Author Topic: Skm100 coil  (Read 584 times)

Offline oneKone

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Skm100 coil
« on: December 18, 2019, 04:48:35 AM »
Originally I wasn't going to post this coil, I thought it was just another coil, or not very interesting... Bit that's what this forum is about! It's convenient to post random pics and vids on Facebook but information does get lost there.

Scope of the coil:
Fullbridge of Skm100gb125
Epcos 4700uf 400v bus cap
MMC: 2 X kemet 220nf 3kv snubber capacitors in series
Driver: Profdc9 tht ud2.7c
Secondary is still up in the air.

*Incomplete post, just to save*






« Last Edit: December 18, 2019, 04:52:23 AM by oneKone »

Offline Mads Barnkob

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Re: Skm100 coil
« Reply #1 on: December 18, 2019, 09:43:46 AM »
Thank you for sharing, there is many small and interesting details in putting things together that is always nice to see!

At first I could not see it was two snubber capacitors bolted together, I thought it was some kind of primary tap clamp until I saw it was solid filled boxes :)

What kind of current limit are you planning for this? SKM50-200 have historically been running at some 350-700A ( http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/ and https://4hv.org/e107_plugins/forum/forum_viewtopic.php?85229 )

Would you consider making another thread about your CNC router? Laboratories and Tools needs some content :) https://highvoltageforum.net/index.php?board=29.0
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Offline Hydron

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Re: Skm100 coil
« Reply #2 on: December 18, 2019, 09:49:19 AM »
I have run SKM200GB125s up to maybe 700A (without any failure). They switch very fast and clean, if the 100s are the same or better you'll likely be able to run quite high frequency if needed (I have done over 300kHz, albeit for a short test only!)

Offline oneKone

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Re: Skm100 coil
« Reply #3 on: December 18, 2019, 10:02:55 PM »
cheers @mads. tbh i think it would have been selfish towards the community not to share. there's so many documented TO-247/cmX00 builds, not so many skm builds. I'll most definitely post about the router, i'll also link to the parts.

also to @mads and @hydron,

I have two secondaries i'm going to try. The first is the one pictured, its 80mm diameter X 230mm winding length with 0.14mm wire (i think it was 170khz loaded). The second is 110mm diameter, 305mm winding length with 0.3mm wire (with a very rough calculation to be around the same frequency of the first coil). So far I've set the ocd to 500a, initially i think i had the ocd set around 600/700a as the primary was heavily detuned to get maximum streamer length, the only problem with this was i had a pretty hard time with racing sparks. I think with the 80x230 coil i got 660mm streamers, with the 110x305 it was 770mm (not really tuned at all, and running 150v ac). To me if i continued being haphazard i would have killed the bridge.

To the bridge! they're also aliexpress switches! they cost $27AUD  (around $18USD). So far they've been rock solid, and awesome thermally.   

Offline Weston

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Re: Skm100 coil
« Reply #4 on: December 19, 2019, 06:44:05 AM »
The CNC'ed base looks really nice!

What is the part number for the MMC capacitor? It looks rather undersized and I am a bit dubious about it's ability to withstand a high peak current or modest repetition rate.

Offline oneKone

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Re: Skm100 coil
« Reply #5 on: December 19, 2019, 08:02:20 AM »
The CNC'ed base looks really nice!

What is the part number for the MMC capacitor? It looks rather undersized and I am a bit dubious about it's ability to withstand a high peak current or modest repetition rate.

Cheers,
This is the data sheet for the capacitors:
https://docs.rs-online.com/5fa1/0900766b81524bec.pdf

During testing I've noticed no heating from them, I like to think I'd notice heating from the caps before failure.

Offline oneKone

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Re: Skm100 coil
« Reply #6 on: January 06, 2020, 04:06:28 AM »
Some time has past but there is still much to be done!

After my last quote of "I've noticed no heating from them" (the MMC) I started to notice heating, and the data sheet confirms why.... The most simplistic fix was to just order 2 more capacitors and have a 2p2s MMC. This did change the capacitance by double (going from 110nf to 220nf) but a higher amp rating.

The next part I need to change is the topload as it's too small now, i think I'll order a 300mm toroid in a couple of weeks. Aside from that I've upped the OCD from 500 to 600, the extra 100a really has helped streamer growth!

 I'm now getting 670mm streamers to a pole. At 180khz i feel like I'm abusing these skm100s, but they're taking it! I think once I have the toroid I'll get some temperature readings with the bridge, atm the bridge is passively cooled but I will be switching to active cooling.



Offline milkman2046

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Re: Skm100 coil
« Reply #7 on: January 06, 2020, 08:02:05 AM »
This coil looks great! It looks exquisite!

What is the frequency of this coil?

Offline Mads Barnkob

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Re: Skm100 coil
« Reply #8 on: January 06, 2020, 10:38:05 AM »
I have two secondaries i'm going to try. The first is the one pictured, its 80mm diameter X 230mm winding length with 0.14mm wire (i think it was 170khz loaded). The second is 110mm diameter, 305mm winding length with 0.3mm wire (with a very rough calculation to be around the same frequency of the first coil). So far I've set the ocd to 500a, initially i think i had the ocd set around 600/700a as the primary was heavily detuned to get maximum streamer length, the only problem with this was i had a pretty hard time with racing sparks. I think with the 80x230 coil i got 660mm streamers, with the 110x305 it was 770mm (not really tuned at all, and running 150v ac).

80mm diameter X 230mm winding length with 0.14mm wire would have a impedance above some 60-65 kOhm
110mm diameter, 305mm winding length with 0.3mm wire would have a impedance around the magic 50 kOhm

I would naturally prefer the latter, also for its height, so that you do not limit spark length because it all goes to ground.

After my last quote of "I've noticed no heating from them" (the MMC) I started to notice heating, and the data sheet confirms why.... The most simplistic fix was to just order 2 more capacitors and have a 2p2s MMC. This did change the capacitance by double (going from 110nf to 220nf) but a higher amp rating.

If you want to maintain the impedance of the system, you would need 8 capacitors in total, for 110nF, 2p4s. Now that you have lower impedance system, you should aim for shorter on-time and higher primary current to utilize the new configuration. Since you do worry a bit about the primary current, going back to 110nF and a higher impedance system, you could run longer on-time and lower primary current.

The picture of your sparks is lovely, love it :)
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Offline oneKone

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Re: Skm100 coil
« Reply #9 on: January 07, 2020, 06:25:30 AM »
@milkman2046
Cheers,
I think it's about 170-180khz loaded.

@Mads
You know it's bugged me since I wound it! I think when I order wire for the big coil I'll also order wire for this coil, I'll get a diameter to suit the 80mm diameter, but have the coil at a 4:1 ratio.

Offline AstRii

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Re: Skm100 coil
« Reply #10 on: January 08, 2020, 04:54:44 AM »
Those are some nice streamers, yet i couldn't not notice you're running it with no shielding on the driver. Don't you have any problems with noise generated by the sparks?

Offline oneKone

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Re: Skm100 coil
« Reply #11 on: January 08, 2020, 07:42:56 AM »
Those are some nice streamers, yet i couldn't not notice you're running it with no shielding on the driver. Don't you have any problems with noise generated by the sparks?

Cheers,
As for noise problems not yet. I've run all of my drsstc without the driver being shielded. I think bits more of a risk of a streamer hits the driver and risking the driver and/or igbts.

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Re: Skm100 coil
« Reply #11 on: January 08, 2020, 07:42:56 AM »

 


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