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Custom Bus Bars From Copper Flat Bar

HRTKD

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The first iteration of my system used all 2/0 cabling between the big components such as between the battery and the shunt and fuse. I'm in the process of rearranging my system to make way for an inverter/charger upgrade. In doing so, I decided to ditch the 2/0 cable where I could and use copper flat bar as bus bars. This is a learning process for me since I've never worked with copper bar.

I started by ordering copper flat bar from MidWestSteelSupply.com in 1/8"x3/4"x72" and 1/4"x3/4"x72". I've ordered aluminum square tubing from them in the past with good results and good prices. In another thread I compared prices between Midwest and another online source and a local source. The local source for this order - which didn't have it in stock (two weeks minimum) - quoted more than $400 while Midwest was $146 including shipping.

Here is the box my copper from Midwest arrived in. It was taped very well with nothing sticking out. An order from a different online vendor arrived with aluminum flat bar sticking out and all banged up.
1641932993328.png

Here's where I was surprised. They didn't just stick the copper in a box and ship it. They attached the copper to wood slats with plastic wrap with tape outside the plastic wrap. The flat bar came out of the box unbent. It was still nice and flat and not banged up. When the plastic wrap was removed there was no adhesive residue like there might have been if they had used tape directly on the copper.

1641933108001.png1641933302684.png

I drilled a test hole using my Cobalt drill bits in a drill press with the copper held by a drill press vise. I punched a dot on the copper for the drill to follow, but it still wandered, causing the hole to be a bit off center.

Drilling copper isn't as straight forward as I thought it would be. The drilling process produced a significant burr crown around the hole. I had to file and sand that down, which took a lot more time than drilling the hole did. I used Tap Magic cutting fluid. That helped quite a bit and I'll use more of it next time.

In the picture below, the area around the drilled hole has been sanded with progressive grits of sandpaper starting with 150 and ending with 400. There's still a nick at the top of the hole that I'm not going to address. The other side looks better with no nicks. The right side was not sanded at all.

I'm looking at different drill bits to use for this project. They should help with the burrs (different type and drill bit angle) as well as the wandering (different tip). The recommendation for those drill bits came from a friend that does fabrication. I found the drill bit set for much less at NationalToolWarehouse.com. It's still a lot of money though. Twice as much as my Cobalt drill bits.

1641933464607.png

I cut the bus bar to length using my Dewalt chop saw that has a Freud Diablo Non-Ferrous blade. This was the easiest part of the project. The blade went through the copper like a hot knife through butter. The bus bar pictured above has not been dressed on the cut end (right side). You can see minimal burring on the edge. A quick swipe of 320 grit sand paper took care of that.

I'm a bit uncomfortable with the ampacity of the 1/4"x3/4" flat bar. It may be at the margin of how many amps my inverter could pull so I put in new order for 1/4"x1" and 3/8"x1" bar. I'll stack the narrower flat bar for now and use it for lower amp connection later.
 
I'm a bit uncomfortable with the ampacity of the 1/4"x3/4" flat bar. It may be at the margin of how many amps my inverter could pull so I put in new order for 1/4"x1" and 3/8"x1" bar. I'll stack the narrower flat bar for now and use it for lower amp connection later.

Why? It's beefier than 4/0, and it has no insulation rating. :)
 
Use some scrap wood on top of and below the copper bar when drilling. Drilling through the clamped wood/copper sandwich will help with bit wandering and burrs.

Yeah, that's the plan. I was told it had to be metal though. You think wood will do the trick? I'll be happy if wood works as I have plenty of that and it will be less expensive.
 
I used wood to drill my 1/4" copper bar stock when I made my bus bars. Seemed to work well enough. Maybe the ideal way is to use one piece of metal with the correct sized hole on top of the copper. You don't need to keep drilling new holes that one piece of metal. Just reuse the same hole over and over as the initial guide. A piece of wood under the copper should be enough to make a smooth exit hole in the copper.
 
Well that is certainly a High Recommendation for MidWestSteelSupply.com !

I made my own busbars from 110 bar stock and the first few "experiments" was an education with working copper. I found that setting my drill press to medium speed, using HSS bits with a bit of oil really made the difference. I tried wood which made a good "guide" it did nothing for the burs, I did not use hardwood though, maybe that would have made a difference. I also tried aluminium, don't bother. With the HSS bit & Oil it was not so bad really, just has to be fast enough but not too fast.

