Good source of cheap (but safe) usb chargers/"wall warts"? - Page 1
Forum section: electronics / general

author: jeremy
author_rank: Super Contributor
timestamp: December 13, 2014, 09:35:14 pm
content: Hi all,We've probably all seen the videos showing the inside of the fake usb chargers, not the safest option. Unfortunately, they are really handy for powering projects direct from the wall. Does anyone have a cheapish and good source for these, but in a form that has UL or TUV or CTick? I think 5V @ 1A would be perfect, and I'm hoping apple chargers are not my only option.Also, I've seen a lot of people use laptop bricks for higher power/voltage projects. Again, anyone have a good source for safe ones of these? Maybe a Lenovo/hp/acer replacement part or something?

author: XOIIO
author_rank: Super Contributor
timestamp: December 13, 2014, 09:49:18 pm
content: Haven't seen many that would be safe, I don't think the knockoff apple ones can supply 1 amp even.I did use one to power an 8x2 character LCD and arduino pro mini in a permanent project, but I gunked the crap out of it with hot glue to immobilize the parts and keep things from shorting out.They are probably fine for small stuff like that but you may be able to build your own safer ones for a few bucks a pop depending how many boards you get made.I'll definitely be following this for future power supply needs.

author: Monkeh
author_rank: Super Contributor
timestamp: December 13, 2014, 10:01:44 pm
content: Farnell sell one for the Raspi which may or may not be worth a crap.I might throw one in on my next order to gut if nobody else gets there first.For some reason they have UK stock of the Aussie model cheaper than the UK version..

author: jeremy
author_rank: Super Contributor
timestamp: December 13, 2014, 10:12:15 pm
content: Well just to put it out there, I use an Anker 5 port 40W charger from Amazon for US$25. It works great for powering a few projects at once. It doesn't have UL, but it does have TUV.

author: dannyf
author_rank: Super Contributor
timestamp: December 13, 2014, 10:30:58 pm
content: QuoteDepends on what you meant by "safe". turn-on / off transient for example could pose a safety concern for your circuits powered by the supply; low output impedance / high output current could be another safety issue; heat dissipation another one....I have used tons of those Apple knock-offs as power supplies, for their wimpy output current capability: even if they are shorted, they don't kill anything. I haven't found them to be of any issue, safety or otherwise.The best I have found to be phone chargers. You can get from a phone store real cheap, particularly NOKIA, Blackberry and Samsung / LG chargers: generally well made and inexpensive.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 14, 2014, 05:17:10 am
content: Take a look at the Innergie brand. They often go on sale at electronics stores and are manufactured by Delta.

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: December 14, 2014, 07:47:02 am
content: I bought one made by Belkin a couple months ago, from a computer store. Any big-box electronics/computer store should have them.

author: Red Squirrel
author_rank: Super Contributor
timestamp: December 14, 2014, 09:53:02 pm
content: Never opened one so not sure if these are safe or not but I use them for various permanent setups and no fire yet.http://www.canakit.com/accessories/ac-dc-adapters

author: JonnyBoats
author_rank: Regular Contributor
timestamp: December 15, 2014, 05:17:34 am
content: I find that when I go into a Salvation Army or Goodwill store they generally have lots of these for about $1 (US). I look for ones from known manufacturers.Has anyone come up with a good way to test these devices?

author: westfw
author_rank: Super Contributor
timestamp: December 15, 2014, 08:19:22 am
content: There are these "Duracell" chargers:http://local.sears.com/Duracell-Mini-USB-AC-Charger-Black-DU/p-00342328000PA bunch of retailers carry them (I think I got mine at Staples.) With a brand name, being sold in big-name B&M stores, they ought to be pretty OK. I haven't (and can't) do a good detailed analysis, but mine has a fuse, full-wave bridge, and not-awful clearances (not great, either.) No actual ICs for regulation, though.I'll second the recommendation for thrift stores. LOTS of "orphaned" OEM phone chargers and such, for $1 or so.

