Thanks for making this modest-seeming video. It's laudably clear and concise, compared to a number of other overly elaborate efforts attempting to cover this same territory. Well done!
I started with Arduino about 2 years ago. Now I make my own dc lab bench power supply’s. Robot arms. The famous eggduino for Easter. I think you get it. I’ve become absolutely fascinated with electronics and building them. I have used your video’s throughout my journey. They are very helpful. They deal with components and situations I come in contact with on a day to day basis’. Thank you very much for taking the time to talk to use newbies and in a way I ,and many others can understand . If you could dive into , and explain how to use, some of these lower end oscilloscopes new people like myself are forced to buy due to financial constraints. I’d greatly appreciate it. Once again. A large thank you for all you’ve done.
Thank you for an outstanding presentation explaining 4-Wire low resistance measurement! Knowing sub-Ohm Resistance is an OK theoretical exercise, but I am using this presentation as a reference for explaining practical results when in-line Resistances occur in vintage automotive electrical systems.
Thank you for making this! I adore your videos, they are practical and easy to understand and yet I find them handy for my electronics hobby! Your teaching style is perfect and your humor makes it even better! Thanks and I hope you keep making these! (ps your site is AWESOME!)
i've made a constant current source using an opamp an a mosfet built into a bench supply i made, it has 6 presets which connects different shunt resistors so i get different current ranges i've made it so it has 100uA 1mA 2mA 10,20 and 40 mA, handy for testing LEDs, zeners up to about 15 volts (or high voltage diodes) and 4 wire resistance measurements
You can convert a constant voltage source into a constant current source with a transistor and a resistor. The resistor goes on the base and draws a negligible current, avoiding power resister and regulator.
Why doesn't the resistance of the wire matter when measuring voltage? Should you get voltage drop as well and basically have the same error from the wire resistance? Why don't multimeters implement resistance measuring this way? Thanks for the video!
Without the lm317 or any other Ic regulator, it won't be constant current. Right? I have that same power supply, but every time I across the current thru a resistor, the current flow will vary the consumption in the amperimeter based on value ohm resistance, so drop voltage. But an Ic like lm317 it will give constant current no matter watt resistance value I use. Right? I don't get it at all yet.
I don't think i can use this method to measure the internal resistance of a car battery, can i? the battery will have its own voltage unlike a piece of wire or anything else tested in this video. Any info on the topic would be much appreciated
well you'd do basically the same thing. firstly, figure out the voltage at zero load. next, put some load on it and measure the load's current and the new voltage. calculate the voltage drop and divide it by the current to get the internal resistance.
And if you don't have a variable power supply, how can you do it? you need 2 multimeters,one in series to measure amps,and another one to measure voltage, and then use ohms law, V=RI.
I don't know how exactly current limiting works in power supplies. But a basic current limiting technique is the BJT foldback circuit. What you do is put a sense resistor across Base and Emitter of a BJT and size it so that the drop across the resistor is 0.7V when you hit your set current limit. At this point, the BJT turns on and output voltage drops to insignificant value like 0.1 to 0.3V, this limits the power dissipation. Just google Foldback circuit for details.
Does it matter whether I used AC excitation source or DC excitation source? If yes which one will be good as per your suggestion if I want to measure very low resistance? Please give you suggestion.
At 3:02 did you connect the resistor to the test leads? Parallel or series? Cause whenever I turn the knob of current limiter on my bench supply it jumps back to voltage control...
if you put 1amp through a coil, doesn't it get too hot and changes its ohmian resistance so that dont measure the resistance that interests you but the resistance of the coils temperature at 1 amp?
