Sonsivri

Spot Welder based on PIC 16F684 with LCD. The firmware is in PBP. Tested with Proteus. I am making the PCB in ORCAD now. When finished I will send pictures and samples. Any suggestion will be welcomed :)

Nice project, i always want thing like this, waiting for your progress.

One of my interest: http://www.ultrakeet.com/index.php?id=article&name=cdWelder (http://www.ultrakeet.com/index.php?id=article&name=cdWelder)

Firmware changed:
Added welding time MIN and MAX limit with display
Added welding voltage MIN and MAX limit with display

I think you need to add Green and Red Led's and a weld only button. in the workshop I see you set voltage and time then forget about settings, then you only need leds to say when you can weld, and then hit the start button.

Unfortunately there is no free I/O. But when the device is not ready LCD shows "CHARGING"(not ready) and when cap charged LCD shows "READY". When in working mode (MODE=1) LCD shows all the time selected TIME and VOLTAGE so operator can see current parameters. Also in working mode "UP" button works as "WELD" button and I am planing to connect an foot switch in parallel with "UP/WELD" button.
Another option is to  replace 16F684 with 16F88 for example which have more I/Os and then a buzzer and dedicated WELD button can be added.
Your opinion is highly appreciated.

This would make a good plastic bag sealer project too. I would go for more I/O ports too, as using Just the LCD and not LEDS in the work place, would make it hard on operator in repeat operations.

Yes probably a bigger pic  will be better for this task - i will remake it for 16f88. Plastic bag welder is interesting idea

 No need for a bigger PIC - here's how to cheat and get three more pins (BTW, did you forget to pullup pins 11 & 12?)....

You can easily add LEDs and their pullup resistors to pins 4, 11, 12 of the uC. They will also come on when the button (or footswitch) is pushed (who cares if they do? may actually be a good thing to ack the button press...), but more importantly, when the button is not pushed, the uC can turn them on....you can also add a buzzer by simply putting the buzzer in as a load to VCC for the drain of a source-grounded FET and also attach it to one of these three pins along with a pullup.

But to use leds i have to make the  I/O an output and then to turn on LED in this time I can miss a press of button Am I right or I miss something. Using diodes I can add buzzer find attached file. Best regards

One more observation - how are you limiting the current through the second FET?  Through its Rdson? Counting on the load resistance of the metal being welded?

I get 3700 amps at 24V, assuming a dead short for the weld resistance, and the IRL1004 is only rated for 520 amps...

I think you might need a power choke and its snubber diode in there to current limit the cap dump into the short that is the load (when spot welding copper for instance...)

Posted on: April 04, 2010, 08:37:52 20:37 - Automerged

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You can pulse the LEDs, say 1000Hz, 50% DC, and look at button presses when they are dark - you won't miss a thing.

i will try it in 10 minutes

Same trick for the FET/buzzer ad reading the buttons, only a very low positive duty cycle for the buzzer to keep it from being audible yet allowing a read of the button at that time to see if it is grounding the FET gate pullup.  You have the option of a quick buzz in firmware using the fet on button presses versus an annoying buzz as long as the button is pressed using the diodes you've shown.  Can't buzz while button is pressed, though.  This one's up to you, of course.

Dibs on a blank board if you found all this useful :-)

Some thoughts:

1. No need to use high amperage mosfet for charging the cap.
2. Gate driver need to be modified, pnp transistor will be better.
3. Better put the electrode on the Drain not Source.
4. Wiring + contact resistant will be very important, at 24V 0.1 ohm resistance will limit the peak current to 240A.

-ichan

Capacitor charge voltage is limited by firmware to 15V and I hope that resistance of wires and material will be enough to limit the current but if this is not enough I will have to pare two transistors in parallel.

Posted on: April 04, 2010, 10:32:32 22:32 - Automerged

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1. I have a lot of them and it is easy for me to use one
2. You are right , I will change it
3. And again You are right , I will change it
4. Voltage is 15V and I think that I will manage to reduce resistance using proper wires
Many thanks for advice

if you have a good supply of mosfets use one as power resistor in place of 0.1 ohm

But this 0.1R resistor is only for simulation in Proteus. In real life it will be formed by wires and resistance of material which is being welded.

updated with leds and piezo

I am proposing the circuit below for the gate driver, Q1 need to have Ic >= 2A, low ohm resistor (< 10 ohm) might be needed between this driver to the gate of the mosfet. On your original driver, the turn on time of the mosfet will be very slow, as the Gate-Source capacitance will be charged via 10 K ohm resistor.

