18:25 - "The path of least resistance" is a misnomer and has gotten some people killed: current takes all available paths back to the source. Mere milliamperes will kill a man. So even if the resistance path back to the source is high, if the voltage is high enough, up to several milliamps will flow through a body.
The electrical ground reference on the power grid is for lightning and atmospheric static charge arrestor. It’s also essential for safety during service and repair of the distribution network .. de-energized lines must be grounded by the work crews to perform their work.
I remember when the first colour tv came out that used a bridge rectifier in its SMPS with one leg of the bridge connected to the chassis .So the chassis was always at half mains potental. there was a whole page artical in practical television explaining the pitfalls of sevicing these sets.
I also think it’s worth to mention the issue with double insulated SMPS due to EMI Y capacitor coupling. Ie, a USB shield can have around 100V AC to true earth at about 50uA short cct current. This is particularly relevant to USB powered soldering irons that can have 100V on the tip. I solved this problem by using a USB branch connector feeding the soldering iron and connected 0V only to plug top earth. This reduced the tip voltage from 103v to 15mv.
Yeah that's what the guy on my channel said , that the Switch mode Usb PSU would induce a 90v floating potential . would this also happen with a power bank ? or batteries with a linear voltage regulator ?
A similar issue can arise with audio equipment which has only a Live and Neutral mains connection. Exposed metalwork and things like cable screens will float above earth potential. This can be dodgy when connecting it to other equipment such as a PC soundcard where the PC’s chassis is properly tied to earth by a 3 pin LNE mains connector I have blown up the front end switching IC on two different amplifiers before I got wise to this!
@Jogmaster9 awsome so if i build in a power bank in to the scope replacing the power connector with the power bank charging port and internally connect the 5V output from bank to ossiloscop. I would have a safe portable unit 😁
No problem with operating from a power bank anywhere providing you do not plug it in to charge it whilst using with a scope. Another point; when using a SMPS without a system earth the voltage on the secondary ov line (approx 100v) will not provide a risk of thermal destruction or electrocution since the PSC current is only about 50 to 100uA max but it could destroy components if using a USB soldering iron without mitigation per my original comment.
The reason I understand for grounding at the station is for lightning suppression. Without the ground, if lightning strikes anywhere along the path, it CAN follow the lines all the way into your house, until it finds a suitable ground. Being a Ham operator grounds are the most confusing for people to understand, but a ground on one side of your house can cause strikes to go through equipment to the ground, which is why I have had friends lose all of their internal home electronics due to spikes, even when the wires were grounded. ua-cam.com/video/I3sVEahjWa4/v-deo.html
Great explanation , so atmospheric electrical phenomena is the root cause for the ground , thank you for sharing . could not find this on the web at least not on a quick google search
Wonderfull full bridge explenation It is easy to make a usb cable....with shield only conected on one side..in this case the computer.The data will be fine
I 'm old school and still using an analogue scope, but of course this problem is still an issue. I also use an old school method to to prevent shocks and damage to equipment. An Isolation transformer. A 1:1 ratio mains transformer with the ground removed from the output side. You plug the DUT into the isolated output and you can now connect your scope safely as there is no path back to earth via the neutral of the DUT.
Important topic👍👍 30:52 Attention Richard, it is important which power network is installed on site. There are three basic forms: TN system, TT system and IT system as well as the following versions of the TN system: TN-S, TN-C and TN-C-S systems . Did you know which system you have?.
