about all the commercially built electrical panels these days use aluminum buses.

    The only place to avoid using aluminum is when placing bus bars directly on battery terminals. The lead and aluminum sets up a galvanic couple and the aluminum become the sacrificial annode.
    --
    Chris
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Copper Bus Bar Design
    ChrisOlson wrote: »
    Bare copper does the same thing. But instead of the oxide being white it's green.

    In my experience 6061 T6 works perfectly fine for DC buses - at least as good as copper, and in many cases better. Just about all the commercially built electrical panels these days use aluminum buses.

    Chris

    Copper oxide is not nearly as good an insulator as aluminum oxide (remember the days of copper oxide rectifiers? The reverse breakdown voltage of a single junction is not much above 2 volts.) And copper oxide is not as physically strong and hard to disrupt.

    When you use an aluminum bus bar, I suspect the much of the reliable conductivity comes from the path through the screw and its threads, rather than the metal lug to aluminum connection. A star washer under the lug helps too.

    And by the way, copper oxide is not green. The green stuff is hydrated copper carbonate and hydrated copper sulfate (very common with acid rain and with batteries nearby.)

    Copper is a pretty soft metal too, and not really good for holding threads. Some aluminum alloys are much harder.

    Anyway, experience is a better teacher than theory in many cases, so thanks for sharing your experiences. :-)
    SMA SB 3000, old BP panels.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Copper Bus Bar Design

    inetdog - thanks for the clarification on that green copper "scuz". Whatever it is, it's bad. Real Bad :D

    If you do use aluminum for bus bars always use a tempered alloy. They are very hard and accept threading and whatnot with no problems. Soft aluminum is worse than soft copper for tapping threads - it just won't work.

    Like I stated above, in my previous bus I used stainless steel bolts with dielectric grease on the connections and never had a problem for 9 years. There is no galvanic corrosion between aluminum and stainless steel. There can be between aluminum and copper, but only in the presence of an electrolyte (like salt water). Sealing the connection with dielectric grease keeps moisture in the air off the connection and it remains good for at least a decade (in my experience using it).

    Our old bus went from 12 volt originally, to 24 volt. It was a four-bar bus and not suitable for 48 volt. The bars I used in the new one are 3/8" thick x 1" wide.
    --
    Chris
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Copper Bus Bar Design
    ChrisOlson wrote: »
    inetdog - thanks for the clarification on that green copper "scuz". Whatever it is, it's bad. Real Bad :D

    Chris

    One of the worst things about it, from my point of view, is that it is conductive when damp, making it very unfriendly to electrical and electronic gear! (And since it sucks moisture out of the air, it is almost always damp!)
    SMA SB 3000, old BP panels.
  • ouelloouello Registered Users Posts: 21
    Re: Copper Bus Bar Design

    I see a lot of pictures of buses that are "off the wall"... Do they have to be in open air or I could screw a 1/4" x 1" x 8" piece of cooper or 6061-T651 flush to plywood or plastic???
  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Copper Bus Bar Design

    I would avoid direct wood contact where electrical power connections are involved--Just take a bit of a loose connection to heat up and set fire to a wood panel.

    Personally, I would prefer to see a panel of sheet rock over a wood panel (or concrete backer board). Dry wood is just so easy to light off. You should also have non-flamable flooring under the electrical installation (if not mounted in metal or screened cabinents). Sort of like installing a fire place/wood stove.

    Even flame rated plastic will catch and sustain fire very nicely if there is an ignition source continuing the combustion.

    -Bill "may or may not be overkill" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Copper Bus Bar Design
    ChrisOlson wrote: »
    inetdog - thanks for the clarification on that green copper "scuz". Whatever it is, it's bad. Real Bad :D

    If you do use aluminum for bus bars always use a tempered alloy. They are very hard and accept threading and whatnot with no problems. Soft aluminum is worse than soft copper for tapping threads - it just won't work.

    Like I stated above, in my previous bus I used stainless steel bolts with dielectric grease on the connections and never had a problem for 9 years. There is no galvanic corrosion between aluminum and stainless steel. There can be between aluminum and copper, but only in the presence of an electrolyte (like salt water). Sealing the connection with dielectric grease keeps moisture in the air off the connection and it remains good for at least a decade (in my experience using it).

    Our old bus went from 12 volt originally, to 24 volt. It was a four-bar bus and not suitable for 48 volt. The bars I used in the new one are 3/8" thick x 1" wide.
    --

    Chris

    i'm not sure i understand your reasoning here chris as buses are rated for current, not voltage. when going to a higher voltage the current often goes lower and is why we often recommend higher voltages be used so as to reduce the size of wire needed. a bus is metal just like wire and can often handle more current than the wires do. there is nothing wrong with going to a bigger bus either, especially if in doubt and i suspect your old bus may have been fine to use at 48v.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Copper Bus Bar Design
    niel wrote: »
    i'm not sure i understand your reasoning here chris as buses are rated for current, not voltage. when going to a higher voltage the current often goes lower and is why we often recommend higher voltages be used so as to reduce the size of wire needed. a bus is metal just like wire and can often handle more current than the wires do. there is nothing wrong with going to a bigger bus either, especially if in doubt and i suspect your old bus may have been fine to use at 48v.

