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Turn Your Power Supply into an Ohmmeter - It's Free!
I got tired of switching the leads of my DMM. Suddenly if dawned on
me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
Watson A.Name - 'Watt Sun' wrote in
: I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. Also, you must now consider the combined accuracy, of two meters, instead of just one. Yes it works, but, so do pliers on a hex-nut. Something about the right tool for the job. |
Turn Your Power Supply into an Ohmmeter - It's Free!
Congratulations. You proved Ohm's Law works. Of course it's only as accurate
as your meters, then you have to use your calculator. Sorry, but give me a decent digital multimeter. Your method is certainly worth remembering in a pinch. Mark Z. "Watson A.Name - 'Watt Sun'" wrote in message .. . I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Watson A.Name - 'Watt Sun'" wrote in message
.. . I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. Yep, that's how ohmmeters work actually. I'm currently designing a digitally controlled PSU which includes a dot-matrix LCD that shows a lot of info about the state of the PSU. For e.g., it multiplies V * I so the user can see the load power in real-time. Simple, but very handy. I suppose I could also have it display V / I to show the load resistance in real-time. I think the PSU approach is good for measuring very small resistances (when you need to generate a lot of current to have a voltage drop large enough to measure accurately. cheers, Costas |
Turn Your Power Supply into an Ohmmeter - It's Free!
In article ,
"Costas Vlachos" wrote: "Watson A.Name - 'Watt Sun'" wrote in message .. . I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. Yep, that's how ohmmeters work actually. I'm currently designing a digitally controlled PSU which includes a dot-matrix LCD that shows a lot of info about the state of the PSU. For e.g., it multiplies V * I so the user can see the load power in real-time. Simple, but very handy. I suppose I could also have it display V / I to show the load resistance in real-time. I think the PSU approach is good for measuring very small resistances (when you need to generate a lot of current to have a voltage drop large enough to measure accurately. At a local electronics store, there was a sale of multimeters for $5. I bought a bunch and have velcroed some to my workbench. I set them for voltage, current or resistance and leave them there. Good cheap way of doing some quick and dirty measurements. Surprisingly accurate too. If I smoke one, I just toss it. After all, it is a toss away world nowadays. Al -- There's never enough time to do it right the first time....... |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Mark D. Zacharias" wrote in message
link.net... Congratulations. You proved Ohm's Law works. Actually it is the resistance formula that works. What you think is Ohm's (V=IR) is not. See the links below and a good physics book. Ratch http://maxwell.byu.edu/~spencerr/websumm122/node50.html http://www.launc.tased.edu.au/online...Resistance.htm Of course it's only as accurate as your meters, then you have to use your calculator. Sorry, but give me a decent digital multimeter. Your method is certainly worth remembering in a pinch. Mark Z. "Watson A.Name - 'Watt Sun'" wrote in message .. . I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
Watt Sun:
Just a little cumbersome.... isn't it?? As you indicated, there is a risk of smoking low ohm, low wattage resistors unless you already know the value... if that is the case then why are you measuring it??...... .....and the accuracy is compromised because you are measuring the voltage and then measuring the current..... and you are at the mercy of the regulation of your power supply. 2 meter operations instead of one... the inherent innaccuracy of one of the readings is further compromised by the inaccuracy of the 2nd reading..... give me a DMM or VOM with a dedicated OHMS function any time.. Actually, the much more used and handier version of this is the "flip-side" where you measure the voltage across a known-value resistor in the circuit to determine the approximate current.... most techs do this all the time while routinely troubleshooting. -- Best Regards, Daniel Sofie Electronics Supply & Repair --------------------------------- "Watson A.Name - 'Watt Sun'" wrote in message I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. |
Turn Your Power Supply into an Ohmmeter - It's Free!
In sci.electronics.misc Watson A.Name - 'Watt Sun' wrote:
I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. This isn't especially usefull usually. However, with low ohm resistors, it can be. Given a constant current of an amp, the $5 meters mentioned elsewhere can now measure with a resolution of .1mohm. -- http://inquisitor.i.am/ | | Ian Stirling. ---------------------------+-------------------------+-------------------------- My inner child can beat up your inner child. - Alex Greenbank |
Turn Your Power Supply into an Ohmmeter - It's Free!
