If your digital meter has a LoZ or Low Impedance mode the cap discharge in a LoZ voltage mode will be quick. Normally a high impedance digital meter loads a circuit with an equivalent impedance of ~10 megohm where a low impedance mode, when available, is typically a 3k to 100k ohm load.
Great point RJ! This causes me a new question. If my Fluke 116 in AUTO-V LoZ has an impedance of 3 k Ohms and it can accept 600 volts (600 V/3000 Ohms = 0.2 Amps; 0.2 Amps X 600 Volts = 120 Watts). Does this mean the load in the meter can dissipate 120 Watts for an indefinite period of time? I certainly wouldn’t think so. But I can find no warning or limit on the use of this function in the Fluke 116 Users Manual. Maybe it has a temperature overload function which is not described in this manual? Or, , , they will be glad to sell me a new meter when AUTO LoZ no longer works correctly?
The Fluke 116 manual says LoZ input impedance is 3k ohms and is dc coupled so you are probably right in your calcs. It may have a heat sink. I would imagine they can handle it.
Chuck brought up his Fluke 116 so I checked its specs. Many Klein, Flir and Extech clamp meters have LoZ. The primary purpose of LoZ is to determine when ghost voltages of little significance (usually induced) are being picked up by the high impedance of digital meters. Personally I like my UEI 429 with dual displays and data logging capabilities even though it does not have LoZ. For ghost voltages I have an old reliable analog meter which needs no battery in voltage modes. I do keep a wire wound power resistor much like Bryan describes but it rarely gets used.
I'm glad you still showed a multimeter discharging the cap, because all one has to do is have alligator leads handy, hook up the multimeter, and do something else for 15 or 20 minutes, and it works.
You discharged 40V in 10 seconds with a multimeter. At that rate, you will fully discharge the capacitor in 40 seconds, not the "half hour" you mention.
Thank you for making this video. I had to replace the run capacitor in my AC. Didn't have a discharge tool so I figured the multimeter was better than arching screwdriver. The capacitor was totally uncharged but I am thankful I had this option !
Great job Bryan! Thanks! You made a believer out of me. And this with only 5 MFD. Imagine 40 or 50 MFD. Added: I stand corrected. This video is a perfect example of how old dogs can learn, correctly, what they thought they already knew.
The time constant for capacitor discharge/charge is capacitance x resistance. With the rule of thumb, 5 time constants for essentially fully charged/discharged. Assuming some extremes, a 100 mfd capacitor @ 450 v. The time constant with a 20k ohm resistor is 2 s, 5x=10s. 450v on a 20k resistor = 22.5 mA. Not bad, that is an initial power discharge of 10 watts.
This whole debate is missing the entire point. Both sides are wrong. You are never going to measure voltage on a capacitor out in the field unless you pull the wires off while power is still hooked up. You don't need a 20k ohm resistor to discharge a capacitor that's installed in a unit. There's already much smaller resistors that are shorting the terminals at all times. They are called motor windings. Herm > Start > Compressor Common > Run > Contactor > Capacitor Common. If you pull the disconnect, the capacitor will discharge through the motor windings almost immediately. Older capacitors might be an exception. Those old capacitors that you can shake and hear liquid sloshing? Those might actually take a while to discharge. That's the only time I've ever been shocked by an unhooked capacitor.
I made a video about this a few years ago, only that I really used an analog meter! Now, I have supercapacitors (10 F, 5.5V) which needs more current to discharge, and a short-circuit won't work well
It really is not a race. Do it right because an ounce of prevention is worth more than a pound of cure. It's your right to do it your way, but why teach beginners how to do it wrong? I know I don't have the brass to dead short a 7 farad cap. Yes they can get very large. All the best to you sir.
He didn’t short it. The discharge tool has a resistor in it. It’s just a homemade tool made of a screwdriver, a resistor, and a length of wire. I made one using the probe leads from an old DMM that I had lying around. It simply removed the plug ends and inset into the DMM ports and soldered a resistor between the 2 probes. So it’s not a straight short, it goes through a resistor.
Makes perfect sense! And no, I don't think I want to use a screwdriver. That might be OK for lower powered DC devices, though. (I do think that's how I messed up a circuit on a bass distortion pedal once... long story!)
