PSU Snoring ¿What does it mean?

[JAY X]

Hi Friends,

I have built a PSU with two transformers of 30w and 0.83 amps 2x18v secondaries. First i built the Psu with only one trafo to feed about 30 opamps. As the project got mor complex, i decided to add a second transformer (30w 0.83 amp 2x18) that i had around, to supply leds, relays and phantom.

There is an IEC inlet block with switch and one fuse holder, and an independent EMI filter.Ok so far.

Both transformers primaries are hooked at the EMI filter load side.
After calculation: w/v x 1,4 = 60/230 x 1,4 = 0,365 -> 400ma T fuse. Well, it snores a bit, i try with a 315ma T fuse and 500ma fast fuse and still snores... In all cases the fuses resisted intact.

So ¿What does it mean when a PSU snores? It supplies too much current or not enough?.

The other option i have is to use a new IEC inlet with emi filter, a new AC switch and TWO fuse holders with 200ma T fuse each, that i bought yesterday... it may work...¿or not?

Thank you for your help,
JAY X

 

[DF96]

Never heard of 'PSU snoring'. What do you mean? What does it actually do?

 

[JAY X]

Hi DF96

Well i really thought the term snoring was common!! in Spain, when a supply makes a continiuos noise we say "Roncar" which is translated to "To snore"

It refers to the noise hmmmmmm the transformers make. I try a 400ma fuse and it still makes a slight hmmmmm. or Ehhhhhhhhh.

With only one trafo and a 200ma fuse there is no problem.
with a 400ma fuse and two trafos there is a slight hummmmm
with a 500ma fuse and two trafos the hummm increases a bit....


So, Humming, ¿what does it mean? a lack of current? or Too much current? Overload?...

JAY X

 

[DF96]

Changing the fuse will make no difference. Transformer humming can be caused by the transformer (badly made, wth loose parts), mounting (try loosening or tightening fixing bolts, or adding rubber washers), mains harmonics or mains DC (especially with toroidal transformers).

 

[JAY X]

Hi DF96,

Okay, yes, the two toroidal transformers are stacked horizontally, on a 70mm long M6 screw, and a 1mm full trafo diameter rubber and metal washer in between the two transformers. I will try to tighten the bolts a bit more and hear what happens.

Now i remember that someone told me that tightening toridals reduces hum noise. I'll try right now.... i will tell you..

Thanks a lot

JAY X

 

[DF96]

Toroidal transformers have low external field, but not zero external field. Try moving them apart.

 

[Mooly]

Growling toroids can be due to DC on the mains but it's usually a problem with larger VA ratings.

Mains DC and Transformers

 

[rrrremus]

Have you tried to switch/reverse the mains wires of one of the transformer ?

 

[JAY X]

Hi All,

I got it!! Now it works perfectly.. Let me explain the story:

First i built a Dantimax dual psu for the opamps : +/- 18v and two cascoded regulators fro the DC outputs, for the +/-15v supply rails. This arrangement always worked perfectly.

The problem came when i needed more supply rails. And i thought to add a second transformer to feed a second supply board : A ssl9k psu. with +18v, +15v (in the place of a negative regulator, switching its pins) and +48v.

When i tested this afternoon this single 9k psu board alone, immediately the transformer started "complaining" grungeling, humming...

The first suspicious was the +15v rail. I pull out the regulator and the 1000uf 35v capacitor behind it. After that change, the psu didn't any noise...¡¡hurray!!... but i still needed a 15v regulator for the leds... so i built a tiny 15v psu card, and connected the input of this 15v regulator at the output of the +18v psu rail...¡¡and it worked!!

After that i re-wired the first supply, and now i have both supplies and both transformers feed by a single socket and a 400ma T fuse. And ¡¡¡¡completely silent!!! Bufff!!

JAY X

 

[KatieandDad]

Glad you are sorted.