Resistance-No Resistance wire welder

[TomCatt]

Thanks guys, didn't realize the board would drain the caps, will try that next. That wouldn't be why I have to rapidly press the switch to charge up the caps, would it?

Oh well just another day in my world SNAFU


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[BikerBob]

If you put the switch between the LM2577 and the caps, you'll have a current spike into the caps through the switch--I've seen that cause switch contacts to weld closed. Throwing power into discharged caps (at zero volts) is much like a short-circuit at the start. Put a resistor in series to limit the inrush current.

 

[dsy5]

If you put the switch between the LM2577 and the caps, you'll have a current spike into the caps through the switch--I've seen that cause switch contacts to weld closed. Throwing power into discharged caps (at zero volts) is much like a short-circuit at the start. Put a resistor in series to limit the inrush current.

Very true, I use a 470Ω resistor in there; it doesn't cause too much of a time-constant delay in the charging of the caps - maybe 4-5 seconds for a full charge.

EDIT: Had an extra "0" in the resistance value...

 

[bapgood]

Very true, I use a 4700Ω resistor in there; it doesn't cause too much of a time-constant delay in the charging of the caps - maybe 4-5 seconds for a full charge.

Dsy5....did you add an extra zero?

 

[BikerBob]

3000µF = .003F, so 333Ω would give time constant (TC) of 1 second. 1 TC is 63% of charge, 5 TCs for nearly full charge. 4700Ω looks like TC of 14 seconds to reach 63% charge. Hope I'm remembering this correctly--EE-101 was 35 years ago for me.

 

[bapgood]

I'm no EE but I used a 470 ohm resistor and it seems to work fine...I also use capacitors between 1000uf and 4700uf+

We talked about it a ways back and I even posted a video showing charge time.

 

[LucentShadow]

Here's a handy calculator for charge time:

Charging a Capacitor

For me, with a 470 ohm current limiter and 4400 uF of capacitance, 5 seconds gets 91% charge, and 10 seconds for 99% charge.

 

[dsy5]

Dsy5....did you add an extra zero?

Yeah, hehe, fat fingered it and didn't notice...also using a 1500µF capacitor. (No, extra zero there!)

 

[jimbalny]

This is awesome! I want one!

Speaking of the dangers of disposable camera guts.. In my younger, inquisitive, wonder how this works stage (when I was taking everything apart and never being able to put em back together) I took apart a disposable camera and got a REALLY NICE shock (twice! dont know what possessed me to pick it back up). Gotta love those high voltage dc shocks, they can be brutal. The only worse shocks i ever got was by a T12 HO (High Output) Fluorescent lamp ballast and through the chest by 277vac. After the initial "holy sh--, i almost couldve just died" moment it really just feels like you drank way too much caffeine.

 

[breaktru]

This is awesome! I want one!

Speaking of the dangers of disposable camera guts.. In my younger, inquisitive, wonder how this works stage (when I was taking everything apart and never being able to put em back together) I took apart a disposable camera and got a REALLY NICE shock (twice! dont know what possessed me to pick it back up). Gotta love those high voltage dc shocks, they can be brutal. The only worse shocks i ever got was by a T12 HO (High Output) Fluorescent lamp ballast and through the chest by 277vac. After the initial "holy sh--, i almost couldve just died" moment it really just feels like you drank way too much caffeine.

That's a shocking story Jim.
Back in the day when I was in H.S. shop class, we worked on Televisions. Imagine a shock from a flyback transformer feeding a CRT picture tube at 20,000 to 50,000 volts. That is one nasty shock. Not to mention the several times I was zapped with high voltage ignition coils working on cars w/ 30,000 to 60,000 volts.

 

[dsy5]

That's a shocking story Jim.
Imagine a shock from a flyback transformer feeding a CRT picture tube at 20,000 to 50,000 volts.

Been there, done that.

 

[bapgood]

high voltage ignition coils working on cars w/ 30,000 to 60,000 volts.

I hate those

 

[mre777]

Yup, I picked up fast when opening up the tube TVs, you need to discharge them before you go mucking about or it will bite you hard.

 

[jimbalny]

That's a shocking story Jim.
Back in the day when I was in H.S. shop class, we worked on Televisions. Imagine a shock from a flyback transformer feeding a CRT picture tube at 20,000 to 50,000 volts. That is one nasty shock. Not to mention the several times I was zapped with high voltage ignition coils working on cars w/ 30,000 to 60,000 volts.

Dayum! I've heard that those transformers in CRT's could literally throw you across the room from a good blast.

 

[LucentShadow]

Dayum! I've heard that those transformers in CRT's could literally throw you across the room from a good blast.

An old 1960's oscilloscope CRT was the highest I was ever hit by. I can't recall the voltage, but I thought it was only a few thousand volts. It flung my arm back behind me, spinning me around, and I dropped to my knees. Quite painful, and I didn't feel right for a few hours. I learned to keep my thumb back farther when I pulled the plug toward nearest chassis point.

I was 19, then. I don't think I'd want to try it now, a couple of decades later.

 

[dsy5]

I've been an electrician/electronic technician for over 30 years and have been bit by almost every conceivable voltage source. The real damage done is to your hands and arms: as you pull away quickly from the surprise of receiving the shock, you end up scraping your hands or arms on whatever you happen to contact. One time I was hit with 440VAC working in a machine panel and hit my arm on a very sharp part of the panel door; required 10 stitches.

 

[Stephenst4470]

bummer....

These should work, 100 M input impedance

Low Cost LCD Panel DC Volt Meter Voltmeter Volts Only | eBay

 

[breaktru]

Yup, I picked up fast when opening up the tube TVs, you need to discharge them before you go mucking about or it will bite you hard.

Yeah, but when you are taking meter readings it has to be live.

 

[breaktru]

I've been an electrician/electronic technician for over 30 years and have been bit by almost every conceivable voltage source. The real damage done is to your hands and arms: as you pull away quickly from the surprise of receiving the shock, you end up scraping your hands or arms on whatever you happen to contact. One time I was hit with 440VAC working in a machine panel and hit my arm on a very sharp part of the panel door; required 10 stitches.

The first thing they taught us was never to wear rings so not to get caught on anything when pulling away. Lots of sharp stuff in an old tube TV.
AC throws you and DC holds you.
I worked in the NYC subways around the 3rd rail. I've hit it on a few occasions working on equipment very close to it. Lucky I wasn't grounded. 600VDC, 2000+ amps

 

[TBinAZ]

The first thing they taught us was never to wear rings so not to get caught on anything when pulling away. Lots of sharp stuff in an old tube TV.
AC throws you and DC holds you.
I worked in the NYC subways around the 3rd rail. I've hit it on a few occasions working on equipment very close to it. Lucky I wasn't grounded. 600VDC, 2000+ amps

Ok, now we know what happened to you. LOL