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#1
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power supply hums when electric blanket on
When I dare to use an
A) electric blanket, or a electric frying pan set on "low", at the same time when there is a B) UPS computer power supply, or Ham radio power supply also turned on anywhere in the house, the power supplies hum most worryingly. One must make a choice: A) food, warmth, or B) fun. What is the name of this waveform resonance with the current limiters of A phenomena? Is there some kind of filter I can apply? |
#2
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power supply hums when electric blanket on
wrote in message ... When I dare to use an A) electric blanket, or a electric frying pan set on "low", at the same time when there is a B) UPS computer power supply, or Ham radio power supply also turned on anywhere in the house, the power supplies hum most worryingly. One must make a choice: A) food, warmth, or B) fun. What is the name of this waveform resonance with the current limiters of A phenomena? Is there some kind of filter I can apply? Check for a loose wire somewhere in the circuits that are affected. Check the voltages at the affected devices to see if they change when the frying pan is cut on and off. |
#3
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power supply hums when electric blanket on
"RM" == Ralph Mowery writes:
RM Check for a loose wire somewhere in the circuits that are affected. Check RM the voltages at the affected devices to see if they change when the frying RM pan is cut on and off. Thanks but a ham told me (in Chinese) that this is a well known phenomenon with cheap current limiters, that take a bite out of each crest of the AC sine wave as their method of limiting. That's why such appliances cause power supplies in the same house to hum when such appliances are switched to LOW or MEDIUM, but not HIGH. If only I could find the English name of this phenomenon, I could look up what to do about it. |
#4
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power supply hums when electric blanket on
In article , wrote:
"RM" == Ralph Mowery writes: RM Check for a loose wire somewhere in the circuits that are affected. Check RM the voltages at the affected devices to see if they change when the frying RM pan is cut on and off. Thanks but a ham told me (in Chinese) that this is a well known phenomenon with cheap current limiters, that take a bite out of each crest of the AC sine wave as their method of limiting. That's why such appliances cause power supplies in the same house to hum when such appliances are switched to LOW or MEDIUM, but not HIGH. If only I could find the English name of this phenomenon, I could look up what to do about it. You've got a cheezy SCR-based control in the electric blanket. When it turns on, you get a fast current spike. IR products in your power wiring turn this into a voltage spike (drop), and since it's a reasonably fast, sharp edge, it's rich in harmonics. Now let's look at your power transformers, such as the one in your ham radio supply, or in the UPS. When they're getting nice clean sine waves, they hum along merrily (they hum because they don't know the words). But when that spike from the SCR wanders in, the windings in the transformer try to reproduce it, humming now at harmonics of the power line, and humming a different and more irritating tune. When the electric blanket is on high, the SCR is essentially turned on through the entire cycle (or half-cycle depending on topology). Turning on at close to zero voltage minimizes the switching spike. Fixes: Brute force filter at the electric blanket, and/or a snubber on the SCR. Get an electric blanket that uses a (zero-crossing) triac control. Heavier, shorter power wiring to the electric blanket, the UPS and ham radio gear, or both. Ditch the electric blanket and get a live-in friend! Before we rebuilt our house, when the fuser heater in the laser printer in the office kicked on (another cheap SCR switch), the fluorescent lights in the room would flicker. After rebuilding, and replacing all the wiring, going from AWG 14 to AWG 10 and 12, that laser printer didn't make the lights flicker any more. Replacing it with a more efficient laser printer helped a lot, too. -- Namaste-- |
#5
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power supply hums when electric blanket on
a You've got a cheezy SCR-based control in the electric blanket.
