Resistance-No Resistance wire welder

[yo han]

Not welding wire any longer... going to give away

That's a nice gesture SB!
I've already ordered most of the parts and like to DIY a bit so I hope you can make someone happy with it.

OK, my latest try:

 

[awsum140]

Now you've nailed it, yo han!

 

[tobarger]

Looks like a good starting schematic to me
Needs prototype and testing

 

[awsum140]

A little update on welding. I started welding with the larger wire in the negative terminal and smaller wire in the positive terminal. Getting a good and durable weld can be a problem. Overheating of the smaller, resistance, wire makes it quite brittle so getting the voltage/capacitance right can be a lot of trial and error.

I switched to the opposite with the smaller, resistance, wire in the negative terminal and the larger wire in the positive terminal. It seemed to work better for the first few weld but I'm now back to the overheat/brittle syndrome. It gets really frustrating to wind a coil, mount it in the device and then have a lead break off during final assembly.

I think that controlling the voltage more precisely for any given capacitance is going to be the key. There are variations in the wire itself that can make getting it "exact" each time impossible but I think if the voltage is "clamped" rather than wandering slowly down as you work better results will be possible on a consistent basis.

I'm currently using 4000mfd and am welding at about 25 volts. I am putting the parts together for a second welder that will go as high as 60 volts and allow capacitance selection from 500mfd to 4500mfd in 500mfd steps. I'm hoping the boost module I ordered will let me control the voltage down to a tenth of a volt. I'll basically "haywire" things together for testing purposes before I put it in a project box with all the bells and whistles.

 

[Mad Scientist]

Yes, that's the idea behind S2.
By the way, I'm going to use a 12V wall wart. How much mA does it need to be?

The only design characteristic you need to worry much about is the inrush current for charging the caps. The LM2577 is about 80% efficient and you have the 220 ohm limiting resistor. Treating the caps as a dead short upon initial charging, I=E/R = 35/220 = 159 mA. W=EI = 35*.159 = about 5.6 Watts produced by the LM2577. At 80% efficiency, the LM2577 will draw about 7 Watts from the wall wart at inrush. I=W/E = 7/12 = 583 mA from the wall wart at inrush. I think this is right. Any wall wart that can produce an intermittant current of at least 583 mA will work fine (I think it would be hard to find one that can't). Keep an eye on your limiting resistor as it is dissipating about 5.6 Watts for an instant when charging the caps.

 

[yo han]

I'm currently using 4000mfd and am welding at about 25 volts. I am putting the parts together for a second welder that will go as high as 60 volts and allow capacitance selection from 500mfd to 4500mfd in 500mfd steps. I'm hoping the boost module I ordered will let me control the voltage down to a tenth of a volt. I'll basically "haywire" things together for testing purposes before I put it in a project box with all the bells and whistles.

May I ask what made you choose the 4000MFD and 25V you're using now?
This topic started with people using much less capacitance and higher voltage (1000MFD + 35V) so what made you decide to up the capacitance and lower the voltage?

Keep an eye on your limiting resistor as it is dissipating about 5.6 Watts for an instant when charging the caps.

Thanks for the advice on the wall wart. I have a couple of 12V 1A lying around so these should be fine.
But about the limiting resistor, wouldn't it be wise to get a 5W or even 10W 220 ohm then?

 

[awsum140]

My original thought was that Joules of energy was the true determining factor for a successful weld. To some extent, that is true. Enough energy has to be supplied to make the metals go molten at the contact area to produce a weld. The energy supplied by lower voltage and higher capacitance is the same as the energy from a higher voltage and lower capacitance, or at least that was my theory. That combined with what I had handy around the house and available locally led me to lower voltage higher capacitance.

Now I am questioning that basic assumption and wondering if the higher voltage can produce better results. I read this entire thread and several people are working at 70 volts with 330mfd of capacitance. I want to find out if that will produce a more reliable weld and not make the resistance wire too brittle to handle when winding a coil and assembling a device. I am rebuilding CE3s which limits my resistance wire to 33 or 34 gauge Kanthal. Welding that to 30 gauge for the zero resistance wire reliably has become a daunting task. Welding similar sizes seems to be quite easy, but dis-similar sizes pose a whole new set of problems to overcome.

