victor@rigel.econ.uga.edu (Victor Grubbs (stat)) (11/21/90)
I have a problem:
In many countries the AC power is 50 Hz instead of 60 Hz (like here in the
states). This basically messes up american equipment taken overseas. Clocks,
timers, electric induction motors, and such.
I need a 500 - 1000 watt 60 Hz (110 VAC or 220 VAC) power supply and I can
think of a couple of solutions:
1) Buy locally (overseas) -- generally expensive IF you can get equipment
2) Take a 60 Hz generator -- expensive (gas costs overseas), bulky, noisy
3) Convert american equipment by replacing motor, timers, drive
ratios, etc -- what if the manufacturer didn't make a conversion kit, why
change ALL the equipment if you could condition the power?
4) Run a 50 Hz motor into a 60 Hz generator -- bulky, inefficient
5) A step up ocillator that runs on 50 Hz and produces 60 Hz.
a) Transform 50 Hz power down to 12 VDC and use an inverter to produce
60 Hz 120 VAC -- not bad except it's going to be 50% efficient and
I can't find anyone that makes it.
I would like to find a number 5 type solution if possible. I don't mind
making a #5, but I would prefer to buy one.
Oh, Radio Shack DOESN'T have it.
Please send suggestions, comments, manufacturer names & number, etc to the
following E-mail address:
mth@rolf.stat.uga.edu
Thank you
MARK HOLCOMBgrege@gold.gvg.tek.com (Greg Ebert) (11/22/90)
victor@rigel.econ.uga.edu (Victor Grubbs (stat)) writes: >I have a problem: > > [...] >I need a 500 - 1000 watt 60 Hz (110 VAC or 220 VAC) power supply and I can >think of a couple of solutions: > >5) A step up ocillator that runs on 50 Hz and produces 60 Hz. > > a) Transform 50 Hz power down to 12 VDC and use an inverter to produce > 60 Hz 120 VAC -- not bad except it's going to be 50% efficient and > I can't find anyone that makes it. > >I would like to find a number 5 type solution if possible. I don't mind >making a #5, but I would prefer to buy one. > I built a 10kW 3 phase inverter with power bipolar transistors. Since you are only running about 1kW, try a 450v/30 amp device such as the Mitsubishi QM30DYH. It's a Darlington totem-pole device which actually has 2 switches inside. You'll need 1 if you have +/- 170 VDC, or 2 if you have +170 VDC only. Rectifiers/caps are cheaper, so I'd opt for the former. You can also get an opto-isolated driver for the transistor from Mitsubishi. This beast will give you any frequency you want: 50Hz, 60Hz, 400Hz, etc. For laughs, run a 3450 RPM induction motor at 200Hz! You *dont* have to have sinusoidal waves; Induction motors are very happy with square waves. The key is to provide a signal with the same RMS and peak values as a sinewave. If you rectify the AC line, you've got the peak-voltage part solved. For a rectangular pulse, RMS = SQRT(duty_cycle)*Peak or in this case, a 50% duty cycle gives you what you want. The waveform will look like this: __ __ _| |_ _| |_ |__| The only potential problem is if you are driving a capacitive load, such as a power supply. High dv/dt gives big current spikes. Solution: add some inductance. Once you get that running, you can get tricky and wipe-out the 3rd and 5th harmonics with a waveform that looks like: _ __ __ _ __ ____ _| | | | | | | | | | | | |_| |____| |__| |_| |__| |__| I can dig-up the timing parameters if you're interested. You can also do a Fourier analysis and solve 'N' simultaneous equations for 'N' zero (or near-zero) harmonics. SPICE is helpful, too. >>> IMPORTANT <<< Make absolutely certain that your control circuit *NEVER* turns on transistors between the + and - supply, even during power-up/down and failures. I used a Z80 and it choked on a power-down, and caused 2 devices to turn on between the supply rails. The transistors *exploded*. There was enough 1/2LI^2 energy in a 12" wire to destroy another transistor. Yes, it was a costly mistake.