Ah, http://en.wikipedia.org/wiki/Silicon...lled_rectifier a Brute force filter at the electric blanket, and/or a snubber on the SCR. Ah, http://en.wikipedia.org/wiki/Snubber a Get an electric blanket that uses a (zero-crossing) triac control. But its my http://en.wikipedia.org/wiki/Security_blanket a Heavier, shorter power wiring to the electric blanket, the UPS and ham a radio gear, or both. OK, and what is that brute force filter, and do those snubbers come in AC inline versions that you just plug into requiring no snippers for dumbo me? a Ditch the electric blanket and get a live-in friend! Tried that last time. |
#6
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power supply hums when electric blanket on
When I dare to use an
A) electric blanket, or a electric frying pan set on "low", at the same time when there is a B) UPS computer power supply, or Ham radio power supply also turned on anywhere in the house, the power supplies hum most worryingly. One must make a choice: A) food, warmth, or B) fun. What is the name of this waveform resonance with the current limiters of A phenomena? Is there some kind of filter I can apply? That sounds to me as if you're running into a "harmonic currents" issue. This occurs if you have something connected to the mains which draws current in a nonlinear fashion (i.e. current drawn is not linearly related to the instantaneous value of the voltage sinusoid). In my experience, the commonest cause for this is a device which uses a triac "chopper" to control the amount of current being used. Such devices "switch on" partway through each powerline cycle (120 times a second), so the current jumps from zero to a fairly high value. The sudden jump creates a load on the line with frequency components at harmonics of the 60 Hz powerline frequency... hence the name. The devices you indicate (electric blankets, frying pans), and light dimmers are notorious culprits. Some of these devices may draw current in an asymmetrical fashion... e.g. they might use a half-wave rectifier diode, and thus draw current on only the positive half of the AC cycle and not on the negative (or vice versa). "Light bulb saver" discs (little disc-shaped diodes that go into a light socket before the bulb) do this. In effect, the asymmetrical load creates a DC offset on the voltage "seen" by other devices on the same circuit. All of these "bad loads" can cause transformers in other devices to start humming or buzzing. Toroidal power transformers are particularly subject to buzzing if there's an asymmetrical load / DC offset on the line. I don't know of any good way of filtering out this sort of problem... an isolation transformer can help somewhat, sometimes, but it's an expensive solution and I don't think it's very effective. If you've got really severe humming/buzzing with something as simple and low-wattage as an electric blanket, , I'd be a bit concerned that this might indicate that there's a problem in your house wiring... overloaded circuits, a bad or loose connection somewhere, or even a loose or open neutral. The latter is a dangerous situation. If you should notice lights getting brighter, or appliance motors speed up, when you turn *on* a light or appliance elsewhere in the house... then you may have an open neutral and should call the power company immediately. I've had this happen twice (squirrel chewed through the neutral wire in our building's drop from the pole transformer), and PG&E always reacted immediately... their dispatcher said that they consider a "low voltage / high voltage" situation to require immediate action. You might want to have an electrician check out your house wiring. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#7
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power supply hums when electric blanket on
"Dave Platt" wrote in message ... When I dare to use an A) electric blanket, or a electric frying pan set on "low", at the same time when there is a B) UPS computer power supply, or Ham radio power supply also turned on anywhere in the house, the power supplies hum most worryingly. One must make a choice: A) food, warmth, or B) fun. What is the name of this waveform resonance with the current limiters of A phenomena? Is there some kind of filter I can apply? That sounds to me as if you're running into a "harmonic currents" issue. This occurs if you have something connected to the mains which draws current in a nonlinear fashion (i.e. current drawn is not linearly related to the instantaneous value of the voltage sinusoid). In my experience, the commonest cause for this is a device which uses a triac "chopper" to control the amount of current being used. Such devices "switch on" partway through each powerline cycle (120 times a second), so the current jumps from zero to a fairly high value. The sudden jump creates a load on the line with frequency components at harmonics of the 60 Hz powerline frequency... hence the name. The devices you indicate (electric blankets, frying pans), and light dimmers are notorious culprits. Some of these devices may draw current in an asymmetrical fashion... e.g. they might use a half-wave rectifier diode, and thus draw current on only the positive half of the AC cycle and not on the negative (or vice versa). "Light bulb saver" discs (little disc-shaped diodes that go into a light socket before the bulb) do this. In effect, the asymmetrical load creates a DC offset on the voltage "seen" by other devices on the same circuit. All of these "bad loads" can cause transformers in other devices to start humming or buzzing. Toroidal power transformers are particularly subject to buzzing if there's an asymmetrical load / DC offset on the line. I don't know of any good way of filtering out this sort of problem... an isolation transformer can help somewhat, sometimes, but it's an expensive solution and I don't think it's very effective. If you've got really severe humming/buzzing with something as simple and low-wattage as an electric blanket, , I'd be a bit concerned that this might indicate that there's a problem in your house wiring... overloaded circuits, a bad or loose connection somewhere, or even a loose or open neutral. The latter is a dangerous situation. If you should notice lights getting brighter, or appliance motors speed up, when you turn *on* a light or appliance elsewhere in the house... then you may have an open neutral and should call the power company immediately. I've had this happen twice (squirrel chewed through the neutral wire in our building's drop from the pole transformer), and PG&E always reacted immediately... their dispatcher said that they consider a "low voltage / high voltage" situation to require immediate action. You might want to have an electrician check out your house wiring. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! cut the ground off the blanket that will make the hum go away |
