Tab Welder II

LEDs Applications OPTICS Misc. Power Links

Batteries AC & other Battery Tab Welder


Important update below: 2-7-08

The under $200 battery tab welder!!!

This is the second generation homebuilt Capacitive Discharge spot welder (primarily intended for welding nickel tabs to batteries for building professional quality battery packs in the home workshop).

It is basically the same as the welder described on the previous page, just upgraded components, a little more power and a little more expensive, but still less than 1/10th the price of the cheapest commercial tab welder.  And I'm very happy (so far) with its performance.


You will, of course, insulate all of the exposed metal, (except for the very tips of the electrodes),  with electrical tape, heat shrink, self vulcanizing rubber tape or something safe, and submit it to Underwriters Laboratories for safety approval before you plug it in and try to use it, won't you?

If you short it out, anywhere other than the electrode tips on semi-resistant material (steel, nickel etc.) you will get a big spark, and possibly a major meltdown, fire, death and destruction.

Just because I don't show something or write about it or am completely ignorant about it myself, doesn't mean it should be ignored.

Lithium batteries especially are inherently hazardous.  Understand the chemical and electrical characteristics of them before you even touch one, much less try to weld one, charge one or use one in any device not specifically designed for the specific battery.  They can blow up, burn, stink, release poisonous gasses, fluids,  particulates and solids.  If you swallow one, it will probably kill you in several unpleasant ways.  Do not stick them in any other bodily orifice.

Nickel Metal Hydride, Nickel Cadmium,  Alkaline, Silver Oxide, Carbon Zinc, Zinc Air, and Lead Acid batteries are only slightly less dangerous in general.  Don't abuse them either.

It is very likely that I forgot something important;  So unless you absolutely know what you are doing around electricity, electrical components, hot and sharp tools, ask an expert licensed electrician and/or electrical engineer.  Make sure that all your wiring is up to code, and get it inspected by your local code and zoning authorities.  If disaster befalls you from following the previous and following instructions, don't call a lawyer and try to sue me.  I spent the last of my money on parts for this thing and on batteries.  I'm broke, and there will be nothing for you or your lawyer.

Here is the new setup:

Click for larger view!

The first item is a 12 Volt / 14 Amp regulated power supply.  I got mine off eBay for $28.95 from VM Innovations.  They have the same thing on their website for ten dollars more, but it is still a decent deal at that price.  I'm pretty impressed with its quality and power output.

The Power supply is adjustable internally to between about 10.5V - 14.5V  by a variable resistor:  While I had the case open to crank u the volts to maximum, I also quieted down the warning buzzer that sounds off when there is a polarity problem or when it is putting out maximum power, by injecting a little hot melt glue inside the piezo element. Now it is audible but not annoying, and provides an audible signal so you can tell when your caps are charged.  Only takes about 3/4 to 1.5 seconds to charge the new capacitor setup between welds.

One of the next things I'm going to do with this project is to relocate the variable resistor to the outside of the power supply case, so that it is easily adjustible;  I'm pretty happy with my welds at its maximum setting of 14.5V for general use, but if you are welding to really thin material, it would be better to crank the volts down.
The next item is a 5 Farad ('nominal') car audio capacitor of the Power Acoustik brand from the same place:

I seriously doubt that it is really 5 Farads...  Probably somewhere between 2-3F.  But it appears to have a good 'E.S.R', suitable for welding.  And for a price of about $60.00 dollars, I won't complain about a little hype.

Inside of its extruded aluminum case are 3 parallel capacitors connected with heavy brass bus bars:

The capacitor is rated as 20V with 24V surge......  But as usual with these car caps, its electronic reality falls short of its marketing promises.  I blew one of the safety seals at 17.5 volts / 2 Amps; while testing with a lab type adjustable power supply. 
Not a big disaster; It lost only the tiniest possible fraction of its electrolyte, and the vent hole was easily patched with a dab of silicone sealant, and it works with no noticeable degradation of power.

Unlike all the other car audio caps I have worked with, the digital voltage readout / circuit board  will operate without stealing a significant amount of welding power.

Nonetheless, I pulled some of the components off the board to minimize any losses:

Click for larger view: 

Besides, the 'neon' (actually, merely fluorescent) tubes were kind of irritating, as was the warning buzzer and the two blue LED lights on the circuit board...  So, I de-soldered them. plus the HV transformers for the tubes.

While I had everything apart, I drilled a bunch of holes in the top plastic dome, and the plastic cap under the circuit board for a future modification:  I'm going to install some computer CPU fans on the bottom of the case to cool the capacitors....  With some forced air cooling, I think they will handle 17V OK.

