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wrote ... Yeah no wonder you're tripping the breaker! That primary will draw >50A! (though I'm wondering how you calculated the primary impedance if you can't measure frequency or inductance). I don't have a LCR meter either, but modeling in JavaTc does a good job of determining rough low frequency inductance, and from there you can calculate impedances at various frequencies; Xl = 2PiFL.
Oops, I feel like an idiot. I thought impedance meant resistance. I'll try JavaTC.
No worries, you weren't really wrong. Resistance is a form of impedance. Impedance = resistance and/or reactance. Impedance is measures in Ohms as well, so that adds to the confusion.
I generally start at 10turns of 10ga on a 4.5" form for primaries; this yields about 15Ohms at around 200KHz iirc. You can still get a LOT of power through 15Ohms without popping standard breakers but I'm on 120V service (180V DCbus). If you're in 240V land you probably want around 30Ohms impedance as a good starting point.
I generally start at 10turns of 10ga on a 4.5" form for primaries; this yields about 15Ohms at around 200KHz iirc. You can still get a LOT of power through 15Ohms without popping standard breakers but I'm on 120V service (180V DCbus). If you're in 240V land you probably want around 30Ohms impedance as a good starting point.
Thanks.
EDIT: I switched it to 11.5 turns primary, ~2.75" form. Still tripping the breakers, and I noticed a puff of smoke coming from something, probably a MOSFET. :(
JavaTC gave me this, btw (4 turns):
J A V A T C version 13.2 - CONSOLIDATED OUTPUT
Wednesday, January 15, 2014 4:08:09 PM
Units = Inches
Ambient Temp = 68°F
----------------------------------------------------
Surrounding Inputs:
----------------------------------------------------
10 = Ground Plane Radius
0 = Wall Radius
0 = Ceiling Height
----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_BARE
2 = Radius 1
2 = Radius 2
0.5 = Height 1
11.5 = Height 2
932 = Turns
30 = Wire Awg
----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
2.75 = Radius 1
2.75 = Radius 2
1 = Height 1
1.6 = Height 2
4 = Turns
26 = Wire Awg
0 = Ribbon Width
0 = Ribbon Thickness
0 = Primary Cap (uF)
0 = Total Lead Length
0 = Lead Diameter
----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
----------------------------------------------------
Secondary Outputs:
----------------------------------------------------
395.13 kHz = Secondary Resonant Frequency
90 deg° = Angle of Secondary
11 inch = Length of Winding
84.7 inch = Turns Per Unit
0.00178 inch = Space Between Turns (edge to edge)
976 ft = Length of Wire
2.75:1 = H/D Aspect Ratio
99.8914 Ohms = DC Resistance
51873 Ohms = Reactance at Resonance
0.3 lbs = Weight of Wire
20.894 mH = Les-Effective Series Inductance
25.732 mH = Lee-Equivalent Energy Inductance
27.369 mH = Ldc-Low Frequency Inductance
7.765 pF = Ces-Effective Shunt Capacitance
6.305 pF = Cee-Equivalent Energy Capacitance
21.076 pF = Cdc-Low Frequency Capacitance
4.77 mils = Skin Depth
0 pF = Topload Effective Capacitance
273.0955 Ohms = Effective AC Resistance
190 = Q
----------------------------------------------------
Primary Outputs:
----------------------------------------------------
0 kHz = Primary Resonant Frequency
100 % high = Percent Detuned
90 deg° = Angle of Primary
5.76 ft = Length of Wire
235.07 mOhms = DC Resistance
0.134 inch = Average spacing between turns (edge to edge)
0.737 inch = Proximity between coils
0 inch = Recommended minimum proximity between coils
4.35 µH = Ldc-Low Frequency Inductance
0.03729 µF = Cap size needed with Primary L (reference)
0 µH = Lead Length Inductance
88.661 µH = Lm-Mutual Inductance
0.257 k = Coupling Coefficient
0.129 k = Recommended Coupling Coefficient
0 = Number of half cycles for energy transfer at K
0 µs = Time for total energy transfer (ideal quench time)
Though the puff of smoke hints that there may very well be else at play in addition, if not instead of the impedance issue. If you could take photos of your driver and coil we may be able to help more.
Well, it just exploded. I was testing it without the mains even connected to the bridge so I could test the gate drive section with my scope, and suddenly - FOOMPH! There was a little burst of fire and a few glowing pieces flying a short distance. The breaker didn't even trip - a neon lamp I had connected to mains stayed on.
I can't find any blown components, but three out of four of the wires connecting to the GDT secondary have been popped cleanly (except for some singeing) off the wires to the gates.
Only one mains wire was disconnected, could this affect anything?
Thanks.
Sigurthr wrote ...
Though the puff of smoke hints that there may very well be else at play in addition, if not instead of the impedance issue. If you could take photos of your driver and coil we may be able to help more.
I'll try to get some photos. Before I do, here are some details:
The low-voltage power supply and bridge are done "rat's-nest" style. I didn't have an extra PCB and didn't want to go out and get one. GDT is 16T 30awg trifiliar wire (left over from my secondary) Primary is 11.5 turns of paralleled zip cord, 24awg I think. Everything is hackish and horrifying, I don't know if you want photos. You might want to scrub your eyeballs with a gentle solution of bleach and hydrochloric acid.
Only disconnecting one of the mains wires is hazardous if you aren't sure WHICH wire is the neutral line (for places with a HOT and neutral line, places using two HOT lines it isn't ever safe).
Your wire gauges are horrifyingly undersized. I get nervous using 16ga for my low current (~7A pk) primaries. Secondary side of the GDT sees full DC bus voltage so it needs to be able to withstand that PLUS any spikes. I like to use 22ga solid Cu insulated (NOT enameled) wire.
The words "bridge" and "rats nest" should never coincide in the same sentence unless it is a warning about how they should not coincide. I once tried making a half-bridge using 14ga connections... the I2R losses were extreme and the stray inductances killed many a FET. I use 10ga or thicker only now, if using wire at all.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
The interrupter IS necessary. These things just consume too much power to operate continuously. When debugging the system, use first short bursts widely spaced, and insert a 100W incandescent lamp in series with the power line. In this way you will not damage anything, with some luck. With the device properly tuned the lamp will barely light up.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
the mini sstc relies on the interrupter pulse to start oscillation. if there is no interrupter, you must include a "start" button. of course an SSTC can run cw, but the coils and transistors must be dimensioned adequately, use more turns on the primary and larger coils.
Only disconnecting one of the mains wires is hazardous if you aren't sure WHICH wire is the neutral line (for places with a HOT and neutral line, places using two HOT lines it isn't ever safe).
Your wire gauges are horrifyingly undersized. I get nervous using 16ga for my low current (~7A pk) primaries. Secondary side of the GDT sees full DC bus voltage so it needs to be able to withstand that PLUS any spikes. I like to use 22ga solid Cu insulated (NOT enameled) wire.
The words "bridge" and "rats nest" should never coincide in the same sentence unless it is a warning about how they should not coincide. I once tried making a half-bridge using 14ga connections... the I2R losses were extreme and the stray inductances killed many a FET. I use 10ga or thicker only now, if using wire at all.
Thank you. I'll rebuild everything.
wrote ...
Secondary side of the GDT sees full DC bus voltage so it needs to be able to withstand that PLUS any spikes.
I guess I didn't read the design guide closely enough.
I sure have done a lot of stupid things on this project. I'll see if I can find a cheap place to order PCBs or manufacture my own. And I'll order some 10ga or thicker wire.
the mini sstc relies on the interrupter pulse to start oscillation. if there is no interrupter, you must include a "start" button. of course an SSTC can run cw, but the coils and transistors must be dimensioned adequately, use more turns on the primary and larger coils.
Well you're sort of right; there needs to be some kind of ping to start the oscillation. A simple change in operating procedure can solve the issue though; simply power the DC bus before powering the UCC chips. When the UCC chips start up (same as when they received an Enable HIGH from interrupter) they will ping the circuit, starting oscillation. I started this procedure because my UCC chips oscillate at around 8MHz (and subsequently overheat!) when there is no feedback to their Inputs but there is a HIGH or float on their Enables. So, I only power the driver boards when I am ready to run the coil, and as a result, it starts up oscillating every time.
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Can I run Steve Ward's Mini SSTC without an interrupter?
