How to stop singing transformers?

rogerg (Roger) · #1 12-08-2009, 09:40 PM

G'day all,

I have a 5v transformer which powers the glo-wire which surrounds the open half of my observatory. The annoying thing is that it "sings" - that high pitch noise you sometimes get from transformers. I've tried a couple and they both have the same tune. Does anyone know if there's a particular type of transformer or something which I can use to avoid having that high pitch noise? It's just a little distracting

Thanks!

MrB (Simon) · #2 12-08-2009, 10:15 PM

Sounds like a switchmode supply.
Try finding one of the older transformers that actually has a heavy copper transformer in them.

DavidU (Dave) · #3 12-08-2009, 10:46 PM

Quote:

Originally Posted by MrB

Sounds like a switchmode supply.
Try finding one of the older transformers that actually has a heavy copper transformer in them.

Just beat me to it.
Switchmode p/s are noisy.

rogerg (Roger) · #4 12-08-2009, 10:50 PM

OK, thanks, I'll have to have a dig around in my old box of disused transformers and find one of the old ones.

renormalised (Carl) · #5 12-08-2009, 10:52 PM

Better still, get a whole heap of them...all with different "singing voices", and you'll have a nice ensemble and good accompaniment for your observing

rogerg (Roger) · #6 12-08-2009, 11:01 PM

Quote:

Originally Posted by renormalised

Better still, get a whole heap of them...all with different "singing voices", and you'll have a nice ensemble and good accompaniment for your observing

Doesn't complement the new outdoor speakers I just installed in the open half sorry

citivolus (Ric) · #7 13-08-2009, 12:20 AM

You are getting inductor whine from the conversion stage in the switching part of the power supply. This can be worked around in design by using frequencies outside of the audible range, or in the design of the case.

Switching power supplies are going to be more efficient than the alternative, and anything sold in Australia these days needs 80% or better efficiency to get licensed for sale. Unless you have an old one around, you will likely find that you are stuck with using a switch mode supply.

You may find a sealed design (without vents), such as those used for laptops and sold at places like Jaycar, will block enough of the noise as to be inaudible. These are also a better choice for use in potentially dewy situations anyway.

Regards,
Eric

citivolus (Ric) · #8 13-08-2009, 12:23 AM

Oh, another thing, power supplies often have a minimum operating current needed to maintain regulation. Outside of that current range, they will not perform at spec and voltages may be high or low, and the conversion stage could be functioning in a range it was not designed for. This could be potentially contributing to the noise. If the supply has too much unused capacity, I would be suspicious of this possibility.

Regards,
Eric

wasyoungonce (Brendan) · #9 13-08-2009, 01:32 AM

Switchmode supply transformers generally run anywhere from 15Khz to 42Khz and this can cause a squeal between their windings, laminations or indeed if the frequency of oscillation is out (usually a dried out electrolytic capacitor) this can cause a squeal.

As suggested many of the good older AC (non-switchmode) transformers do not squeal, but they can buzz (at 60Hz) between their core laminations (if they are cheapies).

It's also possible that the "glow wire" is a capacitive load causing the switchmode to operate outside it's tolerances. Was the supply designed for these lights?

In any case I'd go and get one of those jaycar torrodial transformers with the desired output you need. Make sure you overrate and get a transformer with more current capacity than you need.

MrB (Simon) · #10 13-08-2009, 02:04 AM

60Hz?

wasyoungonce (Brendan) · #11 13-08-2009, 01:09 PM

Quote:

Originally Posted by MrB

60Hz?

Sorry...I keep thinks of international terms. Most equipment in Australia comes from 60Hz designs. This is because most of the designs are for OS markets that are a lot bigger than ours. Manufacturers don't change the designs for Australian equipment they just build in more power factor tolerances so they run ok on our 50Hz.

Most of the world is split between 50Hz & 60Hz.

They also build in designs that accommodate anything from 220V to 240V for the same reason

renormalised (Carl) · #12 13-08-2009, 01:23 PM

Quote:

Originally Posted by rogerg

Doesn't complement the new outdoor speakers I just installed in the open half sorry

What a pity. You could've had them do a rendition of Bohemian Rhapsody for your own edification

MrB (Simon) · #13 13-08-2009, 01:24 PM

Quote:

They also build in designs that accommodate anything from 220V to 240V for the same reason

Most equipment these days will run happily on 100-240v.
Sure makes it easy to travel with mobile phone, laptop and camera chargers only needing an adaptor

Last time I went OS I packed an aussie 4-way powerboard and put the adaptor on that

rogerg (Roger) · #14 13-08-2009, 02:10 PM

Thanks everyone, I will be trying out the other type of transformer in a few days time.

rogerg (Roger) · #15 13-08-2009, 02:13 PM

Quote:

Originally Posted by wasyoungonce

It's also possible that the "glow wire" is a capacitive load causing the switchmode to operate outside it's tolerances. Was the supply designed for these lights?

No.. from what I could tell of it's statistics it's an exact match for the one which came with the glo-wire but the one that came with the glo-wire died after about 2 hours of use

They were both light switch-mode ones. The glo-wire was bought direct from the US (and came with it's transformer, the one that died, which did handle our 240v and plug type).

Quote:

Originally Posted by wasyoungonce

In any case I'd go and get one of those jaycar torrodial transformers with the desired output you need. Make sure you overrate and get a transformer with more current capacity than you need.

I'll give the old ones a shot (seeing as I think/hope I have some of them that will suit) and then consider the Jaycar toroidal .. thanks.