How to make a spot welder.

[capwizard]

The easies video I ever found. I will try it with 120vAC. the capacitor in the video is a 440 volt 20uf AC capacitor. we can make a one with two DC capacitors.

How to make a spot welder.
https://youtu.be/sYR4RuqEIjs

[Curious.George]

Re: How to make a spot welder.

The easies video I ever found. I will try it with 120vAC. the capacitor in the video is a 440 volt 20uf AC capacitor. we can make a one with two DC capacitors.

How to make a spot welder.
https://youtu.be/sYR4RuqEIjs

You DO understand that you've now got ~150V sitting on those test leads (lying on the bench)?

[capwizard]

Re: How to make a spot welder.

I am so blessed by the God. unlike the video he used 240v and we're in the US only 120v.

I connected two capacitors polarized reverse together I thought I've made an AC capacitor but the fact was I only make a nonpolar DC capacitor. So it blow out with white smoke.

Does anybody know who make the decision USA uses 120v I need to say thank you to that person.

I going to use real AC capacitor from HVAC unit.....to be continued...

[petehall347]

Re: How to make a spot welder.

you should wire capacitors in series so you end up with 2 negatives or 2 positives .

[R_J]

Re: How to make a spot welder.

Petehall347, I just looked at the first picture that is NOT the way to make a bi-polar cap. they must be connected like you said, in series (+2+ or-2-) Those caps also likely won't handle the current.

[eccerr0r]

Re: How to make a spot welder.

I've seen 1F capacitor discharge at ~4V, so to not need a 1F capacitor,
1F * 4^2 = 440uF * x^2
x=191V
So yeah looks about right, need those high voltage in order to not need those low ESR 1F caps...

Note that you can just rectify the line voltage and not deal with bipolar capacitors. And yes the capacitor needs to be low ESR...

[capwizard]

Re: How to make a spot welder.

you should wire capacitors in series so you end up with 2 negatives or 2 positives .

But can DC capacitor use in AC? From the experience I just got they became really hot. what are those difference?

[Curious.George]

Re: How to make a spot welder.

Note that you can just rectify the line voltage and not deal with bipolar capacitors. And yes the capacitor needs to be low ESR...

To be clear, you're proposing rectifying the mains to CHARGE the cap; not to use in place of the cap.

(the point of the capacitor is that it represents a fixed energy reserve; once spent it automatically "shuts off" without any "timing controls")

I think a smarter approach might be to dump the charge from the cap (or even a voltage source) into the load through a step-down transformer (trade I for V). Sort of like a CDI -- but in reverse!

[eccerr0r]

Re: How to make a spot welder.

The original "idea" is sort of flawed, you can't really "charge" a capacitor with AC. The charge that happened to be on the capacitor is pretty much luck of the draw depending on when in the cycle it got disconnected. It doesn't make sense to "store" AC on the capacitor.

You have to charge the capacitor with DC no matter what.

On the other hand, I was wondering is whether just using a old solder gun to weld with... Get rid of the resistive tip and use two probes there instead, and depend on that low voltage high current to weld with. It's on the order of a hundred amperes, which is a bit low, but might be enough...

[Curious.George]

Re: How to make a spot welder.

The original "idea" is sort of flawed, you can't really "charge" a capacitor with AC. The charge that happened to be on the capacitor is pretty much luck of the draw depending on when in the cycle it got disconnected. It doesn't make sense to "store" AC on the capacitor.

But, most of the time, the AC waveform is >> 0V, so the odds are that you will have substantial potential across the cap, regardless of where (randomly) you break the cycle.

On the other hand, I was wondering is whether just using a old solder gun to weld with... Get rid of the resistive tip and use two probes there instead, and depend on that low voltage high current to weld with. It's on the order of a hundred amperes, which is a bit low, but might be enough...

I had recently asked a colleague if I could use a Mig welder "shorted" to the surface to be welded to act as a spot-welder (I was actually looking to weld something substantial -- not flimsy battery tabs). He seemed to think I "needed" to draw an arc for it to work.

(I doubt that but am reluctant to try without some better information)

E.g., in "shop", the spot welder was just a pair of semi-stationary electrodes (brought together by a foot pedal), a giant transformer and an electro-mechanical timer. Turn sweep arm of timer to desired pulse duration, engage power, watch timer arm spin to zero, hear laminations in transformer groan as sparks flew, done!

(i.e., could I do the same with the Mig's transformer?)

[capwizard]

Re: How to make a spot welder.

yes, AC capacitor was worked good but not enough energy. i need to add more capacity or raise up the voltage.

One thing very strange is i measured charged capacitor which has no AC output only has DC around 80v then slowly drop down the voltage? why?