It takes 2 minutes to make a capacitor discharge tool. Id much rather do that than wait for the meter for 10 minutes. A 5w, 10k resistor, a couple of lengths of properly sized wire, and heat shrink tubing and you got everything you need. Or you could use some old probes from a multimeter along with a screwdriver. I just ordered some 20k, 5w resistors to make one for my tube amps. I also ordered a pre-made discharge tool so I can compare what I make to s commercial product.
Thank you for nice video. Is there a formula can use it to get an accurate reading? Second q should position the capacitor vertically or horizontally I saw some duct less mini split is positioned horizontally? Thanks.
What about a meter with Loz function, is that quicker or even possible? I'm pretty sure I read you could use the Loz function to discharge a cap. I need to solder some new IC's on an led tvs power supply board and figured I should discharge the caps first. 450v caps I believe. I got a power supply repair kit for my model ps board off shopjimmy cause the ps board was out of stock. Hope it's pretty straight forward, my soldering skills are decent. Nvrmnd it looks like the LoZ method has been addressed here in the comments already lol
You gotta do it fast because HVAC guys are always in a real big hurry and never, ever just sit there yaking on their phones while they pretend to be working.
I found you today through watching you with MATT. I trust Matt and he trusts you, so I am a new subscriber. I have now watched several of your videos and I have a few questions. It just so happens that one of our daughters is having a new system installed this week and also my parents are having an issue or two. So without a lot of explanation, here are my questions. Starting with my parents ACHV system. We live in the Tampa Bay area, so hot and humid most of the year. We also have hurricanes and sometimes need alternative power. My father recently bought a portable generator that maxes at 7500 Watts surge. 6000 Watts normal run. He'd like to be able to run the house AC (WITHOUT HEAT), in times of long power outages. He's got a 3.5 ton unit that is 16 seer. I don't remember the brand. I think he could run his AC ONLY if the generator can handle the surge. NOT being a tech or even an electrician, I believe I understand that the capacitor is to give the fan and compressor motors a jolt to start up. His system has a cap on it from the factory, but I don't understand why we do not use a second cap for this surge/boost? Is it feasible? Can a second cap be added to reduce the pull or surge on the incoming power? I'd also like your opinion on using UV LIGHT to kill and keep mold from growing? Last Q. Is it true that the air handler and the indoor and outdoor units cannot be mixed as they use to be? My daughters air handler is pretty well plugged and in a inside closet. Very difficult to work on and the entire unit must be removed to pull the fan. She got an estimate and asked what it would cost to put in a new air handler that COULD BE serviced. She was told it is no longer legal to mix units. I realize they would have to be compatible, but that sounds like BS to me. Please advise on all. I truly appreciate it!!
A 7500w generator will start most systems without modifications. The generator usually has to wired in to the house wiring with a "transfer switch" in order to work on a central system. An add on "hard start kit" will give an extra boost and has a mechanism to take it out of the circuit after a start. Emerson also sells a soft start module which will absolutely do the job in the worse cases. It is called a "Copeland Secure Start" but normally requires ordering and few techs know about it. The biggest problem with generators is stale gasoline clogging them up such that they won't start when needed. Plus supplies of gasoline dry up after storms. I would recommend a propane or natural gas generator of the same size instead. Propane stores for years without problems. UV lights work well, Bryan recommends the Air Oasis Nano. Most likely your daughter's unit has a plugged evaporator coil. Or a leaky system. It is possible to change the evaporator for another with the same size and refrigerant. The old ones have R22 refrigerant and most new are R410. I doubt the whole unit has to be pulled to change the fan or the evaporator. Second opinion time.
RJPARKER , Thank you very much for this excellent reply. I will certainly be looking into the "HARD START KIT" and the "COPELAND SECURE START". My father had already bought the generator. It made me sick, because they have natural gas at their house already, but my mom is afraid of it as it is a corner house and the meter and piping is exposed. I tried to talk them into a slightly bigger NG permanent mount, auto start system as thy are not as young as they think they are. lol.. I have been a mechanic most of my life and know all too well about old gas. So for many years he has know to put all things "GAS" away with empty tanks. Plus I normally go through their systems before the hurricane season begins. We are about to change out their power panel and add an outdoor outlet for the generator and a "D RING" to chain it down. They live in a nice area, but you never know what people will do when you have something they feel they need. The more I read about the UV lights, the more I want a pair of them myself. So I will check out the Air Oasis Nano for all of us. The AC system at our daughters house was changed out today. 13 hours and they have to come back Monday to finish removing the old air handler in the closet. We had the new unit put into the attic, so close to a new install. I just spoke with my daughter and she says she cannot even hear this unit run!! Also that she can feel the cold air blowing across every room now. Something she doesn't remember from the old unit. Such a difference.. The old closet unit was allllways very loud. Even when brand new. I am going to bring it home and clean it well with hopes of installing it in my back shop. It will be far from perfect as my shop is not insulated at all, but Florida heat keeps me from doing anything in the shop for 8-9 months out of the year. Something has got to give!! I thank you again for your reply. Steve
BUT... If I am on, what was supposed to be, a plumbing call, in a crawlspace at 11:30 PM with only a meter checking a 220v, 126 MF capacitor, my meter is better than nothing.
