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Tetris

Fri Nov 16 2012, 05:59AM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

If QCW sparks are "safe" to touch, and DRSSTC sparks are deadly, where does your soon-to-be-built coil fall in the "safe" range?

Goodchild

Fri Nov 16 2012, 06:51AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

a positive tempco is a good thing to look for, but it wont just cuase load shedding to the other bridges, it will accerlerate the heating, even at the same or lower power. As for derating, thats your best bet for controlling this situation. over spec the components and under power the system.

You can also back-calculate the thermal resistance from temp rise, and predict your power red line.

This is what we plan to do as I said before. That is why we have 8 bridges, we don't plan to run the snot out of the IGBTs but rather run them at a reasonable leave at a little lower than datasheet spec. For the thermal calculations we have already done this falls well within this operating margin.

A single 3/8" line is a little on the small side, but it is amazing what having a decent pump (a few gpm at 50psi is what I usually see) can do to make up for lack of area on the waterblock. I started out using elaborate waterblocks designed for cpu watercooling, and when I saw the cooling channels in my big laser ( ) I thought it had no chance of working, but the 500w of heat over the roughly 5in^2 of copper/water area is enough and keeps it at about 5 degrees above the water temperature.

In any case it looks like an amazing project, can't wait to see the sparks!

Well that is promising for us considering each bridge only dishes out about 267W in heat at full power. And we have similar pump specs. We also plan to have a radiator system on the coil as well to help keep the water at a little about room temp.

If QCW sparks are "safe" to touch, and DRSSTC sparks are deadly, where does your soon-to-be-built coil fall in the "safe" range?

The short answer is that they would probably not kill you but I'm not willing to stake my life on it considering the massive amount of pulsed power this coil will dish out per burst.

DRSSTC sparks are also not deadly (i'm still living to tell the tale), they just hurt a heck of a lot more. Not entirely sure why.

teravolt

Fri Nov 16 2012, 05:10PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi Eric if you plan to use the fets in a SSOA 100A is at 25C. you could solder some brass studs in a 1/8 copper plate and solder a water jacket around the copper sheet or solder lots of tubing to it

Patrick

Fri Nov 16 2012, 05:38PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

given what "..." siad goodchild might be able to calculate a single holes' surface area and get a high enough thermal transfer with low thermal resistance, with a few GPM. that would be easier than anything else.

but Goodchild, are you using multiple fluid circuits or just one fluid path from you primary to the bridges? are your transistors internallt isolated from the tab or are you using the mica/silicone isolators extrernally?

Intra

Sat Nov 17 2012, 07:49PM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

where you found 10Kv 5.6nF high RMS current MICA caps? google tell nothing about it((

Goodchild

Sat Nov 17 2012, 09:19PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

As for our water cooling design we know that it's not an "optimal" design, but the fact remains we used materials we have on hand. We also don't plan to run the bridges at any extreme levels so out current design fall into the spec we plan to run at.

The MICA caps are from

Jrz126

Sat Nov 17 2012, 10:57PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

Looks good.

Any fancy scheme for driving the gates?

Goodchild

Sun Nov 18 2012, 02:34AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Jrz126 wrote ...

Looks good.

Any fancy scheme for driving the gates?

The gate dive will be GDT but with a twist, because the two sides of the half bridge are not 180 out of phase like a normal DR we will be using two GDTs one for each half bridge. Each bridge unit has it's own driver and OCD circuitry and they all link back to a main controller via a fiber optic link that sends gate dive signals. The main controller has all the circuitry for timing and modulation along with yet another fiber input for an analog input that will be used as the reference to set the overall modulation level.

When we get our final PCBs designed I will update the thread with some photos.

tobias

Mon Nov 19 2012, 04:12AM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Hi Eric

Really nice work!
Are you using SolidWorks? If you are, adding "Exploded Line Sketch" lines can make your Exploded View look even nicer =)

Goodchild

Mon Nov 19 2012, 08:21AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I indeed am using SolidWorks, and I did have the line sketch but it made it look so cluttered.... So many lines for so many parts.

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