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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hello again guys
Firkragg, how actually you have glued it together? I mean, is there a special technique to prevent arcing or you just did it?
There are smaller and larger rings of plexy wich are tightly superglued to each other. They give excellent insulation to core but it is somewhat tricky to pull the wire from the inside of the former.
Number of turns must be low (much lower than your stun gun!) and I don't expect to exactly get some very high voltages from it, few kilovolts at most. I guess I'l have to reconstruct this transformer If I wanted more. (I already pointed out some of problems in upper posts). That transformer also needs it's size fixed so I can fit the core properly without an airgap... if I ever get time for it.
Rickr: One thing I just didn't understand, are you using just normal enamelled wire (your turn counts look pretty big!).
True, corona in general is a big consideration, but I found a specific instance that really affects coil construction - arcing between the top windings of a section and the wire that leads to the bottom of the section. For example, I only wind on 5 of the 9 grooves I cut in the form for this reason. Think about it. You wind a section by running your winding wire to the bottom of a section and then wind until you get just about to the outer lip of the groove. Well, you're already in trouble because wires in each winding layer of that section are in intimate contact with the wire that runs down the side of the section to the bottom of the winding. At high frequencies arcover is almost a certainty when the section contains 500-600 turns!
I now see how you battle the problem! But I can imagine this would be great waste of core space unless sections are really tiny. This seems to be biggest hurdle for this winding type.
Oh, and thanks for great tips!
I'm running out of my time, but, but I got what I waited for... some nice SUM65N20 mosfets! 200V and 30 miliohms.. they are slow, but in resonant operation I guess it won't be a big problem!
And first board ever to be layed out and printed with my laser printer. Toner transferring technique didn't work too well without proper photopaper (I used transparency), I had to fix it a lot, but here is a little (experimental) royer driver for some beefy output power. It's not in aligator clip mode, for first time!
Just to give a clue what I want to drive that transformer with, not to go OT too much!
Registered Member #93
Joined: Thu Feb 09 2006, 04:11PM
Location: Houston, Texas
Posts: 64
Firkragg said:
Rickr: One thing I just didn't understand, are you using just normal enamelled wire (your turn counts look pretty big!).
Well, most of my winding has been with 34 gauge, single-build (least insulation) wire, with the grooves being about about 1/8 inch wide and about 1/2 inch deep. The barriers between the grooves are a little more narrow. I've collected quite a number of ferrite cores and was lucky enough to find a few that are relatively wide and tall. They will accept a bobbin that's about 2-1/4 inches tall. Combine that with the relatively fine wire and you can get a pretty big turns count.
I just purchased some 37 gauge wire on eBay and I'm going to try winding with that.
You're right about the wasted space. Of course the answer is to make the grooves and barriers more narrow and use finer gauge wire (or use fewer turns and boost the voltage delivered to the primary). I'm still experimenting with that approach. Naturally, there's a tradeoff that involves groove spacing, wire gauge, wire insulation, number of turns per groove, volts per turn for a given core, and my amount of patience. But at the moment, it's still fun to experiment so I'll try to post my results from time to time.
Registered Member #528
Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166
Hey, I bought not long time ago a 38 AWG wire. Quite small diamter, but it was cheap (2 kilograms for ~12 dollars). Now, after making one layer of coil, 4cm long and 1.5cm diameter (estimated 350-380 turns) I'm thinking seriously about making home made coil winder. There's a 230ACV 5 RPM 5W motor, so I guess I'll play a bit a gold hand - some of wood, glue, nails, belts and simple coiler will born. Only if I knew, how much mA this wire can take, anyone knows?
And, I'm curious what's the melting temperature of ferrite. My aunt has a 1000*C heater and I thought it would be a interesting idea to do in that way :
- collect unnecessary ferrite (from TV transformers, PSUs etc.) - put those victims into bag - hammer it continously until they will be dead and form in "dust" - put "dust" into two small boxes with diameters of cores you want to build - put boxes into heater and melt this "dust" into solid forms - grind those forms to U shapes
Or, to simplify life, build U shapped boxes.
Now, what do you think? Is it worth to try? Surely it would be nice to build tall and wide cores. They wouldn't need to have big masses - the only matter that interests us is preventing from arcing to cores or primary winding. Bigger space will allow to insulate better.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
If you are going to make a rod of ferrite (as opposed to a closed loop) then you do not need to melt ferrite (if it can be melted) just smash ferrite pieces of all kinds to small pieces and dust then fill a plastic tube with it.
You do not need very high permeability as the permeability of a rod compared to air is approximately 3.5 x (length/diameter)
e.g. an air-core coil with 100 uH inductance would have about 3.5 mH inductance with a ferrite core of (length/diameter) = 10 Assuming a relative permeability of the ferrite/air core is >> 35 So no need for really compact ferrite, IF it's a straight core.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi guys..
Well there's nothing more fun than some HV transformer torchout on easter.
The transformer has 160 turns of PVC wire (leftovers from gutted LPT cable) and seems to work beautifully for now... I had to remove one notch in order to fit the core properly in, losing about 40 turns and getting 3mm more space for primary...
I use 3+3 turns of ~2mm dia litz wire for primary.. ant it still gets warm.
Fed with 24V ~5A it puts out blindingly bright arcs wich start at 1mm (corresponding 8V/turn => 1280 volts) and can be stretched up to 2cm.
They almost instantly turn the copper wire incandescent and put out uncomfortable amount of UV...
Mosfets get warm to some 40 degrees C, cap is cold, and actually the hottest thing is the ferrite core itself!
With no load the circuit works at 50kHz, but rises even up to 100 with heavy arc, and this seems to be pretty bad for this core material.
If I left it arc for few minutes core would probably start to melt plexy... and it dissipates heat really slowly! Really need to get frequency down!
I actually planned to use a pulse-train controlled dimmer to power this thing, but it never made it over the breadboard/aligator clip state. Adequate PFC inductor would also be a good idea in that case.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
With no load the circuit works at 50kHz, but rises even up to 100 with heavy arc, and this seems to be pretty bad for this core material.
If I left it arc for few minutes core would probably start to melt plexy... and it dissipates heat really slowly! Really need to get frequency down!
Have you even considered that your transformer is saturating? 3 turns with a 24V input, plus the fact that the voltage probably rings up to 2-3X the input, so you might be putting 24V per turn on that dinky ferrite? My largest ferrites (which are easily 3-4X the cross sectional area of your flyback core) can run about 45V/turn at 50khz (just for some perspective), so it sure sounds to me like you are saturating the poor thing.
By the way, reducing the volt/turn works in the same positive way for core losses as lowering the frequency. Id personally keep the higher frequency, but run at a more sane flux density.
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Homemade high-freq HV transformers
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