@@raybradshaw8444 Hey, yeah so if you have a cheap multimeter, I wouldn't do it.. The thin insulation on the leads may not be able to protect you from getting shocked in the event you are grounded and you become a path for electricity.. As far as damaging the device, stay under 1000v. Again, this is just what I've read and it totally depends on the quality of your multimeter. Hope this helps.
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If your digital meter has a LoZ or Low Impedance mode the cap discharge in a LoZ voltage mode will be quick. Normally a high impedance digital meter loads a circuit with an equivalent impedance of ~10 megohm where a low impedance mode, when available, is typically a 3k to 100k ohm load.
Great point RJ! This causes me a new question. If my Fluke 116 in AUTO-V LoZ has an impedance of 3 k Ohms and it can accept 600 volts (600 V/3000 Ohms = 0.2 Amps; 0.2 Amps X 600 Volts = 120 Watts). Does this mean the load in the meter can dissipate 120 Watts for an indefinite period of time? I certainly wouldn’t think so. But I can find no warning or limit on the use of this function in the Fluke 116 Users Manual. Maybe it has a temperature overload function which is not described in this manual? Or, , , they will be glad to sell me a new meter when AUTO LoZ no longer works correctly?
The Fluke 116 manual says LoZ input impedance is 3k ohms and is dc coupled so you are probably right in your calcs. It may have a heat sink. I would imagine they can handle it.
RJParker. Those meters aren't cheap and not usually carried by techs, they're also not clamp ons.
Chuck brought up his Fluke 116 so I checked its specs. Many Klein, Flir and Extech clamp meters have LoZ. The primary purpose of LoZ is to determine when ghost voltages of little significance (usually induced) are being picked up by the high impedance of digital meters. Personally I like my UEI 429 with dual displays and data logging capabilities even though it does not have LoZ. For ghost voltages I have an old reliable analog meter which needs no battery in voltage modes. I do keep a wire wound power resistor much like Bryan describes but it rarely gets used.
RJParker. I stand corrected.
I'm glad you still showed a multimeter discharging the cap, because all one has to do is have alligator leads handy, hook up the multimeter, and do something else for 15 or 20 minutes, and it works.
You discharged 40V in 10 seconds with a multimeter. At that rate, you will fully discharge the capacitor in 40 seconds, not the "half hour" you mention.
I think he is trying to patent his device! lol
Thank you for making this video. I had to replace the run capacitor in my AC. Didn't have a discharge tool so I figured the multimeter was better than arching screwdriver. The capacitor was totally uncharged but I am thankful I had this option !
"Oh, I'll be fine!"
- famous last words ;)
Great job Bryan! Thanks! You made a believer out of me. And this with only 5 MFD. Imagine 40 or 50 MFD.
Added: I stand corrected. This video is a perfect example of how old dogs can learn, correctly, what they thought they already knew.
I didn’t know either until I tried it
@@HVACS where can I buy a cap discharger and a cap these days?
The time constant for capacitor discharge/charge is capacitance x resistance. With the rule of thumb, 5 time constants for essentially fully charged/discharged. Assuming some extremes, a 100 mfd capacitor @ 450 v. The time constant with a 20k ohm resistor is 2 s, 5x=10s. 450v on a 20k resistor = 22.5 mA. Not bad, that is an initial power discharge of 10 watts.
Hello Bryan would it be possible to upload a video on how you made your personal discharge tool?
noted!
Love the video. What gauge wire should I use for the cap discharging tool?
This whole debate is missing the entire point. Both sides are wrong.
You are never going to measure voltage on a capacitor out in the field unless you pull the wires off while power is still hooked up.
You don't need a 20k ohm resistor to discharge a capacitor that's installed in a unit. There's already much smaller resistors that are shorting the terminals at all times. They are called motor windings.
Herm > Start > Compressor Common > Run > Contactor > Capacitor Common.