@Serostern Liquid nitrogen doesn't stay cool forever, so I need to measure the resistance of the coil once it warms up, so I know how much longer I can make it run before shutdown is necessary : ]
if i use figure 1 from this website with 3 AA batteries what resistor should i use? what ohm and what watt. and what gauge speaker wire should i use? diyaudioprojects.blogspot.com/2008/11/simple-low-resistance-measurement.html?showComment=1522613613163#c7552392211450068627
@Serostern My power supply is made of a computer PSU so every time i connect the 12V output to a relay or an inductor it will shut down. Is there any way to prevent it from shutting down
I'm not really into electronics at all, but I might actually try this. I need to know the exact resistances of the liquid nitrogen cooled fullerene superconductor electromagnets in my deuterium-deuterium fusion reactor : P.
battery holder springs have like 60 mOhm. If you insert battery in a parallel pack in reverse, its not the battery that will smoke, but those springs. They cannot handle 5A.
Afrotechmods I guess it comes down to getting a feel for what works and what doesn't without having to calculate everything all the time -- in a word "experience." I've very much enjoyed your vids and learned a lot. You're a very good presenter. I now need to spend time at the bench making mistakes and learning the hard way!
You can use an incandescent flashlight bulb and a single "D" size battery as your current source. It won't be exactly 1 amp, so you will have to measure the current then use some math on your voltage measurement but it is a very cheap solution.
The explanation doesn't sound logical to me. How can a constant current source be possible? I thought that the current depends on the sourevoltage and the resistance, because I=U/R. If the current should be constant the sourcevoltage would have to be variable and thats not the case, or is it? Could someone please explain that to me?
Using this method on thinner wires can cause them to heat and that would mess up your measurements Wheatstone bridge may be a lot more complicated but better
Was just searching for an explanation on this method of measurement and was suddenly hit by the word „coilgun“ in the first 20s as if you would already know why I came here😅😳
4 x 5R1(5.1Ω) 5W ceramic resistors, wired in parallel... should get pretty close to 1A with LM317(1A limit= warm), (LM338 rated for 5A=not warm)... FWIW... For 12VDC situation: 120Ω 5W (ceramic 'J" series) resistor, in series, should get you in the ballpark of 100mA (0.1A)... do the math.
Funny.. I'm watching this video in an effort to measure the resistance of the commutators installed in the L-3 Brashear KTM mount (deathray) you show at the very end of the video.. Bizarre.
Thanks for making this modest-seeming video. It's laudably clear and concise, compared to a number of other overly elaborate efforts attempting to cover this same territory. Well done!
I started with Arduino about 2 years ago. Now I make my own dc lab bench power supply’s. Robot arms. The famous eggduino for Easter. I think you get it. I’ve become absolutely fascinated with electronics and building them. I have used your video’s throughout my journey. They are very helpful. They deal with components and situations I come in contact with on a day to day basis’. Thank you very much for taking the time to talk to use newbies and in a way I ,and many others can understand . If you could dive into , and explain how to use, some of these lower end oscilloscopes new people like myself are forced to buy due to financial constraints. I’d greatly appreciate it.
Once again. A large thank you for all you’ve done.
This is one of the most useful electronics tutorials I have ever seen!
@Imran Davis no problem :D
Finally made me understand what our shop micro-ohmmeter is for after not being able to "get it." Thanks
Thank you for an outstanding presentation explaining 4-Wire low resistance measurement! Knowing sub-Ohm Resistance is an OK theoretical exercise, but I am using this presentation as a reference for explaining practical results when in-line Resistances occur in vintage automotive electrical systems.
Thank you for making this! I adore your videos, they are practical and easy to understand and yet I find them handy for my electronics hobby! Your teaching style is perfect and your humor makes it even better! Thanks and I hope you keep making these! (ps your site is AWESOME!)
imho , the best electronics tutorials on youtube..
i'm your fan!!!
I always learn a lot by watching your awesome videos! Thank you for putting them on TH-cam.
You could be the best teacher EVER!
i've made a constant current source using an opamp an a mosfet built into a bench supply i made, it has 6 presets which connects different shunt resistors so i get different current ranges
i've made it so it has 100uA 1mA 2mA 10,20 and 40 mA, handy for testing LEDs, zeners up to about 15 volts (or high voltage diodes) and 4 wire resistance measurements
Couldn't you use a pot together with the LM317 instead of fixed resistors to tune it to 1A with the multimeter?
