Switch Mode Power Supplys

[VK4GJW]

Greetings one and all,

I am currently in the market for a 12VDC (13.8VDC) power supply, capable of running a few receivers, a scanner and a mast head amplifier. After having been absent from the amateur scene for a number of years, I see that Linear power supplys seem to be not as available as they used to be. Everything seems to be going the way of switch mode power supplys. Now while I am not particularly worried about them powering things such as laptops and the like, I was always of the beleif that they were not that good around RF equipment. Am I right or has this changed over the years? I see plenty of switch modes capable of supplying 20, 30 and 40 Amps or more, the Manson types and the like. Are they a problem with modern day RF equipment? Or should I still try and source a Linear one, meaning transformer, bridge rectifier, etc etc? Any thoughts on the matter would be welcomed.

Cheers
Greg
VK4-GJW

[ZL3ADT]

Hi Greg
I have recently purchased a Manson SPS- 8400 from VK.
I have not noticed any RFI to my gear yet. It has a fan I dont hear and it stays cool.
Only thing I dont like is, the output terminals are on front.
IT appears Manson is one of the better power supplies.

Ross

[VK5RC]

Hi Greg
I think the better quality SMPS are getting pretty quiet regarding RF noise, they also feature pretty well in the size, price, heat/efficiency and weight categories as well.
Manson have made some good gear.
My Avair 45A switch mode has served me well for 5 or so years now with no noticeable RF noise.
If by some chance you do get a noisy one there are circuits to help tame them!
I recently built a linear 28V 20A supply, Now I wished I bought a switch mode and spent the time quietening it, would have been a lot easier and cheaper!
Regards Rob

[VK2OMD]

Greetings one and all,

I am currently in the market for a 12VDC (13.8VDC) power supply, capable of running a few receivers, a scanner and a mast head amplifier. After having been absent from the amateur scene for a number of years, I see that Linear power supplys seem to be not as available as they used to be. Everything seems to be going the way of switch mode power supplys. Now while I am not particularly worried about them powering things such as laptops and the like, I was always of the beleif that they were not that good around RF equipment. Am I right or has this changed over the years? I see plenty of switch modes capable of supplying 20, 30 and 40 Amps or more, the Manson types and the like. Are they a problem with modern day RF equipment? Or should I still try and source a Linear one, meaning transformer, bridge rectifier, etc etc? Any thoughts on the matter would be welcomed.

Cheers
Greg
VK4-GJW

There are two important issues bearing on your choice:
1. switched mode supplies unavoidably make noise, better ones prevent it escaping the box; and
2. switched mode supplies may be more challenging to repair should they fail.

1: external filtering is rarely a good route, filtering needs to be integrated with the design, and "letting the genie out of the bottle" (the noise out of the box) is near impossible to tame.

2: not only are the circuits new to most hams, but safe working practice really requires an isolation transformer to reduce the risk of injury, and to allow connection of a scope if needed.

Some people will sing the praises of Manson, but they have produced some less reliable too.

You can get circuits from Manson, but they will put you through the third degree requiring you to 'sign' a declaration before they hand it over. Remember that the Chinese would be the world's greatest copyists, and the Chinese know that! Of course, if you wanted to copy one of their power supplies, you would buy it, make the declaration and get on with production... all the rigmorol is there for is to put genuine customers off if they don't follow the thing through.

I have a bunch of Manson supplies, and they have all been good... but I have repaired some Dick Smith branded Manson supplies for others (the ones that have sometimes blown diodes and transistors).

Make the Australian Consumer Law work for you, tell the retailer you intend using it to power communications equipment (I doubt you need to ask if it is suitable, just that they know your intended application before contract) and then if it has noise that makes it "unfit for purpose" you have opportunity for resolution.


Owen

[VK2AAH]

My employer uses locally sourced "Powerbox" SMP supplies and to date we have had almost zero failures over a decade of use in some of the more lightning prone locations around NSW. Ironically, they replace a well known linear PSU that was chronically prone to lightning/surge damage. I was very cautious at first because of the noise issue but our tests showed that what noise there is doesn't leave the case. In addition, weight is a fraction of the linear PSU.

I have a 40A Manson SMPS here- it doesn't get worked hard but I'm happy with it. In principle SMPSs are now very good- but like anything if you choose cheap junk then you only have yourself to blame. Same could be said for some of those old "CB type" linear power supplies...

Cheers

Richard
VK2AAH