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Need help soldering onto brass flatbar and copper tube

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jpoopdog

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Hi,

Im putting together a capacitor bank and thought, ok, this one is going to have to last, so i bought some tiny brass flatbar and copper tube to use as heavy duty rails.

Now, ideally ide like to use the brass bars, since, being rectangular i can securely bolt them down, though i dont know how well they will solder.

Does anyone know how i go about soldering onto brass? I have 70% nitric acid and 95% sulfuric acid at my disposal which used together (or diluted sulfuric acid alone, but poorly) will strip the brass surface and electrochemically displace everything but copper leaving a pure copper finish, so i can solder directly onto copper which, as we all know is very much possible, from there a standard flux would keep the surface clean, also i have co2 and argon gas cannisters here if oxidation is an issue.

I want to do it using a soldering iron, looking up on the net, theres mixed results, some people say use an oxyacetylene torch, for soldering components to brass which seems strange, others say a soldering iron works just fine. I think they are mixing up soldering with welding and brazing.

So, does anyone have any pointed for soldering onto brass? or copper?
I have a feeling that i might stuff something up but i dont know what or where.
 
Why brass?

Brass has about 4X the resistance of copper. It is used for electrical components as it is easy to machine compared to pure copper, and it is harder than pure copper or copper-tellurium alloys (machinable copper) . However, if you have a big section, it conducts well enough for what you are doing.

Brass solders as easily as copper, and like copper, it conducts heat well. You need a higher power soldering iron than for small electronic components. A 40W iron should work well with strips. I would pre-tin the area to be soldered and would not use any etching solution to make it look like copper. You will quickly know if your soldering iron is big enough when you try to pre-tin.

If I were to use any torch for soldering brass, I would not use oxy-acetylene, as temperature control with the flame is more difficult. I would use propane or MAPP.

John
 
Why brass?
Because as you said, its way harder than copper, its going to be the rails in a capacitor bank, they need to be structurally strong, and easy to fasten to something solid. not really possible the tube which would easily bend if moved wrong, also the tubes would be way hard to drill into and fasten to something.
I just checked and both give a reading of 0.1-0.2 ohm so there isnt any significant differences, my capacitor bank is 450v anyway so even if there was a difference by 4 times it wouldnt do much.

Also, my soldering station i think is somewhere between 50-70W but i do currently own a 40W soldering iron i bought from the hardware store which has been pretty overkill for every application its ever had. i messed up the tip accidentally so ill have to use the screwdriver head instead since it has all its oxidizer protection stuff on it, ill try pretinning it tomorrow. Also, since i dont know how fast brass oxidizes, would it be worth it to use the argon? or shouldnt i bother. I really dont want to mess this up is all.
 
Give us an idea of what sizes of materials your trying to solder together. You may be able to get away with a butane torch such as: https://www.autobarn.net/pt220.html

Remove the oxide with some sandpaper and use some flux, but not ACID flux. Heat the material and don't DRIP the solder.

You may be able to flatten your copper tubes as well.
 
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my brass bar is 6.4 x 1.6mm the tube is 4mm across and is 0.4mm thick, ide rather not flaten the tube unless i could do so in a way the entire thing is flattened evenly.
Also your link doesnt work, but i do have a small pencil torch and a butane can mountable torch also plus a benzomatic propane torch that uses those small propane bottles you can get for $20 or so.

im just soldering some capacitor tabs to the brass, they are about the size of what you get in heavy duty (5A+ ) power transistors.
Its important i get a good bond because any one of these capacitors has enough juice to blow up a foulty joint. im testing one capacitor now discharging it rapidly, it shoots arcs out of every crocodile clip contact.
 
You don't need argon to solder brass or copper. All you need is a rosin flux. Plumbers use an acid flux (ZnCl2). I would not use that.

Here is a capacitor bank I made a few years ago:
Capture.PNG

I used copper rails. They were plenty strong. Brass will work too. Will you be using screw connections to your capacitors or wire? If it is wire, is the wire copper or, more likely, plated steel?

