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4hv.org :: Forums :: High Voltage
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Winding a flyback secondary

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HDF49
Sat Jul 27 2013, 08:40PM Print
HDF49 Registered Member #977 Joined: Thu Aug 30 2007, 06:57PM
Location: England
Posts: 74
I'm working on the power supply for a laser project of mine. I wound a 1315 turn primary, with two layers of paper, superglued in place between the layers, and when winding I brought the end of each layer back to the beginning of the last and carried on winding. I then held the coil under vacuum in oil for an hour, but once rigged up to my half bridge with 250 watts in at 70 volts the sparks were pretty pathetic and the coil shorted out under the oil through the top layer of insulation. The small arcs make me thing that there may have been an internal short in the first place, has anyone got any experience with winding flyback secondaries? I'm aiming for 15kv at 20mA
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Newton Brawn
Sat Jul 27 2013, 09:18PM
Newton Brawn Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
your info could be organized.
specify:
primary max voltage
primary turns
secondary max voltage
secondary turns
a dimensional dwg from your magnetic core

primary and secondary coils sketch also



secondary coil
fist tryal
sketch a coil as:
1320 turns in 20 layers
66 turns per layer
kraft paper 0.2mm thick (or 2 x 0.1mm) between the layers
kraft paper with 10mm margens, one each side of wire.
Then check if the coil fit in the core.

so the voltage between 2 adjacent turns may be 1.41 x 15000/1320 = 16V
the voltage from each layer may be 1056 volts
and max voltage between two adjacent layer may reach 2112V
0,2mm kraft paper imerse in oil is good for 2500V if no air bubles

redesign and add safety coeficients

regards


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ZakWolf
Sat Jul 27 2013, 10:43PM
ZakWolf Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
Hi HDF49, I think I can help you out.

First of take a look here Link2 and here Link2

Both flybacks are using the same core and are insulted with 2 layers of overhead projection sheets that are submerged in mineral oil. (not put under a vacuum, which would greatly improve the lifespan). I have recently made two "dry" flybacks both with 2 layers of the projection sheets, and they have a very nice output at 40v in and no corona what so ever.

Since homemade flybacks usually have a high amp output it is better to use thinner wire, I like to use 32 awg for flybacks, It gives it the same characteristics of a factory made one at high turns like(2500+) meaning it doesn't melt metal instantly but can still melt steal if the arc is held for a couple seconds.

Make your layer or insulation as wide as for coil form is.

Hope this helps

Im having trouble upload a picture to this thread, i will try again later
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HDF49
Sun Jul 28 2013, 09:54AM
HDF49 Registered Member #977 Joined: Thu Aug 30 2007, 06:57PM
Location: England
Posts: 74
Ok thanks for the help guys, I think I'm going to take the top layer of turns off and add a lot more insulation on top to stop the same again. I've submerged it in a mineral gear box oil, did you use a proper insulative oil?
If all else fails I'll buy some overhead transparencies, and possibly make a zvs driver for more current. I'm ust very annoyed as it was my last spool of wire!
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ZakWolf
Sun Jul 28 2013, 06:43PM
ZakWolf Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
HDF49 wrote ...

Ok thanks for the help guys, I think I'm going to take the top layer of turns off and add a lot more insulation on top to stop the same again. I've submerged it in a mineral gear box oil, did you use a proper insulative oil?
If all else fails I'll buy some overhead transparencies, and possibly make a zvs driver for more current. I'm ust very annoyed as it was my last spool of wire!

Yea, i use mineral oil. it works really well and is pretty cheap. You can get it at most stores.

You also wont see very impressive results without a zvs or some kind of half bridge driver, What driver are you using?
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HDF49
Sun Jul 28 2013, 06:53PM
HDF49 Registered Member #977 Joined: Thu Aug 30 2007, 06:57PM
Location: England
Posts: 74
A half bridge of irfp260s, I'm having variac trouble at the moment too so I need to sort out my power supply. I think I might make a zvs driver, less to go wrong, the oscillator of my half bridge section is giving me grief again!
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ZakWolf
Sun Jul 28 2013, 11:09PM
ZakWolf Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
with a zvs driver im sure that 20ma wont be a problem, especially with a homemade secondary
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HDF49
Mon Jul 29 2013, 08:10AM
HDF49 Registered Member #977 Joined: Thu Aug 30 2007, 06:57PM
Location: England
Posts: 74
Ok, good to hear, I'll get some overhead transparencies and some more wire soon. Thanks for the help!
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ZakWolf
Mon Jul 29 2013, 07:24PM
ZakWolf Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
HDF49 wrote ...

Ok, good to hear, I'll get some overhead transparencies and some more wire soon. Thanks for the help!

No problem, let us now how it turns out
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HDF49
Thu Aug 01 2013, 09:25PM
HDF49 Registered Member #977 Joined: Thu Aug 30 2007, 06:57PM
Location: England
Posts: 74
I will, I have plenty work to do with the rest of the laser too so it may be a while!
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