If you pull the disconnect, the capacitor will discharge through the motor windings almost immediately.
Older capacitors might be an exception. Those old capacitors that you can shake and hear liquid sloshing? Those might actually take a while to discharge. That's the only time I've ever been shocked by an unhooked capacitor.
Is there a specific order to disconnect the Common, Fan, Herm?
Will it discharge thru windings without pushing in contactor?
What about the tongue method?
not sure, perhaps nobody lived to tell the tale?
@@hycron1234
You can do it. I have have faith.
just be sure to add a little salt, like a shooter it will stick better.
That’s for a different type of channel… 🤣
Why not use the ohm feature of your multimeter and set it to the highest setting ?
Any quick videos like this one that show the making of that capacitor discharge tool?
I made a video about this a few years ago, only that I really used an analog meter!
Now, I have supercapacitors (10 F, 5.5V) which needs more current to discharge, and a short-circuit won't work well
It really is not a race. Do it right because an ounce of prevention is worth more than a pound of cure. It's your right to do it your way, but why teach beginners how to do it wrong? I know I don't have the brass to dead short a 7 farad cap. Yes they can get very large. All the best to you sir.
So what's wrong with this method?
He didn’t short it. The discharge tool has a resistor in it. It’s just a homemade tool made of a screwdriver, a resistor, and a length of wire. I made one using the probe leads from an old DMM that I had lying around. It simply removed the plug ends and inset into the DMM ports and soldered a resistor between the 2 probes. So it’s not a straight short, it goes through a resistor.
Makes perfect sense! And no, I don't think I want to use a screwdriver. That might be OK for lower powered DC devices, though. (I do think that's how I messed up a circuit on a bass distortion pedal once... long story!)
you could also use a diode as well.
That's probably all there is in his "capacitor discharger", it's literally just a diode or a decently low ohm resistor.
It takes 2 minutes to make a capacitor discharge tool.
Id much rather do that than wait for the meter for 10 minutes. A 5w, 10k resistor, a couple of lengths of properly sized wire, and heat shrink tubing and you got everything you need. Or you could use some old probes from a multimeter along with a screwdriver.
I just ordered some 20k, 5w resistors to make one for my tube amps. I also ordered a pre-made discharge tool so I can compare what I make to s commercial product.
how do you make the capacitor discharge tool?
What percentage of capacitors you check will actually have a voltage and why do some not ?
Best is to use the volt meter to discharge then you know there is no voltage because the meter says so , it doesn't take very long what's the rush !
Thank you for nice video. Is there a formula can use it to get an accurate reading? Second q should position the capacitor vertically or horizontally I saw some duct less mini split is positioned horizontally? Thanks.
Can you discharge the capacitor using the amperage setting on the multimeter?
What about a meter with Loz function, is that quicker or even possible? I'm pretty sure I read you could use the Loz function to discharge a cap.
I need to solder some new IC's on an led tvs power supply board and figured I should discharge the caps first. 450v caps I believe.
I got a power supply repair kit for my model ps board off shopjimmy cause the ps board was out of stock. Hope it's pretty straight forward, my soldering skills are decent.
Nvrmnd it looks like the LoZ method has been addressed here in the comments already lol
1/2 hour on the clock!
😎👍
You gotta do it fast because HVAC guys are always in a real big hurry and never, ever just sit there yaking on their phones while they pretend to be working.
I just set my meter to LoL after reading this.
I found you today through watching you with MATT. I trust Matt and he trusts you, so I am a new subscriber. I have now watched several of your videos and I have a few questions. It just so happens that one of our daughters is having a new system installed this week and also my parents are having an issue or two. So without a lot of explanation, here are my questions.
Starting with my parents ACHV system. We live in the Tampa Bay area, so hot and humid most of the year. We also have hurricanes and sometimes need alternative power. My father recently bought a portable generator that maxes at 7500 Watts surge. 6000 Watts normal run. He'd like to be able to run the house AC (WITHOUT HEAT), in times of long power outages. He's got a 3.5 ton unit that is 16 seer. I don't remember the brand. I think he could run his AC ONLY if the generator can handle the surge. NOT being a tech or even an electrician, I believe I understand that the capacitor is to give the fan and compressor motors a jolt to start up. His system has a cap on it from the factory, but I don't understand why we do not use a second cap for this surge/boost? Is it feasible? Can a second cap be added to reduce the pull or surge on the incoming power?
