True sine wave inverter

Thread Starter

banzai

Joined Jan 3, 2014
71
Hi Guys

i got my self a 1000W True sine wave inverter which is running perfect except that i got this annoying problem, when i plug in my laptop to the inverter i get this annoying buzzing sound in my headphones, i tried different headphones but the same sound is still buzzing.

what could cause this and is there a way to fix this



Thanks in advance guys :)
 

Alec_t

Joined Sep 17, 2013
11,800
It's called interference and it's due to inadequate filtering inside the inverter. If you have access to an oscilloscope, check the output waveform to identify if there's noise on that. You could also try surrounding the inverter with a Faraday cage to determine if the interference is being radiated.
 

Thread Starter

banzai

Joined Jan 3, 2014
71
It's called interference and it's due to inadequate filtering inside the inverter. If you have access to an oscilloscope, check the output waveform to identify if there's noise on that. You could also try surrounding the inverter with a Faraday cage to determine if the interference is being radiated.
Oscilloscope shows a pure sine wave :confused:

Is there a way to fix this ?
 

AnalogKid

Joined Aug 1, 2013
8,810
There are two ways to make a sinewave output inverter. One is linear - with a true analog sinewave into a power amplifier into the primary of a step-up transformer. The other is switching - a pulse width modulated squarewave into the primary of a step up transformer. Sounds like you have the latter, and are hearing a beat frequency from the PWM. Depending on exactly where the EMI source is, a shielded line cord might help.

ak
 

Thread Starter

banzai

Joined Jan 3, 2014
71
There are two ways to make a sinewave output inverter. One is linear - with a true analog sinewave into a power amplifier into the primary of a step-up transformer. The other is switching - a pulse width modulated squarewave into the primary of a step up transformer. Sounds like you have the latter, and are hearing a beat frequency from the PWM. Depending on exactly where the EMI source is, a shielded line cord might help.

ak

The one that i am using is not a square wave inverter, its a pure sine wave
 

Brownout

Joined Jan 10, 2012
2,390
Can you post your scope's output? Also, make sure you probe your inverter with a load plugged in, preferably the computer you're using. Having a load will make a difference.

And please try your computer/headphones on household power, just to make sure.... If that works well, then leave your computer plugged into house current, and place your computer next to your inverter, running with a load attached, and see if you still get the noise.
 

Thread Starter

banzai

Joined Jan 3, 2014
71
Can you post your scope's output? Also, make sure you probe your inverter with a load plugged in, preferably the computer you're using. Having a load will make a difference.

And please try your computer/headphones on household power, just to make sure....
OK i will send you guys a picture of the scope output

The computer is running on mains and with no problems i even got a Square wave ups that i run the computer on sometimes with no problems, this buzzing sound is only heard when the laptop is plugged to the inverter
 

Brownout

Joined Jan 10, 2012
2,390
Looks like a switching transient. You also have some ringing in it, barely seen because of the lack of resolution in your scope trace. Hard to tell if this is causing your issue or not. You can also try a line noise filter. I don't have much experience this them, but this is the sort of thing they are made for. Have you tried using you computer plugged into house power and placed near the running and loaded inverter?
 

Thread Starter

banzai

Joined Jan 3, 2014
71
Looks like a switching transient. You also have some ringing in it, barely seen because of the lack of resolution in your scope trace. Hard to tell if this is causing your issue or not. You can also try a line noise filter. I don't have much experience this them, but this is the sort of thing they are made for. Have you tried using you computer plugged into house power and placed near the running and loaded inverter?
Sorry for the low resolution this is the only scope i got near me at the mean time.

The computer runs just fine on main power, it only starts to buzz when its connected to the inverter, what is the purpose of running the laptop on main while standing near the inverter loaded ?
 

Brownout

Joined Jan 10, 2012
2,390
The purpose is to determine if the buzzing is caused by radiated noise from the inverter, or form noise on the wire connecting between the inverter and computer.
 

Brownout

Joined Jan 10, 2012
2,390
Well, now you know it's radiated noise. You might just try a long extension cord to move your computer away from the inverter, or using a metal shield around the inverter. Be careful to not overhead the inverter if you use a metal box. You'll still need ventilation. You could also try a wire mesh.
 

Thread Starter

banzai

Joined Jan 3, 2014
71
I am already running my computer in a different room from the one that the inverter is in and i get the annoying buzzing sound. When standing near the inverter the buzzing sound is not very high compared to when the laptop is plugged in to the inverter
 
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