Yes, and Ohm's Law describes the interaction of resistance, voltage, and
current. Not just resistance. I'm not an engineer, granted, but I don't require an education on Ohm's Law. Mark Z. Actually it is the resistance formula that works. What you think is Ohm's (V=IR) is not. See the links below and a good physics book. "Ratch" wrote in message et... "Mark D. Zacharias" wrote in message link.net... Congratulations. You proved Ohm's Law works. Actually it is the resistance formula that works. What you think is Ohm's (V=IR) is not. See the links below and a good physics book. Ratch http://maxwell.byu.edu/~spencerr/websumm122/node50.html http://www.launc.tased.edu.au/online...ctric/resistnc /Resistance.htm Of course it's only as accurate as your meters, then you have to use your calculator. Sorry, but give me a decent digital multimeter. Your method is certainly worth remembering in a pinch. Mark Z. "Watson A.Name - 'Watt Sun'" wrote in message .. . I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Mark D. Zacharias" wrote in message link.net... Yes, and Ohm's Law describes the interaction of resistance, voltage, and current. Not just resistance. I'm not an engineer, granted, but I don't require an education on Ohm's Law. Mark Z. I belive that you are missing the point. The resistance (or impedance) formula V=IR (or V=IZ), describes the describes the interaction of resistance (impedance), voltage, and current. While correct and true in all cases, those formulas are NOT Ohm's law, and it is wrong to call them that. As shown in the second link I gave, Ohm's law is a property of resistive linearity in a material. Just as the specific gravity of a material is a property. If it conforms to Ohm's law, it is ohmic. Otherwise it is nonohmic. Ratch Actually it is the resistance formula that works. What you think is Ohm's (V=IR) is not. See the links below and a good physics book. Ratch http://maxwell.byu.edu/~spencerr/websumm122/node50.html http://www.launc.tased.edu.au/online...ctric/resistnc /Resistance.htm |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Mark D. Zacharias" wrote in message link.net... Yes, and Ohm's Law describes the interaction of resistance, voltage, and current. Not just resistance. I'm not an engineer, granted, but I don't require an education on Ohm's Law. Mark Z. I belive that you are missing the point. The resistance (or impedance) formula V=IR (or V=IZ), describes the describes the interaction of resistance (impedance), voltage, and current. While correct and true in all cases, those formulas are NOT Ohm's law, and it is wrong to call them that. As shown in the second link I gave, Ohm's law is a property of resistive linearity in a material. Just as the specific gravity of a material is a property. If it conforms to Ohm's law, it is ohmic. Otherwise it is nonohmic. Ratch Actually it is the resistance formula that works. What you think is Ohm's (V=IR) is not. See the links below and a good physics book. Ratch http://maxwell.byu.edu/~spencerr/websumm122/node50.html http://www.launc.tased.edu.au/online...ctric/resistnc /Resistance.htm |
Turn Your Power Supply into an Ohmmeter - It's Free!