Actually I have a 240V:240V 2KVA Isolation transformer that powers any device I'm working on. This way I can connect any grounded test equipment to it wherever I like including on hot ground, but I didn't mention this in the video. All my test equipment is ground isolated because it is either hand held or powered from a wall wart or USB-C type power supply, apart from my Analog scope, my PC which I sometimes use as an audio source and my Rigol scope. My bench power supplies are also ground isolated (though I can set them to grounded if I so wish)
@LearnElectronicsRepair ,,, the problem is, didn't have you a two isolated transformer. Leak currents from the PLC could destroy the device being repaired (experience 😭). But, I don't think this is the case with the subwoofer. Perhaps the error lies in the supply voltage of the AD-DA converter or possibly in the PWM stage. Unbalanced sine at the output without load / input signal. Maybe i'am wrong too, 😔
Brilliant Brilliant Brilliant. What a great explanation so even I understood 😜 The combination of the 2 of you gives a great dialogue as you agree or disagree or correct eithers knowledge. And the practical use of Carlos's @RetroUpgrade oscilloscope without editing shows what its really like to use. Not so easy if the tester is a wiz with the tech while us beginners are pressing buttons and twisting knobs in the vague hope we might work it out 😅 Read the manual ? 🤔🤣
One thing to note if you are working with mains is that some of the cheap digi scopes only have a 25V maximum signal input. Using a 10x probe will work to 250V *but* the probe must be 250V rated ... Old CRTs could have input channels that would deal with 500V so it wasn't so much of an issue.
Can't thank you enough for this information. I'm new to scope usage and wasn't aware of this issue other than the next to useless chinglish user manual. Now I know and better still, have a way around the issue.
According to U.S.National Electrical code, All circuits must have ground as part of the circuit. This is done usually by tying one of the current carrying conductors to ground, the white neutral wire. Your mains neutral wire is tied to ground in the breaker box. Most countries use the U.S.National Electrical code, some with slight modification.
Well. Just power the board (not: the scope) through an isolation transformer and you can hook your scope up where you want as there's no current path existing through the scope then. Also, that makes touching things on the board safer (like heatsinks).
The inclusion of Carlos in the preceedings, especially when you were explaining theory on paper is just not required. It's a background, chattering voice that is not necessary, adding filler comments and simply detracts from your quality Richard. You, your voice, your manner and your presentation is for me what makes Learn Electronics Repair the huge force it is. OK, this is probably a one off, I hope so because you definitely don't need it so don't be tempted into thinking it does.
I cannot believe the amazing timing of this video. Luckily I'm already aware never to clip the ground clip of a scope probe to the negative of the main input capacitor after the bridge rectifier..... however last night, my probe ground clip swung down from my hand and hit a heat sink attached to the bridge rectifier.....which was connected directly to the negative side of the bridge rectifier!!!!! BANG!!!!! My house went dark and my alligator clip was blown up!!!!!
Luckily the scope is fine. I have a grounded scope and the TV board I was working on had a 4A fuse on it too. The board fuse exploded, so did the alligator clip tip, but thankfully no damage to the oscilloscope! Thanks for the upload! Great video all round. Take care!
I guess a way to remember is Hot-GND burn fingers, Earth + Hot-GND = Boom. I seem to remember the reason for Neutral been connected to Earth (and why we have an Earth wire), is so when an appliance (a Metal Appliances) shorts (loose Live wire) to Earth (metal case) it blows the fuse (Old wire fuses) which is on the Live side. Could be wrong?
Hi, yeah exactly for old style fuses for older machines it was necessary , now a days we have thermal breakers that don't actually need it , and it will trip if anything shorts internally witch would require both Live and neutral to touch the metal work . because of the concept of floating supply voltage you are the ground reference if only one wire touches the case, so nothing would happen . maybe some Mains voltage tech can clarify that is the case and there is no other rezone for this :)
Thanks for your importent guidence. Please enlighten me elaborately how to find fault of a power supply with oscilloscope . Is isolation transformer required for fault finding job? I am from INDIA, 63 years old.
Hi Richard. Thanks for this very informative video. You should have also mentioned how all this ties into the use of the isolation transformer. You dont really need to worry about hot ground then?
The bandwidth rating of a scope isn't the max frequency it can measure. Waveforms are made up of components of different frequencies put together. Square waves are very high bandwidth, for example, as they are constructed from a basically infinite amount of sinusoids. So a 100MHz scope may only be able to accurately recreate a 10MHz square wave.
