*Before someone else mentions, you also find dangerous high voltages in the large capacitors in Audio Amplifiers, and in the LED backlight drive circuit for LED TV, amongst other places*
A little 230V 20W incandescent bulb permanently attached to old short probes, covered with semi-transparent buble wrap so it's indestructible, is always hanging on my tool wall for exactly that. Self limits the current to less than 100 mA but draws almost same current from much lower voltages, so discharges caps almost instantly to safe levels. Made it right after I got a real nusty shock while repairing a board many years back...
This was an awesome video and... Covers a lot of the basics and you sure explained everything quite well very in-depth explanation and then we proceeded to make a discharge device, and demonstrate how it works with real-world examples. I enjoyed it immensely.
Wow. This is an excellent and informative video. It certainly has been an eye opener. I have seen so many shorting the capacitors to discharge them, but it is very dangers to do so and bad for the capacitor. I liked the resistor and diod method. I will try it. Thank you once again.
Interesting video! An alternative if you only want 1 led, would be to use a bridge rectifier before the discharge resistor, depending on what parts are available, so it won't matter which way the probes are connected. It's great this can be made from salvaged parts!
For the simplest circuit with the lowest component count, use 2 bridge rectifiers connected in series (AC side) to the probes. On the DC side connect the negative of the first to the positive of the second and the LED+resistor between the positive of the first and the negative of the second. 5 components including the bulk resistor. You can use very small bridge rectifiers (>0.1A) and a bulk resistor of 4K7 ohms for fast safe discharge even at 440V. If you use a 5W resistor it will exceed its rating but for such a short period there's no time for it to overheat.
Built a variant of your LED version using a dead soldering iron as the body with a probe sticking out and a single flying lead for the other terminal. Instead of two diode strings and two LEDs I put a bridge rectifier on the input so it will work either way round with just one LED. Best thing I ever made and really useful
My boss in work discharged the input cap of an induction heater with a screwdriver, was bigger than my closed fist and the noise it made. Was like a grenade going off.
I like to charge a big, HV cap and then discharge it with a 2 Ohm, quarter Watt resistor. Pieces of the resistor fly all over the room! I had to do more than just wear my safety glasses, as little pieces of hot resistor were hurting my hands and the leads left burn marks on them. So I made up a set of alligator clip jumpers 3 feet long out of 8 gauge wire and also put the discharge resistor in a clear plastic box. It's surprising how many of those resistors it takes to discharge a really big cap or a bank of them. :)
You can as well use filament based lightbulb as discharger. No diodes, no soldering even required. Just bulb socket, connector and well insulated leads with good tips to make connection.
I very rarely need to discharge high voltage caps, but it does happen occasionally, so I decided to build one of these. Thanks for the inspiration. Got me wondering about the other end of the safety spectrum - low voltage supercaps. I have 5V supercaps with a rating of *5 Farads*! They terrify me more than the HV caps for some reason, so I keep them stored with a 10K resistor soldered across its terminals just for safety. If I had to discharge a cap like that (to avoid sparks or accidentally welding things together) I think I'd probably use a DC programmable load so I can see the voltage dropping in real-time. What would you do in that situation? Thanks for the instructive videos. 👍
And here I have only used either the old short with a screwdriver connected to the earth pin in the outlet or water raidator. Or used a big wattage transisor. And yes the bigger ones are brutal when you discharge. Just like old tube tv's when you need to discharge the tube.
The ability to recover charge of capacitor is calling Dielectric absorption... in electrolytic capacitor it can run to 10-15% which is quite high (from 390V PFC driven cap), it's good to check cap in some time after discharge again
Mr Carlsons is complicated, lots of parts and would cost a hell of a lot more, for exactly the same job. Richard, yours is one of the best ideas I've seen with a couple of scrounged parts and 30 mins to put together. Thank you, I'll certainly be building one with an old multimeter. Cheers!
There are cheap device for this on Ali express. Comes with leads and builtin voltmeter. There's also a tweezer-like version but that is inflexible. Oh yes, and it exploded in my hand. So better take the one with leads 😄 But yeah, if you have an old MM lying around, why not.
You also need to watch out for the fact that once discharged if the load is removed the terminal voltage can start to creep back up. Can i point out hearts don't give a fig about voltage, it's current that counts. the voltage is just there to break the skin insolation. Old saying "Volts jolt but mils kills" (IEC) 60601-1. Body and Body Floating (i.e not earthed) have similar values (e.g. normal AC leakage current of 100 μA) notice no mention of voltage in the safety standard.