In article ,
mentioned... Watt Sun: Just a little cumbersome.... isn't it?? Less cumbersome than removing the DMM leads and then reconnecting them. As you indicated, there is a risk of smoking low ohm, low wattage resistors Yes, as I indicated. unless you already know the value... if that is the case then why are you measuring it??...... If you already know the value, then there'd be no point in measuring it. So you would be measuring the unknown value to determine it. ....and the accuracy is compromised because you are measuring the voltage and then measuring the current..... It still finds the value with a reasonable accuracy. and you are at the mercy of the regulation of your power supply. The regulation of the power supply makes no difference. 2 meter operations instead of one... the inherent innaccuracy of one of the readings is further compromised by the inaccuracy of the 2nd reading..... You're repeating yourself. As I said above, it still finds the value with reasonable accuracy. give me a DMM or VOM with a dedicated OHMS function any time.. If you reread my post, you would see that I already have the DMM. I was using an alternate method. If the VOM you mention above is an analog wiggle stick meter, it may be less accurate - maybe only 3% - than using my PS method. Actually, the much more used and handier version of this is the "flip-side" where you measure the voltage across a known-value resistor in the circuit to determine the approximate current.... most techs do this all the time while routinely troubleshooting. Right. Now you've stated something useful. -- Best Regards, Daniel Sofie Electronics Supply & Repair --------------------------------- "Watson A.Name - 'Watt Sun'" wrote in message I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
In article ,
mentioned... In sci.electronics.misc Watson A.Name - 'Watt Sun' wrote: I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. This isn't especially usefull usually. However, with low ohm resistors, it can be. Given a constant current of an amp, the $5 meters mentioned elsewhere can now measure with a resolution of .1mohm. I bought a few of those $5 DMMs from Futurlec a few months ago, actually I think they were about $6. 9V vattery included(!) -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
During a canal boat holiday, my brother enquired what current the
starter took from the battery. I found that my cheap pocket DMM would read the millivolts across the earth strap when we turned on all the lights of known wattage; and it would also read the volts across the strap whilst the starter was turning. So we were able to calculate the starter motor current as around 200 A whilst turning steadily (but not the peaks). I forget how we strangled the engine (diesel) to stop it starting during this experiment. Could we have let air in somehow? Maybe there was a stop valve? BillJ (Edinburgh) On Wed, 16 Jul 2003 01:34:28 -0700, Watson A.Name - 'Watt Sun' wrote: I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Watson A.Name - 'Watt Sun'" wrote in message .. . In article , mentioned... "Mark D. Zacharias" wrote in message link.net... Congratulations. You proved Ohm's Law works. Actually it is the resistance formula that works. What you think is Ohm's (V=IR) is not. See the links below and a good physics book. Ratch http://maxwell.byu.edu/~spencerr/websumm122/node50.html http://www.launc.tased.edu.au/online...Resistance.htm And both Mark Z and Ratch are barking up the wrong tree. If they were to reread my post below, they would see that I used the formula, R=V/I, which in both URLs above was shown first and named Ohm's Law. Doh. No, both the above URLs make a point of saying that R=V/I is not Ohm's law, and the first refers to R=V/I as the resistance formula. In other words, Ohm's law referring to V=IR is a misnomer. The second URL points out that Ohm's law really and truly refers to the resistive linearity of a material. Dah. By the way, you did not turn your electrical energy supply into a ohmmeter. You applied a method of using the energy supply to determine resistance. Ratch Of course it's only as accurate as your meters, then you have to use your calculator. Sorry, but give me a decent digital multimeter. Your method is certainly worth remembering in a pinch. Mark Z. "Watson A.Name - 'Watt Sun'" wrote in message .. . I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. |
Turn Your Power Supply into an Ohmmeter - It's Free!
In article ,