Holding your probe near the transformer shows it’s working. How does it help you when the power supply isn’t working? No point in troubleshooting a working psu. I only ask because I have a ucc2800 that will not start switching for anything. This psu has thrown me for a real loop.
It helps you narrow down the fault because you know if the switching IC/Mosfet is running or not. Regards your UCC2800 based power supply. I would start by looking what is happening on Vcc (pin 7) most likely this IC uses one or more high value resistors in series which connect from HT+ ~320V from the main smoothing capacitor and these charge an electrolytic capacitor connected from pin 7 to hot ground. There could be a zener diode here too. This gives the initial voltage supply to start the UCC2800 oscillating. Then there will be an auxiliary secondary winding on the SMPS transformer which generates the voltage to keep the UCC2800 running. This will be on the high voltage side of the power supply and connect via a diode and possibly a resistor back to the electrolytic capacitor on pin 7 UCC2800. If the staryt up high value resistors are open circuit the UCC2800 can't start. If it starts but the aux supply does not come up due to some fault condition , or the electrolytic capacitor/zener diode on pin 7 is faulty, the voltage on pin 7 will drop quickly and it will stop running. Depending on the type of IC it will then either shut down until you remove mains power and reapply it, or it will continually try to start sometimes making a chirping sound. I hope that helps
Eureka ! I am starting to remember some of that circuit from your numerous wonderful drawings, so I can actually follow what you are saying, mainly 😅 Thanks Richard.
Can't help you with another sub, already subbed ;) but I can give some tips on ranking, you might mention this Dickie: Read all comments replied to *by the channel* and click the LIKE button on at least the replies by channel owner, this makes screwchoob put the channel in the "recommended videos" for others, increasing sub count very quickly (if you ask) and overall popularity of the channel, I usually do it HERE you may have noticed clicks on YOUR like button but not the comment before it - vital info to pass on. Cheers guys.
Sorry, guys, have to spoil the fun: the grounded N in a TN-C / TN-CS net is important. Without it, RCDs will not work: the failure current will have no where to go. In industrial enviroments, IT is used to get around ground failures, but that's not a good idea for us human beeings :)
There is an intermediate solution which is a high resistance ground. But solidly earthed neutrals are by far the safest. If you believe that systems not grounded to earth can’t shock you, you’re not thinking it through. Anyway, AFCI/GFCI protection is far safer than any non earthed SDS.
Perfect. Would be nice to have a full video on the topic so it can be referenced by all as the information is hard to find if you don't know what you ar looking for. Detlef are you familar with grid level systems ? Would be a interesting conversation and video 😁
18:25 - "The path of least resistance" is a misnomer and has gotten some people killed: current takes all available paths back to the source. Mere milliamperes will kill a man. So even if the resistance path back to the source is high, if the voltage is high enough, up to several milliamps will flow through a body.
Thats a great tip on using inductance to see whether the chip is running. Thanks for showing us.
The electrical ground reference on the power grid is for lightning and atmospheric static charge arrestor.
It’s also essential for safety during service and repair of the distribution network .. de-energized lines must be grounded by the work crews to perform their work.
This video is very helpful. I think every budding tinkerer should see it, because safety is always a priority. Thank you for the good work 👍
Exactly 🙂
I learnt a lot here, thank you!
Hi guys thanks for all the support 😀,
and thank you Richard always a lot of fun doing stuff with you , Cheers mate
Congratulations Carlos on 1000 subs, well done 😃
@@LearnElectronicsRepair thank M8
Heya, congrats on 1K and yes do more indept about this scoop
I remember when the first colour tv came out that used a bridge rectifier in its SMPS with one leg of the bridge connected to the chassis .So the chassis was always at half mains potental.
there was a whole page artical in practical television explaining the pitfalls of sevicing these sets.
