Most affordable power supply solution?

I find that several projects I’ve built end up buying a $7 9V wall wart from Amazon, and then take the circuit board out of the wall wart and use as an internal power supply in the enclosure I put my project in. (Amazon Prime helps cut down on shipping costs :slight_smile:
However, this seems inefficient – the 9V supply already has a regulator of some sort (typically, a switching regulator), and then that gets regulated down to 5V by a second level of regulation (a 7805 or something fancier).

First, I might use a 5V USB-style power supply – the 500 mA they put out by spec is probably enough for most of my boxes. I’d save a buck by not needing a separate regulator circuit, instead taking 5V directly from the wall wart. Has anyone tried this? Will that be too uneven?

Second – can you buy those circuit boards from within the wall warts bulk? Or some other kind of mains-to-5V power supply component already built? If I could get < $5 for this part, that would be a win for me!

I use these Apple-knock off adapters to get 5V into my enclosed projects. $5 (with prime.)

http://www.amazon.com/Wall-Charger-Sync-Cable-iPhone/dp/B004911E9M/ref=sr_1_1?rps=1&ie=UTF8&qid=1322693629&sr=8-1

You can get them even less in bulk without prime or on eBay.

Second – can you buy those circuit boards from within the wall warts bulk? Or some other kind of mains-to-5V power supply component already built? If I could get < $5 for this part, that would be a win for me!

I’ve never felt the need to put the circuit inside my boxes. I’d rather run a small DC cable into the box than mains power, but that’s just my preference.

Hello, thank you for your answer James, I had the same question. Before reading your post, I was about to order this item : http://cgi.ebay.fr/1pc-transformateur-3W-220V-pour-E27-GU10-LED-ampoules-lampe-650mA-DC2-5-5V-/120735278999?pt=FR_YO_MaisonJardin_EclairageLumiere_EclairageLampe&hash=item1c1c622797

for my home automation project : arduino nano + RF 2.4Ghz in the ceiling, with 220V power. I was wondering wether this item would do the job, or should I order something like that :

http://cgi.ebay.fr/12V-60W-Acer-Halogen-Electronic-Transformer-LED-Power-Supply-Driver-220V-240V-AC-/400257646265?pt=LH_DefaultDomain_0&hash=item5d3136feb9

or finally :

http://cgi.ebay.fr/AC-DC-220VAC-to-6V-9V-50mA-Save-Price-Assembled-kit-/140367587750?pt=LH_DefaultDomain_0&hash=item20ae8f69a6

http://cgi.ebay.fr/12V-1A-DC-Universal-Regulated-Switching-Power-Supply-110-220V--/260896838374?pt=AU_B_I_Electrical_Test_Equipment&hash=item3cbea9d2e6

Finally I think I'm going to buy a mini usb phone charger as you suggest. The good thing is that the plug is ready to use with the nano.

Some considerations --

Efficiency. Most wall warts I know of are linear supplies. They're heavy, they waste power, they're maybe 60%-70% efficient. A switching PS can be bought for not a whole lot more and may be 90+% efficient.

Voltages and current. What you want to run? Will you need 12V? The same 12V is okay to run the Arduino. Maybe having more is good? A lot of laptop supplies can feed useful amounts of 15V-24V for good price.

$4.50 - Compact regulated switching power supply. Input: 100-240 Vac. Output: 5 Vdc, 1 Amp. Switching wall wart. http://www.allelectronics.com/make-a-store/item/PS-513/5-VDC-1-AMP-SWITCHING-POWER-SUPPLY/1.html

$8.50 - 12 VDC 700 MA SWITCHING POWER SUPPLY - 2.1mm coax power plug, center positive. -- should fit Arduino http://www.allelectronics.com/make-a-store/item/PS-1270/12-VDC-700-MA-SWITCHING-POWER-SUPPLY/1.html

$10.50 - 12VDC 1.5A SWITCHING POWER SUPPLY - 2.1mm id x 5.5mm o.d. coax power plug, center positive. http://www.allelectronics.com/make-a-store/item/PS-1232/12VDC-1.5A-SWITCHING-POWER-SUPPLY/1.html

Those are all enclosed too. They do have more choices with many open-frame switchers.

Actually, the flat wall warts you typically buy from Amazon (at least in the US) all claim to be switching. Maybe there's an energy savings regulation or something? Or maybe the Chinese just say "switching" means something else. Kind-of how "Real Leather" means "vinyl" unless it says "genuine" ...

The reason i want it in the box is that the box already controls mains in all my cases -- basically, I'm too picky for most existing home dimmers/timers/thermostats, so I build my own to get them to work right.

Those are some good links, thanks!

Linear supplies are built on transformers and perhaps chips are cheaper than the iron and time to wind wire? And then there's the shipping weight. $)

There's nothing wrong with making your own box but consider having the PS outside means you won't have the heat from the PS inside. It might save you a fan and it might not.

I like Allelectronics as low-price a surplus house but places like Yourduino and Seeed Studios beat them for some items and AE doesn't have -everything- I could want, not by a shot.