This new Capacitor has nice power distribution blocks:  Each pole will take an up to 8 gauge power input and 4 ga (or maybe even a 2ga.) output.  Makes for neater and more efficient hookup:
Since I acquired both of the aforementioned items from the same place, let me add a couple of warnings:

1: While I am very happy with the Pyramid brand power supply, stay away from the Pyramid brand capacitors carried by 
I don't know if it is just a inefficient ESR or that the product quality in general is bad, but the 3F Pyramid capacitor I tried before didn't have half the welding power of the 1.5F Volfenhag cap I used for the first CD welder project.

2: Their prices are good but the customer service is pretty bad.  When I returned the 3F Pyramid Cap, it took me four days of emails and one long distance phone call  to get an RMA number; once the Postal Service delivered it to them, they ignored it for two weeks until I nagged them about it, then it took four more days of emails to get them to send the new Capacitor after they finally acknowledged the receipt of the RMA.   Plus, I had to repeat everything that had gone before in each email;  Apparently they delete everything as soon as they look at it.  So I can't completely recommend them, even though their prices seem to be much better than the other sources I have found.

(The funny thing is, the lady I was mostly communicating with wrote very curt, bordering on rude, emails but was very nice when I talked to her on the phone.)

I decided to go ahead and use a really heavy SCR on this new setup.  It is probably 'overkill' by a huge amount:  It will probably handle at least 300 Amps continuous and thousands of Amps surge.   I somehow ruined the gate on the original 130 Amp SCR on the previous setup.  I don't know if it was just use, of if it was abuse, but the gate locked in the ON state.  I doubt I'll have to worry about that happening with this one.  In addition, I'm using 8ga cables from the capacitors to the electrodes from the start this time.  They do much better.

Also using a 'real' footswitch that I found in one of the parts bins instead of the kind of crummy one made from cheapie parts.

Instead of mounting a AA battery inside the case with the foot switch, I mounted a C cell battery holder and battery on the back side of the Capacitor box for activating the gate...  Probably get thousands of welds before it is necessary to replace the C cell.

Click for larger view:

I also wired in a 20A circuit breaker 'fuse' between the capacitor and the power supply for safety.  Hasn't come close to breaking the circuit yet, but at 3-4 dollars from Checker Auto, it is definitely worth it for peace of mind.

Other than the addition of the circuit breaker, the wiring diagram is essentially the same as for the previous one, so there is no point in adding a new diagram.

I'm using the same electrodes as on the previous setup:  I have some ideas for improvement, and for making some special purpose ones, but these simple ones will serve well for general use.

SO;  How does this welder perform?   Well, I'm very pleased with my tests so far:



The only one of the welds above that separates on the base metal rather than tearing the spot out is on the steel plate to the bronze shim material. That will only hold for light handling.  The nickel battery tab material holds to the bronze 'ok' if not as well as to steel or titanium.  Don't even have to clean off light rust on steel to get a good weld.  

Also;  Unlike the previous welder, this one welds very well with BOTH electrodes on the nickel strip rather than needing to have one electrode on the base material and one on the tab.  I think that welds are better with one electrode on each, but they are plenty strong enough the other way.

Still haven't been able to weld to aluminum though, so this probably won't work for tabbing the superb A123 systems Lithium Nanophosphate cells;  On thicker aluminum, it doesn't even tack, much less weld, and on thin material it just burns right through.

And one more general hint:  Use a firm and fairly equal pressure on both electrodes prior to and during the weld pulse.  Uneven pressure, especially if too light  can cause a burn through even on fairly thick materials;  You can get an arc, that is hot enough to 'stick' or TIG weld or cut with... although the duration is, of course too, short to actually do anything useful with.

I also put the old 1.5F cap in parallel with this new capacitor bank;  It doesn't seem to work any better, in general;  Sometimes it is TOO powerful and blasts through the tabbing and base metal.  Charging time is noticeably, if not irritatingly longer. There is more 'spatter';  enough so that wearing goggles or at least safety glasses is a necessary (Wearing goggles is a good idea even for the lower power units).

Using the extra capacitor does allow you to get welds at 9 or 10 volts equal to the ones that require about 13 V or more without the extra cap, but it really isn't worth the extra hassle for battery pack building.  If you are doing assembly of heavier materials, it might be useful though, as penetration at 14-17 volts is significantly deeper.  Four spot welds through two of my 1/32 inch thick little steel testing tabs were strong enough to require torquing away with a couple of pair of pliers  to break.

