Build your own CD battery tab welder for about $100.00+-

Thanks for the help Jeremy.

I think I can find an SCR on ebay for a reasonable price.

As for the electrods, after reading I saw that some copper chromium were a good choice. I found some on mcmaster-carr for a good price so I ordered some to try. If they don't work I can always run to the local hardware store and buy some solid copper ground wire to use.

I am looking at power supplies right now. Is there a minimum amp rating that I need? There are some cheap ones that are up to 10 amps, then there are some more expensive ones that are 25-30 amps and up. I would like to get a medium range one to keep the costs down. So what is the minimum amp rating that I need to weld battery tabs. Not looking to weld anything more than battery tabs for now.

I am going to look for a 5 fared or so capacitor for now. Maybe build up a bank of capacitors down the road.

So besides the power supply the only question I have is about the relay. You say that a normal car relay will work so I should be good because I have a bunch of them laying around. Can you provide the details about how to hook the relay up? And also what size wire should I use for the connections between the power supply to caps, relay, etc?

Thanks again for your help and hopefully will be able to post some pics of my battery tab welder soon! And once I get the basics down I want to design a setup that will use a foot pedal to lower the electrods to the batteries and thinking a limit switch to trigger the relay. To make it "hands free" so I can hold the battery and use my foot to lower and trigger the welder. This will be down the road, just focusing on a basic welder for now.

Scott
 
Having a really big power supply only has one effect, speeding up the time between welds. Some people have used 2 amp power supplies and just put up with the wait while the capacitor recharges. I use a supply rated at around 6 amps and find that the short delay between welds isn't too big a problem, as you often need a few seconds to reposition things anyway. So, any supply that has a variable voltage over the right range and will deliver at least about 5 amps should do.

5F is a big capacitor. I'm working OK with less than 2F at around 16V. One slight advantage of having a big capacitor is that you can turn the voltage down a bit, but I'd have thought that 5F would have been more than adequate for near enough anything that this type of home welder can do, if the capacitor is genuinely 5F (many cheaper car audio caps are seriously misrated!).

Here's a PDF of the welder circuit diagram which should be easy enough to follow: View attachment Welder.pdf

The relay needs to be a changeover relay, one that has a normally open, a normally closed and a common terminal. These are less common than standard car relays and usually have five terminals rather than four. They are pretty cheap if you need to buy one.

Most of the wiring only needs to be rated for the power supply current, so any suitable hook up wire that will take around 10 to 15 amps should be fine. The main discharge cables from the capacitor to the thyristor and electrodes need to be the thickest stuff you can lay your hands on, as it will be handling peak currents in the 1000 amp range. I've used 16mm² flexible welding cable and it works OK but is probably the smallest size you'd want to use, this translates into something like 5 gauge in US measurements. If you can find something flexible that's even bigger, then that would be good.

I've put the trigger switch on one of the electrode holders on the ones I've made, as this is easy enough to use. Your thumb is effectively free when holding the electrodes in place and it seems easy to use this way. I guess you could use a footswitch in just the same way, but I'm not sure it'd be worth the extra bother, or risk that you might trigger the welder with the electrodes not on the work ((I've done this, it makes for a heck of a bang when they touch something!).

Jeremy
 
Thanks for taking the time to explain all this Jeremy, I really appreciate it.

That's good news that I don't need a huge power supply. I was under the impression that I needed a pretty big one. I will pick one out and order it now.

Also good news that I don't need a huge capacitor. I know that the car audio is really over rated and that was one reason I was looking at a 5 fared, to leave some room for over rating. You say that you are running a lower fared cap at 16V, most of the power supplies I have found are variable up to 12 or 13 volts. Is yours a better supply to go all the way to 16 volts?

Thanks for the PDF, I understand the relay good now. I will have to look and see if I have a 5 tab relay, have a big box of relays and other stuff I'll have to dig threw. If not I'll just buy one.

I like your electrod holders and the thumb switch. Did you make them or buy them from somewhere? If you bought it do you have a link to where I can buy one? If you made it can you provide anymore details?

After reading your reply and thinking about it the foot switch doesn't make sense anymore. I am focusing on just getting the welder working right now since some of this is new to me. After I have the welder working I am going to make a stand of sorts for the electrods. The stand will have an arm that will hold the electrods. The arm ill be linked to a pedal so that when I push the pedal with my foot the arm will lower and touch the electrods to the battery and tab. Then I will activate the trigger for the weld. This will allow me to use both my hands to hold the battery and tab and get them aligned and then use my foot to lower the electrod arm and the pressure from the electrods will hold the tab to the battery. I believe this is how the proffesional battery welders work.

