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LAN_403

HV Enthusiast

Fri Jul 18 2008, 02:25AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Ultra7 wrote ...

Austin wrote ...

yup thats what i used... however u might have some issues finding some good wired to put on MMC where there is no cap.

I used a paper clip.

Don't use a paper clip. These are made of steel which is not very good. It will get very hot, and fail open.

Use a piece of copper busswire, or solid core wire.

Rollingblackout

Sat Jul 19 2008, 08:06PM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

I'm testing the operation of my 1/2 bridge. testing up to this point has been correct. I have channel 1 on the out put of the 1/2 bridge and channel 2 on the dc neutral connection. Both channel 1 and channel 2 grounding leads are connected to one another and nothing else. Im using a 555 time on the current feed back input. and an advanced modulator on the ext mod input at 250us pw and 100khz pf.

On the scope I only see positive output no negative swing at all.

I expected to see a positive swing with an opposing wave of the same magnitude.

Does this indicate a blown igbt on the negative side?

HV Enthusiast

Sat Jul 19 2008, 08:48PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

I think you might have some things set up incorrectly.
Your 555 time on the current feedback should be set for the resonance frequency (i.e. 100kHz, 50% duty), and the modulator should be set for 100Hz, not 100kHz.

The modulator pulse (250us) should bracket a bunch of the 555 pulses. If the 555 is running at 100kHz, then you should have 25 pulses (10us period) for each burst which occurs every 10ms.

I think this is your problem, as im only seeing a single pulse here.

Rollingblackout

Sat Jul 19 2008, 08:58PM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

Im not very skilled with an O scope yet maybe I was zoomed in to fare.

Here is a shot of a sample take with channel 1 on the pos igbt gate terminal and channel 2 on the neg igbt gate terminal.

Rollingblackout

Sun Jul 20 2008, 02:16AM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

As much as I hate to smoke things due to simple lack of knowledge of the components I am using, I assembled the rest of the miniBruts and lit it off.

Time to look into the tuning section of Mr. McCauley's book.

HV Enthusiast

Sun Jul 20 2008, 02:26AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Rollingblackout wrote ...

Im not very skilled with an O scope yet maybe I was zoomed in to fare.

Here is a shot of a sample take with channel 1 on the pos igbt gate terminal and channel 2 on the neg igbt gate terminal.

The polarity is definitely correct. The waveforms look a bit funky, but that could be just an artifact of the oscilloscope - not sure.

Anyways, it looks like you got output, so that means its working. Now the fun part and doing all the fine tuning!

Rollingblackout

Sun Jul 20 2008, 03:47AM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

Im not real impressed with the output. I have experimented with the primary tap and it occurs to me that the impedance of the primary is greatly influenced by the cable being used to make the tap and the tap onto the primary it's self. Is it advisable so rewind the primary so that it contains only the optimal number of turns on it. This would be a little difficult to re bend the copper and another hole through the deck would be required.

HV Enthusiast

Sun Jul 20 2008, 05:29PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Without actually seeing the coil in operation, i can't say for sure if the output is what you would expect given the input conditions (voltage, etc...)

Rollingblackout

Sun Jul 20 2008, 07:52PM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

Currently my input voltage is limited 114 vac. I'm using copper foil strap to tap the primary at exactly 5 turns. Any wire simply diminishes performance. Advanced modulator at the largest pulse width from the stock build and the highest pulse freq. the output arcs to a RF grounded object are 19 1/2 inches. and the current on the primary is right at 400 amps.

The in put voltage is below spec of 140 vac. Maybe that is the next place to tune.

HV Enthusiast

Sun Jul 20 2008, 08:18PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Rollingblackout wrote ...

Currently my input voltage is limited 114 vac. I'm using copper foil strap to tap the primary at exactly 5 turns. Any wire simply diminishes performance. Advanced modulator at the largest pulse width from the stock build and the highest pulse freq. the output arcs to a RF grounded object are 19 1/2 inches. and the current on the primary is right at 400 amps.

The in put voltage is below spec of 140 vac. Maybe that is the next place to tune.

Not sure why wire would diminish performance much. Thats sounds weird.

For Adv Mod, i wouldn't push longest pulsewidth. Keep it as short as pulsewidth possible. There should be a point when you increase pulsewidth where the arc doesn't get any longer. This should be your "sweet" spot. Any additional pulsewidth just makes the arc fatter and consume more power which you don't really want at this point. Also, PRF should be kept around 100Hz. I wouldn't go above that.

Tuning is definteily the next step. 19 inches is an excellent starting point. Remember, DRSSTCs are like finely tuned automobiles. They take a lot of work to get properly tuned (playing with coupling, tuning, etc...) until you find the sweet spot.

With tuning, its going to be a trade-off between maximum arc and maximum current. (See my paper on tuning or in the book on advanced tuning)

My minibrute puts out up to 48" arcs easily. But it took a long time to get the right tuning point. The tuning point in the book was my sweet spot, but unfortunately, no secondary / tororoid / etc... is exactly the same so there is always variacnes and the need to fine tune.

But you're on your way. Just take your time, tune at low power, and proceed slowly.

Remember, using an extension cord from your wall outlet to the variac will definitely improve reliability without sacrificing performance. Acts as a ballast somewhat and protects the coil from power arcs to ground (limits peak currents during these conditions)

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