@@LearnElectronicsRepair Having worked on the design of a product that applied a voltage to arterial blood, so had a direct connection to the heart. knowing the difference was important, well to the person on the other end of the tube anyway. I also knew of a chap who worked on the London underground who had a party trick of putting his tools on the live (+400V) power rail. he had a skin condition which meant that he had extremely dry skin and 400v was just a slight tingle.
@@LearnElectronicsRepair Yes. Its much better/easier watching a needle drop than a digital meter dropping. Especially having one of those large analog displays. (0-500v)
Thank you, I enjoyed the explanations. I need to build a capacitor discharging kit, so the information has came in useful. One question comes to mind tho. What happens if one or both of the LED fails? Would you end up with a false positive (ie discharged capacitor) and risk shocking yourself?
I always "screwdriver" the capacitor terminals after resistor discharge..... that's your absolute backup - beyond measuring things Don't trust any one thing is the best process. Another one would be have a second person nearby whenever doing bare live working - depending on risk level (isolated supply + voltage + amount of stored energy)
Couldn’t you simplify the discharger by connecting the leads to the ac input of a bridge rectifier, and connect the large resistor and one diode tree and LED to the dc output, instead of duplicating this part?
I don't repair microwaves but if you are talking about a capacitor holding several kV but of low capacitance value then use a proper HV probe to discharge it. If you want to use a cheap and nasty method like we were taught to discharge the CRT in colour TV, which could charge to about 25kV then use a long flat blade screwdriver with a good and large plastic handle. Connect a crocodile clip lead to the metal shaft of the screwdriver, clip the other end of the lead to ground on the TV chassis, make sure you have a good ground connection and slide the flat blade of the screwdriver under the rubber cap of the HT lead. Do this one handed and keep your other arm folded behind your back like a sword fencer. You should be OK doing it that way but dont' say I told you to do it.
Just trying to understand? Deducing your logic , arnie, as mr universe ,was not really perfect? My electronics knowledge, has just taken a huge leap backwards. From know on, I will be wearing rubber skivies when playing with caps.
As long as it keeps you safe, wear the gloves. Re the universe if it was perfect it would suggest there is a creator, as it is clearly and provenly not it suggests either it happened by some natural process or if there was a creator he, she or it could not be arsed to do the job properly 😵💫
😂😂😂 High voltage is over 1000V. Main voltage for houses is very dangerous for life, but by the low, that can not be called high voltage. High voltage is in transformer station. DO NOT USE WRONG TERMINOLOGY!
Well for some reason my multimeter lights up red if I probe anything over 30V to warn of High Voltage Google for the dictionary definition of High Voltage and it says ' an electrical potential large enough to cause injury or damage' I've seen many mains voltage electrical boxes with a sign saying 'Danger High Voltage' Other definitions say anything over 1000V. Now if it is by the 'low' (law?) then why are the low makers not prosecuting the multimeter makers, sign makers, dictionary publishers and apparently clueless RUclips influencers, exactly? Really this is pure semantics, call it how you like without fear of prosection, and worry more about electrocution 🤪 And don't worry about how other people call it
@@LearnElectronicsRepair 30V it is high, but for ammateurs. You are proffesional, right? Or not? 🤔 In my country, 50V and 50mA is dangerous for humans, by the low. That is not meant for technician peoples.
@@buck_rrogers8067 This video covered a number of topics and chapters: What does the bridge rectifier / capacitor circuit look like and how does it work How much voltage will you find in a bulk capacitor (with and without PFC) and why the voltage is so high Why you need to discharge the capacitor and what fault conditions cause it not to just discharge by itself Where to measure if the capacitor holds a high voltage - very important so you don't make a dangerous mistake in PFC circuits! How to build the test circuit (yeah possibly i could have skipped this section) How NOT to discharge a capacitor with your fingers and why not How NOT to discharge a capacitor with a screwdriver/pliers and why not How to do discharge a capacitor safely with a resistor (by the way ohms law says 200 ohms give an initial current of 1.6A for a 320V charge. Watts=320Vx1.6A = initial power disipation of 512 Watts! How did *you* calculate a 10W resistor is suitable for this purpose?) How to make using a resistor a bit safer by fixing a stick/holder to it How to make a discharger with voltage indication using a cheap/old multimeter How to make a discharger with LED indicator I'm always looking to improve my videos and take criticism contructively. Which of these sections do you believe contained no useful information and should have been discarded, given that viewers of all knowledge levels watch my videos and this one covers a potentially dangerous topic?
