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ASIAIR Plus Noise with Dew Heaters


Andyb90

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Hi everyone,

I’ve got 3 dew heater bands connected to my new ASIAIR Plus. When the bands are powered up the ASIAIR Plus makes a buzzing/humming noise. Does anyone know if this is normal or if it is anything to be concerned about?

Thanks,

Andy

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1 hour ago, OK Apricot said:

It may be a sign of the power distribution being near its limit - I'm pretty sure it's only good for 6A across all four ports. Do you have anything else connected? Do you know what your power draw is with everything connected? 

I just tested again with only the 3 dew heaters at 30% and get the noise. The power draw is showing as 0.75 amps in the ASIAIR.

I noticed if the dew heaters are set to 100% the noise stops.

Edited by Andyb90
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Without knowing what's inside (electrically or electronically) and without hearing the noise its very difficult to say but it's not something I would not normally expect from this sort of device,, but then it may well be normal.
A power supply then yes maybe it's normal at certain power draws but I would have thought the ASIair just uses electronics to distribute, control and measure power supplied by a separate power supply (but I do not own one so forgive my presumption if that is not the case). 

Like I say I do not know what is in the unit but suspect the only things that could cause a buzzing would be transistors or FETs switching on and off very quickly to control power, normally they are pretty quiet ands you struggle to hear them but at certain frequencies they can get reasonably loud .

So although I would not expect the noise it could well be normal.

Steve

Edited by teoria_del_big_bang
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Ha ha , should have done a search before I replied.

I was going to add maybe worth going on the ZWO forum and searching or asking about it and when I looked THIS came up straight away.

From a quick scan through this thread looks like normal behaviour.

Also seen THIS which does sound like a semi conductor switching at a high frequency.

Steve

Edited by teoria_del_big_bang
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This is a common side effect of PWM (pulse width monulation) switching used to control the dew strap power, as a result of the circuit design and possible PCB board layout. At 0% and 100% there is no actual PWM switching occuring so there is no noise generated. PWM is used as it's very power efficient and easy to implement.

The noise is generally produced by capacitors on the PWM output circuitry, commonly ceramic plate, among others, the plates of which will vibrate at the switching frequency due to the piezoelectric effect. As surface mount capacitors are usually used nowadays, this plate vibration gets transmitted to the PCB itself and it's the PCB vibrating you can hear.

The MOSFET (Metal Oxide Semiconductor Field Effect Transistors) commonly used for the power switching can switch very fast and unless steps are taken to limit the rate at which the voltage changes on the MOSFET gate pin then it's likely the switching output will be too fast and 'ring' after each transition which is a high frequency AC voltage oscillation which decays over time, superimposed on the PWM waveform. This will likely make the audible noise louder, as well as reduce the switching efficiency, making the MOSFETs run hotter than they should.

I made my own Arduino based PWM dew controllers which switch at 4kHz or 8kHz depending on the output used, and using an oscilloscope to check the output waveform, selected components to eliminate any 'ringing' while still switching at a fast enough speed, and also used through hole components rather than surface mount, so any possible vibrating components are mechanically isolated from the PCB. It's totally silent as a result. 🙂

Changing the PWM switching speed in software could make the noise less annoying, or clamping the PCB down more to reduce vibrations. Putting a small resistor capacitor combination in parallel with the dew strap would likely inhibit the ringing, but the capacitor mustn't be too large that it stops the FET switching fast enough which could cause it to overheat.

Probably more than you wanted to know. 😊

Alan

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3 hours ago, symmetal said:

This is a common side effect of PWM (pulse width monulation) switching used to control the dew strap power, as a result of the circuit design and possible PCB board layout. At 0% and 100% there is no actual PWM switching occuring so there is no noise generated. PWM is used as it's very power efficient and easy to implement.

The noise is generally produced by capacitors on the PWM output circuitry, commonly ceramic plate, among others, the plates of which will vibrate at the switching frequency due to the piezoelectric effect. As surface mount capacitors are usually used nowadays, this plate vibration gets transmitted to the PCB itself and it's the PCB vibrating you can hear.

The MOSFET (Metal Oxide Semiconductor Field Effect Transistors) commonly used for the power switching can switch very fast and unless steps are taken to limit the rate at which the voltage changes on the MOSFET gate pin then it's likely the switching output will be too fast and 'ring' after each transition which is a high frequency AC voltage oscillation which decays over time, superimposed on the PWM waveform. This will likely make the audible noise louder, as well as reduce the switching efficiency, making the MOSFETs run hotter than they should.

I made my own Arduino based PWM dew controllers which switch at 4kHz or 8kHz depending on the output used, and using an oscilloscope to check the output waveform, selected components to eliminate any 'ringing' while still switching at a fast enough speed, and also used through hole components rather than surface mount, so any possible vibrating components are mechanically isolated from the PCB. It's totally silent as a result. 🙂

Changing the PWM switching speed in software could make the noise less annoying, or clamping the PCB down more to reduce vibrations. Putting a small resistor capacitor combination in parallel with the dew strap would likely inhibit the ringing, but the capacitor mustn't be too large that it stops the FET switching fast enough which could cause it to overheat.

Probably more than you wanted to know. 😊

Alan

Thanks for the response. Do you think the vibration could damage the unit either imminently or over an extended period of time?

I could always go back to using a separate dew heater controller. Using the ASIAIR Plus for dew heater control is convenient, but not a necessity.

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17 minutes ago, Andyb90 said:

Thanks for the response. Do you think the vibration could damage the unit either imminently or over an extended period of time?

I could always go back to using a separate dew heater controller. Using the ASIAIR Plus for dew heater control is convenient, but not a necessity.

No it won't, unless it gets loud and you can feel the vibration which I can't see happening. Many power supplies in particular make a noise, linear ones can buzz or hum, and switch mode supplies can give of a high pitch whine. This is due to the continuously changing magnetic fields in inductors or transformers which are carrying significant currents creating a force which tries to make them vibrate very slightly, (Fleming's Left Hand Rule). They continue working for years without problems. 😉

Here's an article explaining acoustic noise in switched-mode power supplies. Half way down it mentions the piezo effect which is likely the cause in your case. It states that 

"Ceramic capacitors that undergo high dv/dt swings often prove to be audibly noisy"

High dv/dt means a large voltage swing in a short period of time, which is what's happening in your dew controller PWM circuitry. If the noise isn't too much of a bother then I should leave it as it is. 🙂

Alan

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11 hours ago, symmetal said:

No it won't, unless it gets loud and you can feel the vibration which I can't see happening. Many power supplies in particular make a noise, linear ones can buzz or hum, and switch mode supplies can give of a high pitch whine. This is due to the continuously changing magnetic fields in inductors or transformers which are carrying significant currents creating a force which tries to make them vibrate very slightly, (Fleming's Left Hand Rule). They continue working for years without problems. 😉

Here's an article explaining acoustic noise in switched-mode power supplies. Half way down it mentions the piezo effect which is likely the cause in your case. It states that 

"Ceramic capacitors that undergo high dv/dt swings often prove to be audibly noisy"

High dv/dt means a large voltage swing in a short period of time, which is what's happening in your dew controller PWM circuitry. If the noise isn't too much of a bother then I should leave it as it is. 🙂

Alan

Ok, thanks for the info. As the ASIAIR is attached to my imaging scope I think I'll test with and without the dew heaters powered on just in case the vibration has any impact on the images.

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