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

Johnbear said:
Is there any way anyone has tried to modify a welder like this one: (super long eBay link removed;rlt)
to work on a battery? Is there any hope for this to be possible?

In a word, NO.

Well, it might be possible, but not practical. What you have with that is about equivalent to a rewound M.O.T. with a mechanical 'pincher' added. You might be able to modify it so that it will weld on battery tabs, but you will very likely damage or destroy the battery when you do.

Besides; with the outrageous shipping cost on that thing, it will cost you more than building your own CD welder using my (or Phil Pemberton's ) instructions.
nemo said:
........Since I'm working on 8 FARAD version of the CD welder inspired by this thread I need a small help.
I'm thinking of getting KOLE 8 FARAD audio cap like one here:
Price seems to be favorable. DO You think that inside there are good q. caps? Carbon-foil? ..........

Couldn't even begin to guess if it is any good. As you have discovered, even if you do find some data you can't trust it. Even the good ones I have actually tried fall far short of what they say they are.

Since you are going to be welding A123 cells, I can't even begin to give you useful advice even if it does turn out to have decent ESR. since the construction of the A123s are different from everything else I have been able to work with.

Anyone have any dead (but intact) A123 cells they can send me to experiment with? I'll pay postage, and share the findings with everyone.
I was looking at your setup with 5F cap and I'm actually wondering if it would be possible to test even thicker leads to your copper tips. Also the copper tips could be thicker.
The current is very high with tab welders, about 1000-7000A and one always gets a big losses with this kind of current.
You should get higher peak current and possibly even better welds.

As to A123. Did you actually tried tab welding them?
As I wrote you don't have to tab weld to alu at all. The manufacturer already soldered thin metal( possibly nickel) button onto + side and uses tabs welded to this metal rather than to alu.
I was soldering thick copper tabs to about 100pcs of A123 with 200W soldering iron (takes about 0.5-1sec!/each) and sometimes this button came off completely and only solder stayed on the A123.
So unless you want to first desolder the nickel bit and clean the cell you will have hard time finding the place to tab weld to the alu on the + end.

On the - part there is no aluminium at all.
(note: A123 have reversed polarity in comparing with common AA, AAA etc. batteries)

Most of us need a good weld to A123, low resistance one since we need to pull a high current from A123s.
The only way I see it if to go tab welding A123 is to use coper tabs as on the video in my previous post, use wide tabs, and fold them.
I'll try to ask guys who did the video what welder, setting, pressure, copper tab thickness they use
Here a post from Brian (A123 support forum), about the tabs welded to A123 batteries.
Not sure if he is talking about the development cells or the cells found in the DeWalt packs.

Hello Icarus,

The tabs that are welded on the cells are solid nickel straps. They can handle all the power the cells can deliver, well over 70A continuous. Many people think these tans are attached using a spot welder which has caused some concern. They are in reality attached with a resistance welder. The tabs are welded to the cell with 4500A for a fraction of a second. This yields a weld that has a much lower resistance and allows for this high amount of power.

I would say use the tabs that are on there and save yourself some time and effort.

Power . Safety . Life


nemo said:
....As to A123. Did you actually tried tab welding them?
On the - part there is no aluminium at all.
No; I have never even seen one. That's why I asked for some dead ones to experiment with. I have read in several places that they are aluminum 'cans', and yours is the only thing I have seen mentioning anything more.

I'd like to be able to give a definitive answer, but my present budget does not have room for buying a Dewalt pack or an evaluation kit just to see if I can weld tabs on to them..

As to the other: Yes; of course you could use any thickness of cable and electrode. But what I have been trying to do is make something work with easily acquired parts and as cheaply as possible.
Yes! Let's get some bad A123 and try. I'm pretty sure you will be able to tab weld to them. From the video you can clearly see what I was talking about. Yes the cell is made of alu but that round thin piece of metal is nickel. When pulling original tabs off dewalts be careful, it is quite easy to be lifted where spot welds are!. Then dremmel it down a bit so it's not bumpy. Especially on the - side! Ideally with a dremmel with a diamond bit, it's VERY hard to send down otherwise.
Of course they are talking about Capacitive Discharge spot welding when mentioning 4500A. With your charger you might be in that region anyway.

Good luck, keep us posted.
I have 4x good Chemicon 100 000uF 50V capacitor remooved from an old audio amplifier project. and alot of 000, 1, 2 and 4 gauge cable. I will try to built my welder too... I dont know how many bad cell i will need to practice, but i could send the others to you. I will try with cooper strip. I have 1feet square of 0.4mm that i will cut and try to spot weld.

