audioguru Posted July 22, 2006 Report Share Posted July 22, 2006 Most people throw away their UPS when its battery dies. Maybe that one just needs a new battery to work again. Look up its model number and manufacturer in Google.An LM339 is a quad comparator. It cannot be used as an opamp so it cannot filter a signal. Maybe the output is a modified sine-wave that is a square-wave with steps in it. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted July 22, 2006 Report Share Posted July 22, 2006 But this one is battery dead as well as circuit dead , i used it 4 years back to run television , even a computer , it was known here as a 486 computer UPSYou are right i think it is a Modified Sine wave . we can make a modified sine wave and then step up without heating and also can use mosfets. for low heat dissipation Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted July 23, 2006 Report Share Posted July 23, 2006 IF we make a sine wave inverter with making sine wave instead of square wave and and use mosfets in our design 4 parrallel mosfets oen side and 4 parallel mosfets other side, IT willl minimize heat dissipation and we will have a sine wave inverter.BUt making a modified sinewave wave , a digital which has steps in it , would be easier , but will it run a TV or Computer . The UPS I had , if it produces a stepped sine wave , then , i used it to run a computer , full with CRT monitor also and a TV also ran fine . Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 23, 2006 Report Share Posted July 23, 2006 A sine-wave inverter wastes a lot of power in its output devices. Mosfets or transistors will dissipate the same and heat the same.If you make the peak voltage from a modified sine-wave inverter about as high as the peak voltage of a sine-wave then it should be able to power anything. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted July 23, 2006 Report Share Posted July 23, 2006 Can you suggest a circuit for the Modified SIne wave inverter Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 23, 2006 Report Share Posted July 23, 2006 Can you suggest a circuit for the Modified SIne wave inverterSombody posted one awhile ago but I didn't keep it. Google sells many inverters but no circuit is shown.You could probably use a CD4047 oscillator/divider and some gates. Quote Link to comment Share on other sites More sharing options...
ishaqfunsho Posted July 24, 2006 Report Share Posted July 24, 2006 hum ......i quite follow the discussants with a keen imterest, however, the discussion did not tell us whether the cct worked or not--pls i will like to know..I equally wish to know what has to be done to increase the power to atleast to 1000w. Quote Link to comment Share on other sites More sharing options...
grateful Posted July 24, 2006 Report Share Posted July 24, 2006 ;DHi,audioguru:what i found is the ferroresonant transformer provides squarewave output but just require less filtering......if i use PWM method to convert a low VDC to high VDC through a ferro transformer. Then using H-bridge (which is switch by PWM) to chop the high VDC to obtain 240VAC that have multisteps PWM which look like sinewave waveform.... will this work? ??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 24, 2006 Report Share Posted July 24, 2006 if i use PWM method Quote Link to comment Share on other sites More sharing options...
kachew Posted July 24, 2006 Report Share Posted July 24, 2006 hi grateful,can i know where u put the H-BRIDGE in the circuit? is it at the output of the inverter?thanks Quote Link to comment Share on other sites More sharing options...
grateful Posted July 25, 2006 Report Share Posted July 25, 2006 I c :o...thanks....but is there any low cost but effective ways to convert a 12VDC to 220VDC?Hi,kachew....at the moment i still on thinking...so,i still not certain with this design yet... :-* Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 25, 2006 Report Share Posted July 25, 2006 I c :o...thanks....but is there any low cost but effective ways to convert a 12VDC to 220VDC?You could make a "boost converter" with an IC. It makes a high frequency, high current square-wave with Mosfets driving a small high frequency stepup transformer. Then rectify and filter it into 220VDC. Quote Link to comment Share on other sites More sharing options...
grateful Posted August 2, 2006 Report Share Posted August 2, 2006 Hi there, does anyone know how to convert the different width pulses(vertical) of a PWM signal to different height pulses(horizontal) accordingly....any comparator I C can do this ???Thanks. ;D Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 2, 2006 Report Share Posted August 2, 2006 The output of a comparator IC can't make variable height (voltage) pulses because its output is either high or low.The PWM pulses are converted to a smooth sine-wave with a lowpass filter. Quote Link to comment Share on other sites More sharing options...
grateful Posted August 2, 2006 Report Share Posted August 2, 2006 I c....Thanks :) Quote Link to comment Share on other sites More sharing options...
