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LAN_403

HV Enthusiast

Sun Dec 19 2010, 02:30PM

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

BryanD wrote ...

I'd like to thank Dan for all you've done and everything you've made available, it's greatly appreciated. This site was also very helpful. There's only a couple questions I have before completing the build:

1) In the addendum it states that the thermal sensor (LM35) is no longer suggested. What is the reasoning behind that?

2) Also, concerning the caps on the PVC pipe for the secondary support, the CAD drawings show them to have a diameter of 4.5" which would put them resting on the pipe. However, the picture diagrams all show the caps to be inserted inside the pipe. I'm figuring that the extra 1/4" added to the secondary support would make a big difference in it's position in relation to the primary. I'm not sure which way to go with that, to put them on the outside or inside the PVC pipe.

If anybody could clear those things up for me, it would be greatly appreciated.

Great questions. Anyways, the thermal sensor isn't needed because in actual practice, the sensing point (provided you use a good heatsink with fan cooling), the heatsink is never going to get warm. It was sort of a nice to have in the beginning intitially, but ended up never using it.

Also, another great catch! I'll have to add that to the addendum. That is just a misprint. The diameter of the end cap should fit INSIDE the PVC pipe.

BryanD

Sun Dec 19 2010, 08:46PM

Registered Member #3528 Joined: Sun Dec 19 2010, 12:44AM
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Posts: 14

Thanks for your timely response, and clearing that up for me. I had a personal goal set to have first spark by the new year, but it's looking like it may be a week or two later. I'm trying to learn EVERYTHING as I go along so it's taking a little longer than it should. I figure that considering what I'm working with, I don't want to be guessing on anything, and it will make my design process for the audio modulation a bit easier.

If you didn't mind clearing one more little thing up for me. I went ahead and constructed my own torroid, using two pie plates, a length of dryer duct, and aluminium tape. Since I couldn't find a smaller size pie plate, the total diameter is a few inches bigger than your design calls for. However, from what I understand, the torroid is basically acting as a sort of capacitor, and the size of it would just determine how fast it charges and discharges, making a difference of only milliseconds. Am I out in left field on this one, or am I on the right track?

HV Enthusiast

Mon Dec 20 2010, 01:10PM

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

BryanD wrote ...

Thanks for your timely response, and clearing that up for me. I had a personal goal set to have first spark by the new year, but it's looking like it may be a week or two later. I'm trying to learn EVERYTHING as I go along so it's taking a little longer than it should. I figure that considering what I'm working with, I don't want to be guessing on anything, and it will make my design process for the audio modulation a bit easier.

If you didn't mind clearing one more little thing up for me. I went ahead and constructed my own torroid, using two pie plates, a length of dryer duct, and aluminium tape. Since I couldn't find a smaller size pie plate, the total diameter is a few inches bigger than your design calls for. However, from what I understand, the torroid is basically acting as a sort of capacitor, and the size of it would just determine how fast it charges and discharges, making a difference of only milliseconds. Am I out in left field on this one, or am I on the right track?

The extra few inches could affect the tuning somewhat, as yes the topload does act as a capacitor which affects the resonant frequency.

As long as you retune everything with the slightly larger topload you should be fine, just keeping in mind the tuning point shown in the design will not be optimum anymore.

For toploads, I simply use 4" corrugated heating duct with a plywood center. Makes the perfect size.

Ruben

Tue Dec 21 2010, 04:11AM

Registered Member #3263 Joined: Sat Oct 02 2010, 04:43AM
Location: Sydney, Australia
Posts: 34

Here is my 230V power supply schematic for those wondering, should work great when the load is symmetric

I'm in Australia, so I definitely was! however this thread:

seems to suggest another configuration (connecting the primary return to the DC bus negative rail and a single bus capacitor). I'm confused as to how this would work for a half bridge.

Can anyone clarify, and/or provide consensus as to the best practice for those on 240V.

johncohn

Mon Dec 27 2010, 08:55PM

Registered Member #1848 Joined: Sat Dec 06 2008, 03:24AM
Location:
Posts: 15

Hi friends
I finally had time this holiday to finish up my minibrute build and got to testing. I had first light last night.. Looked very good and strong !. I was beginning to tune this morning at low power (~200 A) when the discharge failed. I heard a sizzle of sorts and smelled burning plastic.. I immediately shut down and did a search for heat. The only thing hot was the middle cap in the primary cap stack. I did a cautious re-power.. got no discharge on my breakout point, but , heard the same sizzle and backed down immediately. Again the cap (c104 0.33uF, 2kv ) was getting hot. I ohmmeter tested the bridge and it seemed fine. as did everything else I spot checked. I used a cap bridge in circuit and found the middle cap was indeed not measuring like it's brothers c103 and c105. I unsoldered one lead form all three and measured them. c103 and c105 were within 5% of the 0.33uf spec. C104 has a resistive short (about 22k). I was doing the test without the fan on.. as suggested.. but only was doing bursts of a few second. I don't think that was the reason for the heating. Is it possible that the cap was just bad ?

