Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: Home Made Spot Welder
Date: Jul 07, 9:07 am
Poster: Mark Harriss

On Jul 07, 9:07 am, Mark Harriss wrote:

>I have been thinking about how I am going to
>fabricate the grids in the upcoming fusor. The
>following idea is where I intend to start. If
>any of you guys already have experinence in this
>area I sure would like to hear your comments
>before I waste a lot of time and energy.
>It seems to me that a reasonable spot welder could
>be made as follows.
>1. Use a transformer out of a microwave oven to
>get the 1000 or so volts that is required. A small variac could be used to set the output level
>and a mechanical stop on the variac could limit
>the upper voltage level. Rectify the output and
>send it to the storage/discharge cap. There can be several discharge caps for the different power
>levels required. A selector switch will select
>the appropriate capacitor.
>2. The power supply discribed above will be discharged through the primary of a conventional
>weller Soldering gun. A solid state SCR can be used to handle the discharge. The soldering gun is nothing but a voltage to current transformer. It seems that the power rating of the weller gun should be plenty to handle the short discharge
>pulses from the power supply.
>All that is left is some homemade copper wire holders that will hold the grid wire, provide the
>proper spring preload and carry the pulse current
>from the high current side (soldering iron tip holder) of the weller gun.
>If the above design works, as I hope it will, then
>it should be simple enough for everyone to in the
>group to have their very own spot welder. All the parts should be availabe from local garage sales and flea markets. The Grid wire holder may
>be a little hard to fabricate but I have seen that
>some of you guys have already done that, maybe someone can post the plans to build the bussines
>end of the spot welder.
>If it seems I am way off track then please let me know, otherwise I will put this thing together and
>let you know the results.
>Thanks Its been fun
>Don Harris

Hello Don,
I thought i'd contribute my two cents worth to the spotwelder discussions:I've used on a number of occasions three small tabletop spotwelders, these had a physical size i would estimate to be around 500-1000VA rating, they were operated by a mains switching footpedal (240 V in Australia)and had copper bars about 20mm (3/4")in diameter and 300mm (12") long coming out to form a pincer type arrangement with a locking mechanism identical to vice grip pliers. They were operated by adjusting the gap screw until the thickness of the sheet metal was allowed for to give firm clamping (which was very critical if the shower of sparks from a loose clamp was any indication)then the foot pedal was operated for a couple of seconds during which the spot was bright orange in heat. I do remember that one of the units was rated at 2 volts ac @ 360 amps output which gives 720 VA rating. keeping the electrodes clean was critical at the point the replaceable tips were screwed into the arms and also the tips too because of the small voltages involved. I hope this helps with building a home unit.

Mark Harriss