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DRSSTC Build again

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colin heath

Wed Jun 27 2007, 04:02PM

Registered Member #123 Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162

Hi All,
on a mission to build another DRSSTC. I have finished the interrupter this weekend and will post pics of other bits as i finish them. This thing will be driven my half bridge of 200A igbt bricks running at 600VDC.

Cheers

Colin

Part Scavenger

Wed Jun 27 2007, 05:08PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

HEY! You stole my jeweling idea!!! =P I like the size. What size did you go with 3/4? I did mine with 3/8 and it was a nightmare!!! What are you using for brush/grit?

colin heath

Wed Jun 27 2007, 05:48PM

Registered Member #123 Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162

Hi,
I used around 3/4 and it was an attachment for a dremel at my local model shop with about 80 grit sanding disks. I f i did again i would buy the proper jeweling tools as they are a rubber type grit compound that gives a more even finish

Part Scavenger

Thu Jun 28 2007, 10:44AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

I've had pretty good results with leather on a dowel soaked overnight with oil. Also, you might try some synthetic steel wool pads cut in a circle loaded with grit, that works really well for large circles, but the edges are not as defined. I use valve compound too if that makes any difference. I don't remember the exact procedure, but I plan to do some this afternoon actually or tomorrow, so I'll post back.

colin heath

Sun Jul 01 2007, 06:23PM

Registered Member #123 Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162

Hi All,
Here are a couple of pics of my mmc finished. 320nF measured 6KV. All mounted inside tube.

next up is the base and primary coil which i hope to finish next weekend.

cheers

colin

Steve Ward

Sun Jul 01 2007, 10:46PM

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

I hate to mention it now, but i never thought the idea of enclosing an MMC in a box was very good. My MMCs tend to get rather warm and id want them to have the best heat dissipation as possible so i leave them in the open (often times with airflow over them). I really dont know how much it matters for short runs, but for long run times (several minutes maybe) the heat does build up a lot.

EDY19

Sun Jul 01 2007, 11:49PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
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Posts: 408

I'm not sure if you filled the MMC with any type of foam or anything, but if the capacitors aren't packed too tightly, you could always stick a small muffin fan in each end to get the air moving over the caps a little

Tom540

Mon Jul 02 2007, 06:12PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

Or maybe fill it with oil? Of course the oil might get warm after awhile.

colin heath

Mon Jul 02 2007, 07:36PM

Registered Member #123 Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162

I will run it till it melts then build it properly

No really I will probably duct air through the tube from an extract fan which will help.

Thanks for the tips guys.

Colin

Part Scavenger

Thu Jul 05 2007, 03:43AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

In no way is this a "mine is better than yours" post. I think you're awesome, and that's that.

Check it out. I've tried a million different ways to do that jeweling pattern. Smaller (less than 1/2") is much easier to do. But it will drive you INSANE. The larger ones tend to be "dark" in the middle due to the large difference in speed between the outside and the inside of the circle and the grit tends to creep outward. The smaller ones perform best with either a brush, or a plug of leather attached to a dowel that is soaked overnight in motor oil. I use 100 grit valve compound because it was handy, plenty of oil and run at the highest speed that won't fling it all over the place. That's for small stuff.

For the larger stuff, the leather or rubber dies in the middle and you usually don't notice until it's waaaay too late. Secondly, I've noticed that the middle dries out much more quickly and tends to send "pills" of grit outward and ruining the circle. Therefore, you need something like a jeweling brush. But I have had very good luck with synthetic steel wool pads glued to a dowel. Do not use grit, and use plenty of oil. Speed is a bit lower.

The dark spots and uneven sanding on your piece are caused by two things. First it is that the 80 grit sandpaper that you are using is attached to a dowel or hard surface I'm guessing. You need something that will "caress" the metal and work with it's unevenness. Sandpaper also clogs especially on aluminum and is totally frustrating!!! Second and most important, IT IS EXTREMELY important to polish the metal beforehand. Talking close to mirror polish, no kidding. You cannot imagine the difference it makes until you do this. The dark spots on the circles all but go away unless you're having the "pill" problem I was referring to. The dwell time of your grind is not nearly as important either, in most cases it can be much shorter.

Anyhow, I hope you have fun with it! For a while just about every scrap piece of metal I had around had little circles on it... =P

Here is a pic of some steel I pulled out of a printer yesterday. 3/4" circles, 10sec dwell time, synthetic steel wool. Steel was polished to the "brown" grit with a buffing wheel prior to jeweling. I can't remember what grit# that is, but it should be all over the net. On nicer metals it is best to go finer before jeweling, but this steel wasn't going to polish any nicer due to quality.

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