You can convert a constant voltage source into a constant current source with a transistor and a resistor. The resistor goes on the base and draws a negligible current, avoiding power resister and regulator.
Thanks a lot! I needed to test IR in my Brushless Outrunner Motor, and Now I can do it pretty easily. I just bought LM317 on ebay!
8 resistors of 10Ω/0.5W/1% connected in parallel will give you a decent 1.25Ω/4W equivalent, which is perfect for this application.
Yeah ! Dont Stop. Is this the method to measure a coil or a solenoid? Or motor coils?
Why doesn't the resistance of the wire matter when measuring voltage? Should you get voltage drop as well and basically have the same error from the wire resistance?
Why don't multimeters implement resistance measuring this way?
Thanks for the video!
did you figure it out?
Without the lm317 or any other Ic regulator, it won't be constant current. Right? I have that same power supply, but every time I across the current thru a resistor, the current flow will vary the consumption in the amperimeter based on value ohm resistance, so drop voltage. But an Ic like lm317 it will give constant current no matter watt resistance value I use. Right? I don't get it at all yet.
I don't think i can use this method to measure the internal resistance of a car battery, can i? the battery will have its own voltage unlike a piece of wire or anything else tested in this video. Any info on the topic would be much appreciated
well you'd do basically the same thing. firstly, figure out the voltage at zero load. next, put some load on it and measure the load's current and the new voltage. calculate the voltage drop and divide it by the current to get the internal resistance.
And if you don't have a variable power supply, how can you do it? you need 2 multimeters,one in series to measure amps,and another one to measure voltage, and then use ohms law, V=RI.
@dealio82 Nope, the power supply is capable of running loads of 10amps, the fuse is to protect the PSU from the input current, not the output =)
cool video!
but could you explain how this current limitation actually works inside the power supply ?
what circuit is inside it, to do that?
I was wondering the same question?
*!
I don't know how exactly current limiting works in power supplies. But a basic current limiting technique is the BJT foldback circuit. What you do is put a sense resistor across Base and Emitter of a BJT and size it so that the drop across the resistor is 0.7V when you hit your set current limit. At this point, the BJT turns on and output voltage drops to insignificant value like 0.1 to 0.3V, this limits the power dissipation. Just google Foldback circuit for details.
Does it matter whether I used AC excitation source or DC excitation source? If yes which one will be good as per your suggestion if I want to measure very low resistance? Please give you suggestion.
At 3:02 did you connect the resistor to the test leads? Parallel or series? Cause whenever I turn the knob of current limiter on my bench supply it jumps back to voltage control...
OMG! Welcome back!
Been a while. Illuminating as usual though. Or should that be electric / electrifying?
if you put 1amp through a coil, doesn't it get too hot and changes its ohmian resistance so that dont measure the resistance that interests you but the resistance of the coils temperature at 1 amp?
@Afrotechmods is that + or - 10%, or 5% ?
yes
so if i want to measure the resistance of a steel rail, which power source is suitable?
@Serostern Liquid nitrogen doesn't stay cool forever, so I need to measure the resistance of the coil once it warms up, so I know how much longer I can make it run before shutdown is necessary : ]
Just when I needed it, thanks!
Thank you a lot for this outstanding explanation on this subject. Found it very useful.
what if the DUT can take no more than 10mA, wouldn't that make your voltage measurement inaccurate?
what should i use for a power supply using the second method?
if i use figure 1 from this website with 3 AA batteries what resistor should i use? what ohm and what watt. and what gauge speaker wire should i use?
diyaudioprojects.blogspot.com/2008/11/simple-low-resistance-measurement.html?showComment=1522613613163#c7552392211450068627
@dealio82 Oh.
