Film-Tech Forum ARCHIVE: Welder as rectifier

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Posted by Colin Penny (Member # 11026) on 10-04-2019, 02:43 AM:

Anyone running a welder to lower their lamp. If so can you show how you have it wired and what components you used to smooth it.

Thanks

Posted by Gordon McLeod (Member # 33) on 10-04-2019, 07:09 AM:

It has been done there were several rectifiers that were modified Hobart welders But they would require filtering and a boost supply
Not for the faint of heart

Posted by Jim Cassedy (Member # 4115) on 10-04-2019, 07:53 AM:

I beleive this topic has been covered once or twice before on this forum.

I was able to find one thread HERE

But I seem to recall seeing one that also had some pictures.

The big 'issues' you'll have to deal with are:
1) Duty Cycle
2) Ripple Filtering
2) Coming up with a way of dealing with Xenon starting pulse.

On the other hand, I have seen a rectifier used as a welder, when I once
dropped a pair of metal pliers into one & it welded them shut! [Wink]

Posted by Dave Macaulay (Member # 813) on 10-04-2019, 10:13 AM:

If you have a Strong lamphouse with the AC ignitor, possibly you can just hook up a DC welder and hit the manual strike button. You will likely need some extra filtering, and some hefty capacitors to provide starting current.
I don't know how much an inverter welder would like a lamp load. The IMAX 15-20kW Millers were "brute force" types with massive transformer and choke. A boost voltage was added but I don't know if that's needed to strike a lamp or just tells the lamphouse that the rectifier is on and triggers an autostrike circuit. The added front panel box was mostly tamperproofing so the power switches couldn't be fiddled with: switching it to "ON" would disable power control from the projector and if you shut down the IMAX system the lamp would stay on... boiling off the internal coolant pretty fast then melting the cathode electrode seal and exploding the lamp when coolant leaks out inside the white hot envelope. Fun times.

Posted by Frank Angel (Member # 248) on 10-04-2019, 07:53 PM:

switching it to "ON" would disable power control from the projector and if you shut down the IMAX system the lamp would stay on... boiling off the internal coolant pretty fast then melting the cathode electrode seal and exploding the lamp when coolant leaks out inside the white hot envelope. Fun times.

Hot DAMN, Dave, I would pay a bucket load of money to see that! [thumbsup]

It sure would make a great documentary...the dangers of tinking with stuff that you shouldn't. And heck, there certainly are enough mothballed IMAX projectors sitting around that no one would miss an exploded one, eh?

Posted by Gordon McLeod (Member # 33) on 10-05-2019, 12:37 PM:

Boost voltage is required to start a lamp
The sequence is The boost supply charges the out put capacitor to (depending on vintage) up to 150VDC This serves to purposes one to trigger the ignitor circuit and Two to provide a large inrush current to establish the current flow ( too much inrush will also damage the electrodes too little the lamp will just go out) I high voltage around 50KV and approx 30Mhz is superimposed by the ignitor to ionize the gas in the lamp and to create the electron path between the two electrodes. This is in serries with the lamp so a bypass capacitor is required across the rectifier
It has to decouple as soon as the arc is established and then the main rectifier provides depending on the lamp the high current low voltage

Posted by Marcel Birgelen (Member # 6801) on 10-06-2019, 12:35 AM:

quote: Dave Macaulay
The added front panel box was mostly tamperproofing so the power switches couldn't be fiddled with: switching it to "ON" would disable power control from the projector and if you shut down the IMAX system the lamp would stay on... boiling off the internal coolant pretty fast then melting the cathode electrode seal and exploding the lamp when coolant leaks out inside the white hot envelope. Fun times.

Geordi La Forge to Bridge: Captain: We have a coolant leak in the projector's core. I'm trying to stabilize it.

10 seconds later...

Geordi La Forge to Bridge: The core's cathode electrode seal is melting, the coolant is boiling off at a very high rate. I can't stabilize it.

Captain Picard to La Forge: Eject the IMAX Core!

Geordi La Forge to Bridge: IMAX Core ejection systems are off-line!

Captain Picard: All hands abandon ship! Repeat, All hands abandon...

Sorry, it was a long night. [Wink]