Does the capacitor has the same rectification function as rectifier diode?

PS: I haven't changed battery for this meter about two years. picture 4.

[eccerr0r]

Re: How to make a spot welder.

There's no such thing as an "AC" capacitor, just a capacitor that won't blow up with AC due to polarization. The rectifier diode is used to convert the AC to DC, and the capacitor will charge from the proper DC.

These low capacity capacitors are easily discharged with a typical 1MΩ-10MΩ input impedance of a multimeter so yes they will drop down in voltage as you keep it connected (plus any leakage resistance within the capacitor, which is also a sign of a bad capacitor). Estimate with the RC time constant and you'll see why it drops visibly, quickly.

[Curious.George]

Re: How to make a spot welder.

[QUOTE=capwizard;877277]yes, AC capacitor was worked good but not enough energy. i need to add more capacity or raise up the voltage.[/QUIOTE]

Or, arrange for it to be disconnected from the line closer to the peak of the mains voltage.

One thing very strange is i measure charged capacitor which has no AC output only has DC around 80v then slowly drop down the voltage?

A capacitor only stores DC. An "AC" capacitor can store DC of either polarity. I.e., some times you may find "lead #1" is positive wrt "lead #2" while at other times lead #2 will be positive. It all depends on the polarity of the charge inside the capacitor when it was disconnected from the (AC) voltage source.

(in theory, half of the time it will be disconnected while the mains voltage is "positive" compared to neutral and the other half of the time it will be disconnected while the mains voltage is negative. Do the experiment an infinite number of times -- for an ideal capacitor -- and the results will be 50:50)

Does the capacitor has the same rectification function as rectifier diode?

No. It's just CAPTURING the charge in one direction -- or the other -- depending on the instantaneous polarity of the AC mains signal feeding it at that instant.

If, instead, you take eccer0r's (?) suggestion and rectify the mains before connecting the rectified signal to the cap, you could use a DC (or AC) cap and always be assured that the lead that is connected to the positive output of the rectifier would always be more positive than the other lead.

Additionally, because the rectifier isolates the cap from the AC line WHENEVER THE INSTANTANEOUS MAINS VOLTAGE IS LESS THAN THE VOLTAGE STORED ON THE CAP, the cap will tend to stay at the peak AC mains voltage, regardless of when you disconnect it from the mains.

(the voltage will gradually decay, over time, but at a much slower rate, based on the cap's leakage characteristics)

A friendlier circuit would include a "ballast" to limit the rate at which charge can flow into the capacitor when charging it up (yet not be present in the "discharge path" as you want maximum current flow, then)

[eccerr0r]

Re: How to make a spot welder.

Incidentally I love my Fluke 77, I got a cheap 50¢ PP3/6F22 battery in there and it's lasted YEARS so far... I think I've gotten its life out of that carbon zinc battery even if knocking on wood fails and dies a minute from now, but suspect it may still keep on working...

My other PP3/6F22 multimeters eat their batteries and I have to replace them biannually at best, but usually much worse, depending on how much I use it.

[capwizard]

Re: How to make a spot welder.

[QUOTE=Curious.George;877286]

yes, AC capacitor was worked good but not enough energy. i need to add more capacity or raise up the voltage.[/QUIOTE]

Or, arrange for it to be disconnected from the line closer to the peak of the mains voltage.



A capacitor only stores DC. An "AC" capacitor can store DC of either polarity. I.e., some times you may find "lead #1" is positive wrt "lead #2" while at other times lead #2 will be positive. It all depends on the polarity of the charge inside the capacitor when it was disconnected from the (AC) voltage source.

(in theory, half of the time it will be disconnected while the mains voltage is "positive" compared to neutral and the other half of the time it will be disconnected while the mains voltage is negative. Do the experiment an infinite number of times -- for an ideal capacitor -- and the results will be 50:50)



No. It's just CAPTURING the charge in one direction -- or the other -- depending on the instantaneous polarity of the AC mains signal feeding it at that instant.

If, instead, you take eccer0r's (?) suggestion and rectify the mains before connecting the rectified signal to the cap, you could use a DC (or AC) cap and always be assured that the lead that is connected to the positive output of the rectifier would always be more positive than the other lead.

Additionally, because the rectifier isolates the cap from the AC line WHENEVER THE INSTANTANEOUS MAINS VOLTAGE IS LESS THAN THE VOLTAGE STORED ON THE CAP, the cap will tend to stay at the peak AC mains voltage, regardless of when you disconnect it from the mains.

