How to make a spot welder.

[eccerr0r]

Re: How to make a spot welder.

So, that's another benefit of the capacitor discharge welder versus transformer based
Alas the recycle time of the transformer based should be quite a bit faster...

[sam_sam_sam]

Re: How to make a spot welder.

All you need is transformer controller and these are easily found today on eBay ( when I get home I will post where you can find some)

The hardest part is getting a 1000 watt microwave transformer (or two of them depending how hot you want the weld to be) and converting it with out distorting the primary winding but if you take your time it can be done

Now the battery spot welder that I have if I change the breaker from 15 amp and went to a 30 amp breaker I could get some very hot welds and I might have to do this I would have to change wiring to go to a 30 amp breaker and just have not been motivated to do it so far but if I keep getting cold welds that the battery tabs do not stay on I will have to do it

Because I can only turn the current controller to no more than 70% with out tripping the 15 amp breaker

Another reason that I have not change the breaker is that when the current controller start taking a shit when you hit the trigger button it bounce and rapidly fires the transformer and trips the breaker

Or

This happens when you first turn power on it rapidly fire the transformer and this might happen a few times before it stops doing it so you can use it

In either case when it works right it does not do this

[eccerr0r]

Re: How to make a spot welder.

Using a car battery, you must have some sort of control like an IGBT or MOSFET bank. People have welded with a car battery but that tends to blow small battery tabs up. A capacitor is good because the amount of energy stored in a capacitor is limited.

Might need to look for a bigger solder gun that has a bigger transformer in it...

[capwizard]

Re: How to make a spot welder.

Yes that will be a workhorse. then we pretty much go back to old solder gun like this guy eccrr0r said...

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 have tried that before I think old solder gun has no enough current.

[stj]

Re: How to make a spot welder.

no, batteries explode!!
what's wrong with using a microwave oven transformer and changing the windings?
others have done it.

[capwizard]

Re: How to make a spot welder.

If you want to make best spot welder then you need to use the best and biggest capacitor in the world and that is battery.

So I'm going to switch my attention to 12 v battery spot welder is that sound right?

[stj]

Re: How to make a spot welder.

shorting large caps can melt the wire inside the bung where it's flattened to go into the foil.
the cap can store more current than the wire can hold.

it's also not a good idea to short a crt anode by shoving a pair of screwdrivers under the cap - you can damage the diode with the emf spike!
i'v seen old gits damage them a few times like that - modern-ish transformers arent as robust as the 70's
besides, does a chain of resistors really cost that much? /sarc

[eccerr0r]

Re: How to make a spot welder.

I guess the trick is for capacitor discharge welders is finding good capacitors...
Ever since I destroyed a capacitor by repeatedly charging and shorting it (for entertainment purposes) it's something to consider...

Currently I've been using a 51mF capacitor charged at ~18V to blast through shorts in NiCd cells... Doesn't always work but at least this capacitor is capable of dealing with shorting, at least its performance hasn't dropped compared to that other capacitor I was playing with when I was younger...

[stj]

Re: How to make a spot welder.

http://ultrakeet.com.au/write-ups/cdWelder

[Sparkey55]

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 once blew a hole into a 1/4 inch screwdriver when shorting a 25,000UF 75VDC capacitor.

[eccerr0r]

Re: How to make a spot welder.

Well, just saying, I spent 50¢ per 9V battery and it lasted at least 4 years so far, I don't think it's a bad deal, and nothing sticking out of the meter... This is specific to the Fluke.

That is not to say the same 9V battery (out of the same 2-pack) lasts less than 2 years, possibly only a few months on my other 7106-based meters...

[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.

[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.

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

[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.

[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

[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.

[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.

[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.

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.