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Isolation transformer buzz with generator


Jaston10078
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5 minutes ago, Phoenix_V said:

Thats interesting though I have lots of stuff with power supplies which nowadays must all be switch mode and its only the printer that does it

 

What impact the harmonics will.have depends on the switching frequency and effectiveness of the filter circuits.

 

Older small SWMP's used an earth connection, down which a small but high frequency current passed. Newer designs use double insulation (no earth connection) to avoid the problem.

Edited by cuthound
To remove a letter masquerading as a space
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12 minutes ago, cuthound said:

 

What impact the harmonics will.have depends on the switching frequency and effectiveness of the filter circuits.

 

Older small SWMP's used an earth connection, down which a small but high frequency current passed. Newer designs use double insulation (no earth connection) to avoid the problem.

That must be it then the printer would be the only electronic item that is earthed

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2 hours ago, cuthound said:

Switch mode power supplies use transistors to switch the supply on and off at high frequencies thus eliminating the need for inductors.

 

This creates the harmonics which Loddon mentions below and it is the harmonics that cause the humming.

 

Since this appears to be a picky and argumentative thread, I will just mention that switch mode power supplies definitely do have inductors?

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10 hours ago, nicknorman said:

Since this appears to be a picky and argumentative thread, I will just mention that switch mode power supplies definitely do have inductors?

 

Perhaps I should have said large inductors.

 

SMPS revolutionised the size of power supplies when they first appeared.

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That racket would certainly drive me nuts in a very short time!

 

So what is it that is being induced to rattle around like that? The cause would certainly seem to be a  changing magnetic field. My first suspect would be a transformer or something transformer like, (something with a sheet iron core surrounded by lot of turns of copper wire), a good transformer after assembly is potted with varnish and then baked to render it a solid lump. All that costs money, was the process skimped? If so would it be possible to have the offending part removed and re-potted?

 

A second thought is could a part of the chassis of the unit be acting as a sounding board? If that was the case the addition of some weights to change its natural frequency might be sufficient.

 

 

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Have you been able to isolate the cause?

Generator, charger, etc; by switching circuits off.

You are right, the noise is the transformer laminations vibrating, if this is ‘potted’ then this should be quiet. At 50Hz mains frequency a good transformer should be quiet, but loads and supplies many be working at other frequencies, which the transformer was not designed for. Also the enclosure may be ‘sounding’, removing bits in a ‘safe manner’ may provide a diagnosis.

Tractor

Edited by Tractor
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3 hours ago, Tractor said:

Have you been able to isolate the cause?

Generator, charger, etc; by switching circuits off.

You are right, the noise is the transformer laminations vibrating, if this is ‘potted’ then this should be quiet. At 50Hz mains frequency a good transformer should be quiet, but loads and supplies many be working at other frequencies, which the transformer was not designed for. Also the enclosure may be ‘sounding’, removing bits in a ‘safe manner’ may provide a diagnosis.

Tractor

 

That assumes a sinusoidal waveform. Waveforms distorted by harmonics will.cause increased noise.

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https://images.mastervolt.nl/files/ManualIVETD030319EN.pdf

 

This I believe, is the manual for the transformer, you may have this.

The transformer is a toroidal type, which is more costly to manufacture, but better quality. Behind the cover is a circuit breaker which will be ok or you would see no power delivered. There is also a 'soft starter', this briefly pre charges the coils, before closing a contactor, to energise the transformer fully. It may be useful to have the soft starter operation looked at to check there is no snag with this. It will be a thyristor circuit board, connected to the bypass contactor.

 

If you have checked all other possible causes, supplies, and loads; I would look at the transformer.

 

This is a well made device, and probably costly to purchase so worth having it looked at.

 

Come back if I can help further.

Edited by Tractor
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