@@buck_rrogers8067 Surely that depends on the capacity of the capacitors. Call it a difference of opinion and I'm not saying the 200 ohms does not work I just think it makes sense to use something a bit higher resistance especially as the same discharge current flows internally across the capacitor dielectric so why would you want to put it under so much stress when you don't need to? On the other topic you didn't reply yet, which parts of this video contained no useful information and should have been discarded?
That's fine if there is some form of dc load on the cap which there might be in circuit. but remove that DC path and you could be in for a shock(pun intended)
*Before someone else mentions, you also find dangerous high voltages in the large capacitors in Audio Amplifiers, and in the LED backlight drive circuit for LED TV, amongst other places*
And in flying insect zappers, and old neon sign transformers, too! So many places to find HV!
Microwaves.
A masterpiece example of no fuss and down to earth didactics. Brilliant!
A little 230V 20W incandescent bulb permanently attached to old short probes, covered with semi-transparent buble wrap so it's indestructible, is always hanging on my tool wall for exactly that. Self limits the current to less than 100 mA but draws almost same current from much lower voltages, so discharges caps almost instantly to safe levels. Made it right after I got a real nusty shock while repairing a board many years back...
This was an awesome video and... Covers a lot of the basics and you sure explained everything quite well very in-depth explanation and then we proceeded to make a discharge device, and demonstrate how it works with real-world examples. I enjoyed it immensely.
Wow. This is an excellent and informative video. It certainly has been an eye opener. I have seen so many shorting the capacitors to discharge them, but it is very dangers to do so and bad for the capacitor. I liked the resistor and diod method. I will try it. Thank you once again.
A 'Back-to-basics' video. Explained with experience extremely well, love it!
Excellent video on an extremely important topic. Thank you 👍
Interesting video!
An alternative if you only want 1 led, would be to use a bridge rectifier before the discharge resistor, depending on what parts are available, so it won't matter which way the probes are connected. It's great this can be made from salvaged parts!
Was wondering if there would be a neater solution requiring fewer components and was trying to run the diagram in my head!
For the simplest circuit with the lowest component count, use 2 bridge rectifiers connected in series (AC side) to the probes. On the DC side connect the negative of the first to the positive of the second and the LED+resistor between the positive of the first and the negative of the second. 5 components including the bulk resistor. You can use very small bridge rectifiers (>0.1A) and a bulk resistor of 4K7 ohms for fast safe discharge even at 440V. If you use a 5W resistor it will exceed its rating but for such a short period there's no time for it to overheat.
A really great video Richard, especially on the dangers of big caps !
Great LED gadget too, I'm going to make one up !
Cheers
Built a variant of your LED version using a dead soldering iron as the body with a probe sticking out and a single flying lead for the other terminal. Instead of two diode strings and two LEDs I put a bridge rectifier on the input so it will work either way round with just one LED. Best thing I ever made and really useful
Genius explanation. As always. These types of videos are the best. Cheers
My boss in work discharged the input cap of an induction heater with a screwdriver, was bigger than my closed fist and the noise it made. Was like a grenade going off.
I like to charge a big, HV cap and then discharge it with a 2 Ohm, quarter Watt resistor. Pieces of the resistor fly all over the room! I had to do more than just wear my safety glasses, as little pieces of hot resistor were hurting my hands and the leads left burn marks on them. So I made up a set of alligator clip jumpers 3 feet long out of 8 gauge wire and also put the discharge resistor in a clear plastic box. It's surprising how many of those resistors it takes to discharge a really big cap or a bank of them. :)
Flip flop & voltage multiplyer circuits, etc. would be an interesting topic
Thank you for the great video! I was thinking of a solution with a current source, but this is way easier to build.
Heya, very nice explanation about the danger of elektrolitics and the does and don'ts I like it
Very nice and simple idea I think I'll do the same circuit and use it thanks Mr. Richard!
You can as well use filament based lightbulb as discharger. No diodes, no soldering even required. Just bulb socket, connector and well insulated leads with good tips to make connection.
The LED version, very handy gadget, cheers.
Thank you 🙂
I very rarely need to discharge high voltage caps, but it does happen occasionally, so I decided to build one of these. Thanks for the inspiration.