Thanks again for your time and sharing your knowledge,

Scott
 
No worries, Scott, glad the info helped.

If you can, I'd go for a power supply that will go up to about 15V, as there may be occasions when you want the extra power. The welding energy is proportional to the square of the capacitor charge voltage, so a small change in voltage makes a big change in energy.

The capacitors I'm using are from computer power supplies (big stuff, not home PCs). They are rated at 20V and I know that they all meet their rated capacity. The same can't be said for some of the car audio ones, so you may be better off buying a big one like the 5F you mentioned and hoping that it is really maybe half it's stated capacity. There's some chat about car audio capacitors and their real ratings back in this thread somewhere, I think. The rated voltage of the car audio capacitors should be around 15V, as that's the sort of voltage a car system can get up to when the engines running.

I made the electrode holders from bits of Delrin rod, turned up on the lathe and drilled to accept the 1/4" copper rod. The one with the push button on has a bit of alloy bar turned up to hold the push button and fit to the Delrin part. The cable ends are just bits of copper tube with one end flattened in the vice, bent around the electrode rod and drilled to accept a nut and bolt to clamp it in place. The 16mm² cable is just soldered in to the remaining open end of the tube.

Some people have just made electrode holders by wrapping lots of tape around the rods, which probably works just as well. You could also just fix them into some pieces of plastic tube (maybe offcuts of plastic conduit) using epoxy resin. Something like a cork that fits inside the conduit, drilled to take the rod, could act as a dam for the epoxy to stop it running out.

I spent a lot of time building a handle operated, clamp-type electrode holder (there are pictures of it back in this thread somewhere. In practice it was a pain to use, much slower than a pair of hand-held electrodes. I made up jigs to hold rows of cells on end, so that I could, in theory, just slider the next cell under the electrodes, pull the handle, press the button and hey presto. The snag is that this actually took more time than just whacking the hand-held electrodes down on the next cell by hand. Add in the challenge of setting exactly the right electrode pressure and the fact that this needs to change slightly for positive and negative ends of the cells (because the positive ends were thicker and made of steel) and it made the whole thing a bit of a waste of effort, in my view. I'm sure a decent enough system could be made, with proper electrode pressure control, but I found it all to be too much trouble just to make a couple of battery packs.

Jeremy
 
I just bought a 0-35 volt 0-5 amp regulated power supply. So now I just need to find a capacitor and I should be in business. Still have to get the SCR but have found some on ebay so will have them soon also.

Thanks again for the help Jeremy
 
Well I just went back and finished reading all 30 pages, don't even want to know how long that took including clicking on all the links and searching threw them!

I have a 20 volt 5 amp variable power supply on it's way, have a SCR on it's way, pretty sure I'm going to get a volfenhag 4 fared capacitor based on others findings and hope for the best. Guess I can always add another one if this doesn't have enough fareds to weld tabs. All I need is a relay which I can get locally and I have all the wires.

The last part is the handle assembly and the electrods. I am going to place an order with mcmaster for some delrin rod for insulators and also get a set of copper chromium electrods from them since someone mentioned they work good and are cheap and I figure I'm placing an order with them anyway. I really like that place, if I place an order by 5 pm it will be at my door by 2 pm the next day. I am going to have to find and rig up some sort of switch on the handles. I don't have lathe access so think I will epoxy it to the top of the handle and then use some shrink wrap to hold the wires to the handle. Bought the best idea I have right now.

Even with others not having good luck with the press type electrode holders I would like to try something down the road after I have the welder working and everything figured out.

Hopefully it will all come together, I've spent hours reading and trying to learn from others success and mistakes.

Thanks for all the help and posting everything on here for others like me to learn from and hopefully I'll have some pictures to share.

Scott
 
Sounds like you have it all sorted, Scott. Your choices look good to me.

Good luck with the project!

Jeremy
 
Hello Jeremy,
I was just reading through your instructions and you say not to exceed "18v or the voltage of the capacitor, which ever is lower". Most of the capacitors I can see for sale are 22v or so. Will these charge up with just an 18v supply into the unit? Thanks.
 
If they're rated at 22V then you're OK to go up to that voltage. My only concern would be: "how honest is that rating?". For a certified electronic component you can be pretty sure that the rated voltage is the minimum that the capacitor will take safely. For a car audio capacitor of "unknown parentage" the rating might be optimistic. Car systems rarely exceed 15V, with just short spikes (which would be damped by the capacitor) above that. If a car audio capacitor manufacturer over-states the rated voltage, they can be pretty confident that they won't get caught out, because of the normal limit on voltage won't get as high as the stated rating.