-ichan

If you want to be totally anal about it, a push pull would be better - now your turnoff has to charge with your R5.  You flipped the problem over, but still have the same gate cap charge problem, but now in discharge....

Real men use FETs, also....

 ;D

Fast turn off is not required in this case - slow would be better, IMHO.

-ichan

Which one is the best for this case ???

 ??? According to PDF IRL1004 is LOGIC-LEVEL GATE DRIVE so it can be operated by PIC without driver or it is better to use microchip's driver like TC4422 or TC4427?

It's really a matter of how much current your output buffers, or transistors, can drive into and out of the Qg of the device that determines the speed.  It'll get to logic level eventually, but as you transition slowly through the triode region, things may get rather toasty for the FET (think about even a few, let alone tens of, ohms times 500+ amps...).  Ichan and I both expressed concerns about doing this via the 10k resistors, as the RC time constant for turnon (or off....) may cook your FETs.

Posted on: April 05, 2010, 11:28:41 23:28 - Automerged

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I like Driver 1, though I think you may need some bleeder current/bias resistors (maybe equal valued ones from the gate of the Fet, one to gnd, and one to Vcc) to make your bipolars happy during steady state.

Driver-1-Gate Drove is best.
Same method used to drive Mosfets in a PWM-EDM power Supply

"Single pulse" and "Double pulse" added. In work mode (MODE=1) UP button switches to Single mode, DOWN button switches in Double mode.

Today I have to buy the capacitor. Does somebody have a rough idea what will be the max thickness of welded material with 1F capacitor or I should go to 2F or 4F?

Posted by: Malcolm
Insert Quote
Driver-1-Gate Drove is best.
Same method used to drive Mosfets in a PWM-EDM power Supply
I am going to try both DRIVER1 and TC4422 chip when I have the capacitor

I use 47000 uF x 12 for a simple battery tab welder, do not know exactly the thickness of the nickel tab - about 0.2 mm i guess.

The wiring resistance and the quality of the electrode will play important factor and the properties of the welded metal too.

-ichan

That is about 0.5F At what voltage level You charge capacitors?

ORCAD schematic and PCB ready. To cut it on CNC machine it is single side with bridges on top layer.

Hi Friend

you did good job and nice add on tool for work shop, i have one question can you please specified working voltage of car audio capacitor (1F)

regards
sadman

24V.

-ichan

As far as I know that type of capacitors are from 0.3F up to 12F +/- 15% and all of them are rated for 16VDC/21VDCpeak or 20VDC/24VDCpeak.  A good ESR is less than 0.002 Ohm. Some of them are equipped with on board digital voltmeter.

Hi Friend kalpakchiev

can you please share pcb file in pdf format as i do not have orcad

regards
sadman

REQUESTED PDF. LCD and KEYPAD will be ready tonight. Best regards

Work is in progress - I have the capacitor :), proper cable and main PCB is ready. Next is LCD and KEYPAD PCB.

Display is ready. Tonight I'll assemble all together for first test :)

Good progress, waiting for it.

So the purpose was to design a reliable, medium power and at last but not least easy to build SPOT WELDER. First tests in real world are done and I think the experiment was successful :).

Next step is to refine the project. Thing to do:

1. Power supply for pic processor MUST be separated

2. Using TC4422 limits the performance up to 18V - I have to change the driver

3. Is You can see in video there are 3 modes SINGLE, DOUBLE and CONTINUOUS - continuous  mode have to be reworked
  
4. I have to think about the charge and discharge circuits - in my opinion there are better ways to do it.

The work is still in progress so suggestion to this will be of great help.

Video 1
http://www.youtube.com/watch?v=PqPzzsDhFFo (http://www.youtube.com/watch?v=PqPzzsDhFFo)

Video 2
http://www.youtube.com/watch?v=Bb6R_LCmBOc (http://www.youtube.com/watch?v=Bb6R_LCmBOc)

Video 3
http://www.youtube.com/watch?v=hG6S0Q5yUoY (http://www.youtube.com/watch?v=hG6S0Q5yUoY)

Some notes:
For discharge are use 5xIRFZ48 in parallel, without sinking and they are enough (up to 18V tested)

For charging is use 1xIRFZ48 again without sinking, but it needs sink or another one in parallel because gets really hot

In my opinion you should increase charge voltage up to 30V. This can help when welding not so clean metal pieces and capacitor can have smaller capacitance. You know formula Q=C*U.