Has this happened to anyone else ? Any suggestions on other things I should check that could have lead to that cap's failing.. or could have been taken out when the cap failed ? Any suggestions appreciated !
-jc

ps. Hope everyone's having a happy holiday !

SunWind

Tue Dec 28 2010, 10:26AM

Registered Member #3482 Joined: Sun Dec 05 2010, 11:04AM
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Posts: 2

Can anyone clarify, and/or provide consensus as to the best practice for those on 240V.

I can't say is my circuit the best way to do it but it clearly works! It has a same principle than the original in the book but it doesn't double the voltage. It also takes less current so 10A fuse can be used. I made my half-bridge as described in the book using FGH50N6S2 IGBT's and replaced VR105 and 106 with 20V TVS diodes, havent blown any components so far ;)

BryanD

Fri Jan 14 2011, 09:38PM

Registered Member #3528 Joined: Sun Dec 19 2010, 12:44AM
Location:
Posts: 14

I was wondering about a couple things. I know that contrary to the schematics, the feedback CTs should be sampling the current from the primary rather than the secondary, but not sure where they should be ideally placed. There's this picture from Austin, is that a good place for them?

Austin wrote ...

Also, c101 calls for a 4.7uF cap, but I was sent a 4.0uF. Could this be used in place, or should I order a 4.7uF?

Edit: Sorry, I should have done more research before posting. I found my own answers :P

Thanks again!

johncohn

Sun Jan 16 2011, 12:43PM

Registered Member #1848 Joined: Sat Dec 06 2008, 03:24AM
Location:
Posts: 15

Folks,
Making progress !. I'm now about to commence tuning. I have a good strong 10" discharge .. but I'm a little scared to take it above about 40% on my variac before I have my fine tuning done. . I'm a little confused as to what would make a good tuning procedure. I chose the primary tap point by first finding the series resonance frequency of the secondary and toroid, then took that frequency and found the parallel resonance point for the primary in parallel with the primary cap. I've never tried to fine tune a SSTC like this before. if it were a disruptive coil I'd just start walking the tap point left and right by 1/4 inch increments and find the paint of maximum spark would that work here ? How do people usually tune these things ?

Thanks again for any help !
-jc

BryanD

Thu Jan 27 2011, 05:18AM

Registered Member #3528 Joined: Sun Dec 19 2010, 12:44AM
Location:
Posts: 14

So I got everything put together and wired. It made my heart warm seeing it all pieced together for the first time. I'm now going over everything with a fine tooth comb to make sure EVERYTHING is correct. Once I'm done that I'll be ready to start testing. I read the testing chapter, and it made another question arise.

Although it may seem common sense to some, I'm a bit unsure. The question is about the primary tap for tuning. Right now I have both ends of the primary going trough the base, and my two leads soldered to them. I'm assuming I need to desolder the lead going to the top of the primary, and tap off the at the appropriate place on the coil itself using something like a grounding clamp or something. Or can I just jumper from my soldered lead to the tap point?

Again I'm sure this is common knowledge, since it hasn't been asked before, I just want to make sure. It's down to the wire now, I got 2 months to get it completed and have my audio modulation circuit designed. Hoping for smooth sailing. :P

Thanks again, in advance.

HV Enthusiast

Wed Feb 02 2011, 12:32PM

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

BryanD wrote ...

So I got everything put together and wired. It made my heart warm seeing it all pieced together for the first time. I'm now going over everything with a fine tooth comb to make sure EVERYTHING is correct. Once I'm done that I'll be ready to start testing. I read the testing chapter, and it made another question arise.

Although it may seem common sense to some, I'm a bit unsure. The question is about the primary tap for tuning. Right now I have both ends of the primary going trough the base, and my two leads soldered to them. I'm assuming I need to desolder the lead going to the top of the primary, and tap off the at the appropriate place on the coil itself using something like a grounding clamp or something. Or can I just jumper from my soldered lead to the tap point?

Again I'm sure this is common knowledge, since it hasn't been asked before, I just want to make sure. It's down to the wire now, I got 2 months to get it completed and have my audio modulation circuit designed. Hoping for smooth sailing. :P

Thanks again, in advance.

Hi Bryan,

Thats an excellent question. If you have built everything exactly to the dimensions provided including secondary winding (height, diameter, winding length), primary winding, toroid, size, etc..., there should be no need to tune the coil. The only reason to tune to the coil would be if you used something different, like different toroid size, etc...

Also, with regards to the capacitor part number question. Some of the capacitors we use are MIL-SPEC M39014 type capacitors. If you download any of our other instruction manuals (i.e. Class-E, SSTC 1.0, etc...) the last two pages of the manual includes an M39014 capacitor cross-reference.

I hope this helps! Good luck with your project!

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