(the voltage will gradually decay, over time, but at a much slower rate, based on the cap's leakage characteristics)

A friendlier circuit would include a "ballast" to limit the rate at which charge can flow into the capacitor when charging it up (yet not be present in the "discharge path" as you want maximum current flow, then)

Thank you very much, but I have one more question. I saw the Amp-meter. It has been using 1.7 amps of AC current even after 3 minutes, This capacitor should be 40 uf now only has 36 uf, long time using 1.7 amps of AC current is because the leakage or low ESR? I mean after capacitor charging up the current should drop down? If I use a DC capacitor will it be better than an AC capacitor.

[sam_sam_sam]

Re: How to make a spot welder.

The easies video I ever found. I will try it with 120vAC. the capacitor in the video is a 440 volt 20uf AC capacitor. we can make a one with two DC capacitors.

How to make a spot welder.
https://youtu.be/sYR4RuqEIjs

I hate to tell you that to me this is real dangerous I would not even give this idea the time of day

If you want to build a spot welder I can give you some very good idea on how to do this

I just bought a battery spot welder that the transformer is not heavy enough to do a good job of welding but I like the controller

I have another battery spot welder that the transformer is heavy enough but the controller board has to many issues to fix

So I am taking out the transformer out new one and put the transformer out of the one that the controller went bad

So now the battery spot welder works real good now


Now if you want to build a capacitor discharge battery spot welder

I have everything figured out except one thing and it a very big problem

I would really like to build one—————>

That this is how to control the discharging the capacitor with out destroying the capacitor or the SCR I have not found a circuit that I like to use

The type of SCR I want to use one that handles about 200amps

If anyone has a good idea on how to do this please post it

I have also tried a capacitor discharge stud welder to do battery welding that was a very bad idea because it was so hot that it burn a hole in the battery to much power

This happen with control set at the lowest setting

[eccerr0r]

Re: How to make a spot welder.

Thank you very much, but I have one more question. I saw the Amp-meter. It has been using 1.7 amps of AC current even after 3 minutes, This capacitor should be 40 uf now only has 36 uf, long time using 1.7 amps of AC current is because the leakage or low ESR? I mean after capacitor charging up the current should drop down? If I use a DC capacitor will it be better than an AC capacitor.

"You're doing it wrong." Capacitors, "AC" or not, show up as reactive resistances under AC. So basically you and the video are shorting line to neutral like a resistor when you connect it like that through the capacitor.

As said, it will never "charge" up, it will continually charge and discharge as long as it's connected. Depending on when you disconnect it will show up as the remaining charge of the capacitor.

[capwizard]

Re: How to make a spot welder.

I would really like to build one—————>

That this is how to control the discharging the capacitor with out destroying the capacitor or the SCR I have not found a circuit that I like to use

The type of SCR I want to use one that handles about 200amps

If anyone has a good idea on how to do this please post it

I have also tried a capacitor discharge stud welder to do battery welding that was a very bad idea because it was so hot that it burn a hole in the battery to much power

This happen with control set at the lowest setting

The type of SCR I want to use one that handles about 200amps.. ..............Kweld (STM32 equipped) will be good for you but they used 6 MOSFETs. i would like to modify to IGBT, i think IGBT is the way to go, I will use plasma TV's IGBT junk parts to built one, can handle 200Amp with just one IGBT.

--------------------------------------------------------------
kWeld - "Next level" DIY battery spot welder
https://endless-sphere.com/forums/viewtopic.php?t=89039

kWeld - The best 18650 spotwelder?
https://www.youtube.com/watch?v=4UgBG0oFAwU

[sam_sam_sam]

Re: How to make a spot welder.

The type of SCR I want to use one that handles about 200amps.. ..............Kweld (STM32 equipped) will be good for you but they used 6 MOSFETs. i would like to modify to IGBT, i think IGBT is the way to go, I will use plasma TV's IGBT junk parts to built one, can handle 200Amp with just one IGBT.

--------------------------------------------------------------
kWeld - "Next level" DIY battery spot welder
https://endless-sphere.com/forums/viewtopic.php?t=89039

kWeld - The best 18650 spotwelder?
https://www.youtube.com/watch?v=4UgBG0oFAwU

Let me know if you get it to work

Thanks

[capwizard]

Re: How to make a spot welder.

Incidentally I love my Fluke 77, I got a cheap 50¢ PP3/6F22 battery in there and it's lasted YEARS so far... I think I've gotten its life out of that carbon zinc battery even if knocking on wood fails and dies a minute from now, but suspect it may still keep on working...

My other PP3/6F22 multimeters eat their batteries and I have to replace them biannually at best, but usually much worse, depending on how much I use it.

PS: I haven't changed battery for this meter about two years. picture 4.

You may misunderstand what I mean. I replaced the no energy and expensive 9v battery with two powerful 18650 batteries.