SOAR confusion

My little 5-watt surface-mount wirewounds are doing fine, pulsing at

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Buzz McCool <Buzz snipped-for-privacy@Yahoo.com wrote: |----------------------------------------------------------------------------| |"[. . .] One company I worked for had a safety engineering | |group that I could never pin down to give me an answer what the rules were."| |----------------------------------------------------------------------------|

Rules must be consultable! I empathize. (S.

A carefully constructed 50 year-old experiment is likely to be more informative than an "experiment" cobbled together by somebody who doesn't know enough about what he is doing.

Using a part in a way for which it wasn't designed is always a crap-shoot. Spreading load over a larger area of thick film might well have prevented long term degradation.

. . . . otherwise you'd not be discussing device body and mounting surface roughness, alone.

It's measurable. Use soft thin copper.

RL

The 35 watt thickfilms died in hours.

The 5 watt wirewounds have gobbled up about half a billion pulses so far, at 3600 watts, and nothing seems to be happening. This is boring, but I guess good parts are boring.

It would be tough to overdesign here. I'd need to use 5000 watt resistors. Not cheap.

What are you designing lately?

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Not all that expensive if you make them yourself. Slate bars for the insulators and lengths of threaded rod for the frame are relatively cheap. For production you could wind them on an adapted scrap lathe but even if you have to wind them by hand, they don't take very long to make.

Mounting them in a ventilated cabinet would be the expensive bit.

Yea, 2 cheap electric heaters will do:-)

Did you say you were using 2x FETs in parallel? That's an overdesign of the datasheet SOAR.

What are you using for a power source? That's liable to go next.

But you didn't make any attempt to work out what they could have survived. What you needed to do was to work out the peak power level that did produce micro-cracking, and stay below that

It is always dead easy to over-design. Design is doing with one dollar what any fool could do with two. You certainly don't need to specify resistors that are good for 5 kwatt continuous dissipation to cope with

Anything John Larkin could copy?

The PCB is 2" x 3.2". It's a 100 amp laser driver, and there's a lot more stuff than these resistors. The capacitors are the real space hogs. Summer intern project.

We may have two versions, one with a tiny fan for high duty-cycle cases.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Sure I did. I stepped up the supply voltage.

Sounds like nothing. That's OK, but you spend a lot of time whining about actual electronic design. That's sad.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

But you haven't specified where the threshold is. Your test for micro-cracking seems to be a persistent and increasing shift in the measured resistance of the device under test, but you haven't been all that specific about that either.

What I complain about is the absence of any element of rational design in the "designs" that get presented here. That is sad.

What you are whining about is the absence of the flattery you seem to think you deserve for the images of the stuff you present here that think you have "designed". That's not sad - just pathetic.