mentioned... "Watson A.Name - 'Watt Sun'" wrote: I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. Dangerous and inaccurate. Inaccurate, because the resistor will warm up and the resistance will increase. Using a volt meter and ammeter is certainly cheap and practical for measuring a very low resistance that the typical DMM can not. Say you have a 25ft 12AWG extension cord and you want to know the total resistance. The average DMM has a resolution down to 100mOhm. The resolution is nowhere near what you need. Connect it to ~12V DC(you don't want to use 120V, because high floating voltage will throw off accuracy on the low voltage meter range) and connect an ammeter in series. Connect a load on the other end that takes about a few amps. Or use a constant current PS and short the far end of the cord, and measure across both conductors on the near end. Measure the voltage across both ends of one conductor in mV range. If you read 54.6mV and the ammeter reads 2.12A, you can figure out the resistance by: 0.0546/2.12=0.02575 three sig dig=0.0258ohms=258mOhms x 2(to accomodate for return path)=506mOhms Or you can just look up the resistance in a wire table and find that 12 AWG has 1.59 milliohms per foot. Then multiply by twice the cord length. As for being "dangerous and inaccurate", electronics experimenting is frought with danger, one being 'letting the smoke out.' As for "Inaccurate, because the resistor will warm up and the resistance will increase", you could have the same problem if you were measuring a resistor with a DMM, and the equipmewnt with the resistor had been powered on before you did the measurement. The resistor could already be hot. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
In article tdvRa.71417$OZ2.13017@rwcrnsc54,
mentioned... "Watson A.Name - 'Watt Sun'" wrote in message .. . In article , mentioned... "Mark D. Zacharias" wrote in message link.net... Congratulations. You proved Ohm's Law works. Actually it is the resistance formula that works. What you think is Ohm's (V=IR) is not. See the links below and a good physics book. Ratch http://maxwell.byu.edu/~spencerr/websumm122/node50.html http://www.launc.tased.edu.au/online...Resistance.htm And both Mark Z and Ratch are barking up the wrong tree. If they were to reread my post below, they would see that I used the formula, R=V/I, which in both URLs above was shown first and named Ohm's Law. Doh. No, both the above URLs make a point of saying that R=V/I is not Ohm's law, and the first refers to R=V/I as the resistance formula. In other words, Ohm's law referring to V=IR is a misnomer. The second URL points out that Ohm's law really and truly refers to the resistive linearity of a material. Dah. This is *still* pointless. I *never* claimed that I was doing *anything* with _Ohm's_Law_!! Quit trying to put words in my mouth! See my OP below. [snip] Ratch Of course it's only as accurate as your meters, then you have to use your calculator. Sorry, but give me a decent digital multimeter. Your method is certainly worth remembering in a pinch. Mark Z. "Watson A.Name - 'Watt Sun'" wrote in message .. . I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Turn Your Power Supply into an Ohmmeter - It's Free!
Watson A.Name - 'Watt Sun' wrote: This is *still* pointless. I *never* claimed that I was doing *anything* with _Ohm's_Law_!! Quit trying to put words in my mouth! See my OP below. [snip] It doesn't matter what your original post said, the OM found a factoid, and wants to show it off! -Chuck, WA3UQV |
Turn Your Power Supply into an Ohmmeter - It's Free!
In sci.electronics.misc Watson A.Name - 'Watt Sun' wrote:
In article , mentioned... In sci.electronics.misc Watson A.Name - 'Watt Sun' wrote: I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. This isn't especially usefull usually. However, with low ohm resistors, it can be. Given a constant current of an amp, the $5 meters mentioned elsewhere can now measure with a resolution of .1mohm. I bought a few of those $5 DMMs from Futurlec a few months ago, actually I think they were about $6. 9V vattery included(!) Very handy indeed. The ones I bought were 3 pounds 99p, ($6us?) I have around 8. Soon after buying one, I thought I'd discovered that they have an overvoltage LED. However, the smell of burning FR4 soon made me realise otherwise. It's amazing how many multimeters you can use when you have them free. I was just discharging a series string of Li-Ion batteries, to measure capacities. In the past I would have taken measurements every 5 minutes to ensure none had approached 3V. Why bother, just hook up 5 of them, and glance over every once in a while., -- http://inquisitor.i.am/ | | Ian Stirling. ---------------------------+-------------------------+-------------------------- Lord, grant me the serenity to accept that I cannot change, the courage to change what I can, and the wisdom to hide the bodies of those I had to kill because they ****ed me off. - Random |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Alan Harriman" wrote to "All" (16 Jul 03 22:18:49)
--- on the topic of " Turn Your Power Supply into an Ohmmeter - It's Free!" Most Englishmen were also expecting biscuits and cheese on the Moon... And so too apples bopped people on the head because the Earth sucked. However, the German physicist George Simon Ohm found that a current flowing through a conductor is directly proportional to the electrical force that produces it. i.e. E=IR So the other fellow with the ohmic and non ohmic materials discussion is trying to pull a fast one. i.e. a troll AH From: Alan Harriman AH C'mon, we've been calling it Ohm's law since elementary school. Now AH you're gonna tell us we're all wrong? If enough people call it Ohm's AH law, then it's Ohm's law. : - ) AH Alan Harriman .... Is reactance then illusory? No, it just appears that way... |
Turn Your Power Supply into an Ohmmeter - It's Free!
