Monday, November 15, 2010

NIC Coil Project

The conduit box's have been painted a flat black, the PVC pipe terminations have bolted to the top of the conduit's removable panel. You can see the low voltage supply transformers bolted to the inside top right of the conduit box's. These transformers are high quality audio amplifier type with dual primary and secondary. Only one of the primary and secondary coils have been used to limit the inrush current associated wtih paralleling them. They are a bit overkill with a VA rating of 2kVA when I/P and O/P coils are parallel'd. The inrush current into these things is 80 times higher than their running current comapired to 30-40 times on a standard E core laminant transformer. These toriodial style transformers do have benifits including high noisy immunity, high current, higher power for given core consectional area, low losses and they dont even ~humm when you draw 135A from them! This is due to their core design, smooth rounded shape and coils covering the entire area of the core.

The purpose of the transformers is to supply multiple voltage regulators. 5V regulator for logic chips and controller board, 12V regulator for GDT driver board and a seperate 12V supply for computer fans that will be added for cooling of the H-Bridge. Due to core characteristics they also seem to have the natural abillity to cancel high frequency noise on the mains. However I may still consider a line filter and passive Power factor correction - PFC and line filters are nice but not totally necessary for coils which are only going to operate for short periods of time. The solid state coil acts very close to a resistive load when tuned and the power factor wont be an issue at near resonant frequency. It will be detuned into the capacitive region when frequency modulate to play music.

You can also see the power cords, plugs, and main power switches have been installed and are ready to be wired. The conduit box's came in at 23$ each on sale at a local hardware store. The power cords are salvaged from old computer powersupplies. The transformers were 50$ each off ebay and are excellent quality. The box and transformers so far are the most costly part of the coils, with everything else mostly made from salvaged parts. The secondary and primary coil of the TC will not cost anything to make as I already have the materials. So far the project budget is 200$ for each coil. One of the coils is going to North Island College - Core Electronics Program the other I will use as a testbed for faults and design changes for future coils. Making two coils not only makes troubleshooting easyier but lowers part costs as I get deals in buying bulk materials not to mention ending up with a new and much better designed coil for myself.

The difficult part will of course be designing them to be safe and reliable. My previous coils were not what you could call reliable or safe to run for more than 5mins. Since one coil will be going to a educational institution - it must last on its own and more considerations for safety and long operating life must added to the existing design.

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