AC-AC wallwart plug - Page 1
Forum section: electronics / projects

author: circuithead
author_rank: Contributor
timestamp: April 12, 2015, 11:20:59 pm
content: Hi,I'm making a power supply and would like to keep the high voltage out of the box so was thinking about using an AC/AC adapter and then bringing the lower AC voltage into the case for the bridge rectifier etc..However I'm stuck on a problem with the connectors.. Am I right assuming that they're the same plugs that DC adapters use? ie. DC connectors.. eg. 2.1mm - 5.5mm dimensions.. Because they're only rated in DC it appears. eg.http://www.mouser.com/ds/2/222/Kycon_KLDHCX-8-0202-371173.pdfWould it be a like for like rating? ie a rating for 12V DC would work for 12V AC?Any assistance greatly appreciated!Also.. are there any tips for choosing good ones to use as I know wall warts connectors have a bad reputation!

author: Andy Watson
author_rank: Super Contributor
timestamp: April 12, 2015, 11:44:51 pm
content: Quote from: circuithead on April 12, 2015, 11:20:59 pmI don't thing there are any "standards" when it comes to wall-warts and plugs/sockets. I would not worry about differences between AC and DC ratings at the levels of current and voltage that are typically produced from wall-warts.QuoteDeservedly soJust use it! And remember you can (usually) use an D.C. wall-wart with an A.C. device, because the bridge rectifier will take care of the polarity, but not the other way around.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 13, 2015, 01:25:07 am
content: Unless you specifically need AC, DC wall warts are much more common nowadays.

author: circuithead
author_rank: Contributor
timestamp: April 13, 2015, 03:07:21 am
content: Thanks Andy.. that's kind of what I thought until I had a browse on Mouser and there's very specific ratings.. ie. 12V, 18V, 24V. Seemed strange.I have found these which seem like they could be good.. at least by screwing them in they won't fall out constantly!http://www.canford.co.uk/Products/44-243_SWITCHCRAFT-S760K-DC-connector-female-cable-with-locking-nut-2.1mmIn regards to AC.. I need a 25V at 0.3A and 50V at 40mA so I was going to use a voltage doubler.. on an AC/AC adapter.. Actually I'm having a little trouble with the scheme I'm going to use.. shall I post to this thread or a new one? Not 100% sure on correct forum etiquette..

author: Zero999
author_rank: Super Contributor
timestamp: April 13, 2015, 07:50:48 am
content: What sort or project is it? Audio by any chance?Voltage doublers and bipolar power supplies are the two common reasons why AC wall adaptors are still occasionally used.An alternative is to use a DC wall adaptor and boost converter for the 50V.The disadvantage of switched mode power supplies is they're noisy, which is can be a problem for audio.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 13, 2015, 09:37:30 am
content: Good idea if you don't want to deal with the mains.Some Ikea lamps come with nice 24v AC wall warts. They're quite useful as they can shift a couple of amps no problems. They do have 2 pin DIN sockets though which is a bit odd if you ask me. DC seems to standardise on 2.1mm center-positive plugs/sockets although there are exceptions so you have to keep your eyes peeled.I use one as of those Ikea lamp transformers as a "portable" bench power supply. I have a bridge rectifier, couple of electrolytic caps with bleeders and two basic LM317 circuits straight from the datasheet with 4mm plugs attached to a bit of 4mm aluminium stock that gets plugged into it. It's not even in a box and is point to point wired. Caps are held on with cable tiesI was going to do a dual rail 317/337 version with a current limiter but I haven't got around to it yet. Gets a bit warm but not enough to cause any problems. If it blows up, it costs about £3 to make a new one so not the end of the world.

author: paulie
author_rank: Frequent Contributor
timestamp: April 13, 2015, 11:14:59 am
content: Quote from: Andy Watson on April 12, 2015, 11:44:51 pmActually there are ad hoc standards to prevent using one type in the wrong application. 5.5/2.1mm usually reserved for 12v applications like hard drives and video cameras with a smaller size for 5v and another reserved for AC. This tends to be the case for chinese products but unfortunately domestically and some other countries like India "creativity" often trumps common sense.Quote from: Andy Watson on April 12, 2015, 11:44:51 pmIn some cases the AC is required for timing like with clocks. I discovered this the hard way trying to use DC with my caller ID box. It took me a while to figure out what was wrong.

author: SeanB
author_rank: Super Contributor
timestamp: April 13, 2015, 07:54:23 pm
content: Quote from: paulie on April 13, 2015, 11:14:59 amI had a similar problem with a US made telephone answering machine, that wanted 60Hz for the internal clock. Rather than looking to see if they had a 50/60Hz option ( the days before Internet, only dial up BBS and very limited here at the time) I just looked through the box f spares and found a crystal that would divide down to 60Hz, and put a 4060 divider in the unit to give it the 60Hz it wanted. Worked well enough, and even kept the time accurate to within a minute a month. Not bad for a slightly used crystal stuck to the IC on a tiny bit of SRB board with some NPO random ceramics as loading and fed with 5V from the board.