the bottom line is that you are recreating an ohm meter except that it
has two meters. a standard ohm meter does exactly the same thing using an internal battery |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Ratch" wrote in message
news:BZmRa.80118$Ph3.9181@sccrnsc04... While correct and true in all cases, those formulas are NOT Ohm's law, and it is wrong to call them that. Dude, go back to school, Algebra 1. V=IR I=V/R R=V/I etc. The equation can be rearranged to any of the others by simple multiplication and division by whichever variable. Tim -- In the immortal words of Ned Flanders: "No foot longs!" Website @ http://webpages.charter.net/dawill/tmoranwms |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Watson A.Name - 'Watt Sun'" wrote in message
.. . As for "Inaccurate, because the resistor will warm up and the resistance will increase", you could have the same problem if you were measuring a resistor with a DMM, and the equipmewnt with the resistor had been powered on before you did the measurement. The resistor could already be hot. And besides that, it measures actual in-circuit conditions, because a resistor is *supposed* to get hot, at least if it's doing its job... Tim (can't believe the number of negative replies on this thread) -- In the immortal words of Ned Flanders: "No foot longs!" Website @ http://webpages.charter.net/dawill/tmoranwms |
Turn Your Power Supply into an Ohmmeter - It's Free!
How hot?
-------------- And besides that, it measures actual in-circuit conditions, because a resistor is *supposed* to get hot, at least if it's doing its job... |
Turn Your Power Supply into an Ohmmeter - It's Free!
How hot? One solution is P=EI, where power in watts is equal to the product
of voltage and current. So the voltage drop across the resistor multiplied by the current in amps through the resistor will yield watts of heat created by the resistor. Now, if you know the composition of the resistor, you can look up the specific heat of the material and calculate how much energy it takes to change its temperature. You will need to know how many joules of energy have been applied. Calculate the joules by multiplying the time that the power was applied in seconds by the power in watts. Now look at the specific heat table and it will tell you how many joules per Kelvin it takes to raise the temperature. If you have any physics experience, it will be very simple. Cheers! Chip Shults My robotics, space and CGI web page - http://home.cfl.rr.com/aichip |
Turn Your Power Supply into an Ohmmeter - It's Free!
Sir Charles W. Shults III:
That is a good in depth, overly complicated, answer but not the one I was looking for..... obviously since the Tim Williams posting said ".And besides that, it measures actual in-circuit conditions, because a resistor is *supposed* to get hot, at least if it's doing its job..." ..... and since the overly discussed "2 meters and power supply" ohm meter method can overheat low-ohm resistors..... and the resistance of any resistor will vary with temperature..... I was wondering at what exact "hot" temperature the resistor should be at to make an accurate measurement..... LOL Obviously I am not looking for any kind of answer here....... I just think that this thread went bonkers when all the original poster wanted to do is, as Chuck Harris indicated in his reply post, show off his new found factoid.... however it seems clear that it may not be a very practical and convenient method as evidenced by the length and tone of the majority of the reply posts. -- Best Regards, Daniel Sofie Electronics Supply & Repair - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "Sir Charles W. Shults III" wrote in message . com... How hot? One solution is P=EI, where power in watts is equal to the product of voltage and current. So the voltage drop across the resistor multiplied by the current in amps through the resistor will yield watts of heat created by the resistor. Now, if you know the composition of the resistor, you can look up the specific heat of the material and calculate how much energy it takes to change its temperature. You will need to know how many joules of energy have been applied. Calculate the joules by multiplying the time that the power was applied in seconds by the power in watts. Now look at the specific heat table and it will tell you how many joules per Kelvin it takes to raise the temperature. If you have any physics experience, it will be very simple. Cheers! Chip Shults My robotics, space and CGI web page - http://home.cfl.rr.com/aichip |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Sofie" wrote in message
... Sir Charles W. Shults III: That is a good in depth, overly complicated, answer but not the one I was looking for..... obviously since the Tim Williams posting said ".And besides that, it measures actual in-circuit conditions, because a resistor is *supposed* to get hot, at least if it's doing its job..." Thanks, I think. Well, for most applications, the variation does not really matter. But "overly complicated" is a relative thing. Without all those steps and facts, you can't really derive an answer at all. That is, unless somebody has made a chart like a nomograph where you pick out the resistor type and go to a table, start at the room temperature, drop a ruler across to a power value, and derive the reading from a scale. Cheers! Chip Shults My robotics, space and CGI web page - http://home.cfl.rr.com/aichip |
Turn Your Power Supply into an Ohmmeter - It's Free!
