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Sicode
Apprentice
67 Posts |
 Posted - May 26 2011 : 7:15:19 PM
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Audioguru and all, a little headache here:
I noticed that majority of the digital multimeters do not read rectified voltages accurately, except maybe when used on load. reading without a load to the rectified dc givesa strange readings. It is a different case with DCs from batteries. DC voltages read out exactly their ratings when new.
I did a rectified DC from a 24vac transformer output using two diodes and two capacitors. The configuraition is of voltage doubler circuit.What could be the true nature of the voltage value?
Diode, 1N4007
Capacitors 470uF each
meter reeading on load = 23.5v
meter reading on no load = 30.2v
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - May 27 2011 : 01:57:31 AM
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| It sounds like you don't know what the meter is actually measuring. DC is fine but as soon as you start measuring the voltage of signals, you need to know what your meter is actually measuring in your signal. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - May 27 2011 : 02:21:31 AM
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Cheap non "True-RMS" meters are calibrated to show a reasonably accurate RMS voltages usually only for sinusoidal waveforms. What you need is a "True-RMS" meter. That way, your voltage measurements will equal the same RMS voltage of a voltage signal defined in a mathematical function which describes your signal.
I think you may be wondering what the hell I am talking about since you didn't give the impression you understood my mathematical model I posted on another one of your threads.
Understand what your meter is measuring. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
Edited by - wasssup1990 on May 27 2011 02:23:00 AM |
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pebe
Nobel Prize Winner
United Kingdom
1078 Posts |
Posted - May 27 2011 : 04:38:37 AM
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| I don't know what circuit you are using, but a 24V fed voltage doubler with no load and the caps you state will give almost 68VDC measured with ANY meter. |
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Sicode
Apprentice
67 Posts |
Posted - May 27 2011 : 07:18:35 AM
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| Ok wasssup. By signal I mean the dc |
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Sicode
Apprentice
67 Posts |
Posted - May 27 2011 : 07:30:14 AM
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| Pebe, you are close to my astonishment. I mean, I wonder why most meters read alot higher than the rated volage, eg., from an adaptor. My musical instrument uses a 12 adaptor. Measuring the voltage when the keyboard is powered gives the true voltage. On no load, it is much higher. Have you noticed such? I have noticed this with most phone chargers. |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - May 27 2011 : 10:05:05 AM
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All cheap unregulated power supplies have a series resistance in the windings of their transformer so have a voltage that is higher than their rating when they do not have a load. They are designed to produce their rated voltage when fully loaded.
I have a cheap 9VDC/100mA power supply that is 9.2VDC with a 100mA load and is 17.4VDC without a load.
Many of my cheap 9VDC/500mA power supplies are 9.0VDC with a 500mA load and are 11.5V with no load. Their transformers are pretty big and heavy so have low resistance.
A phone has its charging circuit inside the phone. The "charger" is simply a cheap unregulated power supply. |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - May 27 2011 : 10:46:31 AM
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Oops! For some reason I was seeing your two voltages in reverse in your first post. Not enough sleep.  That lead me to that assumption in my last post.
Power adapters with inbuilt Switch Mode Power Supplies (SMPS) have fairly good voltage regulation typically because the device they are supposed to power has tight input voltage tolerances. These devices can include phones laptops and some USB hubs. I have never had a phone that used an unregulated power adapter. These unregulated power adaptors are just simple linear power supplies consisting of only a laminated steel-cored transformer with a filtering capacitor and two rectifying diodes at the least. I have a network router power adapter that is a linear type, supposed to be 12V but measured 16V with no load. As audioguru mentioned, it's mostly due to the internal resistance of the transformer windings. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - May 27 2011 : 10:48:28 AM
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This guy's CRAZY!
Enjoy:
http://www.youtube.com/watch?v=uRriZ_ofxOk |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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Sicode
Apprentice
67 Posts |
Posted - May 27 2011 : 11:09:45 AM
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Audioguru, pebe, wassssup, you people are fantastic. Thanks for the enlightenment. Thanks for saving my meters - I could have thrown them away thinking they are bad.
But for wassssup, this quote, 'When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion'. I suppose it is not 'religion' but 'mass insanity'. A doctor in Psychiatric hospital will agree with me. Kidding, right? Nice quote.
Once more, thank you all.
FC Barcelona |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - May 27 2011 : 11:53:58 AM
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quote:
Originally posted by Sicode
Audioguru, pebe, wassssup, you people are fantastic. Thanks for the enlightenment. Thanks for saving my meters - I could have thrown them away thinking they are bad.
But for wassssup, this quote, 'When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion'. I suppose it is not 'religion' but 'mass insanity'. A doctor in Psychiatric hospital will agree with me. Kidding, right? Nice quote.
Once more, thank you all.
FC Barcelona
Religion is mass delusion. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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Sicode
Apprentice
67 Posts |
Posted - May 27 2011 : 12:18:09 PM
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Ok, wasssup. Looool!
FC Barcelona. |
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Sicode
Apprentice
67 Posts |
Posted - May 27 2011 : 12:31:40 PM
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Church people will quarrel with that: religion is mass delusion. Sciences disbelieve religion.
Thanks once more
FC Barcelona |
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Sicode
Apprentice
67 Posts |
Posted - May 27 2011 : 12:32:37 PM
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Church people will quarrel with that: religion is mass delusion. Sciences disbelieve religion.
Thanks once more
FC Barcelona |
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pebe
Nobel Prize Winner
United Kingdom
1078 Posts |
Posted - May 27 2011 : 2:26:34 PM
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quote:
Originally posted by wasssup1990
Religion is mass delusion.
Darwinians think they have all the answers, but they are just as deluded. |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - May 27 2011 : 9:30:19 PM
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Some people pray to Allah.
Other people pray to Jesus.
Other people pray to The Virgin Mary.
There are too many gods for me to select one.
If I select a god then what? |
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DC Voltage
