Are AC Wall-Warts an Endangered Species?

[thermionic]

Hi,

AC wall-warts seem to get more and more scarce every time I look at the various suppliers' catalogues, with models being discontinued on a monthly basis. Do you think it's daft to design a product that's powered from one?

How much of this is this due to the legislation in California, with OEMs suspecting it'll spread?

Employing an SMPS will put the product's cost up massively...

Thanks in advance for any comments you may have.

Justin

 

[sodderboy]

I think it's more like they are being standardized and consolidated at the low qty end and pennies each for oem qty over 2000 pieces.
Mike

 

[Rochey]

Dc Output wall warts are still a major part of products sold world, and should continue to be for many years to come, as they significantly lower the effort required to pass safety certifications.

Ac outputs are a different matter. Harder to get hold of, as most systems run single supply.

Can you DC bias your entire system, and AC couple the input and output?

 

[thermionic]

Thanks.

I need 4 rails:

+/- 18v (audio)

+22v (relay)

+5v (logic - very low current)

With an AC WW I can use linear regulators to get a very clean analogue rail. Using DC-DC converters (i.e. if I go for an SMPS WW) adds considerable cost and introduces reliability concerns (DC-DC converters are a hotly debated topic - maybe I'm being influenced by some of their negative press here...). I've already had to make design changes to accommodate discontinued components, which has created delays in the product being ready (making client restless). The last thing I need is to worry about WW sources...

Justin

 

[Rob Flinn]

Justin,

Have you looked in the CPC catalogue ? That was only place I could find one I needed recently.

 

[thermionic]

Hi Rob,

The CPC one is what I'm planning to use for the product. What prompted me to ask a question here is the fact that CPC was the only distributor that seemed to have the right unit. In my experience, if you can only source a part from one supplier, that's not a good sign...

I can get SMPS WWs all over the place...but this involves implementing DC-DC converters... Rupert doesn't have a problem with them on his Portico range, but I'm sure his team have been experimenting with the things for yrs. In my case, because I don't have that experience, I am a little nervous about reliability, cost and noise (the latter being a cost concern - you can always get rid of noise, but inductors and caps add cost).

Cheers,
J

 

[mcs]

I used to be able to get AC wall warts very cheaply, but they are getting harder to find. If you look at the manufacturer's websites, they are still available. The problem may be the minimum order... I have a couple of products that will only run on AC (a transformer doesn't run well on DC...), so I'm "affected" also...

Best regards,

Mikkel C. Simonsen

 

[gemini86]

well you can still get transformers, and you can still get little plastic enclosures... let's put 1 and 1 together and DIY a wall-wart...

 

[JohnRoberts]

Of course california has a damping effect on the whole market just like ROHS rules for Europe. Small companies can not afford to engineer multiple solutions for the same product.  most will just engineer one that works for all markets even if slightly more expensive.

I hope my US customers don't mind ROHS solder in my product...  8)

JR

PS: Customers generally hate wall warts. There are some off the shelf switching PS module solutions that accept universal mains voltage that are already agency listed making approval simpler. Not as cheap as wall warts but nice for several considerations.

 

[thermionic]

Of course california has a damping effect on the whole market just like ROHS rules for Europe. Small companies can not afford to engineer multiple solutions for the same product.  most will just engineer one that works for all markets even if slightly more expensive.

I hope my US customers don't mind ROHS solder in my product...  8)

JR

PS: Customers generally hate wall warts. There are some off the shelf switching PS module solutions that accept universal mains voltage that are already agency listed making approval simpler. Not as cheap as wall warts but nice for several considerations.

Can you drop a link to one of these SMPS suggestions? The concern I have is, once you've modified a 3rd party SMPS in any way, i.e. put your own plug on it, its UL certficate is invalid. I'm choosing an external PSU as the client has stated the main unit must be small; a WW's safety certficate is an added bonus.

A typical laptop PSU will give +24v DC with oodles of current. I will then have to use an inverting DC-DC converter (e.g. http://www.rapidonline.com/pdf/82-1088e.pdf ) to get my -ve feed. +ve and -ve then go to conventional monolithic Vregs to give +/-18v for audio. Relays get powered directly from +24v. Logic comes from 7805 dropped off relay feed - current is so minute heat shouldn't be an issue due to drop.

Added benefit to SMPS is that the same one will work anywhere in the world.

Thanks again.
Justin

 

[JohnRoberts]

The last time I looked at this was over 5 years ago, and in connection with a pricey DSP unit, but the account I was advising  stuck with an external wall wart, too keep it cheap.

