Speaking of a diode bridge for a tombstone...

Managed to scrounge up four 250A diodes the other day. Big sumbitches. Is the conversion as simple as a bridge for the conversion? Is it best to have any kind of choke (reactor) or is this something I can whip up as well? For my 180 amp Lincoln, how big of a heat sink would I need for these diodes? I wasn't sure if there was a rule of thumb for diodes not working very hard. I also managed to pick up a couple 125A triacs at Boeing surplus the other day for five bucks a pop. Was wondering how much fun they would be on the input to control the current a little better. Anyone done this?

I used to be an electronics tech many years ago and forgot all the good stuff. Sorta feels embarrassing asking these questions, but welders tend to have issues normally not on common electronics circuits.

Reply to
carl mciver
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The power loss is voltage drop multiplied by average current (in a full bridge rectifier, diodea are conducting half the time).

There are several web calculators that compute power dissipation of a heatsink. For safety, you can always place a temperature switch on the heatsink and use that to signal an alarm if the heatsink overheats.

I went through this with my inverter.

I did that, but I used a commercial SCR controller. I heard some people controlled SCRs using their own PIC.

sci.electronics.design was and is very helpful to me, full of big experts.

i
Reply to
Ignoramus15692

A bridge setup will have 2 diodes conducting half the time, 2 the other half. Effect is to have half the current of average. Voltage drop across each diode is perhaps .75 volt so running flat out at 180 amps would give you 67 watts dissipation for each of 4 diodes. The welder duty cycle won't let you run full amperage continuously so you can derate the heat sink if needed. But keep in mind the response time to heat the diodes is going to be much faster than the response time to heat the core windings.

N> Managed to scrounge up four 250A diodes the other day. Big sumbitches.

Reply to
RoyJ

The Miller Thunderbolt does.

GWE

Reply to
Grant Erwin

Just a followup, it's called a "stabilizer" in the parts list. See for yourself: page 30 in

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If the Lincoln AC/DC tombstone doesn't have one then that's a real serious reason to buy Miller over Lincoln.

I was talking to a guy recently on a ferryboat going across Puget Sound. He's a welder from Illinois who spent his whole life welding on mining equipment. He told me back in Illinois he hardly ever saw a welder that wasn't made by Lincoln. I told him I'd grown up working in Seattle shipyards and around here I was about 30 years old before I ever saw a welder that wasn't Miller blue. Interesting hypothesis, brand loyalty by region.

GWE

Reply to
Grant Erwin

Reply to
RoyJ

I have noticed this effect in tractors, automobiles, and other items. My theory is that it is caused by presence, lack of, or characteristics of dealers, sales reps, etc. for the different brands.

Don Young

Reply to
Don Young

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