You are right but the capacitor I use in these project is rated 20VDC/24VDC Peak so 20V is highest limit. When this project is finished I can make some tests with these capacitors. It will be fun :).

Capacitors on picture are 250V. If longer charge time is acceptible you can charge through greater resistance constantly without FET switch. 

Yes they are. But in this project is used this one:1F/20VDC - attached picture.

 Probably longer charge time will be acceptable and constant charge will make circuit more simple, but in this case I have to take precaution that charging voltage not to exceed 20V and also to control voltage of the capacitor when welding very thin material.

Have you try it welding things?

-ichan

only a few beer caps and a screw driver by mistake :o. My camera battery is flat now. I'll upload video later when recharge it and also I have to buy a tripod

I want to rebuild charging circuit and Your opinion will be very helpful for me. What do You think about these two:

Hi,

In my opinion, i prefer the original design.

The First one (old schematic.jpg) doesn't work, you need charging CAP and then Discharge then on Load, on your design CAP is in parallel with Load, CAP never charge.
The Second One (new schematic.jpg), the charging MosFet is at the best place, but the discharge MosFet is floating, since charging MosFet is open when discharging, you could not turn off discharge MosFet.

something that is important for driving mosfets,  is that more powerful the mosfet is and more capacity Gate Source is important.
So you need have to charge the small capacity between Gate Source very quicky, and when you want it to turn off quicky, discharge it quickly.
Each IRL1004 has 5330 pF between Gate and Source, if you put 10 Mosfets in parallel you have 10*5330pF= 53.30nF, it is for that there is IC Driver (to accelerate turn on and off).
If you want to do a good driver, the best is a push pull but it is very important to put a small resistor beetween push pull and the gate to limite charge and discharge current on the gate (10 or 6.8 Ohms).
In that configuration turn off and turn on time are the same.
If you charge with 470 Ohms and discharge with 10k, you will have somes problems.
In your design, don't forget to put a resistor between Base and Emiter for transistors (for 2 PNP it is very important).

I hope, it will help to improve your design.

Best Regards.

Indeed You are very helpful.

On bot schematics Resistor 0.01R is only for tests in Proteus and represents resistance of the circuit during weld (when output is shorted). In real PCB it does not exists.

On first schematic (old one) I see a problem with place of the charging transistor. I wanted to change the place of the load (capacitor) and to put the transistor at LOW SIDE. And trying this I come to second schematic (new one).

But the main reason to post my question is just that floating SOURCE of discharge transistor. I can not figure out how to fulfill both requirements : both charge transistor and discharge transistor to be at LOW SIDE.

Do You mean to add these two resistors R21 and R22

In this configuration I have to use P channel and N channel MOSFETS.

You are right and firing P FET will not work. Idea removed.

I am sure there is a way just i can't see it >:(

Again this schematic with floating SOURCE. If during weld I also turn on charge transistor then discharge transistor will have GND. The voltage of the capacitor can't exceed max. allowed because it is discharging at the same time. But with this method  welding current will have to pass trough both the transistors, which I think is no good. There must be some other way ???

Isn't it so that in welding time weld current flows only through weld FET and main C and through charge FET only a current which is almost the peak charge current because battery is practicaly loaded with 1ohm+Rweld+Rcharg?

In this case the SOURCE of weld FET will receive GND from DRAIN of charge FET that's why I think that welding current will have to pass trough both the transistors. Am I right?

No

Posted on: April 12, 2010, 11:46:29 11:46 - Automerged

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You solved the problem without knowing it...

I tested it in PROTEUS but I am still not confident that the problem is solved.

I used Microcap to show start and end currents during weld time. At end time it is supposed that C is totally discharged.

So it appears that this is the solution. I'll give it a try. For charging FET I am going to use  2xIRL1004 and for weld 5xIRL1004.

What about this schematic as final decision ?

What circuit is connected left side to pins 1 and 2 of CON4 .

Pin.1 - charge control from PIC16F88
Pin.2 - weld control from PIC16F88
Pin.3 - analog input of PIC16F88
Pin.4 - GND

I know it and expect that you have 15V voltage swing on them.

