Author Topic: My first drsstc  (Read 4823 times)

Offline Mads Barnkob

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Re: My first drsstc
« Reply #20 on: January 29, 2018, 10:35:06 PM »
Cut to size acrylic is often very expensive, I resorted to buying it over ebay from UK, somehow I could get twice as much for the same money. So that possibility is worth checking out!

When you want to calculate primary coils with copper tubing, you just assume it is a solid wire and use the outer diameter. The relatively low skin depth will do that you would not carry any current in the centre of a solid conductor anyway. Brakeline copper tubing is actually a good and "cheap" source of small primary coil :)
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Offline oneKone

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Re: My first drsstc
« Reply #21 on: January 30, 2018, 02:10:34 AM »
For some reason it seems to be the opposite in Australia, eBay seems to be more expensive. eBay aus that is. I'm going to have to abandon the acrylic rod, the shop closes before I finish work so I'll use acetal (natural/white) rod instead.

Cheers for the info about the tube. Calculated it's about 2khz different from your primary coil. This morning the apprentice didn't have much to do so I got him to machine the primary supports. It's exciting times because the coil is getting closer to being finished!




Offline oneKone

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Re: My first drsstc
« Reply #22 on: February 03, 2018, 09:16:07 AM »
So after a few days of messing about the coil is done! I set the theoretical over current voltage by adjusting the reference voltage for the lm311.... It should trip at 350 amps I then ran the coil with an external ct 1:33:33 with a 6ohm burden resistor with current in the 300amp range. I'm going to be doing a few more tests in the next few days just to makes sure I have it set correctly.





Offline oneKone

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Re: My first drsstc
« Reply #23 on: February 03, 2018, 03:10:59 PM »
I've finally had a proper run tonight. It produces about 250-300mm sparks. I'm thinking about getting a 200 or 250mm toroid for hopefully longer sparks, I'm currently using a 160mm toroid. Overall I'm happy!

 I think I might also add a 90mm PC fan. The heatsink doesn't get hot but it would be nice just to have one on a switch.

Video:

Offline oneKone

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Re: My first drsstc
« Reply #24 on: February 04, 2018, 02:35:36 PM »
after a few successful runs i blew up a set of ixgn60n60. i found the problem was that the ocd was not getting triggered at all. after some scoping i found the ct's are not operating correctly, but well enough for the feedback. i'm not sure if I've used the wrong wire as i used what i had laying around. its marketed as tinned hookup wire link: https://www.jaycar.com.au/green-light-duty-hook-up-wire-25m/p/WH3005.

basically i was wondering if there's a specific wire people use, or should i be using something like Ethernet wire (individual strand) for both ct's.

cheers     

Edit:
I'm going to buy some cat5 cable. I've been thinking about it at work, it seems weird that it was all working fine until I started doing some real runs with it. Unless the windings were cut when I made an acetal insulator.
« Last Edit: February 05, 2018, 01:48:23 AM by oneKone »

Offline oneKone

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Re: My first drsstc
« Reply #25 on: February 05, 2018, 02:18:31 PM »
i rewound the ocd ct and tested it, it seems to be working fine... but the ocd does still not work! i remember when i was first setting the ocd theoretical point my probe slipped so maybe that damaged it. so i think for now i'll order a new lm311 just incase i have damaged it. another thing i noticed is that one of steve wards drsstc schematics says "do not set r3 more than 3.75v!" but again i dont know if it was this.

if anyone has any other point for me to test on the board please let me know.

cheers

Offline Laci

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Re: My first drsstc
« Reply #26 on: February 05, 2018, 05:02:38 PM »
Maybe connect a 1-5V PSU to the OCD input and scope the LM311's output.Then change the reference voltage by the potentiometer and see if the output goes high at a higher voltage then the PSU voltage-diodes voltage drop(LM311 input),else low.The OCD LED should indicate this.
« Last Edit: February 05, 2018, 05:10:48 PM by Laci »

Offline oneKone

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Re: My first drsstc
« Reply #27 on: February 06, 2018, 11:11:14 AM »
cheers for the guidance Laci.
i set a reference voltage of 1.5v and set a probe on pin 7, which was always outputting 5v. I then tried 1.5, 2 and 2.5v on pin 3 without the 5v getting pulled to ground (i'm assuming the lm311 output is always high and gets pulled to ground when a voltage is reached above the reference voltage set). I've ordered "a few" from rs components.... they only ship in quantities of 20 for the ones they had for next day delivery. I'm actually looking forward to some smd soldering, i think the last time i done any was when i modded an rc controller.     

Offline Laci

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Re: My first drsstc
« Reply #28 on: February 06, 2018, 11:17:57 AM »
To make sure it really works connect like 3V to pin 3 and change the voltage on pin 2 by the pot.Just measure the voltage on pin 2 and see if it is high at higher voltages then pin 3,low at lower voltages at pin 3.

Offline Mads Barnkob

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Re: My first drsstc
« Reply #29 on: February 07, 2018, 10:05:11 AM »
You had a great MIDI run in that video, a shame that it blew up :)

I was going to mention the OCD voltage setting can not be in the extremes, but has to be somewhere in the middle where it can actually work, but you already found the notes on it in the schematics, good luck getting it to run again :)
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Offline oneKone

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Re: My first drsstc
« Reply #30 on: February 07, 2018, 12:20:14 PM »
You had a great MIDI run in that video, a shame that it blew up :)

I was going to mention the OCD voltage setting can not be in the extremes, but has to be somewhere in the middle where it can actually work, but you already found the notes on it in the schematics, good luck getting it to run again :)

cheers. the song it blew up on was fireflies by owl cities. man that song has some looooooong notes!

so the driver is now fixed! it ended up being the lm311... luckily! Since I've scoped the current draw before i might set the voltage/amp rating on the reference voltage for 300 amps. Steve ward did mention how to setup a voltage to current limit, for what seems to me a "ball park" figure.

