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current ballast/choke construction
Posted by dave baehr on 11/21/2004, 9:11 am
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Re: current ballast/choke construction
Posted by Bert Hickman on 11/21/2004, 1:11 pm, in reply to "current ballast/choke construction" Hi Dave, Congratulations on finding the baby pig and the transformer laminations. You have an excellent ballast core - a 2" x 4" core can easily handle 3 kVA. And your pig should easily handle intermittent overloads of 100%. Since you don't plan to use high temperature magnet wire in your ballast, I'd suggest using high temperature #12 AWG THHN (90 degree C) wire. This has PVC insulation housed within a nylon jacket that will help prevent insulation flow/failure at higher temperatures. The ballast should be good for intermittent 3 KVA duty from a 240 volt supply. Your large core size (2" x 4" or 8 square inches) will give you about 1 turn/volt (with no air gap), so using 240 - 300 turns should be in the right ballpark. You'll need to adjust the air gaps between the E and I core pieces to get the current setting you want - use thin sheets of paper or Mylar. As you are winding the choke, you could add taps to provide a convenient selection of current levels for a given gap setting. For example, suppose you are going to wind a ballast that uses 300 total turns. If you make taps at about 105 turns, 120 turns, 150 turns, and 210 turns, you'll get approximately linear current tap settings (100%, 75%, 50%, and 25% of maximum). Using the entire 300 turns will give you ~12.5% of the maximum current setting. And, if you use #10 AWG for the first 120 turns and then use #12 AWG for the remaining turns, you'll be able to push the higher current ranges of the choke with considerably less heating. Good luck and play safely! -- Bert --
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Re: current ballast/choke construction
Posted by dave on 11/21/2004, 3:48 pm, in reply to "Re: current ballast/choke construction" : Hi Dave,
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Re: current ballast/choke construction
Posted by Bert Hickman on 11/21/2004, 6:21 pm, in reply to "Re: current ballast/choke construction" Magnet wire is made to withstand higher operating temperatures than house wire. For example, class H polyester-imide insulated magnet wire is made to withstand 180C (356F), and some types of magnet wire are made to withstand 220 C. If you decide to use magnet wire, get "double build" (two layers of insulation). High temperature magnet wire provides you with greater design margin particularly for the innermost turns that may otherwise overheat under heavy use. Using layers of paper or tape are not mandatory, but they may make winding even layers a bit easier. If you are careful and wind each layer tightly, you don't need any interlayer material. Although you could epoxy the winding, most of the vibration will actually come from the laminations. Many transformer manufacturers use varnish to "glue" laminations together to reduce noise and vibration. You may also find it useful to tightly clamp the E sections, spacers, and I sections together to reduce ballast noise, particularly when running at high operating currents. Best regards, -- Bert --
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