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2.5' SSTC First Light

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LAN_403

Chip Fixes

Mon Dec 16 2013, 02:44AM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

I wound a 4.5" X 30" (32awg) coil tonight and plan to fire it up for the first time tomorrow or the day after. I'll be using Steve Ward's Mini SSTC design (just have to verify it's working properly) and I've got to run to the store to get a blow torch so I can epoxy this thing. Very excited!

Picture:

Chip Fixes

Tue Dec 17 2013, 07:01AM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

I conducted a test run tonight with 12v just to verify everything was working properly. I verified the duty cycle on the 555 timer was 20% but when I hooked it up to the rest of the circuit, I measured the duty cycle on the output of the driver at 50%?? This is a new problem to me. Could it be because of the power supply? I used a computer psu before (I am using Steve Ward's now) and the duty cycle was consistently measured at 20%. A bit annoying because my fets won't last long at 50% when the SSTC is driven from mains.

Pictures:

Sigurthr

Tue Dec 17 2013, 08:28PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

We need a schematic to go off of really. I think ur talking about his basic half bridge (antenna fed 74hc14 to UCC pair). We also need to know how you took your measurements; bridge connected or not, scope points, etc.

If you're measuring the secondary output the f0 waveform will always be 50% duty as interrupter duty just controls the duty of on and off bursts. You'll need a digital storage scope to measure system burst duty cycle.

Chip Fixes

Tue Dec 17 2013, 10:46PM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

Yep just his standard circuit:

I have a short at the resistor sub point and a 1uf (instead of 0.1) cap in series with output from the ucc.

I disconnected the output of the 555 timer from pin 3 of the ucc and scoped it - which gave me 20% duty cycle (frequency @ 100hz). But when I reattached the output of the 555 to the ucc and measured the duty cycle before it entered the GDT (GDT and bridge not connected), it's at 45-50% and around 60hz.

Sigurthr

Wed Dec 18 2013, 07:51AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

It sounds like you didn't have the coil running at the time. Your driver is just picking up the mains frequency and oscillating at that.

Feedback provides the primary operating frequency, and the interrupter (555 timer) tells the gate drive chips to essentially turn themselves off every so often. If you don't have the entire SSTC connected then you don't have any feedback going in.

As I said before, if you're scoping the output to the bridge and everything is working correctly AND you have feedback going in then you'll see bursts of a square wave who's frequency is your resonant frequency, where the burst frequency and duty cycle is the interrupter frequency and duty cycle.

Chip Fixes

Tue Apr 08 2014, 09:41PM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

Sorry for the long delay, I have been quite busy and have not had a chance to fire up the large SSTC until yesterday.
Pictures are here:

The secondary coil is 2,700 turns (Â±50 turns) of 32 awg wire, 27" tall, and 4.5" in diameter.

I was impressed by the output because: I was only supplying it with 40vdc, I didn't have the topload hooked up, and I have 15 turns on the primary. None of the components are heating up and I would have turned it up to max voltage (~170vdc after rectification) but the primary was too close to the secondary, so anything over 80vdc and it would start arcing :/ Right now the primary is wrapped around the cut up parts of clothes hangers. I was going to run to the hardware store and see if I could find some 6" diameter pvc, otherwise, I was thinking of getting some 1" diameter PVC pipe and then sandwiching it between the primary and secondary coil; just like the clothes hangers.

I do have a weird problem though. the coil only sparks if I touch the back of the lm7812 OR the lm7805 voltage regulators that supply the driver circuit with 12vdc and 5vdc respectively, if I don't touch the back of a regulator, it won't spark. Any ideas on how to fix that?

Steve Conner

Wed Apr 09 2014, 09:35AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Sounds like your driver circuit might not be grounded. The feedback antenna needs a ground to work against.

Hydron

Wed Apr 09 2014, 10:45AM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

Good to see a bedroom-floor lash-up making sparks!

Is an antenna a generally reliable way to run one of these coils? I'm also thinking of whipping up a quick and dirty SSTC, and was planning to use a secondary base current as feedback (via a current transformer) with an additional circuit to start the oscillation, but the antenna version (with properly grounded driver as Steve mentioned) seems a whole lot simpler.

Chip Fixes

Wed Apr 09 2014, 03:47PM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

Doh! You are right, my driver circuit is ungrounded and I totally missed that. Thanks! I used Steve Wards design and it has been completely reliable.

EDIT: I grounded the driver and it still doesn't output anything unless I touch it, anymore ideas?

EDIT 2: The farther my body is away from the top of the coil, the lower the output. If I am holding the back of the regulator or touching the top of one of the capacitors and I bring my other hand close to the top of the coil, the output increases.

Chip Fixes

Wed Apr 09 2014, 10:26PM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

I grounded the transformer and I still didn't get any output from the secondary. So I did some more testing and found that if I hooked up a wire to the back of the regulator (or capacitor, or output from transformer, but NOT ground) and then brought that wire close to the coil, the output would increase.

Pictures:

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