switches

[crazycanuck]

Question for all you in the know electrical people!
I am looking for a good power button or push switch.
It must when pushed turn on and off in about 1/4 second and take an electrical shot of about 800 amps.
any sugestions?

 

[briwire]

Thats quite some current. I can't think of any single device off hand. What voltage? AC or DC?

You might have to use a large contactor with operated by a slave relay and standard push button.

If you insist on high current switches, you might find something from a supplier of parts to battery operated vehicles such as fork lift trucks, but 800A might be too big for even them.

 

[crazycanuck]

thanks for your reply.
I think a panic switch is the way to go, it can not stay on when pushed so the charge of 800 amps DC from a car battery will be only for a split second.
i'm building a spot welder for battery packs on cordless drills.

 

[JohnD]

DC currents are much more prone to arcing so an ordinary air-gap contactor will not do. it also might weld its contacts shut.

(AC arcs automatically extinguish themselves 50 or 60 times a second and reverse, so are easier to break)

there might be some kind of oil-filled device used industrially or in ships. Beyond my knowledge.

The word "cheap" does not spring to mind.

 

[TicklyT]

If this is to be a mains-powered spot welder for relatively thin materials, then consider switching the mains supply rather than the DC, as done in small commercial welders.

IIRC spot welders deliver their full output at only a couple of volts, so the amount of energy delivered isn't that enormous, just well focussed.

800 Amps at a couple of Volts is about 1.6 Kilowatts.
2 Kilowatts at 110 Volts is less than 20 Amps.

In the UK, commercial 'DIY' spot welders sufficient for welding 18 - 20 SWG steel require something like a 240 Volt 16 Amp supply.

I have seen a crude, but successful setup for spot welding 0.005" steel using a DIY arc welder with one pencil point copper electrode gripped in the electrode holder and the other in the bench vice.
The work was pinched between them and the welder switched on with a momentary action treadle switch.

Spot welding more electrically and thermally conductive metals like copper or aluminium may require higher currents, although the materials used in battery construction are usually quite thin.

 

[crazycanuck]

maybe I steered you wrong .
I,m using one 12volt 800cranking amp car battery to weld .005 thick nickel tabs on power drill battery cells the switch is for sending a very short burst of current thru to spot weld tab to battery cells.
I just don,t want switch to stay on ,it must only on long enough for me to hit switch and release.

 

[JohnD]

truck starter motor solenoid and a push-button momentary switch of your choice.

or use a soldering iron instead of spot welder

 

[crazycanuck]

soldering iron even a small one can over heat battery cells doing more damage than good, plus it looks like a amateur did it.