Author Topic: Brass vs Copper for spark gap?  (Read 1166 times)

Offline FPS

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Brass vs Copper for spark gap?
« on: September 25, 2023, 01:03:25 PM »
I'm planning on constructing a spark gap to measure voltages amongst other things, for the electrode rod that will be threaded to fit the actual terminal electrode (be it needle or ball etc.) it can be either brass or copper, the price is much the same surprisingly but the difference being brass being more robust and copper more conductive. I'm not referring to that which the actual spark jumps off, rather just the connecting rod.

Will the conductivity difference be totally negligible in every practical sense?

It will be a sliding contact between electrode rod and fixture, I'm not sure is the oxide layer will be better or worse between copper and brass. Probably another insignificant thing I'm considering.

It will be 8mm rod over 250mm, and at most 50kV and perhaps 50mA at a round'a'bout figure.


Offline FPS

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Re: Brass vs Copper for spark gap?
« Reply #1 on: September 25, 2023, 01:36:22 PM »
Attaching reference picture, this is a standardised measurement spark gap, used 2" bronze ball electrodes.

Offline Mads Barnkob

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Re: Brass vs Copper for spark gap?
« Reply #2 on: September 25, 2023, 05:04:19 PM »
I got an old paper saved on corrosion in high current discharges. Here the verdict is clear, brass is superior in wear, over copper.

I think, for the amateur, there is no difference in material for a measurement spark gaps precision. If you needed something more precise, its over in expensive measurement equipment like capacitively coupled voltage measurements.

https://kaizerpowerelectronics.dk/theory/file-archive/?drawer=application_notes*pulse_power Erosion in High Current Discharges
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Offline FPS

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Re: Brass vs Copper for spark gap?
« Reply #3 on: September 25, 2023, 05:32:57 PM »
Haha yeh I come tp that conclusion after posting this, 3x more resistance seems like a lot until you realise 3x more than a poofteenth is still a poofteenth. I ordered some brass and copper so now it'll depend what comes off the lathe the best I guess.

Offline Mads Barnkob

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Re: Brass vs Copper for spark gap?
« Reply #4 on: September 25, 2023, 07:21:13 PM »
Haha yeh I come tp that conclusion after posting this, 3x more resistance seems like a lot until you realise 3x more than a poofteenth is still a poofteenth. I ordered some brass and copper so now it'll depend what comes off the lathe the best I guess.

It is certainly also worth noting that wear from a capacitor discharge, depends on the charge in Coulombs. With higher voltage, you can store a higher charge in joule, with the same Coulomb energy in the spark. I put that into my capacitor energy calculator: https://kaizerpowerelectronics.dk/calculators/capacitor-energy-calculator/
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Offline FPS

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Re: Brass vs Copper for spark gap?
« Reply #5 on: September 25, 2023, 08:55:28 PM »
Yeh the actual discharge won't be off copper, unless I want pretty colours I guess.

I can find 20mm brass and 60mm stainless threaded spheres on aliexpress, and brass "speaker spikes" look like an interesting spark electrode too for a nice clean look. I've asked for a quote on replacement 2" bronze electrodes above too but I'm sure it's going to be outrageous.

Offline Benbmw

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Re: Brass vs Copper for spark gap?
« Reply #6 on: September 25, 2023, 11:27:05 PM »
Yeh the actual discharge won't be off copper, unless I want pretty colours I guess.

I can find 20mm brass and 60mm stainless threaded spheres on aliexpress, and brass "speaker spikes" look like an interesting spark electrode too for a nice clean look. I've asked for a quote on replacement 2" bronze electrodes above too but I'm sure it's going to be outrageous.

Though it is expensive, copper-tungsten is a very durable electrode material. It machines fairly nicely, almost like a cast iron, although it is quite hard and wears down tools. You can get 25mm OD, 200mm long pieces from aliexpress for $50, which is 8x cheaper than McMaster!

https://www.aliexpress.us/item/3256805668149469.html?spm=a2g0o.productlist.main.3.482965aaaVll0M&algo_pvid=df49b8fa-f151-46db-95eb-7b1137dbe21c&algo_exp_id=df49b8fa-f151-46db-95eb-7b1137dbe21c-1&pdp_npi=4%40dis%21USD%2173.29%2121.99%21%21%21532.62%21%21%402103225216956768836838779e3b54%2112000034584336404%21sea%21US%210%21AB&curPageLogUid=umNlRdlgdHXY

Offline FPS

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Re: Brass vs Copper for spark gap?
« Reply #7 on: September 27, 2023, 10:30:04 AM »
The quote is in for the Buckley spark gap measurement apparatus in picture above, $ 5,890.00 Haha. I felt bad asking knowing it was going to be extreme but there you have it.

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Re: Brass vs Copper for spark gap?
« Reply #7 on: September 27, 2023, 10:30:04 AM »

 


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