Thanks Doc.
When you figure out if you have extras, let me know and I'll send money to cover postage. Do you have a PayPal account?

From my tests, copper is a b- (sounds like witch) to weld, so it might require a lot of experimentation to get a decent weld. At least you can crank up the volts with those 50V caps. Too bad you sold off the last Flux capacitor. I'm pretty sure that 1.21 giga-watt-seconds would do the trick. ;)

I can send you some nickel strips to try if you want.
RLT said:
Thanks Doc.
When you figure out if you have extras, let me know and I'll send money to cover postage. Do you have a PayPal account?

From my tests, copper is a b- (sounds like witch) to weld, so it might require a lot of experimentation to get a decent weld. At least you can crank up the volts with those 50V caps. Too bad you sold off the last Flux capacitor. I'm pretty sure that 1.21 giga-watt-seconds would do the trick. ;)

I can send you some nickel strips to try if you want.

for 1.21 giga-watt-seconds capacitor (1,21 giga-joules) you should send me nickel strips that weight 2 or 3 tons each!!!!!!!!! :p the postal cost would be thousand of dollars!

Here's the biggest one you can get these days:

It's a measley 2 megajoules :cry:
"Recent results produced more than 80 times the power output of all the power plants on Earth, but for only a few billionths of a second"

Jigga whaaat?
Yeah, but didn't you say that you sold the last one on eBay? So it is a moot point anyway.

How much is that in coulombs?
(actually, I do know the answer to that one.)

But a few regular nickel strips for your .4F@50V max welder; mailed in a regular envelope should be pretty cheap, even going to your foreign country ;)
If you want some.

EDIT: Oh: Didn't realize this had gone to another page; The above was to Doc's 1:35 Post
i built one based on it includes a relay to disconnect the charge supply. i am using a computer grade 1f capacitor from cornell-dublier and have pretty good results welding .005 thick nickle strips at 9V or so.

for electrodes i used a couple of electrodes i bought from a welding supplier that were a copper chromium alloy. i found that the copper grounding rod electrodes eroded too quicky and i needed a much higher voltage with them

i've considering building a second one to hook up with the first and a couple of LM555 timers to produce a dual pulse unit. but i've got toomany other things on the go.
Thanks for the info RKO. I've been looking for some copper-chrome rod or electrodes online for two hours since I read your post, but can only find manufacturers and distributors, that offer exactly what I'm looking for, so far; No US based webstore retailers..

I did run across this though, might be of interest to everyone who has been following this thread.

Edit: Found some CuCr electrodes at McMaster-Carr. But they are much thicker than I'd want; would have to put them in the lathe. Cheap enough though:
i guess i forgot to mention that i had to turn mine down on a lathe.

the other problem is connecting to them. you need a really aggressive acid type solder flux.

Today I ordered parts for my tab welder from ebay.
The most expensive is: KOLE AUDIO 8.0 FARAD DIGITAL CAR CAP(carbon foil stacked caps) -10 +50%, ESR 0.0014, 85C max, op. voltage 24V max
about £70 including shipping from the USA
2 pcs. IR ST230S12POV
230A, 1200V peak 5700A.. 2 in paralel so peak over 10 000A ! only £20! ebay uk
So far £90.
I had switching 400W power supply (ebay Hong Kong) that can actually be mod using 1 resistor connected in series with the inside trimmer to output something like 8-20V so about 20-30A out!
on ebay under "400W 13.8V 29A Switching Power Supply" £34

Now, putting it all together.....

I'm thinking of using this schematics:

If you have a dual pulse unit in your mind contact me please with your proposed schematics. I'll make a PCB from philpem web and would add a dual pulse if somebody comes up with good idea. Pulse width regulation 1-30msec for both pulses could be interesting and useful too. Pro welders have it. I spent so much on parts that we might as well do it like the pros.
What do you think?

A relay will be automobile relay 60A.

A 1.1 kg 400W power supply's features:
# Over Load and Short Circuit Protection
# Over Voltage Protection
# Auto-recovery after protection
Would you still put some high W, few R resistor in between the power supply and relay (cap)?

I hope I'll be tab welding A123 to coper tabs soon.!
i think that making up a couple of boards based on the phillipem schematic would be a great idea. specifically - i want a couple.

The schematic shows a current limiter and voltage regulator, so I don't think you would need any additional resistor.