Got me wondering about the other end of the safety spectrum - low voltage supercaps. I have 5V supercaps with a rating of *5 Farads*! They terrify me more than the HV caps for some reason, so I keep them stored with a 10K resistor soldered across its terminals just for safety.
If I had to discharge a cap like that (to avoid sparks or accidentally welding things together) I think I'd probably use a DC programmable load so I can see the voltage dropping in real-time. What would you do in that situation?
Thanks for the instructive videos. 👍
Very neat and functional circuit, and all that without a PCB from the the Orient !!!
Ah that nostalgic crack when you discharge a capacitor with your most hated screwdriver.
And here I have only used either the old short with a screwdriver connected to the earth pin in the outlet or water raidator. Or used a big wattage transisor. And yes the bigger ones are brutal when you discharge. Just like old tube tv's when you need to discharge the tube.
The ability to recover charge of capacitor is calling Dielectric absorption... in electrolytic capacitor it can run to 10-15% which is quite high (from 390V PFC driven cap), it's good to check cap in some time after discharge again
MR. Carlson has a nice discharge circuit with LED'S that works safe on almost any voltage
How does it differ from mine?
Mr Carlsons is complicated, lots of parts and would cost a hell of a lot more, for exactly the same job.
Richard, yours is one of the best ideas I've seen with a couple of scrounged parts and 30 mins to put together.
Thank you, I'll certainly be building one with an old multimeter. Cheers!
@@darrenbird2526 Thank you 🙂
There are cheap device for this on Ali express. Comes with leads and builtin voltmeter. There's also a tweezer-like version but that is inflexible. Oh yes, and it exploded in my hand. So better take the one with leads 😄 But yeah, if you have an old MM lying around, why not.
Great! Thanks
You also need to watch out for the fact that once discharged if the load is removed the terminal voltage can start to creep back up.
Can i point out hearts don't give a fig about voltage, it's current that counts. the voltage is just there to break the skin insolation.
Old saying "Volts jolt but mils kills"
(IEC) 60601-1. Body and Body Floating (i.e not earthed) have similar values (e.g. normal AC leakage current of 100 μA)
notice no mention of voltage in the safety standard.
Semantics... you can think about it when you are lying on the floor waiting for your brain to run out of oxygen 😂
@@LearnElectronicsRepair Having worked on the design of a product that applied a voltage to arterial blood, so had a direct connection to the heart. knowing the difference was important, well to the person on the other end of the tube anyway.
I also knew of a chap who worked on the London underground who had a party trick of putting his tools on the live (+400V) power rail. he had a skin condition which meant that he had extremely dry skin and 400v was just a slight tingle.
10:18 - Richard, to avoid any disastrous surprises, _always_ test a capacitor for voltage before testing capacitance!
You know, so far that hasn't happened to me - but it is a fair comment
You could also use a dc analog meter with the power resistor across it. Will give a better visualization of the voltage dropping.
Does the analog meter work better then the digital one? Apart from not needing a battery
@@LearnElectronicsRepair Yes. Its much better/easier watching a needle drop than a digital meter dropping. Especially having one of those large analog displays. (0-500v)
@@CliveTrezona I have an analog meter, I'll try it on a future video
Thank you, I enjoyed the explanations. I need to build a capacitor discharging kit, so the information has came in useful. One question comes to mind tho. What happens if one or both of the LED fails? Would you end up with a false positive (ie discharged capacitor) and risk shocking yourself?
I always "screwdriver" the capacitor terminals after resistor discharge..... that's your absolute backup - beyond measuring things
Don't trust any one thing is the best process.
Another one would be have a second person nearby whenever doing bare live working - depending on risk level (isolated supply + voltage + amount of stored energy)
just connect the discharger across a battery or power supply before using it/ Belts and braces is a good idea when safety is concerned
Couldn’t you simplify the discharger by connecting the leads to the ac input of a bridge rectifier, and connect the large resistor and one diode tree and LED to the dc output, instead of duplicating this part?
It has been mentioned... and it wold work just as well
the only question i have can this be used on a microwave cap
I don't repair microwaves but if you are talking about a capacitor holding several kV but of low capacitance value then use a proper HV probe to discharge it. If you want to use a cheap and nasty method like we were taught to discharge the CRT in colour TV, which could charge to about 25kV then use a long flat blade screwdriver with a good and large plastic handle. Connect a crocodile clip lead to the metal shaft of the screwdriver, clip the other end of the lead to ground on the TV chassis, make sure you have a good ground connection and slide the flat blade of the screwdriver under the rubber cap of the HT lead. Do this one handed and keep your other arm folded behind your back like a sword fencer. You should be OK doing it that way but dont' say I told you to do it.
