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

Hi, guys. A while back I posted a welder project with 3 .3F Spraque powerlytic caps. I gave up after a bug in my circuit. The good news is I reconstructed the welder and got it working.

Here is the good: I can blow holes in 5mil nickel on A123 26650s, dual pulse is working, and SOMETIMES I get a good weld.

The bad: when I have a good weld, the battery sticks to the copper electrodes, often leaving a smidgen of copper on the nickel. Most of the time the weld blows out and pops, leaving a little splatter/crater of nickel and blackness.. I can't find a good setting. I have been trying 300-600microsecond first pulses, 30-90millisecond pulse width, and 600-1200 Microsecond pulses. This is all at initial voltage of 15V (ending as low as 8-9V).

My theory is it has something to do with electrode contact. My electrodes are reworked sunstone double sided electrodes spaced at around .14 C-C and .065" in diameter. I file them even, weld, then one or the other wears faster (I understand that is common.

Any advice?

Update: after an hour of tinkering, I found that the positive needs to be like .005-.015" longer than the negative. I also made the structure more rigid for more consistent weld pressure. I also have it tuned in currently to 230microseconds first pulse, 20milliseconds width, and 1280microseconds second pulse. This is all at about 13.4V (using 4S A123 pack for instant cap recharges). Better results, but the welds aren't quite strong enough. I may try a bigger power supply to auto charge to 15V or maybe try a smaller initial pulse.
 
K. Care to elaborate? What do you recommend for the ratio between pulses and the width? I'm having better luck right now at 440 microseconds first pulse and 2000 microseconds second pulse. You want the first pulse to be say around 800 microseconds and the second pulse to be like 3000 microseconds?

BTW I just obtained a 20V 1F monster cap to try.. didn't you say these were the best?
 
I have 8 3703 FEts capable of something like 1000A bursts each. Assuming 6500A is the max safe current for FEts that may or may not be closely matched, how would u calculate the corresponding voltage and pulse lengths for the monster cap?

Is it safe to assume that. The FETs will be okay say at 7000-7500A since they appear to fire at the same time at 2000-3500A currently?
 
hillzofvalp said:
K. Care to elaborate? What do you recommend for the ratio between pulses and the width? I'm having better luck right now at 440 microseconds first pulse and 2000 microseconds second pulse. You want the first pulse to be say around 800 microseconds and the second pulse to be like 3000 microseconds?

BTW I just obtained a 20V 1F monster cap to try.. didn't you say these were the best?
Click to expand...

I seldom weld by time anymore. My welder lets you specify the energy to put into the pulses. This helps compensate for things like inconsistent connections. As a general rule you start doing single pulses of increasing energy until the material starts sticking and then back off some. Set the delay to the main pulse to the length of the first pulse, and the time/energy of the main pulse to 4-5 times the first pulse.

Monster Cable and Rockford 1F caps work very well. Avoid the Rockford 2F and larger caps... they are "hybrid" caps that don't work for welding.
 
Now that I've gotten into it I kinda want to just specify the energy rather than the pulse lengths. How do you determine first pulse? Is that a separate setting on your welder, but in energy?


How would u recommend sampling the actual current? A shunt (such as a known length of the welding cable)? Or do you just do .5cv^2 sampling with known capacitance values?
 
My own welder needs some work on the case before I can publish my own efforts on these hallowed pages. But it will deliver 12,000 A capable of crushing empty beer cans (some Texan who kindly sold me some real capacitors has has probably downed the contents), welding coins together (who really needs a 30 cent piece?), making real stud welds, blowing holes in sheet sheet, making impressive sparks, beautiful thermocouple beads, and yes - even battery tabs. If you want to estimate the current and energy delivered to your weld then you may want to simulate your welder with a simple LCR model. I have done the maths for you. If you have a moment and an ounce of spare bandwidth have a look at the Excel spreadsheet download at http://turtlesarehere.com/html/how_much_current_.html.

My sincere thanks to all of you that have asked insightful questions, corrected my silly mistakes, and posted your experiences on Endless Sphere,

ob1
 
hillzofvalp said:
I'm sure texas can.. but for most batteries it isn't necessary and more consistent if you use nickel
Click to expand...

Check it out.......

[youtube]hPlcA3ePsFo[/youtube]

Now, I just know one of these can be built at home for a fraction of what Sunstone are asking. :D
 
hillzofvalp said:
How would u recommend sampling the actual current? A shunt (such as a known length of the welding cable)? Or do you just do .5cv^2 sampling with known capacitance values?
Click to expand...

I know the capacitance in my welder (it can measure it) and use the 1/2 C*V*V formula. During the weld pulses it is measuring the voltage on the caps and calculating the energy in the caps every 100 microseconds and will stop the pulse when the specified energy has been extracted. It is not practical to measure the actual weld current. Shunts waste too much energy and just try and find a Hall-effect sensor that can handle 20,000 amps.
 
ob1 said:
My sincere thanks to all of you that have asked insightful questions, corrected my silly mistakes, and posted your experiences on Endless Sphere,
Click to expand...