You needa power supply where you can adjust the amperage, the computer PSU always gives its max.
Hi. I need a low resistance tester or megger circuit diagram for graphite to voltage-current diagram on Pspice. Do you help me ?
You just earned another subscriber.
@Serostern My power supply is made of a computer PSU so every time i connect the 12V output to a relay or an inductor it will shut down. Is there any way to prevent it from shutting down
Al sacar el cable del tester cambió la resistencia, y por lo tanto, cambió la intensidad
I'm not really into electronics at all, but I might actually try this. I need to know the exact resistances of the liquid nitrogen cooled fullerene superconductor electromagnets in my deuterium-deuterium fusion reactor : P.
battery holder springs have like 60 mOhm. If you insert battery in a parallel pack in reverse, its not the battery that will smoke, but those springs. They cannot handle 5A.
can I use an precision resistor
Doesn't running a whole amp through a wire make it very hot?
Good question! It depends on the gauge (diameter) of the wire. 1A is fine for anything but extremely thin wire.
Afrotechmods I guess it comes down to getting a feel for what works and what doesn't without having to calculate everything all the time -- in a word "experience." I've very much enjoyed your vids and learned a lot. You're a very good presenter. I now need to spend time at the bench making mistakes and learning the hard way!
You can use an incandescent flashlight bulb and a single "D" size battery as your current source. It won't be exactly 1 amp, so you will have to measure the current then use some math on your voltage measurement but it is a very cheap solution.
Really nice explanation. Thanks.
sir if the wire so thin ,then how it will handle one amps
A wire with very little resistance isn't necessarily that thin. Actually the thinner the wire, the greater the resistance
good stuff. Thanks for taking the time to explain.
smart guy!! Outstanding description! Thanks so much..
isn't that a short at 3:21?
+danh le Constant current is applied at the PSU
Thanks for the response!
Ok, so i gonne google it. Sounds like an interesting idea.
The explanation doesn't sound logical to me. How can a constant current source be possible? I thought that the current depends on the sourevoltage and the resistance, because I=U/R.
If the current should be constant the sourcevoltage would have to be variable and thats not the case, or is it?
Could someone please explain that to me?
Using this method on thinner wires can cause them to heat and that would mess up your measurements
Wheatstone bridge may be a lot more complicated but better
Won't that blow a fuse in your power supply
@Afrotechmods Yeah you should keep up :D
Such a good video! Thank you!
Another great video. Thanks...
AWESOME. Now do a video on death rays XD
Great one, thanks !
Was just searching for an explanation on this method of measurement and was suddenly hit by the word „coilgun“ in the first 20s as if you would already know why I came here😅😳
THANK YOU THANK YOU THANK YOU!!!!
Awesome, thank you so much
Very Nice
As easy as that!!
Thank you
Thanks for sharing.
4 x 5R1(5.1Ω) 5W ceramic resistors, wired in parallel... should get pretty close to 1A with LM317(1A limit= warm), (LM338 rated for 5A=not warm)... FWIW...
For 12VDC situation: 120Ω 5W (ceramic 'J" series) resistor, in series, should get you in the ballpark of 100mA (0.1A)... do the math.
Awesome. Thank you.
@yellowmetalcyborg The resistace of a LN2 superconductor?
0.
That's the entire damn point of a superconductor xD
Cool tutorial
Thank you :)
i take a transformer, an electrolytic capacitor and a diode bridge. or a car battery charger.
More vids. Please!!!
Cool video
damn :-o its EXACTLY what i need :-o THANK YOU !!!!!!!!!!!!!!!!!!!!!
thx for explaining :D
Hey thanks, man.
so nice..
NEED MORE
Funny.. I'm watching this video in an effort to measure the resistance of the commutators installed in the L-3 Brashear KTM mount (deathray) you show at the very end of the video.. Bizarre.
THANKSSSSS
Damn this is hard!
cool
@dealio82 THX Man for your tips
:O
kkk