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Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Daedronus wrote ...
Would white delrin be a good choice for a bobbin? For something like a flyback transformer...
Delrin/Acetal is nice stuff. It's not cheap, but it machines beautifully and I've used scraps of it for a number of different things. As far as I know it's quite chemically resistant too.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Well here's the coil assembly with the feed through insulators attached to one flange of the bobbin. I guess it's ready to have the wires attached, the outer cylinder put in place, and then be potted.
The only thing is, I don't like it very much. Sometimes it's hard to imagine just what something will look like until it's built and sitting right in front of you.
It will probably hold up...but I just don't like the idea of running the lead from one side of the coil to about 0.125" away from the other side of the coil.
If I could only think of how to make some "saddle washers" that would seat against the outside cylinder (i.e., that would match the outer radius), I would bring the terminals out radially, which would reduce the field to a more conservative value.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
jpsmith123 wrote ...
The only thing is, I don't like it very much. Sometimes it's hard to imagine just what something will look like until it's built and sitting right in front of you.
It will probably hold up...but I just don't like the idea of running the lead from one side of the coil to about 0.125" away from the other side of the coil.
Excellent!!! I see you will be using the sparkplug type boots and sockets.
125 x 300V/mil = 37.5kV of standoff, so your probably fine.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Well Patrick I just did a quick low power test of the coil, and it seems quite good. Everything looked flat from 20 to about 40 kHz.
The coil I tested was not the multisegmented one, but the layered one I just wound, which has 560 turns of 26 gauge wire.
I'm going to do some more tests later, but so far I'm happy with it. (The only problem is the fact that it's short about 40 turns because I foolishly didn't measure the wire diameter before winding it).
Apparently making the coil "tall and skinny", along with extra layer insulation, really helps.
With 26 gauge wire, it should be capable of 4 to 5 kw throughput I would imagine. Moreover, there's still quite a bit of room inside the coil housing. It seems to me that I could also reduce the width from 0.75" to 0.5", switch from 26 to 28 gauge wire, and put two coils in series, which would produce much more voltage.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
It looks excellent. A point of advice though...I assume everyone knows about skin effect... but many fail to realise the significance of the proximity effect (With 26 Awg I think youll be fine below 80kHz).
How did you arrive at the 4-5kW number? --How many turns would your primary normally have? --What is the core number and maker?
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
The core is a ferroxcube U100/57/25-3C90. (BTW I was satisfied with it until I saw TSC's new "50all" material, which looks much better than 3C90).
My estimate of as-built power throughput capability is based on the wire size (26 gauge, assuming 0.5 A max current), the number of turns (about 560) and a drive level of approximately 23 to 25 volts(peak)/turn.
Anyway, I compared the segmented coil pictured above with the layer-wound coil, and although the layer wound coil seems good, and is quite useable, IMO, the segmented coil appears to have a better frequency response.
Basically what I did is load the secondary coil with a 68k resistor (to present about 50 ohms to the generator), set the generator for a 1 volt output, and then sweep the primary, while looking at the primary and secondary voltages.
The layer-wound coil started to noticeably load down the (50 ohm) generator at about 45 kHz, whereas the segmented coil didn't do it until about 80 kHz, IIRC.
The segmented coil is wound with 30 gauge wire, so it would not be able to handle as much power. I might be able to make a similar segmented coil with 600 turns of 28 gauge, but as a practical matter that would be pushing that particular design right to the limit, IMO.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
jpsmith123 wrote ...
The core is a ferroxcube U100/57/25-3C90. (BTW I was satisfied with it until I saw TSC's new "50all" material, which looks much better than 3C90).
Yes, your welcome.
jpsmith123 wrote ...
My estimate of as-built power throughput capability is based on the wire size (26 gauge, assuming 0.5 A max current), the number of turns (about 560) and a drive level of approximately 23 to 25 volts(peak)/turn.
Its not the wire guage that limits the curretn you can push through, the Guass, determines V/T, which is overall Vout, the H (in Oersteads or whatever) determines your current passability.
EDIT: assuming 450 Amps/cm^2, then:
26 Awg = 0.0159 nom dia. 0.00795^2 x 3.14 = 0.00198 in^2 0.000198 in^2 = 0.001278 cm^2 450 Amps x 0.001278 = 0.575 Amps for 26 awg.
so... 0.575 Amps for 26 awg. X.XXX Amps for 28 awg. X.XXX Amps for 30awg.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
wrote ...
Its not the wire guage that limits the curretn you can push through, the Guass, determines V/T, which is overall Vout, the H (in Oersteads or whatever) determines your current passability.
Huh? You've lost me there...
wrote ...
assuming 450 Amps/cm^2, then:
26 Awg = 0.0159 nom dia. 0.00795^2 x 3.14 = 0.00198 in^2 0.000198 in^2 = 0.001278 cm^2 450 Amps x 0.001278 = 0.575 Amps for 26 awg.
so... 0.575 Amps for 26 awg. X.XXX Amps for 28 awg. X.XXX Amps for 30awg.
The wire table I generally use recommends a maximum current based on 500 circular mils/amp, but I suppose you can always squeeze a little more.
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Grooved Bobbins For Segmented Windings
