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20KW DRSSTC

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Steve Ward

Wed Apr 04 2007, 10:46PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Why would a 20kW input not be impressive compared with 20kW output? Even if efficiency isnt that great, then would you say a 25kW input (20kW output) DRSSTC is impressive? Or have we all missed the point?

Dr. Drone

Thu Apr 05 2007, 12:01AM

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HV Enthusiast

Thu Apr 05 2007, 01:01AM

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Steve Ward wrote ...

Why would a 20kW input not be impressive compared with 20kW output? Even if efficiency isnt that great, then would you say a 25kW input (20kW output) DRSSTC is impressive? Or have we all missed the point?

Because input power is a very poor way to characterize a system unless you state efficiency as well. For example, I could take a mini-DRSSTC, load it down with lots of losses, and have 20kW DRSSTC.

I'm not saying 20kW is not impressive, but i think we need a bettery way to actually characterize the output power capability of a DRSSTC other than input power.

hvguy

Thu Apr 05 2007, 03:36AM

Registered Member #289 Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154

Thanks again Chris. I hope I don't have to keep tweaking this thing to keep it running; not that I mind that much but there just doesn't seem to be any reason why the system can't work right 100% of the time.

Dan, youâ€™ve got a good point about power measurement. I can assume, based on my experience with other switchers, what the primary efficiency of this system is. However I have no real way of knowing what the line to arc efficiency really is. As far as I know no one does. Any ideas?

I did some testing on IGBT over voltage strain. Here is a short write up:

Ken M.

Thu Apr 05 2007, 03:51AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
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Very Nice,

Steve Conner

Thu Apr 05 2007, 08:13AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I never bothered that much about the distinction between input and output, for the reasons mentioned. Our IGBTs and tank capacitors must be fairly efficient because they would catch fire or explode if they weren't. So if you can get 20kW to go into something, and it stays in one piece and sparks come out, I am impressed. Dan's afore mentioned mini DRSSTC would be a flaming stain on the bench in about 10 seconds.

As for how to measure the input power, the only real mistake you can make is measuring line voltage and line current into your coil, multiplying the two, and calling it "kW". The poor power factor of a rectifier with big filter caps leads to an inflated reading. You should say "kVA" unless you used a true power meter like a Kill-A-Watt. Aron mentioned power factor, so I assume he did this.

If you don't have one, you can measure DC bus voltage and DC bus current (average with a moving coil meter) and multiply them to get the power in kW.

Marko

Thu Apr 05 2007, 12:26PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

The biggest error with such a conclusion would be if we measured apparent power instead of effective power, but regarding power dissipation I agree with Steve as none could allow himself to disspiate large fraction of input power and live, especially on coil this big...

If that really is still controversal, could the coil be just called 16inch DRSSTC, or 20' arc DRSSTC?

Steve Ward

Thu Apr 05 2007, 07:57PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

That was an *excellent* test Aron! Only one problem, it doesnt apply to the bricks we use. But, that really is astounding to see it avalanche with no ill effects, especially since the dissipated power eventually got to 150W! It was a simple test but revealed much about the behavior of those smaller IGBTs.

When i go home this weekend, i will grab up my "half-dead" CM300DY-24H IGBTs and do a similar test when i can get some time. I will have to build a quick voltage divider for my scope to read the 1.2kV+ spikes. I will aim to re-create the 10MHz switching noise that i saw on my bridge. Of course, if you could perform this test, it would likely happen much sooner (university leaves me little spare time).

Finn Hammer

Thu Apr 05 2007, 09:28PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Steve Ward wrote ...

But, that really is astounding to see it avalanche with no ill effects,

Would someone pls. explain, or point to an explanation of IGBT avalanche.
I suppose the effect of it is seen on the scope traces, where the voltage flattops, and it appears that the IGBT takes on the action of a tranzorb. Perhaps even, there is a built in tranzorb in those little critters?
Anyone?

Cheers, Finn hammer

Marko

Thu Apr 05 2007, 09:47PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Pretty much all semiconductors will avalanche when their voltage rating is exceeded to a limit.
Some that are 'avalanche rated' have an energy rating they can eat up without harm, some have no such rating.

Various TVS are either beefy zeners or avalanche diodes, with main difference of avalanche effect having a positive tempco, while zener having negative.

TVS just have the job of removing the avalanche effect from the IGBT onto themselves.

I'm curious to see how will various IGBT's (avalanche rated and unrated) behave in these conditions.. If 40N60 could dissipate 150W from avalanching alone I actually wouldn't be much of concerned with that problem!

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