 

[Mad Scientist]

Thanks for the advice on the wall wart. I have a couple of 12V 1A lying around so these should be fine.
But about the limiting resistor, wouldn't it be wise to get a 5W or even 10W 220 ohm then?

Unfortunately there doesn't seem to be an easy way to find the over rating of a resistor based on the type of duty cycle we have here. As a guess, a half Watt or 1 Watt would do the job but keep an eye on it (if your wire welder suddenly stops working, likely that's what failed). A 10 Watt would be overkill unless you have a cheap pile of them laying around.

 

[yo han]

My original thought was that Joules of energy was the true determining factor for a successful weld. To some extent, that is true. Enough energy has to be supplied to make the metals go molten at the contact area to produce a weld. The energy supplied by lower voltage and higher capacitance is the same as the energy from a higher voltage and lower capacitance, or at least that was my theory. That combined with what I had handy around the house and available locally led me to lower voltage higher capacitance.

Now I am question that basic assumption and wondering if the higher voltage can produce better results. I read this entire thread and several people are working at 70 volts with 330mfd of capacitance. I ant to find out if that will produce a more reliable weld and not make the resistance wire too brittle to handle when winding a coil and assembling a device. I am rebuilding CE3s which limits my resistance wire to 33 or 34 gauge Kanthal. Welding that to 30 gauge for the zero resistance wire reliably has become a daunting task. Welding similar sizes seems to be quite easy, but dis-similar sizes pose a whole new set of problems to overcome.

Interesting. Ah well, if I decide to change the specs later on it's just a matter of replacing parts.

Unfortunately there doesn't seem to be an easy way to find the over rating of a resistor based on the type of duty cycle we have here. As a guess, a half Watt or 1 Watt would do the job but keep an eye on it (if your wire welder suddenly stops working, likely that's what failed). A 10 Watt would be overkill unless you have a cheap pile of them laying around.

Thanks. I've decided to go with these. Price is ridiculous

 

[awsum140]

No worries with that resistor, yo han. A little overkill, but that's my middle name anyway, LOL. I meant to compliment you on the nice schematic by the way. I've got to find my electronics templates from tech school, 50 years ago.

 

[yo han]

No worries with that resistor, yo han. A little overkill, but that's my middle name anyway, LOL. I meant to compliment you on the nice schematic by the way. I've got to find my electronics templates from tech school, 50 years ago.

Thanks! I have no background in electronics and do everything with logical reasoning and you guys are of great help. The components used in this project are more or less everything I know about electronics

 

[awsum140]

That's OK, my knowledge is basically 50 years old! Luckily, the basics still apply.

 

[yo han]

That's OK, my knowledge is basically 50 years old! Luckily, the basics still apply.

Yup, only resistance has increased.

 

[Lentulusbatiatus]

But it's futile....

sorry I couldn't resist, i'll get my coat.

 

[LargeD]

I ordered all of the parts that were listed in the instructables tutorial from Digi-Key. They were out of the 2A 125V slow axl fuse (part # 507-1032-ND), so I substituted a pico slo-blo 2A 125V fuse (part# F2342CT-ND). Would someone please be kind enough to tell a noob if this will do the job.

Thanks.

 

[awsum140]

As long as it's a 2a slo blo and it fits the fuse holder you're using you should be fine.

 

[LargeD]

As long as it's a 2a slo blo and it fits the fuse holder you're using you should be fine.

That's what I thought, but I wasn't sure. Thanks.

 

[dezyner]

wired this up before putting it in the box, I get power to the board and led, no shorts or anything, but no zap, anybody see my glaring boneheaded mistake from this? can anybody help please? maybe?

 

[awsum140]

Move the 470 ohm resistor so it is between the capacitor and the power supply and the welding clips are directly attached to the capacitor. As it is connected it limits welding current surges, not charging surges. Connected between the power source and capacitor it will limit initial charge current and isolate the power supply from the welding clips, preventing it from seeing that short as the weld is done.

 

[dezyner]

Move the 470 ohm resistor so it is between the capacitor and the power supply and the welding clips are directly attached to the capacitor. As it is connected it limits welding current surges, not charging surges. Connected between the power source and capacitor it will limit initial charge current and isolate the power supply from the welding clips, preventing it from seeing that short as the weld is done.

thank you very much for that. it was a bad diode that was causing the main issue. so if I understand you correctly, put the resistor on the IN+ of the board, and the other side of the resistor to the switch lead? like this?