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Help needed, bad circuit diagram + poor understanding

  1. Oct 7, 2009 #1
    I need some help. This may not be the right place but IL give it a go anyway. I have built a Single to Three phase converter and it is working OK, but it could be better. It was built to a set of plans downloaded for a small fee. The person selling these plans has since dissapeared, website/e.mail dead etc. The plans were rather vague and were only any use as a basic outline to the method of building the converter. I have since lost the plans as they were PDF and lost them with a computer wipe... no back up copy No big loss as all the basic principal is in my head but I do have a few pages printed out which seemed special. Basic outline of the system; 240/415 transformer(doctored from an old a/c arc welder with dual input voltage(apply 240v to the 240v winding and you get 415v from the 415v winding with a common neutral and strip out the sec.) The artificial 415v 2 phase is feed to an idle motor with the 3rd phase coming from a motor run cap placed between one of the 415 legs and the 3rd input of the motor. The motor is starts in star with a motor start cap paralleled with the motor run cap. When it runs up to speed it changes to delta and the start cap drops out. At the minute the system is using a timer relay to control the star/delta changeover but it works better with a voltage sensing circuit. The circuit senses when the voltage between one of the transformer phases and the capacitor phase is, and when it reaches a certain point(approx. 380v) it changes over the S/D and drops out the start cap. This is better because when a heavy start load is placed on the output of the converter it will cause the voltage to drop on the cap. phase and it will bring on the start cap and change back to star to aid starting the 3 phase motor load. This is where I need help (I should prob have done my HND in electronics instead of mechanical Eng. but it seemed the right thing at the time). The circuit uses zener diodes to switch the relay controlling the S/D changeover. The circuit looks like a transformer less voltage dropper but it seems incomplete and wrong. The diagram is like the rest of the instruction... vague and indefinite. It shows a rectifier but two tails have nothing on them? What propose does it serve if the coil is 240ac? Does anyone here know how to make this circuit work. I have built it and it doesn't work. It says in the notes that when the voltage reaches~380v it energies the relay. I would appreciate it if some one could dummy the circuit so I can double check I have it right i.e. draw pictures of the components with annotations as to their orientation... ac/dc side of the rectifier and the positioning of the zeners. Some one with a better knowledge of this stuff will prob sort it in two minutes! I have a good understanding of electrical systems etc. but never studied circuit manufacture in any great depth but I have some experience and with some guidance I could build this. The top LH is transformer phase and the bottom LH is capacitor phase.

    Any help greatly appreciated.
  2. jcsd
  3. Oct 10, 2009 #2
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