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: December 15, 2014, 09:18:44 am
content: Quote from: JonnyBoats on December 15, 2014, 05:17:34 amIf you're just looking to see if it's up to specs, you could take a breadboard and whack a bunch of resistors on it and connect it to the output and measure current and voltage drop. I guess in theory you could just leave it connected that way for a more extended testing.

author: con-f-use
author_rank: Unknown
timestamp: December 15, 2014, 08:44:26 pm
content: I have used theRAC02 familyof supplies in projects after a recommendation here on the forum. I can recommend them as well. They are, however, not exactly cheap. They have just brought out theR-78E series, which is considerably cheaper ($3 p.p.) but not isolated. No idea if the 78E are any good.

author: ju1ce
author_rank: Regular Contributor
timestamp: December 15, 2014, 09:35:48 pm
content: "Goobay" power supplies are sold by many retailers throughout Europe. TME has them for about 4 euros a piece:http://www.tme.eu/en/details/zsi-46554/mains-power-supplies/goobay/EDIT: Price has apparently gone up since I ordered. TME seems to like to change prices often based on supply and demand. Anyway, they are still cheap.

author: DavidMenting
author_rank: Contributor
timestamp: December 17, 2014, 07:49:31 am
content: The older HTC charger is apparently alsodesigned/manufactured by Delta.It's small, inexpensive, easy to get hold of and perfectly capable of supplying > 1A.In general, sticking to the cellphone brand chargersseems like a good idea. Steer clear of aftermarket ones (that includes Belkin and such).

author: jeremy
author_rank: Super Contributor
timestamp: December 17, 2014, 11:34:31 am
content: Well after some searching, this looks like the best one:http://au.element14.com/powerpax/ksas0060500100d5u/power-supply-usb-5v-1a-intl/dp/225479301AU$6.63! and it comes with a bunch of international plugs.Edit: or AU$9.26 for 2A:http://au.element14.com/stontronics/t5584dv/psu-raspberry-pi-5v-2a-micro-usb/dp/242750001?in_merch=New%20Products

author: rsjsouza
author_rank: Super Contributor
timestamp: December 18, 2014, 04:35:17 am
content: Quote from: DavidMenting on December 17, 2014, 07:49:31 amI have an original HTC charger andthis charger from Amazon, and they are of exceptional quality.

author: theoldwizard1
author_rank: Regular Contributor
timestamp: December 22, 2014, 05:06:11 am
content: Not the cheapest, butAdafruithas1Aand2AUSB chargers. Both are UL listed !

author: JonnyBoats
author_rank: Regular Contributor
timestamp: December 22, 2014, 06:07:25 am
content: Slightly off topic, but here is a nice data sheet from Microchip on USB power delivery:http://ww1.microchip.com/downloads/en/AppNotes/00001825A.pdf

author: Monkeh
author_rank: Super Contributor
timestamp: January 23, 2015, 12:22:13 pm
content: Okay, so, a month and change later, I have one of Farnell's Raspi supplies.Haven't finished testing it yet, but construction is fine. Obviously there's no brand name caps at this price, but they're all 105C, the visible one are Aishi, I can't see what's under the sleeve on the main output cap yet.Sadly, these seem to be twice the price in Australia. The AU version is stocked in the UK cheaper than the UK version, though!

author: LabSpokane
author_rank: Super Contributor
timestamp: January 23, 2015, 06:27:32 pm
content: I'm not seeing a mains filter cap and the zener for the output appears to be missing.

author: Monkeh
author_rank: Super Contributor
timestamp: January 23, 2015, 06:28:14 pm
content: Quote from: LabSpokane on January 23, 2015, 06:27:32 pmThe two 400V caps don't strike you as mains?And yes, the crowbar zener is missing.

author: LabSpokane
author_rank: Super Contributor
timestamp: January 23, 2015, 06:34:54 pm
content: Those electrolytics are after the rectifier. I think there is typically a film cap directly across mains. I'll post a pic of a wall wart I've been messing with later.

author: Monkeh
author_rank: Super Contributor
timestamp: January 23, 2015, 06:38:09 pm
content: Quote from: LabSpokane on January 23, 2015, 06:34:54 pmOn a supply of this size? Not really needed.If you want X or Y class caps and a choke crammed in, you can pay four times as much and buy an Apple one.

