Re: [CAD_CAM_EDM_DRO] A bit off topic - resistance welding

Hi Jon and everyone else,

Thanks for your advice, once again the list has provided a mind-blowing
wealth of expertise!

I do, of course, need to get better control of my fingers - the size I'm
looking at is 1/64" diameter welds and not 1.64"! - must be a metric
computer!!

The ASCII art came through a bit garbled so, if you could just confirm where
the trigger capacitor and resistor go I'd be grateful - is the resistor in
series with the capacitor and push button across the supply?

The system you describe is pretty much exactly what I had in mind. There are
still a couple of things I'm not too sure of -

1) I suspect that a wire-wound resistor in series with the power supply and
before the main capacitor would be a good idea to save having a dead short
across the transformer but I'm not too sure how to size this. For example,
if I used a 24volt 5amp supply, would a 4R7 at 5 watts be enough or should
there be some allowance for the total power the capacitor is able to dump?
Maybe a mains voltage 200watt light bulb would be a better prospect?

2) How would I determine the size of SCR to use?

Thanks.

Ian
--
Ian W. Wright
Sheffield UK

----- Original Message -----
From: "Jon Elson" <jmelson@...>
> work when everything is ready. I'll try some ascii art :
>
>
> _________________________________________\
> | | + | /
> ___|__ | o |_ PB SW
> | PS ___ o | weld
> ------ M ___ __| electrodes
> | | | ___
> | | \ ___ T
> | | / |
> | | R\ |
> | | / \ | /|
> _________|____\|/ |__________________\
> |\ | /
> | \|
>
> Here, M is the main energy storage cap, R is a 100 Ohm
> resistor, and T is a capacitor of about 1 - 5 uF to deliver
> a trigger pulse to the SCR when the pushbutton switch is
> pressed. A resistor can be put between the power supply and
> the main cap to prevent overloading of the power supply
> every time it charges the main cap. If you go much above
> 18 Volts, it might be a good idea to put a 22 to 100 Ohm
> resistor in series with the trigger cap, T.