No, 5V when corresponding port of PIC16F88 is HIGH and 0V when LOW

CHARGE MODE                                 PIN.1=5V PIN.2=0V
READY(capacitor is charged) MODE     PIN.0=5V PIN.2=0V
WELD MODE                                    PIN.1=5V PIN.2=1V

Nice job, buddy. Very nice.

A suggestion for V2.0 - two caps in series.  This will half the capacitance and double the voltage.

Here's my evil plan....

E (energy) is C*V*V/2

If you half the cap value and double the voltage by placing two caps in series, you DOUBLE the energy that you can dump into the weld....

Bonus is punchthrough of crud on the metal, as mentioned by a prior poster, due to higher voltage.

That's a very interesting idea. I want to clean up schematic for charge and discharge and when it is ready I certainly WILL give it a try. IRL1004 is rated up to 40V.

Hi,

Do not forget to add a resistor across each of the caps in series. (say 1K ohm).

Cheers.

You mean these capacitors I suppose. I usually use 2.2k.

What about a "ohmmeter" which first detects that electrodes are well pressed on object and then enables firing.

It is cool  ;) but I prefer to control the process myself. What about last power schematic? What is Your opinion - is there something missing or wrong? I am going to make the PCB tonight.

It looks OK. It is better that resistors in C voltage divider are smaller than 1k. Actually a C leakage currents difference at full voltage determines the resistance. Idivider=10*Ileak.

Tonight I'll start the PCB. Thanks for the verification. About C voltage divider - I will have it in mind.

hi

1F audio cap hard to find in my country if found price is two much can i used alternative such 47000uf cap in parallal to achive value that required

regards
sadman

Yes, you can.

Do you solder over all the power track on the pcb? I think standard copper foil alone is not enough to carry the peak current, with the software below 10mm width of standard copper foil can only carry 7.7 Ampere current.

-ichan

http://saturnpcb.com/pcb_toolkit.htm (http://saturnpcb.com/pcb_toolkit.htm)

It's Free  8)

-ichan

I also had some embarrassment about thickness of the power tracks and I decided to flood them with tin. Many thanks to Ichan.  This software will be very helpful to check the tracks. Best regards

I prefer most of the older version of the circuit, it seems inherently safer and more correct.  

As far as I can see, a common ground for the charging supply, the - weld electrode and the cap
is the best way to go.

With this version neither of your electrodes is at GND potential and one is always live to your + supply
through 4 Ohms of resistance.  This design risks an avoidable fire and shock hazard.

When not charging, your voltage measurements measure your charging supply voltage because the - of
your weld capacitor is not at GND potential, but left floating.  When charging they will be somewhat off
because of the voltage drop across your charging transistors.

I'd also add a bleeder capacitor resistor to the circuit so the weld capacitor isn't left charged for days and surprises you by erroneously welding a screwdriver, ring, etc.

Edited to correct a brain fart.

And all those negatives that Oldvan talks about are result of hunting for LOW SIDE to improve the circuit.  
Now when the new PCB is ready to test it I am also wandering does it really worth's or Oldvan is right?

Putting the business end at the source of the N-Channel mosfet will need high side mosfet driving which will add an unnecessary complexity.

-ichan

Anyway the new PCB is ready, tonight I'll test it and will post the results

I beg to differ with the word "unnecessary."  High-side MOSFET drive indeed adds a bit of circuitry.

Driving the N-Channel MOSFETS on the high side of things needs little additional, a couple opto-isolators
and a +30V supply capable of a hundred mA or so would do the trick.,

The small additional amount of circuitry provides SAFETY which should always be a driving force in any project.

How many injuries or deaths does it take to negate saving a couple of dollars?

In another project I have successfully used this schematic for Driving the N-Channel MOSFET on the high side, but this requires a free I/O with PWM.

Granted.  ;)

Kalpakchiev, i really want to see you are successful with this as i will copy it if so  ;D.
My old tab welder is only a crude wiring of caps, scr, relay, and switches. I need to upgrade it.

-ichan

You are not going to copy it - I can say that we are making it together  ;D ;D ;D ;D

Thats the spirit we r herewith ............

PCB is ready. Tests are done. Here some pictures. Next I have to write a conclusion ;D

So here come conclusion based on experiments with both variants:
Second circuit works, but there is no difference in performance compared with first one.

As Oldvan mentioned about second schematic : ''When not charging, your voltage measurements measure your charging supply voltage because the - of your weld capacitor is not at GND potential, but left floating. "

It appears that the first variant is better.

