Transformer Hum

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Auldgeek
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Transformer Hum

Post by Auldgeek » 27 Nov 2019, 15:08

Wasn't too sure where to post this, as it's not home brew. However, as there's plenty of discussion here about Power Supplies, I've taken a punt.

Anyway:- Hello! :wave:

I have an annoying issue with a Daiwa Power Supply. It's a PS-304 30A linear type supply. Supply is, in every other sense of the word, in good working order except some really annoying transformer hum. Supply provides a stable output and a good dose of Amps (I've drawn 20A from it for several minutes) but the hum can be very loud. I'd even go as far as saying that there's a change to its physical resonance when I place my hand on the enclosure and draw current.
It doesn't always do this but more often than not when supplying anything more than 2-3A.

Now, from my experience, transformer hum normally comes about either by stray RF current field effect when the transformer core is magnetised or small variations and uneven vibration from the layers making up the core (magnetostriction)
On this supply, everything is stock, no components have been replaced and from what I can see and measure, everything is as it should be. I've went as far as tightening up the transformer plates and ensured everything else is securely tightened. Ive also sat the supply on sound deadening material.

One other thought occurred to me. Is it possible the transformer itself has undergone a degree of delamination? I'm mentioning this, as the hum increases as more current is being drawn and it could simply be the adhesive layer between the laminations is breaking down.

Has anyone had any experience of this effect and been able to dampen it sufficiently? I've read some stories of folk pouring glue in to transformers but not of the size in this supply.

Cheers

Drew
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Andy
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Re: Transformer Hum

Post by Andy » 28 Nov 2019, 14:27

It may not be the transformer itself, just the steel parts of the case which are vibrating in the magnetic field. Slackening the case screws and doing them up again may make it go away. If it is the transformer, often a sharp whack with a big hammer will re-arrange the windings and cores enough to make it think twice.
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Re: Transformer Hum

Post by Auldgeek » 28 Nov 2019, 23:54

Thanks for the input and suggestions.
I think at one point, it was rattling with the case removed but I'll need to double check.

Cheers.
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Re: Transformer Hum

Post by mr_m3 » 29 Nov 2019, 18:49

I have the exact same issue on my watson W-30AM 35A supply, some advice i was given was to get a big set of locking jaw pliers and squeeze the transformer to almost crimp the wire slightly and re tape.

let me know how you get on i may do something to mine soon
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Re: Transformer Hum

Post by Mikel » 02 Dec 2019, 09:37

mr_m3 wrote:
29 Nov 2019, 18:49
I have the exact same issue on my watson W-30AM 35A supply, some advice i was given was to get a big set of locking jaw pliers and squeeze the transformer to almost crimp the wire slightly and re tape.

let me know how you get on i may do something to mine soon
I have the Watson W-25AM, I have had it for many years and the transformer is pretty good on the noise front, but the fan is a different matter!

Sounds like a helicopter coming in to land!

I eventually modified mine by setting the voltage to 13.8 with the pot on the board and use the voltage adjustment knob on the front panel to control the fan speed - much better for my sensitive ears.
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Re: Transformer Hum

Post by mr_m3 » 02 Dec 2019, 09:45

Mikel wrote:
02 Dec 2019, 09:37
mr_m3 wrote:
29 Nov 2019, 18:49
I have the exact same issue on my watson W-30AM 35A supply, some advice i was given was to get a big set of locking jaw pliers and squeeze the transformer to almost crimp the wire slightly and re tape.

let me know how you get on i may do something to mine soon
I have the Watson W-25AM, I have had it for many years and the transformer is pretty good on the noise front, but the fan is a different matter!

Sounds like a helicopter coming in to land!

I eventually modified mine by setting the voltage to 13.8 with the pot on the board and use the voltage adjustment knob on the front panel to control the fan speed - much better for my sensitive ears.


Funny you should mention that, the temperature controlled fan circuit has died on mine and with a 15A+ load for a long time it overheats and shuts off, eventually coming back on once it cool down. I’ve bought a small PWM fan speed controller to fit into mine to have a variable fan and fix the fan in one go
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Re: Transformer Hum

Post by Auldgeek » 02 Dec 2019, 11:28

Not the supply I have the transformer hum but a more recent My-Del clone had a fan like a jet Turbine.

I replaced the fan with an Artic Silent cooler. Now, the supply is effectively silent and because the fan has better airflow, the supply stays cool.
Auldgeek - Drew
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I've changed radios that many times, I've forgotten what I have :think:

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