2 different things. One set I made and tapped (threaded) the copper, predrilled with drill press, hole chamfered with larger bit, then tapped by hand. This worked ok but tedious ! There are Tapping Drill Bits you can use which also chamfer the holes which may be another option depending on how much you have to do. Examples here: https://www.fastenal.ca/productFami...g/Threading+and+Tapping/Tap+Drill+Bits/601104

As part of my current system refresh, I'm using similar bits to tap all of my cell busbars for sense leads on my whole collection of LFP packs.
 
Well that is certainly a High Recommendation for MidWestSteelSupply.com !

I made my own busbars from 110 bar stock and the first few "experiments" was an education with working copper. I found that setting my drill press to medium speed, using HSS bits with a bit of oil really made the difference. I tried wood which made a good "guide" it did nothing for the burs, I did not use hardwood though, maybe that would have made a difference. I also tried aluminium, don't bother. With the HSS bit & Oil it was not so bad really, just has to be fast enough but not too fast.

2 different things. One set I made and tapped (threaded) the copper, predrilled with drill press, hole chamfered with larger bit, then tapped by hand. This worked ok but tedious ! There are Tapping Drill Bits you can use which also chamfer the holes which may be another option depending on how much you have to do. Examples here: https://www.fastenal.ca/productFamily/Cutting+Tools+and+Metalworking/Threading+and+Tapping/Tap+Drill+Bits/601104

As part of my current system refresh, I'm using similar bits to tap all of my cell busbars for sense leads on my whole collection of LFP packs.

That's good to know Steve. I should have mentioned it in my original post but my drill press is on the lowest setting, which didn't seem all that slow to me. I would have to open up the pulley box to see what that RPM is.

For now, the copper won't be used on the battery terminals. I do think it's a great idea to tap bus bars for the balance/sense leads.
 
Well that is certainly a High Recommendation for MidWestSteelSupply.com !

I made my own busbars from 110 bar stock and the first few "experiments" was an education with working copper. I found that setting my drill press to medium speed, using HSS bits with a bit of oil really made the difference. I tried wood which made a good "guide" it did nothing for the burs, I did not use hardwood though, maybe that would have made a difference. I also tried aluminium, don't bother. With the HSS bit & Oil it was not so bad really, just has to be fast enough but not too fast.

2 different things. One set I made and tapped (threaded) the copper, predrilled with drill press, hole chamfered with larger bit, then tapped by hand. This worked ok but tedious ! There are Tapping Drill Bits you can use which also chamfer the holes which may be another option depending on how much you have to do. Examples here: https://www.fastenal.ca/productFamily/Cutting+Tools+and+Metalworking/Threading+and+Tapping/Tap+Drill+Bits/601104

As part of my current system refresh, I'm using similar bits to tap all of my cell busbars for sense leads on my whole collection of LFP packs.
That's what I did on mine .... used a much larger bit to chamfer it .... worked good for me.
 
May be overkill, but I bought steel drill guides. Not as cheap as wood, they have held up well on the drill press.

Similar to this; Drill Guide - McMaster-Carr

Thanks for this idea. I have some fairly thick aluminum blocks that I could use. If I can get them to the same width as the copper so they fit in the drill press vise, that might work.
 
Here is another idea - I did not drill my copper flat bar, used a “center cutting end mill”.
Leaves a really clean, no burr cut.
Would work in a drill press for light work (soft metals)
mcmastersendmill.png
As for a cutting lube, Tap Magic is great, also on long cuts in sticky/gummy copper I found WD40
works as well, is less $$$, but very stinky!

cuttingcopperbusbar copy.jpg
 
Thanks for this idea. I have some fairly thick aluminum blocks that I could use. If I can get them to the same width as the copper so they fit in the drill press vise, that might work.
I used thin strips of wood as spacers so it would be centered on the copper. Also helped stabilize the copper so it stayed flat against the table.
 
I drilled a test hole using my Cobalt drill bits in a drill press with the copper held by a drill press vise. I punched a dot on the copper for the drill to follow, but it still wandered, causing the hole to be a bit off center.

Wandering drill bits, especially if in a drill press, are caused by:

  • uneven angles on the cutting edges
  • uneven length of cutting edges
  • one of the cutting edges duller than the other
You should never need a guide in a drill press. Do a pilot hole with a very small drill bit first (3/32 max)

The drilling process produced a significant burr crown around the hole. I had to file and sand that down, which took a lot more time than drilling the hole did. I used Tap Magic cutting fluid. That helped quite a bit and I'll use more of it next time.

