Question about 12V electronic downlight transformers

[rubberlips]

Just a quick question about 12V electronic downlight transformers. I've come across a some extremely cheap. Since they're 12V AC with about 5A output I thought they might be good for powering stand alone effects.
My question is if you rectify, add caps and a regulator (like normal power supplies), do electronic transformers tend to induce noise?? Since they're normally used to run globes, I suppose they wouldn't put much noise suppression in them.

Anyone ever try them??

Pete

[ninoman123]

If its regulated and filtered properly it wont cause noise.  Why not make it power a bunch of pedals? If it has 5A output it would power....welllll...a LOT of pedals. Read GGG's page about power supplies.

[niftydog]

5A AC is way overkill in my opinion, but there are other issues with these beasts.

For starters, I have no idea why they call them "electronic transformers." To me that's a tautology. But that's just a comment...

They are in fact just switch mode power supplys. They sit somewhere in between a conventional switch mode and an inverter. They are designed to drive highly inductive loads (ie; filiament lamps) and as such it is not a simple task to rectify them.

Have a look at this page, near the bottom you'll see some pictures and an explanation of why you will find it impossible to use these devices to create a given level of DC.

Besides, they aren't really that cheap! AUD$6.95 seems about the going rate for a centre tapped 12V 150mA transformer. Yeah, it's not 5A, but you're never going to need that much power!

[Paul Perry (Frostwave)]

Rubberlips said in his first post that they were 12v **AC**, and if so, no problem.
But if they ARE switchmode 12V DC, then yes, all that!

BTW I had a power surge (lightning strike in the street) burn out a switchmode supply (and leave the remains dangerously hot, with current still running thru it!). Never saw that with a linear power supply...

[niftydog]

I would call it 12V "AC" RMS.

"AC" meaning it's actually high frequency (40khz, too high for conventional rectifiers) modulated ­±DC shaped to look like AC. Have a look at the link I gave, it is a simple and concise explanation of the problem.

[Paul Perry (Frostwave)]

thanks niftydog, you've taught me somethng! (again!)
guess that's one thing I *WON'T* be looking for in skips..

[niftydog]

unless you plan to have a house full of heat-generating, money-wasting, poor-light-giving halogens! Or unless they're the "real" transformers!

[rubberlips]

Thanks Niftydog,

I thought there might have been something weird with them being switchmode. I hadn't dug into any switchmode power supply circuits before. Learn something new everyday.

Bit of shame though, they're extremely compact.

Well, if they can't be rectified easily enough, they're not that good to me. I'll keep me eyes out for wire wound trannies instead

Pete