Jeremy
 
Jeremy Harris said:
If they're rated at 22V then you're OK to go up to that voltage. My only concern would be: "how honest is that rating?". For a certified electronic component you can be pretty sure that the rated voltage is the minimum that the capacitor will take safely. For a car audio capacitor of "unknown parentage" the rating might be optimistic. Car systems rarely exceed 15V, with just short spikes (which would be damped by the capacitor) above that. If a car audio capacitor manufacturer over-states the rated voltage, they can be pretty confident that they won't get caught out, because of the normal limit on voltage won't get as high as the stated rating.

Jeremy
Click to expand...

Thanks for that. The reason I asked was that I simply could not find any capacitors which were any lower than 20v rated. Is there any particular amperage which the DC power supply should provide? Or..avoid providing, for that matter? One supply I had in mind was an 18v laptop charger which stepped 220v down to 18v @2.3A. Thanks again and sorry to drag on, I just want to get it right!
 
You really need a variable voltage supply, as it's best to fine-tune the weld energy by adjusting the voltage. You can use a low current supply, say one that will deliver 2 amps or so, but the delay between welds whilst the capacitor recharges may get annoying. I use a home made variable voltage (3V to 20V) bench power supply that can deliver about 5 amps and find that the delay isn't too bad, so if possible I'd look at getting something around this size. A supply that has a volt meter on it makes setting easier and also lets you know when the capacitor is fully recharged between welds, although you can just hook up a meter to the capacitor.

Jeremy
 
Jeremy Harris said:
You really need a variable voltage supply, as it's best to fine-tune the weld energy by adjusting the voltage. You can use a low current supply, say one that will deliver 2 amps or so, but the delay between welds whilst the capacitor recharges may get annoying. I use a home made variable voltage (3V to 20V) bench power supply that can deliver about 5 amps and find that the delay isn't too bad, so if possible I'd look at getting something around this size. A supply that has a volt meter on it makes setting easier and also lets you know when the capacitor is fully recharged between welds, although you can just hook up a meter to the capacitor.

Jeremy
Click to expand...

Gotcha. Checking the pertinent websites for one now. Will post a vid as soon as I am good. PS who do you recommend for nickel tabs? It seems Sunstone are the preferred outlet around here!
 
 
Those are the very ones I was looking at. Are you in the UK too Rick? I see you use Ebay.co.uk same as myself, which I find provides the more suitable range of results. I might try the first one, see how it pans out.
They are a few quid, but they seem to have everything, the display, the range, the current rating......no point in being cheap now I guess. It still comes out at very little over €100 for me. all in.

Oh, and beware the old Chinese euphemism of "Expedited Flat Rate Intl"....it means no such thing. :) if you are surfing ebay.com
 
The Mighty Volt said:
Those are the very ones I was looking at. Are you in the UK too Rick? I see you use Ebay.co.uk same as myself, which I find provides the more suitable range of results. I might try the first one, see how it pans out.
They are a few quid, but they seem to have everything, the display, the range, the current rating......no point in being cheap now I guess. It still comes out at very little over €100 for me. all in.

Oh, and beware the old Chinese euphemism of "Expedited Flat Rate Intl"....it means no such thing. :) if you are surfing ebay.com
Click to expand...

no, i left the UK as a child in 1956. i'm in Canada. i returned and lived briefly in Leeds in the late 80's. but i returned to Canada.

I use all of eBay. thanks to Google Translate i often check on the german, dutch and french sites to see how the prices for the same types of items vary internationaly.

i liked that one too. mostly because of it's 8.5A rating.

rick
 
Leeds.......a bit industrial, a bit heavy for my liking. More of a rural sort myself.

The first V.V.C is being touted as 8KG in weight...the seller seems to regard it being so heavy as a good thing, which, of course, is true. That said...a pretty penny to ship. 8.5 A is nice.
 
Pretty much any of those will do the job handsomely, I think.

Nickel strip is a pain to get hold of, I found. I got lucky and found a roll of 99.99% pure sheet nickel, intended for laboratory use, for sale on ebay. It was overkill for battery terminals, but I got it at a really good price.

Jeremy
 
Jeremy Harris said:
Pretty much any of those will do the job handsomely, I think.