Hi Tim! Long time, no see... Hope the move went well.
 
hillzofvalp said:
those work differently I think..
Click to expand...

Different to what? They all must work off a capacitance-discharge of some form or other, no?

Sunstone are asking silly money. It's what moved me to this thread in the first place all that time ago.

Longterm, I am waiting for the balls to fall out of the price of A123 M1 cells and figure on welding up some large capacity strings. I normally tab down nickel and beat copper onto it with an iron but that's OK for ebike batteries. It's not practical for larger projects.

Cheers.
 
Jeremy Harris said:
dannym said:
Also, 1.2v or 1.5v of a single cell is not enough to trigger my gate properly. My SCR is specified for 150mA max gate current, and could drop as much as 3.0v. My gate draws like 70mA with the cell across it. I think there are two problems here- one, it probably needs like 4 batts and a current-limiting resistor (~12ohms) to provide a predictable high current to the gate. Two, any regular button switch "bounces"- it contacts, then not, then contacts, then not, then contacts for real. It's only a few nanoseconds of on-off uncertainty but this may be significantly slowing the SCR's turn-on leaving it absorbing a lot of power like a resistor rather than being a solid open-then-closed switch. I may need to build a circuit with a schmitt-trigger that won't bounce on-off at all.
Click to expand...

I found the same thing about gate drive. The harder you drive the gate, the faster the SCR switches, at least initially, and that tends to make it work more effectively as a discharge welder. To drive my SCR gate I used a simple trigger relay circuit, that uses the voltage on the capacitor bank to drive the gate. This has the added advantage of disconnecting the capacitors from the power supply during discharge, which mean that you can use a bigger power supply without fear of latching the SCR on. Here's the circuit I used:



Jeremy
Click to expand...


Hi friends, I'm jonny from Italy.
Sorry for my bad English ...
I read all the pages of this discussion, but I didn't understand what is the latest version tested and working of circuit spot welder.
Can you help me?
Thanks
 
If u havE good welds with .005" nickel on 26650s and at least 4 inches overlay between groups I would think you woud be fine at high current bursts (400-500A). Having thermal management can help a little.

I am going to weld my pack of 26650s with .005" nickel an a 160 watt second sunstone welder. My friends told me they couldn't get it to weld .01" nickel to 18650s. If I can get it to do .01" that is what I'll use... Other wise I'm safe with PCM thermal management

I am now blowing holes in cells with this 1F monster cap... :).

The reason I think that welder is different is that it looks like they are pwming the energy and somehow going in a circle... How do they achieve one big fperfect puddle?
 
What about this homemade tab welder ? Even I might be able to build this one :shock: :lol:

HERE
 
nobody can help me? :oops:
I try a diagram for the circuit that has been tested and running but in this post there are too many circuit diagrams and I do not know which one to choose :oops:
 
I wanted to report my latest on my project. The monster 1F CAP works very well. I am solely using it to weld .005" nickel to a123 m1 cells. About 16.5V right now. Finishes at about 9 volts. So I'm probably looking at 80-95 watt-second welds.

I'm using 4 gauge ground wire I bought for $0.75 at Home Depot. I belt sanded to a point. The issue I'm having is a very rough nickel surface after all the welds. The welds appear strong. My theory is that the electrodes need to be smoother and I need to go lighter on the pressure.

Your thoughts are welcome. This thing is awesome though... Welding every 2 seconds and fet bar barely gets above ambient
 
Still wondering more about sticky electrodes and splashing.. Can't dig up that information in this thread. This topic needs a wiki.

This is 16.4V with a first pulse of 250 microseconds, 220 microseconds width, and 1.8ms second pulse. It terminates between 10 and 12V. I tried 19V once but I popped a FET.

[youtube]Wxe7ccUJGB8[/youtube]
 
anyone bought one of these ones on EBAY LINK ?

was just about to order the bits I need to build one... but the one above doesn't cost a lot more than the parts, and is already built...

THIS is the same machine, with a different name on it, and a video of it working on the ebay page

for good reliable welds, I'll need a jig of some sort to hold the batteries, and maybe something to lift them up and down - or lift the machine up and down to drop the electrodes onto the tabs
 
Waaaaay back on page 16, I show a picture of my rather rudimentary spot welder. Since that time, I've made thousands of welds with it - - primarily upon sub C nicd cells in the process of rebuilding rechargeable battery packs for tools. We are using .005 nickel tabs and the welder does a quite respectable job with this material.

My system is not at all sophisticated - - no double pulse or any of that downtown stuff.

This forum looks pretty inactive now, so if anyone would like additional info, they could contact me at oldusedbear11@charter.net. I'll be glad to discuss our upgrades, operating characteristics etc.

Roger
 
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