author: amyk
author_rank: Super Contributor
timestamp: January 24, 2015, 12:38:45 am
content: OEM for that RPi one appears to behttp://www.ktec.hk/orhttp://www.qiw.com/based on the KSAS* model number.Here is KSAS005model:http://www.made-in-china.com/showroom/lily-ktec/product-detailcXxmZjKkMzWd/China-5W-Ksas-Series-Power-Supply.html

author: wraper
author_rank: Unknown
timestamp: January 24, 2015, 01:00:13 am
content: Don't see any sign of optocoupler in RPi psu. Wonder about its load regulation.

author: Monkeh
author_rank: Super Contributor
timestamp: January 24, 2015, 04:09:27 am
content: Quote from: wraper on January 24, 2015, 01:00:13 amThat much I've tested already. 4.95V unloaded, 4.85V at 1A, at the end of the cable.

author: SeanB
author_rank: Super Contributor
timestamp: January 24, 2015, 05:24:39 am
content: You can get pretty good regulation just using primary side sensing, you just have to wind the transformer to co locate the feedback sense winding and the output windings, keeping a layer of insulation between the interleaved windings for isolation. Makes for a more tricky winding, but you can get very good regulation figures with it. If you want better then you stick a voltage regulator on the output.

author: LukeW
author_rank: Frequent Contributor
timestamp: January 24, 2015, 07:36:47 am
content: That one looks good.2 x 400v 6.8uF filter caps on the input, presumably an inductor hidden in the middle in between to form a pi filter, and what appears to be a large fusible resistor on the input, and good creepage distances. And a spark gap, and hi-pot testing of the transformer.As far as an output crowbar is concerned - if you want a cheap supply, I think the main thing we're looking for here is electrical safety, appropriate galvanic isolation and creepage distances around the grid voltage. That's the main important thing that is really skimped in the nasty ones. If you're really concerned about protection or regulation to protect the load circuit, not the humans, then either buy the expensive Apple ones or integrate that protection into the design and protection of your downstream hardware, with that hardware designed to a specification that accommodates a relatively cheap off-line plugpack.Quote from: mojo-chan on December 15, 2014, 09:42:55 amhttp://www.digikey.com/product-detail/en/VOF-6-5/102-2212-ND/2441885The CUI VOF series is pretty good for on-board integration at ~6W power levels.Good quality, good electrical safety, has several approvals (at that module level) from reputable international engineering safety agencies.But obviously these things are always more expensive than plugpacks, that's just an economy of scale issue.

author: Monkeh
author_rank: Super Contributor
timestamp: January 24, 2015, 07:38:39 am
content: Quote from: LukeW on January 24, 2015, 07:36:47 amThe inductor is next to the upright cap. There's a heatshrunk fuse on the other side.E: There's also a small SMD inductor on the bottom.

author: Monkeh
author_rank: Super Contributor
timestamp: January 24, 2015, 10:32:15 am
content: Okay, so, fired the scope up for a quick ripple test.21mV RMS at 1A, down to 10mV unloaded. Output voltage rises with load, offsetting the cable losses somewhat. Measured 5.13V at the PCB, 4.89V at the plug, at 1A load this morning.E: It strikes me that I haven't actually given a link for the thing.UK:http://uk.farnell.com/raspberry-pi-psu/rpi-psu-uk-mk1/power-supply-raspberry-5v-1a-uk/dp/2254792EU:http://uk.farnell.com/raspberry-pi-psu/rpi-psu-eu-mk1/power-supply-raspberry-5v-1a-euro/dp/2254794AU:http://uk.farnell.com/raspberry-pi-psu/rpi-psu-au-mk1/power-supply-raspberry-5v-1a-aus/dp/2254795AU with gouging:http://au.element14.com/raspberry-pi-psu/rpi-psu-au-mk1/power-supply-raspberry-5v-1a-aus/dp/2254795Sorry, no US version. Makes a refreshing change.