Date: Fri, 12 Jan 2007 07:50:13 +1100 (EST) From: Debbie Subject: [EE] Coil winding - ideas? To: "Microcontroller discussion list - Public." Message-ID: <20070111205013.43650.qmail@web30305.mail.mud.yahoo.com> Content-Type: text/plain; charset=iso-8859-1 PICers, I'm winding a coil for a pot core inductor. I's for a flyback oscillator, the secondary will be about 500 -> 1000T of really fine wire. Winding the thing by hand is a //major//drudge. You need to put a little tension on the wire to get a tight pack but it's sooo easy to break. Any ideas re making things a bit easier/quicker? I was thinking maybe some sort of bobbin arrangement where you can turn a wheel to wind it on? Thanks - Debbie If you look at most HV transformers for flyback use, you will notice: 1. The HV coil is wound in multiple separate insulated compartments. This prevents the start of the coil from being near the end of the coil. The reason? To prevent arcing and insulation breakdown in the wire coating. Take a look at the tranformers used to drive the fluorescent backlights on a laptop computer. Some of the electronic surplus houses sell these boards with the tranformer attached. They will easily generate 1000 Vdc. 2. Flybacks are usually wound on a closed loop of ferrite. This provides a "high reluctance", long path for the magnetic field to collapse resulting in a higher voltage flyback pulse. Study the HV transformers in a PC monitor. Some pulse transformers use a rod shaped core. See the trigger transformers used to trigger a strobe flash circuit. The pot core is not usually the choice for this kind of transformer. 3. The HV windings are are often spaced away from each other to prevent "inter-winding" capacitance from limiting the HV pulse height. 4. The windings are potted in a vacuum with epoxy or silicone to prevent arcing. The epoxy or silicone will increase the "inter-winding" capacitance. 5. Flybacks are a "two period" transformer. The flyback transformer works by first charging up the core magnetically using the primary during the first period and releases the energy during the second period when the magnetic field collapses through the secondary winding. Keeping the magnetic path "long" and inter-winding capacitance small results in a higher voltage pulse of shorter duration. Drive the primary with short pulses, not a square wave to save power. 6. The mass of the core determines how much power can be transferred. Using a voltage doubler or tripler on the output saves turns on the secondary. Use diodes and capacitors that have a peak voltage above that of your transformer output. Throw away cameras, have some good high voltage parts to study and use. Careful, the big cap can really shock you! Hope this helps. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist