High Voltage Forum
Tesla coils => Dual Resonant Solid State Tesla coils (DRSSTC) => Topic started by: oneKone on October 07, 2019, 02:57:57 AM
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Ok....
Originally I was going to document my 4th drsstc, but thinking about it I don't really see the point of another small simple drsstc build. I'm still going to build it, just in the background.
So the coil I'm planning on building!
The secondary form is being donated by a "mining" company. It's 230mm diameter with a fibreglass construction. I'm thinking of a 1:5 ratio which will make the length 1150mm, with a wire diameter of 23awg (temco wire diameter is 0.63 with polyurethane coating).
The MMC will be the same as the capacitors I used in my drsstc 3, expect in a 4p X 4s configuration for overhead.
The bridge, after much hesitation will.be skm400gb-12x. I'm not sure with 124, 125 or 128 as of yet.
I still have a lot to figure out and this is very much early days. This will be the largest drsstc I can build at my house, I'll be right on the limit of the 25a outlet I have.
My basic plan is to get one part of the drsstc each month. Hopefully by the end of this month or the start of next I'll have the secondary wound. The cost of parts when you go large is pretty daunting...
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Since you are not going to document all detailed calculations and drawings, at least take some pictures along the way and post those :)
A SKM400 bridge on a 1 meter resonator is still a pretty big coil, I would not call that "small simple" ;)
It is a pretty large bridge for such a secondary size, what kind of primary current are you aiming for? When you say 25A limit on the mains outlet, that means you are limited to 120VAC@25A? Even 3kW will get you some 2 meter sparks!
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Oh no, sorry. I was originally going to document a small drsstc build with an 80mm X 230mm secondary. But thought this would be a much better build to document. All I've done with the beginning of this post is confuse people 🤦♂️.
But yes. This 230 X 1150 secondary is huge to me! It will be the biggest build of mine to date. As for the primary current I'm thinking of 1300a, the power outlet I have is 230vac @25a.
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Looks like a fun project! If you want to push the limit of your 25A 230V circuit, some form of PFC helps. The PFC doesn't need to be really proper as in commercial power supplies. It just needs to achieve high power factor at max load. Power factor at lower loads doesn't matter if the only goal is maximum power from a circuit.
My first crude flyback PFC produced 450V 13A DC from 240V 60Hz input, for my Marx generator 3 years ago. I fried it last July when it was dialed back to 250V DC output for initial bring-up of my new DRSSTC. It drew too much current (bug caused high duty cycle operation). I built a new isolated resonant converter version (in panic mode) for my DRSSTC. Control circuitry is a bit complex for my liking, however. Now I'm playing with Royer-oscillator isolated PFC options, with only on/off control on each AC line half-cycle. Both versions use gapped ferrite-core transformers with 80-85% coupling factor.
There are probably more standard and robust PFC circuits available. I just have fun designing things, and like the isolation. That allows my DRSSTC circuitry to be ground referenced.
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Cheers for the info @davekni, I'll look I to PFC. Tbh I'm not sure as to what it is at this stage!
Small update:
I've got the pipe and cut the 1300mm required. This upcoming weekend I'll turn the od to have a smooth surface. As it sits the secondary form is the same height as the entire160mm drsstc!
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What is the pipe material? It doesn't look like anything I've seen before.
PFC refers to "Power Factor Correction". Most DC power supplies start with a PFC circuit, taking the line main in and generating a non-isolated bus supply, often around 400VDC. The main switching-regulator circuitry runs on this bus voltage, generating whatever outputs are needed (ie. 12V or ...) with an isolated forward converter or whatever topology is used. The PFC stage attempts to draw current from the line that is sine-wave shaped and in phase with the line voltage (close to 100% power factor). Most PFC converters are boost topology, generating VBus at a voltage above the peak of rectified line voltage.
The purpose of most PFC circuits is to meet regulatory requirements. But they are also useful to get the most from limited line power. A simple bridge rectifier and large bulk cap can have power factor around 60%. At the rated line RMS current, only 60% of the ideal power is available as DC. Inductance on the input can improve the power factor some.
The PFC circuits I've built are very crude. They draw something close to sine-wave current at full power. At lower power, they just switch on and off to regulate output voltage. Not friendly to the power line, but does get maximum power. (Even a constant-current load achieves 90% power factor, much better than the current spikes drawn by direct line rectification into a large bulk cap.)
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sorry for the extremely late reply @davekni.... its fibreglass, from a mining company.
Basically i've been away from coiling for a few months because of the heat in aus, most weeks it was around 40-45c..... so not very fun! With the weather finally starting to cool down a bit (mid to low 30s) i'm starting a comeback.
the only progress i've made has been ordering of the wire. I ended up going for 23awg red, i'll have enough wire for a 5:1 ratio secondary and also a 2:1 smaller drsstc (235 diameter 470mm winding length, maybe it will be time to look into a high on-time coil). One other thing ill start doing is putting up a price for each component/ component group as i buy, i think this will give a better deciding factor if anyone wants to build a large drsstc. One other thing i'm considering is to get a UD+ from philslab, to me the driver looks the part and has some nice additional features over a regular UD driver, not to mention i'll be able to compare it to @profdc9 tht board.
The price for the wire: $183 USD @ 10lbs spool (about $340 AUD landed).
hopefully this update is the revitalisation of the build!
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Fiberglass makes sense now that you mention it, given how it looks. I was just curious - couldn't figure it out myself, so no concern about any delay. Certainly agree that 40+C is not good weather for outdoor activities.
When my employer (Tektronix at the time) was getting out of winding their own magnetics 30 years ago, we could buy the surplus wire for copper-scrap value, $1/lb. Purchased ~50lbs, but have used most of that in up by now. For more wire, I find EBay is a good source. Not sure what shipping would be for you, but here's an example of 23AWG for $10.50/lb with free US shipping:
https://www.ebay.com/itm/TEMCo-Magnet-Wire-23-AWG-Gauge-Enameled-Copper-10lb-6260ft-200C-Coil-Winding/370690945344?epid=1940008221&hash=item564ee6f140:g:X30AAOSwzc1brp-b:sc:USPSPriorityFlatRateBox!97070!US!-1
Hope the weather cooperates for your continued coiling work!
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Woah, $1 a pound is insane! Also temco is my go-to, even with shipping, bad aud to USD and GST it works out way cheaper from what I've found elsewhere, and not to mention the awesome customer service. I ordered almost the same spool as you linked, only in red.
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I think it's time for a small update haha.
Not much has happened with the coil. At this point I'm just looking into cheaper parts, mainly the MMC. There's a brand of capacitor on AliExpress called "dawncap", they provide no data sheet but the voltage and (I'm guessing) the rms current they list are tempting. I'm thinking of ordering one just to bench test it under drsstc use.
I'm also thinking of using profdc9 pulse skip board, again because of price. Originally I was going to go with the ud+, but at over $300 AUD landed I think I'd rather put that into the bus capacitors. From what i last remember it's about $50 AUD to populate a tht driver board.
The one main achievement I've made is that I've wound the secondary! It ended coming out at 1200mm winding length wich is about 1850t. Even just the secondary alone dwarfs my other coils!
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Look at this thread for MMC capacitor options:
https://highvoltageforum.net/index.php?topic=1051.msg7439;topicseen#new