Ian Stirling wrote:
In sci.electronics.misc Watson A.Name - 'Watt Sun' wrote: In article , mentioned... In sci.electronics.misc Watson A.Name - 'Watt Sun' wrote: I got tired of switching the leads of my DMM. Suddenly if dawned on me that I can just set the power supply to 10.0V for exaample, and read the current, and then divide the voltage by the current to find the resistance. Like I put a resistance on the PS, it reads 10.0V and the current is .018A, so 10 / .018 gives 555.6 ohms. Must be a 560 ohm resistor. I turned my PS into an ohmmeter - FREE! Hee-hee - Work smarter, not harder! Of course, make sure the current stays low so the resistance doesn't overheat. For low resistances use a volt or less. This isn't especially usefull usually. However, with low ohm resistors, it can be. Given a constant current of an amp, the $5 meters mentioned elsewhere can now measure with a resolution of .1mohm. I bought a few of those $5 DMMs from Futurlec a few months ago, actually I think they were about $6. 9V vattery included(!) Very handy indeed. The ones I bought were 3 pounds 99p, ($6us?) I have around 8. Soon after buying one, I thought I'd discovered that they have an overvoltage LED. However, the smell of burning FR4 soon made me realise otherwise. But, But.. Doesn't the FR in FR4 mean flame resistant? If so, how could it burn? Char? It's amazing how many multimeters you can use when you have them free. I was just discharging a series string of Li-Ion batteries, to measure capacities. In the past I would have taken measurements every 5 minutes to ensure none had approached 3V. Why bother, just hook up 5 of them, and glance over every once in a while., -- ----------------(from OED Mini-Dictionary)----------------- PUNCTUATION - Apostrophe Incorrect uses: (i) the apostrophe must not be used with a plural where there is no possessive sense, as in ~tea's are served here~; (ii) there is no such word as ~her's, our's, their's, your's~. Confusions: it's = it is or it has (not 'belonging to it'); correct uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone); but ~the dog wagged its tail~ (no apostrophe). ----------------(For the Apostrophe challenged)---------------- From a fully deputized officer of the Apostrophe Police! Spammers use Weapons of Mass Distraction! I bought some batteries, but they weren't included, so I had to buy them again. -- Steven Wright FOR SALE: Nice parachute: never opened - used once. F o d d e r f o r s t u p i d n o t e n o u g h i n c l d u d e d t e x t e r r o r m s g .. |
Turn Your Power Supply into an Ohmmeter - It's Free!
"Tim Williams" wrote in message ... "Ratch" wrote in message news:BZmRa.80118$Ph3.9181@sccrnsc04... While correct and true in all cases, those formulas are NOT Ohm's law, and it is wrong to call them that. Dude, go back to school, Algebra 1. V=IR I=V/R R=V/I etc. The equation can be rearranged to any of the others by simple multiplication and division by whichever variable. Tim I believe everyone on this newsgroup can isolate each of the terms algebraically. What is your point? What don't you agree with? What is incorrect? Be specific. Ratch |
Turn Your Power Supply into an Ohmmeter - It's Free!
