Tungsten Electrodes...

S

SlyCayer

100 W
Joined
Sep 6, 2010
Messages
173
Location
Limoges, Ontario
Hi,

I got myself a home built spot welder(LEDhacks version) and I bought some tungsten rods to make tungsten electrodes to spot weld nickel tabs to copper buss bars...

Now I can't spot weld the tabs to the batteries anymore due to the tungsten sticking more to the tab then the tab sticks to the cans of the cells... Copper did the work perfectly for the cells.

Please let me know if there is something I don't understand...

Aren't the melting point of tungsten higher then copper so should be better for spot welding? I am confused once again.
 
Tungsten has a pretty high resistivity compared to copper, so I'd guess the tip of the electrode is going to heat up and make it stick. I believe that the alloy used for welding copper sheet is usually Elkanite, a copper/tungsten alloy.

Jeremy
 
Hey, would molybdenum be better? I just found molybdenum which seems better and I am RLT's posts about molybdenum and it seems to be the king of spot welding... Don't ya think?
 
I think they are probably about the same, I think. I've no direct experience of using molybdenum electrodes, but what I've read suggests that they used as much as the Elkanite ones for welding copper. Molybdenum might be easier to get hold of than Elkanite, too.

Jeremy
 
When welding copper to copper or using a spot welder to resistance braze copper to copper, would molybdenum also be a good choice?
 
I have done quite a bit of testing of electrodes with my welder (http://endless-sphere.com/forums/viewtopic.php?f=2&t=2633&start=570#p280216)... forget tungsten, it just does not work well. Tip sticks and/or blows off, etc.

For copper you want molybdenum electrodes on the copper. Also the "+" electrode is hotter than the '-' one. You want it on the most conductive/thickest material.

For welding copper, forget about trying to weld with electrodes on the same piece of copper. Too much current gets shunted through the copper and you won't get a good weld. You also want to use material with weldments (dimples) where the electrodes/welds go.
 
SlyCayer said:
So you are saying I should have 1 copper electrode on the nickel tabs and 1 molybdenum on the copper bar?

Also, you are saying the "+" should be on the copper also?
Click to expand...

Yes, that should work best.

BTW, I got my moly from Ebay seller threerollmillpro: http://cgi.ebay.com/Moly-Molybdenum-UnPolished-Rod-0-1875-D-x12-L-/390119936554?pt=LH_DefaultDomain_0&hash=item5ad4f5d22a#ht_787wt_707
 
SlyCayer said:
Yes, I bought it from the same place... A few hours ago.

Why is 1 copper and 1 moly better then having 2 molys?
Click to expand...

Copper conducts better than moly. Using copper gets more current into the weld. So unless you need the extra heat, you are better off using copper. You should try it several ways and see what works best for your configuration.
 
Those have a 1500A surge rating... a good capacitor bank could fry those puppies in a flash. My welder cranks out 20,000 amp pulses. What caps are you using?

See my post at http://endless-sphere.com/forums/viewtopic.php?f=2&t=2633&start=525#p267768 for the low down on car audio capacitors...
 
SlyCayer said:
I am using 3 Boss 2 Farad Caps, http://www.hookedontronicsbuys.com/show_product_details.jsp?cid=118114&brandtype=0

I ain't sure but MY current system welds .005 nickel tabs to my A123 Aluminum Cells easily with lots of holding strength.

Do you suggest I get a high SCR? And where to source higher SCR?
Click to expand...


I don't think those caps are going to do it.

The trick is to make sure your cabling is HUGE, and to make sure the ESR of the cap bank is as low as possible. Most large capacity audio caps have crap ESR.
 
What does ESR stand for.

I do not know if they are doing it or not, but I am able to weld .005 nickel tabs to my A123 26650 and if you put the tab off with pliers, the tabs stay there in a tear drop, which indicates a strong weld.

What caps do you suggest and what SCR do you suggest would be better?
 
I tested the BOSS 3.5F caps... very fraudulent crapassators. Spec'd at 3.5F +/- 10%... actually around 0.5F They had an ESR around 1.5 milliohms. Your pair of those is equal to one Rockford/Monster Cable 1F cap. For doing a good job on copper, you would probably need 6 of them in parallel.

ESR is equivalent series resistance. It is an indication of how much current the cap can put out. The lower the ESR, the better. The BOSS ESR was actually not too bad.

You can use your SCR until it dies... the welder uses them in a way that they are not spec'd for. Hard to tell for sure how well it will hold up.

There are lots of them are listed on Ebay (serarch for SCR and thyristor, i'd select sort by highest price first to eliminate all the tiny devices) A pain to track down the specs on them. The value that you are interested in is usually called Itsm. Ebay item 250308476753 looks good... I would avoid the hockey puck style devices. They can be a pain to properly mount.
 
Yes, that is the one. I run three in parallel. You control the weld by adjusting the voltage. Usually 12-16V works well. The caps are rated at 16V/20V surge. Since you are running them at room temp and not in a hot car, I have had no problems at 16-20V continuous... YMMV

If you are buying any, PM me first. I have some sets available for a lot less than what you are likely to find on Ebay... They are used and in good condition. I have measured their values and tested them in my welder.
 
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