9V AC power supply - Page 1
Forum section: electronics / beginners

author: mtimmermans
author_rank: Newbie
timestamp: August 26, 2018, 10:34:08 pm
content: Inspired by Dave's video "EEVblog #801 - How To Design A Digital Clock", I am trying to also make a digital clock.This probably sounds like a very stupid question, but for some reason it seems impossible to find a AC/AC European adapter which goes from 230V to 9/12V. Do they even exist? I found one on farnell (https://nl.farnell.com/ideal-power/77de-06-09/power-supply-ac-ac-10w-9v-0-67a/dp/2368012) which would be perfect, but unfortunately they only sell to companies. I also found one on jameco (https://www.jameco.com/z/GPU481202000WAOO-12V-AC-to-AC-Wall-Adapter-Power-Supply_2197581.html) but they don't sell the European variant.Do I maybe use the wrong keywords for my searches? I have tried:AC/AC transformerAC/AC wall plug9V AC adapter9V AC power supplyA second option would be to use a PCB transformer, but I have seen that people generally advise against using these due to safety concerns.Any suggestions?

author: Signal32
author_rank: Frequent Contributor
timestamp: August 26, 2018, 10:56:03 pm
content: I assume you want to build the mains-frequency-clocked transformer and don't want to use another solution for clocking (like c crystal).Spain eBay then ?https://www.ebay.com/itm/ALIMENTADOR-DE-220VAC-A-9VAC-1000MA-50X43X62MM-JACK-HUECO-5-5X2X9-5MM-BD4674/362209595951Personally I would get a regular AC-DC adapter, because of availability and just remove the AC->DC part after the transformer.You can also keep that and add an extra wire directly from the transformer to your PCB that provides the clocking.

author: tooki
author_rank: Super Contributor
timestamp: August 26, 2018, 11:01:54 pm
content: Quote from: Signal32 on August 26, 2018, 10:56:03 pmExcept that linear transformer-based AC-DC adapters aren't sold any more, because they don't meet the various requirements (EU, US Energy Star, etc) for standby power consumption. That's why they've all moved to being SMPS-based.AC-AC adapters remain transformer-based because, well, there's no real alternative!

author: IanB
author_rank: Super Contributor
timestamp: August 26, 2018, 11:06:49 pm
content: I think you will find an AC wall plug adapter is difficult to obtain, mainly because very few items need one of these. However, a simple mains step down transformer should be easy to obtain. If you can't find a transformer by itself, try looking for a door bell transformer.

author: tooki
author_rank: Super Contributor
timestamp: August 26, 2018, 11:06:56 pm
content: Quote from: mtimmermans on August 26, 2018, 10:34:08 pmUse an old-fashioned transformer with wires? Easy to work with, reasonably safe, and easy to get.

author: wilfred
author_rank: Super Contributor
timestamp: August 26, 2018, 11:19:39 pm
content: In Australia and probably other places these were used in magazine projects because it made it safe for inexperience or young constructors to make a mains powered project without needing to do mains wiring. If you choose to, you can just use a mains transformer because that is all these AC/AC adapters are anyway but you then have to make all your own safety choices about ensuring it is wired correctly and safely for not only yourself but any others likely to come into contact with it.Mains wiring is not rocket science but you do need to take care to do it properly.You can just use a transformer in a small plastic project box or inside a larger clock case.If you look on page 14 of this Talking Electronics magazine from decades ago you will find a clock project and it also uses an AC/AC adapter and a 1/2 wave rectified power supply. It also explains the operation of the clock which you may also find helpful.http://www.talkingelectronics.com/TE-1-15_pdfs/TE-Issue8.pdfDo you need to adjust for a different mains frequency?

author: langwadt
author_rank: Super Contributor
timestamp: August 26, 2018, 11:20:38 pm
content: Quote from: mtimmermans on August 26, 2018, 10:34:08 pmThey used to be quite common for adsl modems

author: Seekonk
author_rank: Super Contributor
timestamp: August 26, 2018, 11:38:42 pm
content: You must have second hand thrift stores where you are. The place I go when I need one sells them for 50 cents. They have lots of transformer based ones from a bygone era. Higher output voltage can be easily dealt with. You can always sub in an opto isolator for you clock and use a switch mode wall wart for power.

author: Jwillis
author_rank: Super Contributor
timestamp: August 26, 2018, 11:59:48 pm
content: Who told you PCB transformers were unsafe? Printed Circuit Board transformers are used in all SMPS .Or are you talking about Polychlorinated biphenyls (PCBs) in which case are extremely toxic.But you wouldn't use one of those for a 230V to 12v or 9v.Anyway theirs lots of 230V to 9V and/or 12V on Ebay. .For a digital clock one would think 30VA would be plenty even 7.5VA should be enough not sure. What are you power requirements?

author: IanB
author_rank: Super Contributor
timestamp: August 27, 2018, 12:04:09 am
content: Quote from: Jwillis on August 26, 2018, 11:59:48 pmThe answer to this is obvious. If you are going to have a mains step-down transformer on a PCB, then you will have mains on your PCB. Which introduces a whole bunch of issues about separation, clearance distances, isolation slots and all sorts of safe design considerations. So of course PCB mount transformers introduce safety concerns.

author: Jwillis
author_rank: Super Contributor
timestamp: August 27, 2018, 12:30:25 am
content: Everything we do is inherently unsafe depending on how we approach it and how much we respect it.But you can't be afraid of something just because someone says so.Find out and learn the procedures of safe practices.Taking the appropriate precautions and knowing the risks removes the mystery.

author: Signal32
author_rank: Frequent Contributor
timestamp: August 27, 2018, 01:12:51 am
content: Can find tons of used (and maybe some new got through) ones on eBay / thrift stores / probably already have a few / etc ...

author: mtimmermans
author_rank: Newbie
timestamp: August 27, 2018, 09:28:52 am
content: Thanks for all your suggestions!Inspired by your ideas, instead of trying to find an AC adapter, I tried to find an appliance which needed the AC power. I stumbled acrosshttps://www.poweradaptorsuk.co.uk, where they list many UK AC/AC adapters and the intended appliance for each adapter. Using this I managed to find the European equivalent power supply and found this one:https://www.thomann.de/nl/studio_projects_spps_netzeil.htm#bewertungIt's a lot more expensive than a PCB transformer, but I like the added safety since this is my first big electronics project.

author: tooki
author_rank: Super Contributor
timestamp: August 27, 2018, 09:51:43 am
content: Quote from: Seekonk on August 26, 2018, 11:38:42 pmThat’s a good point, I should check out the thrift stores for adapters!!

author: edy
author_rank: Super Contributor
timestamp: August 27, 2018, 04:55:02 pm
content: Please excuse me if this newbie question, but if all you can find is a 230VAC to 46VAC transformer, and I chain two of them together... would that also work? I figure 230:46 = 5:1, and then 46:9.2 = 5:1... so if I feed in 230VAC into the first transformer, the output of the first (46VAC) going into the input of the second, causes output of the second to be 9.2 VAC? Is that too simplistic and for practical reasons is there a reason why this is a bad idea?