Tim Williams wrote:
"Watson A.Name - 'Watt Sun'" wrote in message .. . As for "Inaccurate, because the resistor will warm up and the resistance will increase", you could have the same problem if you were measuring a resistor with a DMM, and the equipmewnt with the resistor had been powered on before you did the measurement. The resistor could already be hot. And besides that, it measures actual in-circuit conditions, because a resistor is *supposed* to get hot, at least if it's doing its job... Excellent point. If you adjust the voltage (and current) to the same as the V (and current) in circuit, then your measurement reflects a more realistic value of resistance. And another thought. If you are trying to ferret out an intermittent problem, then subjecting the resistor to similar V and I conditions found in the circuit can help make the problem appear, so it an be isolated to a certain component. Tim (can't believe the number of negative replies on this thread) -- -- ----------------(from OED Mini-Dictionary)----------------- PUNCTUATION - Apostrophe Incorrect uses: (i) the apostrophe must not be used with a plural where there is no possessive sense, as in ~tea's are served here~; (ii) there is no such word as ~her's, our's, their's, your's~. Confusions: it's = it is or it has (not 'belonging to it'); correct uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone); but ~the dog wagged its tail~ (no apostrophe). ----------------(For the Apostrophe challenged)---------------- From a fully deputized officer of the Apostrophe Police! Spammers use Weapons of Mass Distraction! I bought some batteries, but they weren't included, so I had to buy them again. -- Steven Wright FOR SALE: Nice parachute: never opened - used once. F o d d e r f o r s t u p i d n o t e n o u g h i n c l d u d e d t e x t e r r o r m s g .. |
Turn Your Power Supply into an Ohmmeter - It's Free!
Sofie wrote:
How hot? -------------- I squared R hot, in watts or fraction thereof. And that value should be (somewhat) less than the maximum rating for that component. You could be running just a few volts across a 1/8W resistor, and it may not feel so hot to the touch, but it may be running at or above its rated dissipation. And that's not cool, no pun intended. :-) And besides that, it measures actual in-circuit conditions, because a resistor is *supposed* to get hot, at least if it's doing its job... -- ----------------(from OED Mini-Dictionary)----------------- PUNCTUATION - Apostrophe Incorrect uses: (i) the apostrophe must not be used with a plural where there is no possessive sense, as in ~tea's are served here~; (ii) there is no such word as ~her's, our's, their's, your's~. Confusions: it's = it is or it has (not 'belonging to it'); correct uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone); but ~the dog wagged its tail~ (no apostrophe). ----------------(For the Apostrophe challenged)---------------- From a fully deputized officer of the Apostrophe Police! Spammers use Weapons of Mass Distraction! I bought some batteries, but they weren't included, so I had to buy them again. -- Steven Wright FOR SALE: Nice parachute: never opened - used once. F o d d e r f o r s t u p i d n o t e n o u g h i n c l d u d e d t e x t e r r o r m s g .. |
Turn Your Power Supply into an Ohmmeter - It's Free!
Sir Charles W. Shults III wrote:
How hot? One solution is P=EI, where power in watts is equal to the product of voltage and current. So the voltage drop across the resistor multiplied by the current in amps through the resistor will yield watts of heat created by the resistor. Now, if you know the composition of the resistor, you can look up the specific heat of the material and calculate how much energy it takes to change its temperature. You will need to know how many joules of energy have been applied. Calculate the joules by multiplying the time that the power was applied in seconds by the power in watts. Now look at the specific heat table and it will tell you how many joules per Kelvin it takes to raise the temperature. If you have any physics experience, it will be very simple. Whew! Sounds like an experiment in calorie whatever, with all the thermometer measurements, etc. Yeah, now I remember. It's called Cold Fusion!! Cheers! Chip Shults -- ----------------(from OED Mini-Dictionary)----------------- PUNCTUATION - Apostrophe Incorrect uses: (i) the apostrophe must not be used with a plural where there is no possessive sense, as in ~tea's are served here~; (ii) there is no such word as ~her's, our's, their's, your's~. Confusions: it's = it is or it has (not 'belonging to it'); correct uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone); but ~the dog wagged its tail~ (no apostrophe). ----------------(For the Apostrophe challenged)---------------- From a fully deputized officer of the Apostrophe Police! Spammers use Weapons of Mass Distraction! I bought some batteries, but they weren't included, so I had to buy them again. -- Steven Wright FOR SALE: Nice parachute: never opened - used once. F o d d e r f o r s t u p i d n o t e n o u g h i n c l d u d e d t e x t e r r o r m s g .. |
Turn Your Power Supply into an Ohmmeter - It's Free!