Hi, One reason you (almost) never see board-level small line-operated switching supplies is the UL/CSA certification situation. Wall warts or cord-inline supplies are used for almost every small device like routers, small servers, laser printers etc. because they are certified once and built in high volume.

One customer told me they took these apart and embedded them: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=176

But they said they were Not Nice like some others that had screws, and they needed a hammer and chisel to open the case! Still $4.50 is pretty good for universal voltage to 12V and 2 amps...

I can get lots of DC to DC switching boards at a good price. Up, Down and one that is supposed to be Up or down. I need to test them and decide. I'd like to get a good low-cost 7.2V to 5V at 3 amps or so for small robots with Arduino and continuous-rotation servos for propulsion..

DISCLAIMER: Mentioned stuff from my own shop...

$4.50 is better than half the price of Allelectronics. Is that plug Arduino compatible? If not, is there an adapter tip?

Is that plug Arduino compatible?

Yes. It seems all these low-cost switching supplies (http://arduino-direct.com/sunshop/index.php?l=product_list&c=18) from 3.3V to 12V have that same 2.1mm connector. It MIGHT have been nice if they were all voltage-specific, but it's handy they are all the same.

DISCLAIMER: Mentioned stuff from my own shop... again! (But the subject WAS "Affordable" ..) $) :)

I got a several good power supplies from a local recycling store, just €1 a piece => remember to take a small multimeter to test them

recycling stores often have very interesting electronic/mechatronic stuff to "disect" into parts

Noob question : is it as simple as testing voltage on them before using them? I mean, I've already seen some power supply showing bad voltage until you put a real load behind (a regulator matter?)

Yes you should always measure with a proper load. The definition of proper will vary. For example, if you know your circuit will draw 1A, don't measure the supply with 100mA and vice versa.

Back around 1990 I was told that running a PC power supply with no load is not good for the PS. The advice was to at least hang a drive of some kind on it. But consumer circuits have gotten much more goof-proof since then. Some of the progress I've seen has been amazing.

Unless I needed more than 5V for something, I'd run everything off of the ultra-mini USB power supplies that you can get "everywhere" there days. They range from really cheap (imported (http://www.dealextreme.com/p/1000ma-usb-power-adapter-charger-100-240v-us-plug-27524 ) or via thrift stores (many "orphaned" game/cellphone chargers are appropriate)) to high quality, are available nearly everywhere with any input (US, Europe, Car, etc.)

And they're getting small enough that they're not worth taking out of their casings.

Also recently seen advertised; modules with 30mW standby power: http://www.digikey.com/product-highlights/us/en/recom-power-rac01-rac02-power-converters/372

I too use a PC power supply and it’s the only way to go if you need more than 500mA on a tight budget, IMO. They’re great for cheap 5V, 3V3, 12V and plenty of current. I’ve been tempted to buy a real bench supply but I’m too tight on funds to justify it since I’m happy with my current setup. I’m thinking about making a nice 2oz copper breakout board for the ATX plug too to make it almost look professional! :slight_smile:

For projects < 500mA and always 5V by all means get one of those tiny wall to USB 5V supplies many others have mentioned and save yourself the space.

Is there a difference in how much electrical noise some of these supplies put out? And is it important?

I know, for example, that I have a 9V supply from SparkFun that doesn't emit much RF noise at all (at least measured by an AM radio), while I have other cheap switchers that do.

westfw: And they're getting small enough that they're not worth taking out of their casings.

I don't like soldering onto the NEMA-style contacts...

Also recently seen advertised; modules with 30mW standby power: http://www.digikey.com/product-highlights/us/en/recom-power-rac01-rac02-power-converters/372

Those look super sweet, but they also command a superior price (at about $14 each...) I do like DigiKey very much, though, so great choice on reference :-)

I’ve used the Recom 5V, 2W converter on a few boards. Aside from the high price ($14.66 apiece in small quantities), I really like them. The output is fairly smooth without a filtering capacitor, but I chose to add a 330uF electrolytic at the output.

Jim

CraigKC:
I too use a PC power supply and it’s the only way to go if you need more than 500mA on a tight budget, IMO. They’re great for cheap 5V, 3V3, 12V and plenty of current. I’ve been tempted to buy a real bench supply but I’m too tight on funds to justify it since I’m happy with my current setup. I’m thinking about making a nice 2oz copper breakout board for the ATX plug too to make it almost look professional! :slight_smile:

For projects < 500mA and always 5V by all means get one of those tiny wall to USB 5V supplies many others have mentioned and save yourself the space.

I have 3 ATX supplies that I can use for bench supplies. One is hard wired to a CB radio under my desk next to my CD drive. Here in Texas, you can’t have enough weather radios. We have a NOAA radio downstairs, but since my CB has Wx channels, I rigged it up. The PSU is on my battery backup for power failure, and I can get the noaa broadcasts. As soon as I get a HAM radio built up (I’m thinking to use the arduino radioshield since it has AM/FM/LW/SH), I’m gonna add it along side so I can eves drop on storm spotters.

I thought you’d appreciate this. Certainly a, uh, “low cost” implementation :slight_smile:

https://plus.google.com/115565509658927739510/posts/6d1obRgDLjn