I'd also like your opinion on using UV LIGHT to kill and keep mold from growing?
Last Q. Is it true that the air handler and the indoor and outdoor units cannot be mixed as they use to be? My daughters air handler is pretty well plugged and in a inside closet. Very difficult to work on and the entire unit must be removed to pull the fan. She got an estimate and asked what it would cost to put in a new air handler that COULD BE serviced. She was told it is no longer legal to mix units. I realize they would have to be compatible, but that sounds like BS to me. Please advise on all. I truly appreciate it!!
A 7500w generator will start most systems without modifications. The generator usually has to wired in to the house wiring with a "transfer switch" in order to work on a central system. An add on "hard start kit" will give an extra boost and has a mechanism to take it out of the circuit after a start. Emerson also sells a soft start module which will absolutely do the job in the worse cases. It is called a "Copeland Secure Start" but normally requires ordering and few techs know about it. The biggest problem with generators is stale gasoline clogging them up such that they won't start when needed. Plus supplies of gasoline dry up after storms. I would recommend a propane or natural gas generator of the same size instead. Propane stores for years without problems. UV lights work well, Bryan recommends the Air Oasis Nano. Most likely your daughter's unit has a plugged evaporator coil. Or a leaky system. It is possible to change the evaporator for another with the same size and refrigerant. The old ones have R22 refrigerant and most new are R410. I doubt the whole unit has to be pulled to change the fan or the evaporator. Second opinion time.
There are also carb conversion kits from to use natural gas on small generators.
RJPARKER , Thank you very much for this excellent reply. I will certainly be looking into the "HARD START KIT" and the "COPELAND SECURE START".
My father had already bought the generator. It made me sick, because they have natural gas at their house already, but my mom is afraid of it as it is a corner house and the meter and piping is exposed. I tried to talk them into a slightly bigger NG permanent mount, auto start system as thy are not as young as they think they are. lol.. I have been a mechanic most of my life and know all too well about old gas. So for many years he has know to put all things "GAS" away with empty tanks. Plus I normally go through their systems before the hurricane season begins. We are about to change out their power panel and add an outdoor outlet for the generator and a "D RING" to chain it down. They live in a nice area, but you never know what people will do when you have something they feel they need.
The more I read about the UV lights, the more I want a pair of them myself. So I will check out the Air Oasis Nano for all of us.
The AC system at our daughters house was changed out today. 13 hours and they have to come back Monday to finish removing the old air handler in the closet. We had the new unit put into the attic, so close to a new install. I just spoke with my daughter and she says she cannot even hear this unit run!! Also that she can feel the cold air blowing across every room now. Something she doesn't remember from the old unit. Such a difference.. The old closet unit was allllways very loud. Even when brand new. I am going to bring it home and clean it well with hopes of installing it in my back shop. It will be far from perfect as my shop is not insulated at all, but Florida heat keeps me from doing anything in the shop for 8-9 months out of the year. Something has got to give!! I thank you again for your reply. Steve
🤔 a new day for a lot of people.
You can use also soldering gun to discharge large capacitor because all Filipinos using it
Why you not use just resistor?
Can I still discharge it and use the same capacitor?
BUT... If I am on, what was supposed to be, a plumbing call, in a crawlspace at 11:30 PM with only a meter checking a 220v, 126 MF capacitor, my meter is better than nothing.
can you discharged a capacitor while its in the circuit?
Set the meter on A/C or D/C volts?
From zooming into the video, I saw AC mode.
I'm surprised you didn't share a link to your DIY capacitor discharge tool.
It's basically a load resistor with heat shrink and crocodile clips: ruclips.net/video/HES4LVQDvJc/видео.html
First of all, if you want to learn somebody to do something, do it properly.
Start with how to set up multimeter for proper measurements.
couldn't you switch it to ohm meter and dischrge it through the meter?
I think your 2 seconds was closer to 3 seconds.
If you did this with a 2000 v microwave capacitor your multimeter fuse would blow, correct?
did you ever find an answer to this
@@raybradshaw8444 Hey, yeah so if you have a cheap multimeter, I wouldn't do it.. The thin insulation on the leads may not be able to protect you from getting shocked in the event you are grounded and you become a path for electricity.. As far as damaging the device, stay under 1000v. Again, this is just what I've read and it totally depends on the quality of your multimeter. Hope this helps.
Fascinating. Very informative. Thanks for sharing. Much Blessings to you. 🙏 Lord-Jesus-Christ ✝c✝o✝m