Объясните пожалуйста работу apfc и схемотехнику ❤
What, like this one? ruclips.net/video/F6OJnjEBk7w/видео.html
@@LearnElectronicsRepair дададада🤗❤️Спасибо ❤️буду смотреть. Очень интересно 👍
tldr: with a resistor.
Just trying to understand? Deducing your logic , arnie, as mr universe ,was not really perfect? My electronics knowledge, has just taken a huge leap backwards.
From know on, I will be wearing rubber skivies when playing with caps.
As long as it keeps you safe, wear the gloves. Re the universe if it was perfect it would suggest there is a creator, as it is clearly and provenly not it suggests either it happened by some natural process or if there was a creator he, she or it could not be arsed to do the job properly 😵💫
@@LearnElectronicsRepair 😂
😂😂😂
High voltage is over 1000V.
Main voltage for houses is very dangerous for life, but by the low, that can not be called high voltage.
High voltage is in transformer station.
DO NOT USE WRONG TERMINOLOGY!
Well for some reason my multimeter lights up red if I probe anything over 30V to warn of High Voltage
Google for the dictionary definition of High Voltage and it says ' an electrical potential large enough to cause injury or damage'
I've seen many mains voltage electrical boxes with a sign saying 'Danger High Voltage'
Other definitions say anything over 1000V. Now if it is by the 'low' (law?) then why are the low makers not prosecuting the multimeter makers, sign makers, dictionary publishers and apparently clueless RUclips influencers, exactly?
Really this is pure semantics, call it how you like without fear of prosection, and worry more about electrocution 🤪
And don't worry about how other people call it
@@LearnElectronicsRepair 30V it is high, but for ammateurs. You are proffesional, right? Or not?
🤔
In my country, 50V and 50mA is dangerous for humans, by the low. That is not meant for technician peoples.
43 min Video about discharging capacitors is reticules.
What, you mean it is well targeted?
Simply short capacitor with 200 ohm 10watt resistor and it is dan.
No Need for 45 min video
@@buck_rrogers8067 This video covered a number of topics and chapters:
What does the bridge rectifier / capacitor circuit look like and how does it work
How much voltage will you find in a bulk capacitor (with and without PFC) and why the voltage is so high
Why you need to discharge the capacitor and what fault conditions cause it not to just discharge by itself
Where to measure if the capacitor holds a high voltage - very important so you don't make a dangerous mistake in PFC circuits!
How to build the test circuit (yeah possibly i could have skipped this section)
How NOT to discharge a capacitor with your fingers and why not
How NOT to discharge a capacitor with a screwdriver/pliers and why not
How to do discharge a capacitor safely with a resistor (by the way ohms law says 200 ohms give an initial current of 1.6A for a 320V charge. Watts=320Vx1.6A = initial power disipation of 512 Watts! How did *you* calculate a 10W resistor is suitable for this purpose?)
How to make using a resistor a bit safer by fixing a stick/holder to it
How to make a discharger with voltage indication using a cheap/old multimeter
How to make a discharger with LED indicator
I'm always looking to improve my videos and take criticism contructively. Which of these sections do you believe contained no useful information and should have been discarded, given that viewers of all knowledge levels watch my videos and this one covers a potentially dangerous topic?
1,6 Amps at 320V vor incredible short time period is harmless for 10 watt. Discharged les as 2 sec. To 0 Volt.
@@buck_rrogers8067 Surely that depends on the capacity of the capacitors. Call it a difference of opinion and I'm not saying the 200 ohms does not work I just think it makes sense to use something a bit higher resistance especially as the same discharge current flows internally across the capacitor dielectric so why would you want to put it under so much stress when you don't need to? On the other topic you didn't reply yet, which parts of this video contained no useful information and should have been discarded?
you don't need to discharge them, unless energy is infinite , just leave them alone for a few hours, that's what I do at my pc repair shop.
😂
I've seen good capacitors keeping 200V after 10hours. Be safe and careful.
In Ireland and we have an Old Saying that is so true:
Is Airgead an t-Am.
That's fine if there is some form of dc load on the cap which there might be in circuit. but remove that DC path and you could be in for a shock(pun intended)
@@francescvilches3967 obviously I don't mean a couple of hours...........I mean if it hasnt been used for a few days.........