When I need to power some of my smaller creations I use an ohmmeter as a
power supply... |
Turn Your Power Supply into an Ohmmeter - It's Free!
Well, if you think about it, doing cold fusion experiments will teach you
everything you need to know about calorimetry and heat measurement! So even if the effect is never shown to yield any anomalous heat, you still got an education. Funny how pursuing even an odd question can teach you worlds. Cheers! Chip Shults My robotics, space and CGI web page - http://home.cfl.rr.com/aichip |
Turn Your Power Supply into an Ohmmeter - It's Free!
Tim Williams wrote: Tim (can't believe the number of negative replies on this thread) Exactly. It is un-eff-ing believable how some people just love to snipe. I wonder how many of the "snipers" ever had to brew a meter shunt? You can use the "Watson ohmmeter" for that - and, as another poster mentioned - toss your Fluke in the dustbin. :-) |
Turn Your Power Supply into an Ohmmeter - It's Free!
Ian Stirling wrote: Very handy indeed. The ones I bought were 3 pounds 99p, ($6us?) I have around 8. Soon after buying one, I thought I'd discovered that they have an overvoltage LED. However, the smell of burning FR4 soon made me realise otherwise. It's amazing how many multimeters you can use when you have them free. I was just discharging a series string of Li-Ion batteries, to measure capacities. In the past I would have taken measurements every 5 minutes to ensure none had approached 3V. Why bother, just hook up 5 of them, and glance over every once in a while., YES!!!! I had a situation where I needed to continually and simultaneously monitor current and voltage into and out of a dc-dc converter with two outputs, while varying the loads and the input supply. Some asshole said he could do it with two meters - another "sniper" who obviously did not understand the word "simultaneously". Anyway, there's a catalog outfit named Harbor Freight, and they had multimeters on sale for $2.99 including the 9V battery. I bought 4 of them. As you correctly pointed out, it's amazing how many you can use at the same time when they are just sitting around waiting for use! -- http://inquisitor.i.am/ | | Ian Stirling. ---------------------------+-------------------------+-------------------------- Lord, grant me the serenity to accept that I cannot change, the courage to change what I can, and the wisdom to hide the bodies of those I had to kill because they ****ed me off. - Random |
Turn Your Power Supply into an Ohmmeter - It's Free!
After all that I still can't get my ohmmeter to work as a power supply!!!
|
Turn Your Power Supply into an Ohmmeter - It's Free!
Ratch wrote:
"Tim Williams" wrote in message ... "Ratch" wrote in message news:BZmRa.80118$Ph3.9181@sccrnsc04... While correct and true in all cases, those formulas are NOT Ohm's law, and it is wrong to call them that. Dude, go back to school, Algebra 1. V=IR I=V/R R=V/I etc. The equation can be rearranged to any of the others by simple multiplication and division by whichever variable. Tim I believe everyone on this newsgroup can isolate each of the terms algebraically. What is your point? What don't you agree with? What is incorrect? Be specific. Ratch I think, for "practical" electronics, the "ohmic" and "non-ohmic" properties of resitance and its implication in the Ohm's Law equation is largely depreciated. All resistors are likely assumed ohmic except for specialty devices or applications, most of which deal with temperature and not voltage. Personally, I find the voltage-dependant-negative-coefficient resistances (such as carbon fiber) particularly interesting. :) |
Turn Your Power Supply into an Ohmmeter - It's Free!
Mark Mcmillan wrote:
After all that I still can't get my ohmmeter to work as a power supply!!! I was going to ask you to check out an image, but I can't find it... anyways it was a simple circuit I drew and simulated in proteus. It was a battery, a lightbulb, and an ohmmeter across the lamp. The lamp was lit and the resistance was 120 ohms... Oh well it might have been funnier with the actual drawing. Man I need to get out more... :) |
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