From your picture:

- Looks like the spark is good, but it happen at the wrong place.
- The material is too thick, try to use battery tab taken from old battery pack, even a small cellphone battery has it.
- Do not use plated material, you may try to find 0.1 - 0.2 mm stainless steel sheet, nickel is the best but harder to find.
- Not enough pressure, spot welding need some pressure so the material bent down at the weld point.
- The electrode material is not good enough.

Please try again, i think you are already close.

-ichan

- Looks like the spark is good, but it happen at the wrong place - these 2 sparks at the left side are from previous try.

- The material is too thick - I want it to be able to weld up to 1mm material, this one was 0.8mm

- Do not use plated material, you may try to find 0.1 - 0.2 mm stainless steel sheet, nickel is the best but harder to find. - thanks, i will have it in mind

- Not enough pressure, spot welding need some pressure so the material bent down at the weld point. - Right, that is important

- The electrode material is not good enough. - It is cooper, but it is not electrode at all - just a piece of thick wire - Do You think a 10mm cooper rod with conical tip will be enough?

Please try again, i think you are already close. - I will, but with first circuit design, it needs some refinements but I consider the entire experimets as successful.

Best regards
 

I meant burnt mark at the right side with copper color, the spark shouldn't be there but between the welded material.

1 mm is to thick for a welder like this, there is a good DIY project on the web which use modified microwave oven transformer, more appropriate for thick material.

For the electrode, pure copper will be to soft but i do not know what alloy it should be, need to try many copper rod available.

I just quick draw a layout for power section if i will build it later. The schematic is still on my head, it use my proposed driver for discharging mosfet and a P Channel mosfet driven with one npn transistor for charging. For R-Charge i would prefer to use 24V 120W halogen bulb for 5A charging current, yes it will be a very bright charging indicator  :D.

-ichan

If you want when you are ready with schematic send it. I can make a protopype and test it.

What is the program with which you draw this PCB?

Regards

Sure i will be glad if you willing to try it, i will draw the schematic tomorrow.

It is drawn with Sprint Layout, if you haven't tried it this software is good to quick draw a pcb layout without drawing the schematic first, you can find it here in Sonsivri.

Attached the Sprint Layout file of the WeldPower, well.. need to rar it as the forum software doesn't allow .lay extension to be attached.

-ichan

Sprint Layout supports direct output for milling and drilling  :D :D :D

Kalpakchiev,

Here is the schematic, you may change anything you want.

-ichan

I will make it. Ichan, do you think one single IRF9540 will be enough ???

I am thinking about 5A charging current set by R-Charge, a 120W 24V halogen bulb to give 5A at 24V Vin is on my mind, so single IRF9540 should be enough as long as it is not a bad quality "clone one".

But you are free to modify it as you like, thanks for the will.

Note: I forgot to put R-Bleeder on the schematic, they are exist on the pcb drawing.

-ichan

This sounds to me like plan ;D

which software you used for cnc job

regards
sadman

At work : Autograv
At home : KellyCAM

It works with both of them  :) :) :)

Best regards

Hello,

To ichan about your drawing "powerweld.png",

there is a problem in the weld driver part.

When WELD input is high, Q7 is closed, and Q6 too, but the current from junction Base-Emetter of Q6 is only limited by R15, so either (Q6 or Q7), or (Q6 and Q7) will by destroyed.

To avoid problem, put a resistor 1K between Base Q6 and Collector Q7.

It whould be better to replace Q6 and R9 by a push-pull with BD139 and BD140 by exemple.

As explain before, this give a strong drive to turn on, and a strong drive to turn off, that give a very precise driving for time to weld and use less power to drive Mosfets.

I hope this help you.

Best Regards.

....and change R9=4k7, and parallel with ziner 12V if VIN>30V. possible remove R1~R5? i prefer less components count.

The resistor is there on the proposed driver (reply #17) but then i was thinking to saturate the pnp transistor harder to make a faster turn-on. I do not use totem-pole driver as i think a slow turn-off would be better for this application(reply #19).


With R9=4K7 the turn-off will be too slow, will it? Yes adding a zener diode would be safer, R1-R5 to reduce the risk of "Gate Ringing" caused by parallel mosfet and/or stray inductance.

-ichan

What turn on-off time is suitable comparing to 10ms to 200ms weld time? 100us is acheived with 6k drive resistance.

