Comments on: Build a spot welder from a battery charger

By: imsolidstate

imsolidstate — Fri, 26 Mar 2010 17:54:25 +0000

Mike, that looks nice. Wonder what they cost though?
Some IGBTs will go there. The high frequency is the reason switching power supplies pack so much power in a small space, since they are becoming so common there will be transistors that do it. The IGBTs I’m going to use in my TIG welder project have rise and fall times of less than 1 microsecond. That’s approaching GhZ territory.
My IGBTs are half-bridges though. http://www.datasheetcatalog.org/datasheet/toshiba/1653.pdf

So you need to calculate how big of a capacitor bank you would need to keep the DC input at the transformer up at a 47A peak draw… Sounds like a lot of capacitance.

That’s what I’m planning on for my setup. Bridge rectifier from 220VAC, capacitors to try and keep it smooth, then into a transformer and out to an H-bridge. Your transformer would be about right. I’ll switch the H-bridge at a couple hundred Hz. I’ve been wondering how to get the output voltage to the right level, that transformer would be perfect.

Thanks for the tip.

By: mike

mike — Thu, 25 Mar 2010 06:04:14 +0000

Saw a link to these guys and thought you might be interested in it as I was.

[url]http://www.paytongroup.com/planar_transformers.asp[url/]

[url]http://www.paytongroup.com/Catalogue/28_29.pdf[url/]

The transformer in the example is designed for welding duty, rated at 3900 Watts, outputs 26 Volts at 150 Amps and weighs, are you ready for this, 250 grams. Now the hard part, the switching frequency is 200KHz, Ouch! I don’t think that beez IGBT territory. Than again, maybe it is.

By: Mike

Mike — Mon, 15 Mar 2010 02:00:05 +0000

Really cool link, hadn’t seen that one.

The big bug-a-boo with any H-bridge is the timing. If the wrong pair of the transistors are conducting at the same time you get a shoot through. Not a good time for the transistors to say the least. The H-bridge driving a transformer output is in fact just the way that Miller does it in their inverters.

I am looking at the transformer right now and working out the turns ratios and inductance etc. It is a bitch to take apart being that the core is ferrite. I will take a couple of pics later and try and get the links up. The primary of the original PS is interesting, I am tracing it out. Trying to get my head around it. I will be sure and share anything I come up with.

By: imsolidstate

imsolidstate — Mon, 15 Mar 2010 00:44:10 +0000

I’ve looked into IGBTs in an H-bridge configuration, but you have to be really careful with switching. I don’t remember the specifics, but I read some white papers from IR about using IGBTs for welding power supplies… here it is: http://www.irf.com/technical-info/appnotes/an-1045b.pdf
If I do anything with the buzzbox, it will be phase control on the primary, no switching or anything. I suspect you would be wasting your time trying to switch with IGBTs through a large transformer that has some unknown inductance.
However, I will be trying my hand at the H-bridge design if I ever decide to build my own TIG. I’ll use a bridge rectifier and a capacitor bank to create the DC for the bridge, and send the power right to the torch, that way I get clean voltage transitions at the workpiece. I think my IGBTs are rated for a couple hundred amps.
I like the microwave idea. I’ve seen some projects along those lines, but they look like modifying the transformer for low voltage / high current is a bit problematic. Send me something if you work it out.

By: Mike

Mike — Sun, 14 Mar 2010 20:53:23 +0000

In the case of the Miller, being that it is a switcher, they use IGBTs after the input side filter caps. The advantage of this being a switching frequency much higher than that of the line, 60Hz. You have much better control. For some reason I remember that the frequency is something on the order of 4KHz, not sure about that though.

The use of a phase control on the front end of the buzz box makes allot of sense, especially if the input is 208-240. The only issue is the noise that the thing will put out, filter, filter, filter! A class D H-bridge might be interesting to try and implement though it would be way beyond my knowledge. I can see the basics in my head. Not sure I have seen any high side class D systems like this. I bet if you could work it out it would be fairly efficient. Since I have the Miller though…..I have little motivation.

I am looking into making a small, portable TIG using a microwave switching supply. The unit outputs in excess of 1000 Watts and the transformer is small. It will be a high side class D H-bridge and use IGBTs. Most of the welding on thin stock that I have done is at less than 60Amps and the voltage across the arc is about 12-15VDC. This is well within the transformer rating. I am thinking that one of the micro controllers would be ideal for this.

By: Building a spot welder from a battery charger « The tech telecom and all

Building a spot welder from a battery charger « The tech telecom and all — Sun, 14 Mar 2010 11:22:03 +0000

[...] at imsolidstate came across an extra battery charger, so he decided to turn it into a spot welder. We’ve seen spot welder projects in the past, however his goes the extra mile, adding a [...]

By: imsolidstate

imsolidstate — Sat, 13 Mar 2010 14:50:21 +0000

The resistor is a made from a carbon-carbon composite, which is machinable. I just cut it out of some scrap with a bandsaw, and then drilled holes in either end for fasteners to connect the terminal lugs. You can calculate the resistance of your physical shape with the electrical resistivity.

By: imsolidstate

imsolidstate — Sat, 13 Mar 2010 14:47:46 +0000

Mike, thanks for the info on your welder, and the tip for making resistance heaters. Turns out I might need to custom build a heater and that will probably come in handy.
It would make more sense to have the control on the input side. I think the diodes and SCR are rated for the voltage. It was wired that way when I got it though so I left it alone. I like your idea though, because I could instead have a “controller” box that could be hooked up to any transformer, i.e. my stick welder.

By: Electronics-Lab.com Blog » Blog Archive » Build a spot welder from a battery charger

Sat, 13 Mar 2010 10:44:43 +0000

[...] a spot welder from a battery charger - [Link] Tags: Charger, spot welder Filed in Power | 1 views No Comments [...]

By: Ernie Frye

Ernie Frye — Fri, 12 Mar 2010 20:29:14 +0000

I have a tool from the 1920’s that uses a car battery to spot weld. The negitive side is 2 clips on a wire lead and the positive side is one clip and a handle with a carbon electrod. I’ve used it on sheet metal up to 1/16 thick and it workes great.