Low noise 12v power supplies

[Peter.N.]

Having been experiencing S9+ of noise on 80m I eventually found that it was coming from two in house power supplies, one belonging to the +Net router, the worst though was on some LED lamps in a display cabinet.

Can anyone suggest a good quiet readily available unit to replace them?

Thanks

Peter

[Electronpusher0]

I think the +net router uses 12V at a fairly low current so the psu could be replaced by a transformer based analogue supply.
The LED lamps could be more tricky. I have tried experimenting with analogue supplies for flat panel LED lights (40W) with mixed success, I have reported about it here
https://www.vintage-radio.net/forum/...d.php?t=162401
I also tried some off the shelf constant current LED driver modules.
A chinese one from e-bay was absolutely filthy as regards radiated noise, it was CE marked but this was clearly fake.
A reputable one from CPC was far quiter, a medium wave radio only picked up noise when right along side the driver.

Peter

[FrankB]

You might try placing some ferrite cores on the leads out of the supplies.
I remember that when the VIC 20 came out it generated noise all over. Placing an FT2 core on the leads solved the problem. (My downfall was I didn't patent the cure. Someone else stole the idea and made a good nut off it.).

[David Simpson]

Hello Peter,
Right enough, 80m is prone to house equipment derived EM noise. Must be 10 years or more ago, when I set up a rig & antenna for ex marine AM Tx/Rx's to work 80m. My solution to deal with noise was to supply the 24V equipment from two 12V tractor batteries, kept charged by an ex marine 24V Sailor mains charging unit. Worked just as silently when a VMARS chum fetched over his 12V 2-20m mobile rig(I can switch between the batteries' connections). My earthing is just that - to the ground outside close to the Doublet's mounting pole - definitely not the house's PME earth supply.

Regards, David

[stevehertz]

I see that Peter has touched on availability above, but what is the situation in general regarding availability of 'non-SMPSs' ie ones that are transformer based or by some other technology do not produce noise that is picked up by AM radios?

Cost be damned, if they're available I've a good mind to change every wall wart in the house to keep the RF noise down.

But what about LED lamps? I suppose they produce noise although in general they're some distance away from radios.

[Julesomega]

You mean, you haven't got a tea-chest full of old transformer wall warts pulled out of skips and donated by friends? Not sure if they would do for your LEDs, they probably need a current supply rather than a voltage supply (though I did find one of those, which has been very useful for charging sealed lead-acid batteries)

[See_Mos]

Some of the cheaper ones from CPC are horrendous!

Medical grade ones are a lot quieter but are almost all open PCB or metal cased.

It's easier to build your own transformer plus linear regulator power supplies than to buy them.

[stevehertz]

I see a small business opportunity for someone. Small, transformer based replacement power supplies for those who listen to AM radio. Hmm, not millions of potential buyers I expect. Nonetheless, neither are there millions of buyers of TV standards converters, but they're made and sold..

I see a small business opportunity for someone.

I don't think it will be "allowed" to be sold, too much standby power. From some regulation about efficiency.

[ex seismic]

Some SMPSUs are OK, I had to mend one from a Lenovo tablet and was impressed, full filtering on both mains input and DC output.

[stevehertz]

Originally Posted by ex seismic

Some SMPSUs are OK, I had to mend one from a Lenovo tablet and was impressed, full filtering on both mains input and DC output.

But surely some RF just 'emits' from the electronics, it's not just input and output that are a potential problem surely?

[Radio Wrangler]

Originally Posted by merlinmaxwell

I don't think it will be "allowed" to be sold, too much standby power. From some regulation about efficiency.

Perhaps as a specialist ultra low noise item where no higher efficiency type exists that can fill the need?
Rather like the rough service bulbs exemption as-was.

David

[Techman]

There are special SMPSUs made for powering CB and Ham radio kit and they emit no interference whatsoever, so it's possible if you throw enough money and electronics at it.

My advice would be to switch off the offending devices when you want to SWL. I find that laptop supplies are horrendous for causing interference. Regarding the router, I would complain to the company that supplied it and tell them to replace it. My router SMPSU causes no interference whatsoever and you could probably do without the LED lighting when you want to listen, although I'm guessing your other half may not be too pleased about that suggestion. As a final note regarding those LED supplies - someone brought one of those LED supplies round for me to test as he wanted to run an RF linear amplifier off it. It supplied and ran the linear perfectly with no interference on receive, so it's down to the quality or otherwise of the particular power supply.

[Megatron]

Originally Posted by stevehertz

But surely some RF just 'emits' from the electronics, it's not just input and output that are a potential problem surely?

Sure the switching creates the noise, however it wont radiate without an effective antenna. Usually in the 30MHz to 1GHz area particularly under 500MHz most radiated emission comes from the cables.
These power supplies vary massively, some are quite good, most are noisy.

[Ian - G4JQT]

A couple of years ago I spoke to someone in the UK selling active radio antennas. He said that it was now illegal to sell equipment with linear power supplies due to their inefficiency, and also claimed it was all to do with European regulations.

With his equipment SMPS are a nightmare and he said it almost ended his business. He did eventually find a make that was just about quiet enough to use, but suggested you'd get better performance if you don't use it and got a regulated linear PSU instead!

I must admit it sounds a bit unlikely, but as far as I know he has no reason to make it up...

[Herald1360]

What's the position if the PSU is built in and there is no "standby" mode, only ON or OFF?

[McMurdo]

I believe that's ok. It's the habit people have of leaving wall-warts plugged in with unconnected output cables or tv's left in standby that had incurred the wrath of the EU legislators.
And the 'transformers illegal' thing is for domestic appliances, AFAIK it doesn't (yet) cover items only for professional use.

Some professional radio mics use wall wart PSUs and I've had clients come in saying they didnt work after buying a replacement wall wart (they're always getting lost or tripped over). The smpsu's can 'jam' the radio mics. I have a stash of linear 'aftermarket' wall warts (as the originals were) for such occasions.

[Peter.N.]

Thanks for all your replies and apologies for not getting back before but my broadband has been off - again!

I have a couple of standby batteries connected to the shack supply, that's how I found out where the noise was coming from, with the mains turned of the noise is about S 2-3, not to bad nowadays. The two aforementioned PSU's were causing 99% of the noise, there are a number of others running which don't seem to cause any noise at all - at least not in the bands I am using.

I have a draw full of old power supplies, many transformer driven but the outputs are anything except 12 volts. The PSU powering the shack is a good old 30a transformer driven one.

I also have solar panels but they are not causing a problem. I did find another 12v router transformer but it has the wrong plug, I could try that I suppose - and another one that is 22 volts!

Thanks again for your help.

Peter

[Herald1360]

Be wary of the actual output voltage of any unregulated small psu- depending on your load it may be much higher than you would like!

And it may be quite noisy too- slow diodes like 1N4007 can generate a lot of rf hash unless they've got a few nF across 'em.

[Techman]

This is such an easy problem to sort out - I wish some of mine with noise on receivers from 'outside' the house were as easy as yours.

Unless I'm missing something - phone up your broadband provider and tell them their router power supply is causing bad RFI.

Display cabinet with LED lighting - just switch them off.

As for the interference caused by 1N4007 diodes - I've never had this problem and never fitted capacitors across them and I've used them in all sorts of mains type power supply applications. I'm sure it's true that they can cause interference as I've heard it mentioned before, I think by you, Chris. It's just that I've never known it, perhaps I've been lucky in this respect - or perhaps the bad diodes are just following you around.