This is from worn, rounded over corners of the drill bit. It doesnt take much, if the corners of the drill are not absolutely sharp it will start plowing up that bur. If you have to apply any serious pressure to drill aluminum your bits are dull, copper seems to have an even lighter requirement for pressure.

WD40 works amazingly well on copper and aluminum.

I'm looking at different drill bits to use for this project. They should help with the burrs (different type and drill bit angle) as well as the wandering (different tip). The recommendation for those drill bits came from a friend that does fabrication. I found the drill bit set for much less at NationalToolWarehouse.com. It's still a lot of money though. Twice as much as my Cobalt drill bits.

You dont need different drills, just have yours sharpened by someone skilled and it will make a massive improvement.
 
I drill copper by hand with an electric drill starting with a mechanical center punch.
1641953629537.png

Next is a 5/32"drill bit for pilot holes. All my drill bits are good quality 118° split point. I'll use any cutting oil that's around.

Step drilling 1/6" at a time keeps bits from getting plugged and breaking.

If the bar has hard wood/plastic (ViseGrip) clamped to it I'll drill thorough if not I stop 1/2 way and come in from the other side but that doesn't work as wall as the backing.

A counter sink removes the burr and make the bars look pro.

Most important is keeping the drill perpendicular to the surface.

That Diablo blade looks like it has a positive (a line along the face of the tooth crosses in front of the center hole) rake. A true non ferrous blade has a zero or a negative rake like this one has. Also note the backing for the teeth is shorter and much stronger.

1641954588604.png

***Be very very very careful cutting copper with a saw blade. I've seen people screw up and rip 10-15 teeth off a blade along with the backing for the teeth. I've also seen the motor come off the rails on compound saws. Cut through the smallest dimension. Make sure it is double/tripple clamped.

I like to used the lesser of 2 evils which is a Walter 1/16" zip cut wheel on a grinder but the copper gets scorching hot. I've seen people that don't know how to use a zip wheel destroy it by side loading or twisting it and have piecs of the disc embed in a wall 20' away.

This is the proper position to for a grinder when zip cutting. Most important is to always have it pulling away from you and use the handle.
1641955958987.png




20180511_181656.jpg
 
Wandering drill bits, especially if in a drill press, are caused by:

  • uneven angles on the cutting edges
  • uneven length of cutting edges
  • one of the cutting edges duller than the other
You should never need a guide in a drill press. Do a pilot hole with a very small drill bit first (3/32 max)



This is from worn, rounded over corners of the drill bit. It doesnt take much, if the corners of the drill are not absolutely sharp it will start plowing up that bur. If you have to apply any serious pressure to drill aluminum your bits are dull, copper seems to have an even lighter requirement for pressure.

WD40 works amazingly well on copper and aluminum.



You dont need different drills, just have yours sharpened by someone skilled and it will make a massive improvement.

My Cobalt bits are fairly new. I don't think the 5/16" bit had been used yet. Other bits in the kit that I've used have been amazing, but it wasn't on copper.
 
My Cobalt bits are fairly new. I don't think the 5/16" bit had been used yet. Other bits in the kit that I've used have been amazing, but it wasn't on copper.
I wont belabor the point other than to say that when I was in the trades, in one of the shops I worked in, when a job came in, all the tooling that was required for that job was presented with the material to the machinist. Carbide inserts and drills (up to a certain size) were considered consumable and new for every job. Both of the machinists I worked with would take the brand new drill bits and sharpen them.
 
I wont belabor the point other than to say that when I was in the trades, in one of the shops I worked in, when a job came in, all the tooling that was required for that job was presented with the material to the machinist. Carbide inserts and drills (up to a certain size) were considered consumable and new for every job. Both of the machinists I worked with would take the brand new drill bits and sharpen them.

Ouch! This might be an excuse to finally buy a drill sharpener.
 
My Cobalt bits are fairly new. I don't think the 5/16" bit had been used yet. Other bits in the kit that I've used have been amazing, but it wasn't on copper.
Allot of the Cobalt drill bits I see are cheap plates steel that would loose the edge 2 min of use. I never buy them.
 
Love this discussion, and the sourcing.

I am considering building bus bars for mounting parallel batteries. I have read the discussion (Steve) on need to balance battery packs if used in parallel and anticipate some work will be needed to accomplish this.

I noted you were using 110 flat bar stock. Pricing looks reasonable on this. Now I need to decide on a width and thickness. Possible power would be an anticipated maximum of 200 amps at 24v if I pursue this route.
 
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