They called it half mains potential but meant all the mains potential half the time 🤪
Well done guys - hopefully that nice explanation helps to keep people and their equipment safe. Very important stuff.
Glad you enjoyed it😊
Thanks for explaining
Onya guys, nice buy there Carlos
I also think it’s worth to mention the issue with double insulated SMPS due to EMI Y capacitor coupling. Ie, a USB shield can have around 100V AC to true earth at about 50uA short cct current. This is particularly relevant to USB powered soldering irons that can have 100V on the tip. I solved this problem by using a USB branch connector feeding the soldering iron and connected 0V only to plug top earth. This reduced the tip voltage from 103v to 15mv.
Yeah that's what the guy on my channel said , that the Switch mode Usb PSU would induce a 90v floating potential .
would this also happen with a power bank ? or batteries with a linear voltage regulator ?
A similar issue can arise with audio equipment which has only a Live and Neutral mains connection. Exposed metalwork and things like cable screens will float above earth potential.
This can be dodgy when connecting it to other equipment such as a PC soundcard where the PC’s chassis is properly tied to earth by a 3 pin LNE mains connector
I have blown up the front end switching IC on two different amplifiers before I got wise to this!
No problem with power banks etc, it’s only mains powered SMPS that do not have a network earth terminal.
@Jogmaster9 awsome so if i build in a power bank in to the scope replacing the power connector with the power bank charging port and internally connect the 5V output from bank to ossiloscop. I would have a safe portable unit 😁
No problem with operating from a power bank anywhere providing you do not plug it in to charge it whilst using with a scope.
Another point; when using a SMPS without a system earth the voltage on the secondary ov line (approx 100v) will not provide a risk of thermal destruction or electrocution since the PSC current is only about 50 to 100uA max but it could destroy components if using a USB soldering iron without mitigation per my original comment.
The reason I understand for grounding at the station is for lightning suppression. Without the ground, if lightning strikes anywhere along the path, it CAN follow the lines all the way into your house, until it finds a suitable ground. Being a Ham operator grounds are the most confusing for people to understand, but a ground on one side of your house can cause strikes to go through equipment to the ground, which is why I have had friends lose all of their internal home electronics due to spikes, even when the wires were grounded.
ua-cam.com/video/I3sVEahjWa4/v-deo.html
Great explanation , so atmospheric electrical phenomena is the root cause for the ground , thank you for sharing .
could not find this on the web at least not on a quick google search
This subject can't be repeated enough.
Wonderfull full bridge explenation
It is easy to make a usb cable....with shield only conected on one side..in this case the computer.The data will be fine
I 'm old school and still using an analogue scope, but of course this problem is still an issue. I also use an old school method to to prevent shocks and damage to equipment. An Isolation transformer. A 1:1 ratio mains transformer with the ground removed from the output side. You plug the DUT into the isolated output and you can now connect your scope safely as there is no path back to earth via the neutral of the DUT.
Very good safety information.
Thanks
Thank you
Important topic👍👍
30:52
Attention Richard, it is important which power network is installed on site. There are three basic forms: TN system, TT system and IT system as well as the following versions of the TN system: TN-S, TN-C and TN-C-S systems . Did you know which system you have?.
Actually I have a 240V:240V 2KVA Isolation transformer that powers any device I'm working on. This way I can connect any grounded test equipment to it wherever I like including on hot ground, but I didn't mention this in the video. All my test equipment is ground isolated because it is either hand held or powered from a wall wart or USB-C type power supply, apart from my Analog scope, my PC which I sometimes use as an audio source and my Rigol scope. My bench power supplies are also ground isolated (though I can set them to grounded if I so wish)
@LearnElectronicsRepair ,,, the problem is, didn't have you a two isolated transformer. Leak currents from the PLC could destroy the device being repaired (experience 😭). But, I don't think this is the case with the subwoofer. Perhaps the error lies in the supply voltage of the AD-DA converter or possibly in the PWM stage. Unbalanced sine at the output without load / input signal. Maybe i'am wrong too, 😔
Very good information!