#8
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power supply hums when electric blanket on
In article ,
KC8QJP wrote: cut the ground off the blanket that will make the hum go away That strikes me as very poor advice, for three reasons: [1] I've never seen an electric blanket or bed-heating pad here in the U.S. which *has* a ground prong. They all use two-wire (hot/neutral) plugs. [2] If there *is* a ground prong on a device which is used in close proximity to a human body, it's probably there for a very good reason (safety). Removing a safety ground from such a device seems like a really bad idea. [3] If the reason for the humming is a harmonic-currents problem (as I suspect) then it has *nothing* to do with the presence or absence of a ground connection. It's due to irregular current flows on the hot and neutral wires. Floating the device free from the safety ground will have not reduce the problem at all. "Floating" an equipment-chassis ground can sometimes help reduce hum in audio/video equipment if the hum is due to a ground loop. I don't believe that ground loops have anything at all to do with the original poster's buzzing-transformer problem. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#9
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power supply hums when electric blanket on
DP [1] I've never seen an electric blanket or bed-heating pad here in
DP the U.S. which *has* a ground prong. No ground prong on my blanket or frying pan. Thick house wiring all done by myself, so that can't be the problem (don't tell Mom about the day I made a loop and all the conduits in the walls shook.) Therefore I shall, as a nod to the less privileged who perhaps don't even have electric power, learn not to eat or sleep while using the computer or my radio equipment (BM4IFV, not on air anymore, now just on email). OK, thanks. Bye. |
#10
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power supply hums when electric blanket on
On Jan 4, 10:40*am, "KC8QJP" wrote:
"Dave Platt" wrote in message ... When I dare to use an A) electric blanket, or a electric frying pan set on "low", at the same time when there is a B) UPS computer power supply, or Ham radio power supply also turned on anywhere in the house, the power supplies hum most worryingly. One must make a choice: A) food, warmth, or B) fun. What is the name of this waveform resonance with the current limiters of A phenomena? Is there some kind of filter I can apply? That sounds to me as if you're running into a "harmonic currents" issue. *This occurs if you have something connected to the mains which draws current in a nonlinear fashion (i.e. current drawn is not linearly related to the instantaneous value of the voltage sinusoid). In my experience, the commonest cause for this is a device which uses a triac "chopper" to control the amount of current being used. *Such devices "switch on" partway through each powerline cycle (120 times a second), so the current jumps from zero to a fairly high value. *The sudden jump creates a load on the line with frequency components at harmonics of the 60 Hz powerline frequency... hence the name. The devices you indicate (electric blankets, frying pans), and light dimmers are notorious culprits. Some of these devices may draw current in an asymmetrical fashion... e.g. they might use a half-wave rectifier diode, and thus draw current on only the positive half of the AC cycle and not on the negative (or vice versa). *"Light bulb saver" discs (little disc-shaped diodes that go into a light socket before the bulb) do this. *In effect, the asymmetrical load creates a DC offset on the voltage "seen" by other devices on the same circuit. All of these "bad loads" can cause transformers in other devices to start humming or buzzing. *Toroidal power transformers are particularly subject to buzzing if there's an asymmetrical load / DC offset on the line. I don't know of any good way of filtering out this sort of problem... an isolation transformer can help somewhat, sometimes, but it's an expensive solution and I don't think it's very effective. If you've got really severe humming/buzzing with something as simple and low-wattage as an electric blanket, , I'd be a bit concerned that this might indicate that there's a problem in your house wiring... overloaded circuits, a bad or loose connection somewhere, or even a loose or open neutral. *The latter is a dangerous situation. If you should notice lights getting brighter, or appliance motors speed up, when you turn *on* a light or appliance elsewhere in the house... then you may have an open neutral and should call the power company immediately. *I've had this happen twice (squirrel chewed through the neutral wire in our building's drop from the pole transformer), and PG&E always reacted immediately... their dispatcher said that they consider a "low voltage / high voltage" situation to require immediate action. You might want to have an electrician check out your house wiring. -- Dave Platt * * * * * * * * * * * * * * * * * AE6EO Friends of Jade Warrior home page: *http://www.radagast.org/jade-warrior *I do _not_ wish to receive unsolicited commercial email, and I will * * boycott any company which has the gall to send me such ads! cut the ground off the blanket that will make the hum go away- Hide quoted text - - Show quoted text - impostor A measure recently taken that will have repercussions that will indicate exactly how severely your actions have impacted upon fellow keyclowns. This measure was taken in your honor. You'll be hearing about it, but not from us. |
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