John
 
the capacitors, while large, are not so big that they use screw connections they dont use wire either, its more of a soldering tab squished to a size that it could still fit through a pcb hole. as i said before im soldering them directly to the brass, it would be allot easier if i could just screw them to the rail. Soldering these things isnt going to be hard though, not in the least, im concerned about getting a good bond with the brass.
 
the capacitors, while large, are not so big that they use screw connections they dont use wire either, its more of a soldering tab squished to a size that it could still fit through a pcb hole. as i said before im soldering them directly to the brass, it would be allot easier if i could just screw them to the rail. Soldering these things isnt going to be hard though, not in the least, im concerned about getting a good bond with the brass.

Brass solders as easy as copper, just give it a clean with wire wool or fine abrasive paper, and solder with normal flux cored solder - as already suggested, make sure you have a big enough soldering iron and bit.
 
What you said about the messed up solder tip reminded me. When I was young, I was soldering sections of model train track together. The tip broke on my Weller soldering gun leaving 2 prongs. Thinking that I just had to complete the circuit, I held the 2 prongs to the track with the solder joint between them. The track got hot right away and worked even better! I think that is the principle for resistance welding / Spot welding.
 
The tip broke on my Weller soldering gun leaving 2 prongs. Thinking that I just had to complete the circuit, I held the 2 prongs to the track with the solder joint between them. The track got hot right away and worked even better! I think that is the principle for resistance welding / Spot welding.

Actually I have done that on purpose many times for soldering heavier solid copper and the like and yes if done right it works very well! :cool:
 
Hello,

I dont see any good reason for using brass instead of copper. Copper is always the choice for better conductance.

As pointed out by John in post #2, brass has about 4 times the resistivity of copper making it less conductive.

Brass should actually require less power heating to solder however. That's because brass also has significantly lower thermal conductivity meaning that localized heating will result in a higher temperature than with copper in sizable blocks of material. So for equal slabs of materials and equal power, the local temperature in the brass will reach a higher level than with copper. The brass thermal conductivity is three to four times less than that of copper so it might be quite significant. This could make or break the ability to solder a larger mass of the material with a given soldering iron or torch. So a slab of copper may not be solderable with a given size iron, while the same size slab of brass might be easy to solder with that same iron.

The arrangement of the capacitors relative to the lead in wires is of some significance also, using copper or brass or anything else. The idea is to minimize the distance between the lead in wire connections and all the capacitors, while at the same time equalizing the distance to each individual capacitor. Minimize for lowest resistance, and equalize for equal added ESR to each capacitor which then equalizes ripple current which prevents one cap from getting a significantly higher ripple current and overheating. You could look for the best arrangement.
So for example for capacitors connected in parallel where they are all side by side in a row with the two buss bars looking sort of like a train track, the best lead in wire connections would be the positive lead on one end of the bank, and the negative lead on the other end of the bank. This makes the total resistance to any one capacitor the same as the others. Connecting the two lead in wires to one end of the train track means the cap on the far end has much more ESR than the cap on the near end, so opposite end connections are preferred. Connecting in the middle of the bank gives lower overall ESR but not equal ESR so that technique would have to be used with care.
 
I used brass because i could get small brass flatbar, opposed to only copper tube, though i still bought the tube just in case
 
Is there a reason not to use tube? Wire is generally round too. I get my copper strip from McMaster- Carr (McMaster.com). There must be a similar industrial hardware store in Oz.

John
 
the tube is too small and too soft. the brass flatbar on the other hand is rectangular in shape and is big enough that i can bolt stuff onto it i checked and the resistances of the brass was negligible in comparison to the copper
 
I don't see any problem with using the brass bar being it's more than likely electrically way bigger than what it needs to be to carry the involved currents.

I have seen brass used in many industrial electronics systems so obviously it works well enough.
 
Hi,

It's not out of the question to use brass, i've used brass screws when i needed to be able to solder to them for electrical stuff, and brass hex nuts are great for that too.

If the application can stand the higher resistance then there are no worries :)

Usually multiple capacitors are used for banks where the ripple rating of one cap is not high enough so they are paralleled. The caps share the current so each one gets less ripple current. In that case current sharing is highly dependent on the conduction paths to each cap.

A question now would be just what is this setup going to be used for.
 
I don't know your country. But, Batteries Plus Company that sells batteries hear in the states have a spot welder. They spot weld batteries together, it should work well enough and they might even have the strips.
 
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