Does phosphor bronze make a good buzz bar material? - Page 1
Forum section: electronics / general

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: April 22, 2021, 09:56:24 am
content: Hi All,I am doing a better job of connecting up our off grid batteries, charge controller, inverters and current shunts etc. The cables are 35sqmm or 50sqmm with crimped on tinned copper terminals. These are bolted on with stainless steel bolts.I want to make up a couple of connection points where multiple things can connect. I have some 3/16" (5mm) thick phosphor bronze sheet I can cut out and use. I am wondering if there may be any weird galvanic considerations using phosphor bronze?The bronze sheet is what the company I worked for, Lola Cars, used in around 1993 on the bottom of the Indy cars. The cars ran only a few millimetres from the track an would touch the track. Anything that sparked was not allowed so the designers wanted a low friction material that didn't spark and was very dense to get the weight as low as possible. The part on the car was a plate about 2ft wide and about 5ft long and very heavy. I ended up with some of the offcuts from the machine making them.

author: Wolfram
author_rank: Frequent Contributor
timestamp: April 22, 2021, 11:00:49 am
content: Phosphor bronze has 10 - 20 % of the conductivity of copper, so if your busbars are dimensioned by current handling then they will need to be massively upsized compared to copper ones.

author: Berni
author_rank: Super Contributor
timestamp: April 22, 2021, 11:13:09 am
content: Interesting application of bronze.I don't think corrosion would be any issue with it unless perhaps it was somewhere constantly wet. However you do have to be aware that bronze is pretty crap at conducting electricity. The exact conductivity depends a lot on the particular blend but is somewhere only about 40% to 12% as conductive as pure copper. So the most conductive blends of bronze might close to aluminium (it's about 60%) or some of the poorly conductive blends of bronze might be even worse than using a iron bar (it's about 17%). The only commonly used metals that are even worse than the brass are lead or steel.So nothing wrong with the bar you have, but do keep in mind that it needs to be significantly thicker than your beefy 50mm2 cables to do the job you want it to do.

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: April 22, 2021, 06:56:03 pm
content: Blimey.I wouldn't have thought that an alloy of copper would be so rubbish in comparison to copper.I think I might go to plan B which was to flatten some copper pipe and use that.

author: Berni
author_rank: Super Contributor
timestamp: April 22, 2021, 07:37:47 pm
content: Yeah because of physics reasons the pure metals tend to have the best conductivity.Flattening copper pipe is indeed a excellent way to get busbars since bar stock is much harder to find.

author: Alti
author_rank: Frequent Contributor
timestamp: April 23, 2021, 11:26:24 am
content: For custom "multiple connection points", I'd recommend using genric brass bolts, clamps and fittings cut into custom arrangement and then brazed together. Brass is super pleasant in machining, cheap and popular and brazes well with propane torch + borax + brazing rods.

author: TimFox
author_rank: Super Contributor
timestamp: April 23, 2021, 02:12:05 pm
content: The resistivity of metals and metal alloys is a fascinating study in its own right. Generally, the resistance occurs because drifting electrons scatter: the scattering centers can be crystal lattice defects, "minority" atoms in the alloy, and a host of other things. That is why the lowest resistivity (highest conductivity) usually is found in a pure single crystal of a single element. For practical use, OFHC (oxygen-free high conductivity) and OFE copper gives the highest conductivity of commercially-available copper materials. (There are other oxygen-free types, but OFHC achieves this by vacuum melting, while phosphorous-deoxydized copper leaves holes in the material where the oxygen used to be). Legitimate uses of OFHC (not golden-ear speaker cables) usually exploit another feature: resistance to metal fatigue from repeated bending. The informal test is to clamp a flat piece, maybe 3 mm thick, in a vise and bend it back and forth with a pliers and see how many bends it takes to break it. ETP copper, the normal form for electrical wires, etc., is <0.04% oxygen, but will fail the bending test before OFHC.

author: Wolfram
author_rank: Frequent Contributor
timestamp: April 23, 2021, 03:11:44 pm
content: Interestingly, most copper pipes are made from DHP copper, which has had the oxygen removed by adding phosphorous to make it less brittle for tube drawing. The 0.015 - 0.04 % residual phosphorous really wrecks the conductivity, reducing it by 20 % typically compared to ETP and OFHC, which is pretty dramatic for such a small amount. So it follows that phosphor bronze is pretty bad among the copper alloys when it comes to conductivity.

author: TimFox
author_rank: Super Contributor
timestamp: April 23, 2021, 04:37:37 pm
content: DHP is usually preferred for non-electrical or mechanical purposes, such as the pipes you mention,since the residual phosphorus helps prevent hydrogen embrittlement. The “minority” component fractions in these commercial forms of copper are small compared with the alloying components of bronzes (including the classic Cu-Sn bronze and the modern Be-Cu alloys) where the alloys are much harder and stronger than the pure Cu metal, with higher resistivity (electrical and thermal).

author: themadhippy
author_rank: Super Contributor
timestamp: April 23, 2021, 04:47:42 pm
content: if youve a fair bit of bronze take it down the scrappy and either see if they'll do a swap or use the cash to buy a suitable lump of copper

author: TimFox
author_rank: Super Contributor
timestamp: April 23, 2021, 05:12:25 pm
content: One thing to watch out for when substituting copper for bronze or brass is that copper is a very difficult material to tap holes in, and somewhat harder to drill, being “gummier” than the (harder) alloys.

author: woodchips
author_rank: Frequent Contributor
timestamp: April 23, 2021, 05:44:42 pm
content: You are in the UK, look on the Model Engineer web site for suppliers of pure copper bars. This is needed for making steam boilers, 106 off the top of my head.Do not tap holes in copper, use through bolts and most important use the Belville dished washers to maintain the bolt tension on the copper. I have dismantled more things than I have had dinners, and the naff high current joints have always been the unit failing, other than ones using Belville washers. Also be aware of the current density through the connection, one bolt may not be enough. Don't forget that copper is ductile and will flow under load.

author: Wolfram
author_rank: Frequent Contributor
timestamp: April 23, 2021, 06:43:42 pm
content: Quote from: TimFox on April 23, 2021, 05:12:25 pmI found that forming taps work much better than cutting taps in ETP copper. They are significantly more expensive, but the affordable ones from China on eBay work pretty well in my experience.

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: April 28, 2021, 11:51:27 am
content: Yes. I have turned copper on my lathe. It is horrid stuff to turn. Like you say it is very chewy. I think I had to use a really high rake angle on the tool and I can't remember what fluid / wd40 / oil / grease wax I used to try and prevent the copper sticking to the tool.

author: elekorsi
author_rank: Regular Contributor
timestamp: April 30, 2021, 11:47:03 am
content: Get yourself some proper "electric" grade copper bars. Available at every decent industrial equipment supplier in various dimensions. You can also get some laminated insulated bars for "flexible" connections (can be bent by hand).If you need small amounts, ask some local industrial electric panel builder for leftovers...