A quick look doesn't turn up anything very cheap in low quantity, but the concept is something like the computer power supply, that is a closed frame (or open frame) but with it's own universal iec mains plug socket.  These just get stuck on the back of your unit and presto, you don't have to every mess with mains voltage. Of course the module needs to be UL/CSA/yadda yadda agency approved.

I didn't say it was cheap, just handy.

I'm am very happy for now to be battery powered.

JR

 

[thermionic]

I've found a 24v SMPS which ticks all the boxes. The problem is figuring out how to get somewhere between -21 and -24v from it at up to 200mA (to feed a monolithic Vreg set for -18v). All the DC-DC converters / inverters I find either don't do the voltage, or the current.

Thanks.
Justin

 

[thermionic]

Just so you know: AC wall-warts are effectively BANNED by the suits in Brussells. Note I say 'suits', not 'engineers':

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:093:0003:0010:ENDF

There are loopholes which some small OEMs are exploiting. One example is to provide an unregulated output on the linear supply, on the grounds that the user 'might' want to use it. If the unit puts out more than one voltage, that won't breach regulations.

I can't believe no one in this thread appeared to know about this!

This is a major, major hassle to me...

J

 

[sodderboy]

Aren't they the robes in Brussels?  Now they will create a wallwart confiscation department?
Mike

 

[Andy Peters]

Just so you know: AC wall-warts are effectively BANNED by the suits in Brussells. Note I say 'suits', not 'engineers':

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:093:0003:0010:ENDF

Pardon me if I don't know how to read European, but what in that document specifically outlaws AC wall warts?

-a

 

[Rochey]

I haven't read it yet, but I know there's a new law coming in January that limits standby in systems to 500mW or less.

Most SMPS's idle at 300mW. I suspect that AC wall warts may be worse. (eek!)

/R

 

[Andy Peters]

I haven't read it yet, but I know there's a new law coming in January that limits standby in systems to 500mW or less.

Most SMPS's idle at 300mW. I suspect that AC wall warts may be worse. (eek!)

I suppose it depends one what you mean by "most SMPSes."

But consider, given an AC-output wall-wart (which is little more than a step-down transformer, right?), wouldn't the current consumption in "standby" (however one defines "standby") be a function of how much stuff is powered down?

And wouldn't that problem exist with a DC-output wall-wart, too?

-a

 

[JohnRoberts]

I try not to pay very close attention to CA, especially now that Gov moonbeam has a supermajority in Sacramento, but to guess about the lumps and wall warts always plugged in, the cheap transformers often have eddy current losses that can be significant when left plugged in 24x7 even if the secondary is unloaded.

A switcher running from from the mains voltage, could swap a big cheap transformer for a tiny cheap transformer, and maybe even turn mostly off when un-loaded. (while I'm not sure exactly how,,, details).

JR

 

[Rochey]

I haven't read it yet, but I know there's a new law coming in January that limits standby in systems to 500mW or less.

Most SMPS's idle at 300mW. I suspect that AC wall warts may be worse. (eek!)

I suppose it depends one what you mean by "most SMPSes."

But consider, given an AC-output wall-wart (which is little more than a step-down transformer, right?), wouldn't the current consumption in "standby" (however one defines "standby") be a function of how much stuff is powered down?

And wouldn't that problem exist with a DC-output wall-wart, too?

-a

I can only tell you what customers are telling me. 500mW is the european standby legislation level. Most Class IV SMPS (I think it's Class IV, could be V) idle with no load at 300mW, leaving systems with 200mW to run with in standby.
I believe that a full linear power supply (AC wall wart outside, plus regulator inside etc) will struggle to hit that level.

Cheers

/R

 

[thermionic]

Just so you know: AC wall-warts are effectively BANNED by the suits in Brussells. Note I say 'suits', not 'engineers':

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:093:0003:0010:ENDF

Pardon me if I don't know how to read European, but what in that document specifically outlaws AC wall warts?

-a

To be honest, I didn't trudge through the document... I went on the basis of what associates had told me (they've all revised their designs to use external SMPS) and what a quick Google provided: http://audio-forum.gspaudio.co.uk/the-linear-external-power-supply-ban_topic61.html

Since posting here, I've had a chat with one of the UK's largest OEM PSU suppliers... They told me that the 'ban' on Linear PSUs was only for OEMs who sold more than 200,000 units per yr, i.e. the likes of Apple. They still sell AC wall-warts and claimed the distributors stopped selling them on account of them simply being an outmoded technology... Who on earth do you believe?

J

edit - from what I've been told, the ban is for wall-warts that output either a single DC voltage that's linear-regulated, or single AC voltage (on account of the latter being effectively the same thing, but in a different configuration)