Brilliant Brilliant Brilliant. What a great explanation so even I understood 😜
The combination of the 2 of you gives a great dialogue as you agree or disagree or correct eithers knowledge. And the practical use of Carlos's @RetroUpgrade oscilloscope without editing shows what its really like to use. Not so easy if the tester is a wiz with the tech while us beginners are pressing buttons and twisting knobs in the vague hope we might work it out 😅
Read the manual ? 🤔🤣
One thing to note if you are working with mains is that some of the cheap digi scopes only have a 25V maximum signal input. Using a 10x probe will work to 250V *but* the probe must be 250V rated ... Old CRTs could have input channels that would deal with 500V so it wasn't so much of an issue.
Can't thank you enough for this information. I'm new to scope usage and wasn't aware of this issue other than the next to useless chinglish user manual. Now I know and better still, have a way around the issue.
The AC tutorial was very nice lad's ...cheers
According to U.S.National Electrical code, All circuits must have ground as part of the circuit. This is done usually by tying one of the current carrying conductors to ground, the white neutral wire. Your mains neutral wire is tied to ground in the breaker box. Most countries use the U.S.National Electrical code, some with slight modification.
Really good explanation many thanks 😀 have you done a video on use of isolation transformers I think that would be interesting too. Thanks 😀
Heya, nice callab you too and nice review thanks
Well. Just power the board (not: the scope) through an isolation transformer and you can hook your scope up where you want as there's no current path existing through the scope then. Also, that makes touching things on the board safer (like heatsinks).
The inclusion of Carlos in the preceedings, especially when you were explaining theory on paper is just not required. It's a background, chattering voice that is not necessary, adding filler comments and simply detracts from your quality Richard. You, your voice, your manner and your presentation is for me what makes Learn Electronics Repair the huge force it is. OK, this is probably a one off, I hope so because you definitely don't need it so don't be tempted into thinking it does.
Yeah well, it didn't really bother me.
I cannot believe the amazing timing of this video. Luckily I'm already aware never to clip the ground clip of a scope probe to the negative of the main input capacitor after the bridge rectifier..... however last night, my probe ground clip swung down from my hand and hit a heat sink attached to the bridge rectifier.....which was connected directly to the negative side of the bridge rectifier!!!!! BANG!!!!! My house went dark and my alligator clip was blown up!!!!!
Hope you didn't get shocked :) and hopefully your scope was fine, ill scarify a probe any day to save the scope 😋 .
Luckily the scope is fine. I have a grounded scope and the TV board I was working on had a 4A fuse on it too. The board fuse exploded, so did the alligator clip tip, but thankfully no damage to the oscilloscope! Thanks for the upload! Great video all round. Take care!
Were you not using an isolation transformer?
I guess a way to remember is Hot-GND burn fingers, Earth + Hot-GND = Boom.
I seem to remember the reason for Neutral been connected to Earth (and why we have an Earth wire), is so when an appliance (a Metal Appliances) shorts (loose Live wire) to Earth (metal case) it blows the fuse (Old wire fuses) which is on the Live side. Could be wrong?
Hi, yeah exactly for old style fuses for older machines it was necessary , now a days we have thermal breakers that don't actually need it , and it will trip if anything shorts internally witch would require both Live and neutral to touch the metal work .
because of the concept of floating supply voltage you are the ground reference if only one wire touches the case, so nothing would happen .
maybe some Mains voltage tech can clarify that is the case and there is no other rezone for this :)
@@RetroUpgrade This is why I try to emphasised on old wiring, like mine, from the 1960s. :)
I'm still living in the 60s haha.
Thanks for your importent guidence. Please enlighten me elaborately how to find fault of a power supply with oscilloscope . Is isolation transformer required for fault finding job? I am from INDIA, 63 years old.