The dual pulse setup would require two capacitor banks, two SCR's, and a timing circuit. I'll have to scratch my head on that. A 555 timer should work.
i think fechter is on to something. to his shopping list add either a switch and a voltmeter to set the variable pulse voltage on each capacitor bank. or use two meters.

add a couple of LED and another timer to show when it is ready to fire again.

throw it all in a case and you have the makings of a commercial unit.

Draw it somebody, I'll redraw it in eagle if you don't have one, make the board and test it!

It needs to be able to take 20V , 20A from my power supply and feed the caps quickly so I justify the use of this powerful beast.
Also some kind of feedback so it can only fire when charged would be nice.
Voltage from 1-18V, pulse 1 width 0.1-10ms pulse2 0.1-30ms), delay in between p.1 and p.2 is 0.1 sec,

"The short pulse lengths and high current allows the welding of highly conductive materials, including copper and brass
Peak weld currents of up to 6400A (1mOhm load) "
but at 16.5V, I can see in one data sheet over 8000A!
18V must be around 10 000A
And 1AWG cable must be used for this!
So when using the welder for coper I would be setting higher voltage 12-18V(5000-10 000A!) but using only shorter pulses (3-7ms?) That's the secret!
It will be in this range depending on the thickness of the coper tab and pressure of the electrodes.

Interesting is how heavy the pro welders are.
The biggest 600ws Dual Pulse Industrial CD Spot Welder I found have 2.4F capacitor inside and is 45 lbs. (21 kg) I doubt the use switch mode power supply inside. Even their external add-on power supply 25A weights 9kg!
2.4F seems too little but I guess they are better caps wit extremely low ESR and higher price tag.
I hope taht my 8F cap bank will be close in practice.
All data are from data sheets of pro welders.
good general reading about CD welders is here:
"Information Wants To Be Free. ......." Stewart Brand
If you have two capacitors, then it would be good to have a separate voltage regulator for each one. Tiggering two pulses in sequence is pretty easy.

The voltage regulators would need to handle the desired charging current, so say 20 amps. A linear regulator is the simplest, but would have to throw off tons of heat. A switching regulator is going to take some expensive parts and add lots of complexity to the circuit.

The switching power supply already has a regulator, so to me it would be much easier to just hack that one rather than build another one to add onto the output.

All switching power supplies have some kind of regulator circuit that could be tapped into to reduce the output voltage. Basically just add a pot to it somewhere. Most of them have built in current limiting too, so you can just hook it up straight to the capacitor (some inductance in the circuit would be good to make the contacts live longer).

For a dual pulse unit, just get another surplus power supply. I think the initial pulse is smaller, so perhaps a smaller supply would do.

Using a surplus SCR to discharge it, there would be no easy way to control the pulse width other than by what voltage you start at. Once those babys turn on, they don't want to turn off.

There is a way to commutate them with another SCR and a bunch of other parts, but it gets real complicated.

I could attempt a drawing of the triggering circuit, but that will have to wait. I need new drawing software (old stuff is not compatible with Vista) :evil: I have other computers that actually work.
Yes, I'll take the 8F audio cap to parts and I'll make 2 sets of caps. One will be 1F, the second one 7F. (I hope there will be 8 caps inside :) )
I also decided to finally buy decent dual power supply. I'll power each cap with a separate power supply.
The power ratio in between first and second shot should be 1:7 .

2 separate electronic circuitry will fire in 100ms sequence. There will be 555 or 556 chip. I want to slightly delay fire in sequence to opening relay.
Welder should fire after the relay disconnects the supply, not at the same time, I think.
I would also like to use mosfets instead of relays. :)

There is also possibility to use solid state relay instead of thyristor. This way I could chop tail part of the pulse and the welder would probably weld coper better. First I would have to find solid state relay that would take the curent and won't cost too much.
Thanks for giving me some ideas.
i tried a quick experiment yesterday. i just wanted to test if any of the 1F computer grade caps i have are still any good or if they were damaged by a couple of years storage. i've got 9 of them big suckers.

well they still work. but i found that welding with the charging supply still connected requires a lot more voltage than with the supply disconnected. about 50% more. so i think that disconnecting the charging supply is important.

from looking at the additional material about commercial welders it looks like the first pulse is only marginally smaller than the second pulse. so if i was to be using cap banks i think both should be almost the same size.

also most of the material charts show that welding copper to copper is pretty iffy. usual recommendation is to weld dissimilar or plated materials.