Nickel strip is a pain to get hold of, I found. I got lucky and found a roll of 99.99% pure sheet nickel, intended for laboratory use, for sale on ebay. It was overkill for battery terminals, but I got it at a really good price.

Recently, I bought some solar cells and they came with termination tape for making cell interconnects, in a couple of different widths. It looks suspiciously like nickel strip to me, but I've not been able to confirm this. It might be worth looking at as a possible source for cell tabs, though.

Jeremy
Click to expand...

Yes I came across that too..........type in "Solder Tabs" on ebay.com and you will get a lot of solar cell results.

Like TV's Columbo...... Just one more question.......seeing as I will need a charger to charge the welded packs.....should I invest in a more expensive DC supply? Could that then be used to charge battery packs in addition to providing the power for the welder? Just trying to kill birds with the same stone here.... :)
 
most of the older supplies use a heavy laminated iron core mains transformer with lots of heavy copper wire windings. that is where all of the weight goes.

i was in Leeds for a job at the university. it was a contract that ended sooner than expected. so much for finishing sooner and under budget. that'll learn me.

rick
 
I'm looking through my junkbox to see what components might be pressed into service to make up a welder. I have a couple of 1000V 600A continuous SCRs (they are from an old X-Ray generator) - don't know what the peak is, but the things are nearly the size of my fist.

Capacitors; I used to build big - as in 2KW+ audio systems - so have quite a lot of 68,000 mfd caps rated at 100v. Bearing in mind that it is the total energy that is important, does half-C-V-squared get me in the right ballpark with, say, 100V and 250,000mfd?

Are there any problems with spatter at higher voltage?

Power supplies and suchlike I already have.

I have a lot of thin copper strip, I gather that it is a bit more difficult to use than nickel - is higher voltage going to make that better - or worse?

The other area of my ignorance is electrodes - I'll plough back through this thread to search for photographs.

dermot
 
I've not heard of any capacitive discharge welders that use high voltage, but that may have as much to do with safety legislation and risk of shock as anything else. The thyristors sound as if they'll be fine, with that high a current rating the Itsm, the peak current rating, is likely to be at least 5000A, probably more.

I think you may be the high voltage welding guinea pig on here, as I've not heard of anyone going higher than maybe 20V or so.

Jeremy
 
Jeremy Harris said:
I've not heard of any capacitive discharge welders that use high voltage, but that may have as much to do with safety legislation and risk of shock as anything else. The thyristors sound as if they'll be fine, with that high a current rating the Itsm, the peak current rating, is likely to be at least 5000A, probably more.

I think you may be the high voltage welding guinea pig on here, as I've not heard of anyone going higher than maybe 20V or so.

Jeremy
Click to expand...

Call me chicken, but... Never mind. just call me a CHICKEN. all CAPS and put it on my name tag.

low votage and high energy is exciting enough. high voltage at low energy makes pretty sparks. high voltage and high energy lights up all kinds of warning signs.

i suspect i'd like to have a fair distance between any part of myself and the discharge electrodes the first few times i fire it. below 20V it is hard to shock yourself. most injury would be splatter burns from melted parts. at 40 or 50V depending on circumstances the voltage itself becomes dangerous.

rick

rick
 
Rick, at what point, in terms of voltage, does the pre-existing current become a real threat? You think it it needs to be 50v or more? We are talking pretty serious current with these welders. Thanks
 
In an earlier post, I mentioned that I was making modifications to my electrode holder system in order to get more equal pressures on each electrode. I'd originally "floated" the individual electrode mounts by drilling oversized holes for the mounting screws, and then putting an O ring over the screw to take up the extra space. This resulted in a sort of flexible mount and allowed the electodes a small amount of adjustment to compensate for other variations. CREDIT - - got the idea from Jeremy's rubber bumper mount.

This was a big improvement over my original rigid mounts, but I was still getting some marginal welds and a few "blowouts." Soooo - - I finally made further modifications to one of the electrode mounts. I altered it to allow about 3/16ths of an inch vertical travel, and then added a fairly strong little spring which vertically loads that electrode.

This works SO MUCH BETTER that I thought I should report on it. For those who haven't seen my setup, there is a picture of it (pre modification)
on page 26 of this thread. I'm using a small arbor press for my platform.

With this new setup, as I lower the electrodes on the tab to be welded, I can feel the spring loaded electrode make contact. Then I apply a little more pressure until I feel the more rigid electode make contact. Then I make the weld. With this new arrangement, I've not had one blowout (results in blowing a hole in the tab and startling me with the loud POP), and all the welds are a much better quality.
 
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