❤
Hi Richard. Thanks for this very informative video. You should have also mentioned how all this ties into the use of the isolation transformer. You dont really need to worry about hot ground then?
Would it really matter using hot ground if you were using a handheld scope, especially an Owon with plastic covered BNCs?
Hello Richard, can you tell us the URL for the arduino function generator, please?
Nice this last (via induction) trick....
You're welcome
The bandwidth rating of a scope isn't the max frequency it can measure. Waveforms are made up of components of different frequencies put together. Square waves are very high bandwidth, for example, as they are constructed from a basically infinite amount of sinusoids. So a 100MHz scope may only be able to accurately recreate a 10MHz square wave.
The waveforms aren’t out of phase they look to be set to different scaling( bottom left corner of the display)
It's Carlos' scope so I leave it to him to set it up properly 😅
I can assure you that half mains shocks hurt too! :-)
Интересно ❤. Лови лайк
Next lesson can be on digital ground v. analog ground v. signal ground lol learn all the grounds!
Holding your probe near the transformer shows it’s working. How does it help you when the power supply isn’t working? No point in troubleshooting a working psu. I only ask because I have a ucc2800 that will not start switching for anything. This psu has thrown me for a real loop.
It helps you narrow down the fault because you know if the switching IC/Mosfet is running or not. Regards your UCC2800 based power supply. I would start by looking what is happening on Vcc (pin 7) most likely this IC uses one or more high value resistors in series which connect from HT+ ~320V from the main smoothing capacitor and these charge an electrolytic capacitor connected from pin 7 to hot ground. There could be a zener diode here too. This gives the initial voltage supply to start the UCC2800 oscillating. Then there will be an auxiliary secondary winding on the SMPS transformer which generates the voltage to keep the UCC2800 running. This will be on the high voltage side of the power supply and connect via a diode and possibly a resistor back to the electrolytic capacitor on pin 7 UCC2800. If the staryt up high value resistors are open circuit the UCC2800 can't start. If it starts but the aux supply does not come up due to some fault condition , or the electrolytic capacitor/zener diode on pin 7 is faulty, the voltage on pin 7 will drop quickly and it will stop running. Depending on the type of IC it will then either shut down until you remove mains power and reapply it, or it will continually try to start sometimes making a chirping sound. I hope that helps
Eureka ! I am starting to remember some of that circuit from your numerous wonderful drawings, so I can actually follow what you are saying, mainly 😅
Thanks Richard.
Can't help you with another sub, already subbed ;) but I can give some tips on ranking, you might mention this Dickie: Read all comments replied to *by the channel* and click the LIKE button on at least the replies by channel owner, this makes screwchoob put the channel in the "recommended videos" for others, increasing sub count very quickly (if you ask) and overall popularity of the channel, I usually do it HERE you may have noticed clicks on YOUR like button but not the comment before it - vital info to pass on. Cheers guys.
Thank you for the support every thing helps. Cheers mate 😊
So the power company in the name of simplicity should not ground the neutral.
Yeah pretty much the conclusion me and Ricard reached as well 🤣😂, cheers mate and thank you for the comment and view :)
Sorry, guys, have to spoil the fun: the grounded N in a TN-C / TN-CS net is important. Without it, RCDs will not work: the failure current will have no where to go. In industrial enviroments, IT is used to get around ground failures, but that's not a good idea for us human beeings :)
There is an intermediate solution which is a high resistance ground.
But solidly earthed neutrals are by far the safest.
If you believe that systems not grounded to earth can’t shock you, you’re not thinking it through.
Anyway, AFCI/GFCI protection is far safer than any non earthed SDS.
Perfect. Would be nice to have a full video on the topic so it can be referenced by all as the information is hard to find if you don't know what you ar looking for. Detlef are you familar with grid level systems ? Would be a interesting conversation and video 😁