Offline oneKone

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Re: My first drsstc
« Reply #31 on: February 07, 2018, 02:11:32 PM »
well...... that was short lived! after a minute run of a midi track it ended. another pair of blown igbts. I think there could be two problems here. I'm not using gate diodes because i'm only driving the gates at 19v and my gdt is a proven one at this frequency, so i thought i didn't need them... or am i just plain wrong?  The other possibility is that i'm using chinese (ebay) ixys ixgn60n60 rather than parts from america.

As i type the american counterparts are about twice the price. china being $13 an igbt and america $26 an igbt.

my logic is to bite the bullet and order from america, and also add the gate diodes.

edit:

so besides on ebay ixgn60n60 don't seem to be stocked anywhere, and from my understanding is that 40n60 are a no-go for a 300khz coil... The one thing i have noticed is that the chinese ixgn60n60 i bought are printed "ixys ixgn60n60" where as the another from china and america at the same price point are printed "ixys ixgn60n60c2d1"

Edit 2:
I've found this listing on eBay that corresponds to the correct price but I'm still unsure as to who is manufacturing these now.
 https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F272782521967
« Last Edit: February 07, 2018, 02:33:21 PM by oneKone »

Offline oneKone

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Re: My first drsstc
« Reply #32 on: February 08, 2018, 04:21:40 AM »
After a while of looking around I ordered two IXGN60N60C2D1 from America.

My question is, should I continue to drive the gates at 19v or should I drive them at 24v.

Offline Mads Barnkob

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Re: My first drsstc
« Reply #33 on: February 08, 2018, 09:09:13 AM »
This is the IGBTs that I bought from Digikey to my DRSSTC1 many years ago, you can see that the markings is on another place, but with so many years passed by, it would make sense that they moved it to the side where you can see it, when the IGBT is installed.

It all depends on your gate drive waveform, if its sloping too much at 19V you should drive it at 24V to get a faster turn on and lessen switching losses.
« Last Edit: February 08, 2018, 09:10:49 AM by Mads Barnkob »
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Offline oneKone

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Re: My first drsstc
« Reply #34 on: February 09, 2018, 02:26:05 AM »
Cheers mads. The ones I bought have the same text as yours as well as in the same position.

I think when I get the new igbts I'm going to double check the gate waveforms, as well as retune the primary. When I was playing midi files the lower notes would trip the OCD. I think I set it up correctly but I'll ask just incase.

 The way I tuned the primary was by moving the tap point until I could achieve the longest sparks I could. I was using a oneTesla interrupter set at 300hz as this seemed to be a decent sounding tone (no logic here!) My understanding is that at lower frequencies my current draw would always be higher and trip the OCD, but at higher frequencies the coil would be in-tune as the spark length altered the secondaries capacitance.

Any feedback would be appreciated


Offline oneKone

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Re: My first drsstc
« Reply #35 on: February 19, 2018, 02:49:59 PM »
the new ixgn60n60 arrived today. they even look better in quality! i done some tests tonight with a weight plate as a load to set the ocd. when running in standard interrupted mode the ocd light comes on when it trips. when a midi track is being played the ocd light doesn't illuminate but the limiting is happening, i'm not sure as to why that would be?

For a ct i used a 33 turn with 5.1ohm burden resistor and 10x oscilloscope probe. at 5v per division this roughly equates to 320amps. I'm not sure yet but i might make a 1:33:33 ct as it would give better resolution for the scope i have.   

« Last Edit: February 19, 2018, 02:53:07 PM by oneKone »

Offline oneKone

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Re: My first drsstc
« Reply #36 on: February 20, 2018, 03:09:13 PM »
So I got a bit of testing done tonight. The tap point has changed by half a turn. I'm more than confident that I was previously running 350-370 primary current with the fake 60n60. I'm now running 330 max with about the same arc length, although it does seem at a longer on time.

So my next thing to check is the maximum on time the oneTesla interrupter has, once I find this I'll be more comfortable running it.

All in all I'm happy it's running again, aswell as the igbts not failing!

Offline Mads Barnkob

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Re: My first drsstc
« Reply #37 on: February 20, 2018, 03:56:06 PM »
Good that you have it running again, as I got mine tuned better and better, the on-time required for maximum spark length went down as expected, but I also seemed to hit a equilibrium where the secondary circuit would accept all power and I was not able to get it above 300 Apeak anymore, so optimum power transfer was achieved or at-least very very close it.
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Offline oneKone

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Re: My first drsstc
« Reply #38 on: February 22, 2018, 12:30:09 AM »
Cheers.

Luckily for me I have your build to reference the on times!
I'm going to use some PCB mount fuse as a simple solution to retune the circuit as I need.

I ran the coil again last night to fault find as I wasn't happy with the performance. I was certain it was interference but it ended up being the OCD. It was limited at 200amps, obviously the cast iron weight plate had more of an affect on the primary circuit. So after a bit of adjustment it's limited at about 310A and seems to be running normal again.

I'm still on the fence about getting a bigger toroid (maybe a 200mm diameter one) I'm interested in seeing if there's a difference going from 160 to 200 but I don't know if I can justify the purchase!

Offline Mads Barnkob

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Re: My first drsstc
« Reply #39 on: February 22, 2018, 10:59:47 AM »
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Re: My first drsstc
« Reply #39 on: February 22, 2018, 10:59:47 AM »

 


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