    Our old bus had four bars in it because the 12V bank was originally split in two with two inverters. When we switched to 24V I just made two bars positive and two of them negative. I didn't like that for 48 volt because the bars were too close together in there and I was afraid that if an arc got going on a 48 volt system in the bus it wouldn't be good. So I built a new one.
    --
    Chris
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Copper Bus Bar Design

    understood now as it was basically a safety issue and not one of ratings.
  • ouelloouello Registered Users Posts: 21
    Re: Copper Bus Bar Design

    When listening to you guys, I guess I should take all of my stuff out of the 2nd floor of my cottage... I started with a 15W amorphous panel and a xantrex 1500W Power pack and was able to have lights!!! Switched to Sunforce 60W and was able to have tv and pressured water... My next jump to 235W, maybe I should dedicate a special place for that system that keeps on growing on me...
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: Copper Bus Bar Design
    ChrisOlson wrote: »
    Hi, I did not use copper, but instead 6061 T6 aluminum. I just rebuild my bus - the old one was build the same way and was still working fine after 9 years. I just replaced it because we changed our system from 24 to 48 volts.

    The bolt holes in the bus bars are 5/16" NF, stainless steel bolts and every connection coated with dielectric grease to prevent corrosion.

    Attachment not found.

    --
    Chris

    Chris those in line fuses are not rated for 48 V I believe. Those type are usually only up to 32 V.

    I know because I've arced and melted those type on my 48 V ebike.:roll:
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Copper Bus Bar Design

    I hope not. It said 250V on the confounded things. Each one is only 1 amp and they've held so far :blush:

    One goes to our MidNite Battery Capacity Meter, one goes to some gauges, and the third one goes to two 24V relays in series.

    --
    Chris
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: Copper Bus Bar Design

    Just to be clear, I'm not talking about the breakers, I'm talking about the 3 orange wired inline fuse holders - at least that looks like what they are. If those are rated to 250V I'd love to know where you got them - I could use some!
  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Copper Bus Bar Design

    In-line glass fuses have different voltage ratings--With the lower current versions (depending on exact fuse type) having 125 or 250 volt ratings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Copper Bus Bar Design
    ouello wrote: »
    When listening to you guys, I guess I should take all of my stuff out of the 2nd floor of my cottage... I started with a 15W amorphous panel and a xantrex 1500W Power pack and was able to have lights!!! Switched to Sunforce 60W and was able to have tv and pressured water... My next jump to 235W, maybe I should dedicate a special place for that system that keeps on growing on me...

    That's a familiar refrain! :D

    You've learned the lesson about how hard it is to expand an existing system, right?
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: Copper Bus Bar Design
    BB. wrote: »
    In-line glass fuses have different voltage ratings--With the lower current versions (depending on exact fuse type) having 125 or 250 volt ratings.

    -Bill

    Yep, I misstated - my first post I meant to refer to the fuse holder. Maybe the voltage rating on the holder is irrelevant if the fuse inside is rated to a higher voltage? :confused:

    I know that for my ebike after melting the plastic and shorting a simlar in line fuse holder(similar orange wired one as in the picture but labelled "heavy duty" with 12 gauge wire) at 48V and 30-40 amps - I had to do quite a bit of digging to find a small fuse holder that is rated for higher voltage.

    For a 1 amp circuit maybe no concerns??

    As an FYI THESE J-case fuse holders are the only ones I could find rated for more than 32 Volts and there is only one line of Jcase fuses that have the corresponding 58V rating.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Copper Bus Bar Design

    The breakers are rated 90VDC.

    I just picked the fuses off the shelf at Farm & Fleet and studied them. They are simply a wire with a copper or brass button soldered to the end of it and a spring over the wire. The wire says 14 AWG Cerrowire 600V on it. The fuse itself is a glass one and the holders came with 5A 250V fuses. I needed 1 amp fuses so I had to buy a box of 5 fuses. Some of the glass fuses said 1A 32V and some said 1A 250V. I bought the 250V ones.

    The only way I could see that anything could arc in there is if you put in too short of a fuse and the springs didn't hold enough tension to keep the brass button in contact with the end of the fuse.
    --
    Chris
  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Copper Bus Bar Design

    Yes, there is a problem with automotive and "non-rated" fuse holders that do not even hold up to moderate currents (Wayne from NS Canada had an automotive use holder melt with a 15 amp fuse an much less current--as I recall).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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