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2n3055 more primary turns = higher voltage?

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Alex M

Sun Jul 10 2011, 03:33AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Hello, after making a 2n3055 flyback transformer driver and trying it out on a number of flyback transformers I seem to have found that the more primary and feedback windings I put on the core, like 30 primary and 13 feedback the longer starting arcs I get from them. The longest arc I can get out my best flyback is around 4cm drawn and 2cm start.

But this seems to be the opposite to what I have read on forums in that less turns should mean more output voltage from the flyback. Like if I only put 5 primary and 3 feedback I only get arcs of under a cm, then the more turns I add the higher voltage I get out of them.

I am using a 12V supply that can deliver several amps easily.

My question is does anyone know what might be going on here as most people on forums seem to say that less turns = more output voltage from the flyback, and I have seen that on some youtube videos people getting huge arcs from using very few turns and the 2n3055 driver.

I seem to be the complete opposite!

Thanks.

Ash Small

Sun Jul 10 2011, 06:11AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'm guessing here, but I'll throw in a couple of suggestions, hoping that someone more knowledgable than me can add something.

I've just about finished a BIG heatsink so I can run some similar tests with 2N3055's and other TO3 devices.

One suggestion is that your supply isn't supplying enough current, so you aren't getting more current by reducing the number of turns.

The other suggestion is the 'volts per turn' thing that gets mentioned quite a lot here. This is something I need to investigate anyway for an H-bridge that I'm going to build once I've worked out the optimum number of turns for the primary for my cores using a rectified 240V supply.

The third suggestion is that, if you have 'snubbing capacitors' or whatever in your circuit, you may be getting some resonance.

Have you tried measuring the current for different numbers of turns? Maybe a schematic of your circuit would help, unless it is the basic, unmodified 2N3055 plus 240 and 27 Ohm resistors.

EDIT: the one I've been playing with recently would only run well at 30 kHz after I added a capacitor across the transistor, but I was driving it from a signal generator rather than using a feedback winding. I've not tried altering the number of turns or capacitance yet to see what effect that has, but I will do once I get the transistor on this new heatsink .

Dr. Dark Current

Sun Jul 10 2011, 09:17AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Depends on the oscillating frequency you get, maybe the high frequency with less urns is above the transformer's resonant frequency and the voltage is getting damped too much (by the leakage inductance and secondary self-capacitance which essentially forms a low pass filter).
As you increase the turns, the frequency drops and the "filter" passes more voltage, maybe some resonant rise plays a role here too.
You can try winding the coils closer to the secondary to get less leakage inductance and possibly more voltage out.

Alex M

Tue Jul 12 2011, 06:11PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Thanks, I am just using the standard 2n3055 driver (with heatsink) with two resistors 22 ohm and 220ohm and no capacitors.Here is a video of one of them running with lots of primary and feedback turns, I get arcs at around an inch of spark gap and reducing the number of primary and feedback turns only reduces the output voltage.

BTW I am using a fully charged 12v 7ah sealed lead acid battery. Do you think it works better on power supply's becuase of ripple current might be somehow driving the coil more efficiently or turns the transistor on and off differently?Thanks.BTW what kind of output can you guys get from a flyback just using the basic 5 primary and 3 feedback configuration using the same 2n3055 driver at 12v?

Ash Small

Tue Jul 12 2011, 10:21PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Not all TV flybacks are the same. Each has different characteristics. The 'basic' driver is supposed to work with all, but won't be the 'optimum' for all.

I don't think 4HV yet has a database of which are the best, and what the optimum configuration is for each type.

This is where your observations are invaluable, some work best with more turns on the primary and feedback windings.

Alex M

Thu Jul 14 2011, 01:30AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Thanks.

BTW does hot glue do a good job of insulating arcing pins or does it make it worse?

Ash Small

Thu Jul 14 2011, 01:57AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Others have said epoxy does the job, but I can't comment from personal experience.

I will also be posting some 2N3055 results in the next few days. (almost finished my TO3 heatsink).

Alex M

Thu Jul 14 2011, 02:54AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

@Ash Small Just how complex is this heatsink you are making?

Looking forward to seeing your results.

Chip Fixes

Thu Jul 14 2011, 04:18AM

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

To isolate the pins I have found that it is best to put a thick piece of wire insulation around each pin and then hot glue the hell out of it. solved all my arcing problems

Dr. Dark Current

Thu Jul 14 2011, 08:52AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Each set of coils (pins connected together) should be at one point grounded to mains Earth, as well as the core. This eliminates the arcing problem on almost all transformers.

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