I have no answer, i didn't calculate anything too.

Just my feeling that it should not turn off too fast, as the very high welding current effected by stray inductance could kicking back to the mosfet destroying the body drain diode if the turn off is too fast.

How slow? Can it be too slow? Frankly, i do not know.

-ichan

I agree but we have to talk with dimensions - too slow or too fast sounds like the saying for comparing BIG ANT and SMALL ELEPHANT ;D.

I have no idea which way is better to turn it off fast or slow.

100m capacitor charged on 30V and discharged through 0.07+rds/5 is practically empty in 30ms.
Troubles with voltage spikes vhich occur on weld start and end because of electrode inductance can be eliminated by diode in series with charge FET.
Rise and fall times on weld FET gates are not important.

Yes I think that's right. In our case capacitor is 1F and voltage is 20V so we are talking for max. weld time about 200ms

Hi,

In the web site : http://www.ultrakeet.com/index.php?id=article&name=cdWelder_p2 (http://www.ultrakeet.com/index.php?id=article&name=cdWelder_p2)

The you-tube video show examples of weld, at 1:58 min they give time of weld of 0.1ms, 0.5ms, 1.5ms, 4.5ms, 9.5ms to weld (Nickel to Stainless).

If these times are really good, if you have not a very fast turn-off, it will be impossible to have these short times.

But it is possible that for your applications, that turn-off time become not important.

Best Regards.

a) yes, R9 increase will couse turnoff timing increase.
b) Q6 will it replace with P-ch FET (small signal to92) type? as long as its -VGS is higer than VIN. or added 12v ziner.
c) ring effect on gate ? i'm not sure, it related to capacitive load effect. refer to link http://rapidshare.com/files/378642574/capacitive_loading.rar , but i think R1~R5 slightly increase turnoff timing.
d) a good weld spot, are determine by a good "intermatalic formation" in its spot by 2 metals, if less will couse loose or "dry-join", too much will properly couse a melted hole in it. a PWM pulse train might help on weld input. 


 

Hi Friend kalpakchiev

can i used uln2003 in place of tc4422 also what is total current of transformer you used for supply and charging purpose

regards
sadman

I am not sure You can replace tc4422 whit ULN2003, transformer is 16VAC 240W with 35A bridge rectifier
Best regards

waicon said a PWM pulse train might help on weld input.
I think back to a DC welder I fixed a few years back its control was with two power Fets.
one had PWM on its gate and other was on/off   

Hi Pickit2, why there is an ON/OFF fet when turning PWM off, also turns the weld off?


How many ONs and OFFs in one post  ;D ;D ;D
Best regards

LCD prepared for test  8)

I am still waiting...  ;)

Can not find my old tab welder, searching for the caps i found a bag of 10000uF/35V, is that a crazy idea to parallel 100 of them making a capacitor farm?

-ichan

i found 47000uf used 24 in parallel to get the required value

It is possible to parallel a few capacitors to reach desired value (make a cap. farm), but you must have in mind that this will increase internal resistance of the whole capacitor.

Best regards

Isn't paralleling capacitors will decrease the total ESR value?

-ichan

I think that all the connection between capacitors have to be added to internal resistance, so it will be increased. Am I wrong?

if you have ESR meter just do a test for us that will help us as in my country 1F audio capacitor hard find, just check ESR of two 2200uf,cap then join both capacitor in parallel and measure ESR again that will clear every thing so we used alternative method, once again thanks for your corporation.

regards
sadman



 

Yes this test can be very useful, but unfortunately I have no ESR meter.

If some one in the forum have, please help Sadman.

Best regards and many thanks in advance for your kind cooperation.
Ivan Kalpakchiev

Hello kalpakchiev, all's

i am new here, i discovered this site and this project.
I follow it since a few day's, and i think that can be my
next electronic build.

Thank's for sharing, i search now the condensator on internet.
Do you think that best result will be with 2 condo in serie,
or one (with 1F) is enough to sold accus ?

Best regard's to all

Fabrice

Hi Fab66,
Sorry for my late post but I was on a place where it is difficult to get connected to internet.
For me using one 1F capacitor gives good results. But it depends on what You are going to weld - type and thickness of the material.
Now I am back and will finish the project with all the final modifications that we discussed with other peoples in this forum.

I wish you success in your project.

Best regards,
Ivan Kalpakchiev.