I still intend to do more experimentation on homebuilt CD welders:

On this model, In addition to mounting some small cooling fans to the Capacitor bank and extending the voltage adjusting resistor to the outside of the power supply as mentioned above;

I'm probably going to wire the footswitch so that it cuts off the current from the power supply during the weld pulse actuation. In addition to helping to protect the power supply, it might allow the SCR gate to unlatch automatically, so you don't have to remember to pull one or both of the electrodes off the work immediately to non-pulsed  power from leaking into your welds. 

In addition, I'm going to try to work out a cheap and simple system to allow for a nearly instantaneous double pulse weld like some of the high end commercial CD welders allow;  Dual pulse is supposed to make for much better welds.

And for my next welder, I'm going to use higher voltage capacitors (45V rated high-grade power supply caps) at about 400,000uF to see if a cheap welder for tabbing aluminum cased batteries is possible. I found some appropriate caps on eBay at a decent price; they are on the way, so It won't be too long before I can figure out if it will work or not.

Another thing I might 'play with' if I have the time and extra money is to see if 10 or 15 of the 1 Farad / 5V 'supercaps' will work in a low voltage welder.  Using the '5F capacitor bank' and  1.5F cap in parallel as mentioned above, I could get an almost serviceable weld at 7.0V...  So if the ESR in those 'supercaps' is low enough, it might actually work with a bunch of them in parallel;  They are cheap enough in surplus channels; about four dollars each.

Here is a little teaser:  I've managed to build a crude, but functional DUAL PULSE CD welder by adding only one fifty-cent component (a reed switch) to the welder on the previous page and combine it with the welder on this page.  Maybe not as fancy and precise as the commercial dual pulse CD welders....  But it IS a couple of thousand dollars cheaper.

Here is a circuit diagram:

A little more info for now over at :

I'm going to try the same idea with the higher voltage CD welder (next page) before I post any more information on the dual pulse implementation here.

UPDATE 2-7-08:    Just a heads up:

I Had a 36V LiIon battery pack fail 'on the bench' last night.

Took it apart;  (Tubular battery column of ten 32650 5AH cells, inside a tube) to find that one battery tab melted through, (at a sharp 180 degree fold, if that is significant) and two other spots on different batteries were intact but singed the plastic insert around the + nipple of two of the other cells.

Was using the 1/4" X .005 Sunstone Engineering nickel tabbing strip. I don't think I pumped more than about 700 watts through it, and then, only for a moment.

So, for those of us building Lithium or NiMH battery packs for e-Bikes, scooters or anything that uses a lot of watts, it would probably be wise to either use double thickness of the 1/4 X .005 strip, move up to the 1/2 inch wide .005 strip, or try to find a source for .007 or thicker tabbing material.

Fortunately the batteries all seem fine, and all the welds held perfectly.

UPDATE:  7-19-2008:

Well, that's what I get for being lazy and not setting it up so that the power supply doesn't shut down during the weld as I intended to do months ago:

A week or so ago, after a few hours of near constant welding, the two power transistors blew on the Pyramid 12A 12V power supply I was using to charge my caps. The amazing thing was that the last weld I intended to do was the one where they blew!.

Fortunately, the replacement transistors only cost $1.69 each at Digikey:

To prevent that from happening again, not only did I put in a solid relay to shut off the AC power to the PS when I step on the switch, I put a CPU fan over the transistor's external heat sink, ad one inside the case to help keep things cooler. I probably could have just used the foot switch's N.C. section to switch the PS power directly, but just to be safe and sure, I used it to activate a solid state relay that fits nicely in the in the PS case.

The two Alkaline C cells are for energizing the SSR., although it can be powered by a 'wall wart' as well:

Set up with a coax power plug so I can use whichever I want .

I also got some .01 nickel sheet from Admiral Steel. I think it will be better for making heavy duty, high current battery packs than the .005 stuff we usually use. Unfortunately it doesn't weld quite well enough at the 14.5V that is the maximum I can get with my normal setup, (Nearly, but not quite as much penetration as I'd like) so I'm going to have to get out the lab power supply and try it between 16-17V. Hopefully that will be enough; otherwise I'll have to dig out the higher voltage setup. I'll let you know how that turns out in the next few days.

Please don't try to contact me for more information.  Everything I know about this is covered on these pages.  For more ideas and information go to:  The guys over there have expanded on my design and tried different approaches.  Maybe you can find out what you want to know over there.


Up Tab Welder II Higher V Weld Electrodes DUAL PULSE!!!



Site Meter



Hit Counter

LEDs Applications OPTICS Misc. Power Links

All information and photos on this website copyright Robert L. Thompson / unless otherwise noted.
hotlinking images or downloading and storing for commercial or public use forbidden without written permission of the copyright holder.