grateful Posted October 4, 2006 Report Share Posted October 4, 2006 Hi there everyone :)I have constructed the H-bridge circuits which is control by PWM, the frequency of PWM is about 4900Hz. Therefore, a single phase PWM sinewave at 220Vrms is generated.Then, my questions are how can i filter this 220Vrms PWM sinewave into a perfect sinewave? Should I choose LC or RC low pass filter?which type of high frequency with high voltage that should i choose for inductor and capacitor component in order to set the cutoff frequency at 50Hz? ??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 4, 2006 Report Share Posted October 4, 2006 Hi Grateful,4.9kHz is very low for PWM. Your transformer will whistle loudly. Usually a frequency higher than 20kHz is used so it is not audible.An RC filter will waste a lot of power. Use an LC filter like class-D audio amplifiers use.The cutoff frequency of a circuit is the frequency where the output is -3dB which is half-power. Use a higher cutoff frequency for less loss. Quote Link to comment Share on other sites More sharing options...
grateful Posted October 7, 2006 Report Share Posted October 7, 2006 Thanks audioguru :)Now i have increase the PWM frequency to 19kHz. But my inverter design at the output there is a bit different. I use ADC to convert a single phase sinewave with peak amplitude of 5V to PWM signals.Then, the PWM is used to switch or chop the 220Vdc.The output that i obtain now is a PWM with amplitude of 220Vdc for positive half cycle and the negative half cycle (in accordance with the ADC signal).Then, my question is how to design the low pass filter circuit (using RC circuit which is easier to control than LC) which able to smoothen this high voltage PWM signals switching at 19kHz?So, how can i design a RC low pass fiter that able to withstand high power(100W) and high frequency. Then, finally output a perfect 220Vac at 50Hz? ??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 7, 2006 Report Share Posted October 7, 2006 Hi Grateful,The 220VAC sine-wave should be 622Vp-p, not 440Vp-p.An RC filter wastes a lot of power and needs a huge capacitor, an LC filter doesn't.An RC filter filters at only 20dB per decade of frequency, an LC filter filters at 40dB per decade of frequency. Quote Link to comment Share on other sites More sharing options...
grateful Posted October 9, 2006 Report Share Posted October 9, 2006 I c....but the reason that i use RC filter is because i used the connected load as R. Rload = R filter. Assume that i am using LC filter, what will be the low pass cut off frequency that i should set?is it 50Hz?If so, i set the C = 1000pF then, the L value will be very large,right? Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 9, 2006 Report Share Posted October 9, 2006 If you use the R of an RC filter as the load, then the filter is highpass not lowpass.The output of any kind of Butterworth filter is -3dB at the cutoff frequency.So if you set the cutoff frequency at 50Hz then the output will be at half power.1000pF if useless at 100Hz or 200Hz. You need a much higher value.Without a load then the LC will be series resonant and a very low impedance. You don't want the resonant frequency anywhere near your PWM frequency.Sorry, I don't know the rules for a suitable LC filter. Quote Link to comment Share on other sites More sharing options...
WildSwan Posted October 12, 2006 Report Share Posted October 12, 2006 Okay.. I built the 500w Power Inverter... it's working but why does it burn my electic fan's motor after running sometimes?All I can do with it now is to light a 50W Incandescent Bulb. :( Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 12, 2006 Report Share Posted October 12, 2006 Hi WildSwan,Which circuit did you build? The defective original circuit, the defective "recently corrected" circuit by MP or the one corrected by me two and a half years ago?This is a square-wave inverter, a sine-wave circuit is much more complicated and more expensive. If your fan has a speed controller then the square-wave will probably upset it, the same for light dimmers. My corrected circuit has been reported to continuously supply 720W so maybe yours has the pins on a transistor or more connected backwards. Quote Link to comment Share on other sites More sharing options...
ante Posted October 12, 2006 Report Share Posted October 12, 2006 Some inductive loads can overheat when using square wave. Quote Link to comment Share on other sites More sharing options...
WildSwan Posted October 13, 2006 Report Share Posted October 13, 2006 I built the original and never returned here again. I was busy trying to figure out why do the Inverter keeps on burning Electric Fans.Tha fan I used was the common type, one with the 0, 1, 2, 3 mechanical control, not electronics like a light dimmer.Now that I am out of aces, I returned here and surprised that the circuit has evolved. :DNow which circuit will not damage electric fans? I managed to destroy some numbers of electric fans over the years. :DI tend to beleive Ante... maybe the inverter are not for Inductive Loads. :( Quote Link to comment Share on other sites More sharing options...
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