I was recently told that if rectify the 120VAC mains voltage and then add a capacitor to smooth out the wave, I will then have something around 167 VDC. Is this true? If it is true, what is the easiest way to get a smooth 120V DC voltage? -- Chris W Gift Giving Made Easy Get the gifts you want & give the gifts they want http://thewishzone.com
If you can find an 85 volt transformer, it would produce approximately 120 volts DC with a capacitor filter. It would also provide isolation from the mains, so that a connection to ground would not be hit with the full current the line could deliver. The 120 volts will not be very smooth, however. It will have ripple at twice the line frequency when loaded and will sag as the load current increases. If you want a clean, accurate and stable 120 volts DC you will have to build or buy a regulated supply. For instance, here is one that is adjustable from zero to 120 volts DC, capable of supplying up to 1 ampere. http://shop.store.yahoo.com/webtronics/lowcosioubep.html
Yes. The 120 VAC mains voltage is 120 VAC, RMS (root-mean-square). This means that if you connect it to a resistor then the resistor produces as much heat as if you connected it to 120 VDC. The peak voltage of a 120 V (RMS) sine wave is 120*sqrt(2) = 170 VAC, minus a couple of diode drops I suppose to get your 167. The rectifier detects the peak value of the sine wave. Use a transformer to turn your 120 VAC into ~85 VAC. An autotransformer (Variac) might be easiest. What are you trying to do? Jonathan http://cq.cx/
--- FWB +-----+ 120VAC----|~ +|----+---+----C E-------+---->120DC | | | | B | | | | [R] | [R] | | | | | | | | |+ +------+----C | | | [C] B--+ | | | E | | | | | [R] | | | | | 120VAC>---|~ -|----+---------------+----+----->GND +-----+
--- Or, perhaps,: FWB +-----+ 120VAC----|~ +|----+---+----C E----------+---->120DC | | | | B | | | | [R] | | | | | | | | | | |+ +------+----C | | | [C] B-->[POT] | | | E | | | | | | | | | | | 120VAC>---|~ -|----+---------------+-------+----->GND +-----+
