AC Source - Page 1
Forum section: electronics / beginners

author: paulca
author_rank: Super Contributor
timestamp: November 18, 2017, 02:42:41 pm
content: What is the easiestcheapway to get a low voltage AC?Googling got me the following options:1. Buy an AC capable bench PSU = £150+2. Hack a wall wart transformer tap = Dodgy / Fixed 50Hz (UK)3. H Bridge and 555 (or RspbyPI PWM) + multi pole RC/IC circuit4. Signal generator ()

author: mariush
author_rank: Super Contributor
timestamp: November 18, 2017, 02:54:48 pm
content: 0. Buy an actual transformer.Get a toroidal and then you can change the voltage by changing the number of windings on the secondary side

author: Shock
author_rank: Super Contributor
timestamp: November 18, 2017, 03:32:22 pm
content: -1. Identify, label and stockpile old transformers people otherwise throw away or can be rescued from the scrapheap.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 18, 2017, 03:32:35 pm
content: Signal generator into an (subwoofer) amplifier driving a transformer.

author: Ice-Tea
author_rank: Super Contributor
timestamp: November 18, 2017, 06:36:29 pm
content: You never defined the load...Not exactly without importance

author: taydin
author_rank: Frequent Contributor
timestamp: November 18, 2017, 06:42:07 pm
content: I use a variac for that purpose. It takes 220V in, and can give any voltage between 0 - 250V with 1V resolution. Get a reasonably high powered variac so you don't have to worry about voltage drop if you load it. The downside of the variac approach is that the voltage will follow the fluctuations on the power line.

author: paulca
author_rank: Super Contributor
timestamp: November 18, 2017, 08:18:49 pm
content: The things I see where AC is needed so far are:Playing with rectifier circuits.Playing with voltage multipliers.Lots of the little circuits in electronics text books that have an AC source.Making a basic little headphone amp maybe.Basically understanding AC current.An AC source can provide a negative current for op amps etc. can't it? I can convert the - side to -DC with an RC? Or am I missing the point?So the load stuff is likely to be 5-12V and <1 amp.

author: alm
author_rank: Super Contributor
timestamp: November 18, 2017, 08:30:04 pm
content: Quote from: taydin on November 18, 2017, 06:42:07 pmPlus that a Variac will often not provide isolation from the mains input, making the output much more dangerous than a common transformer unless you use a separate isolation transformer.

author: Gregg
author_rank: Super Contributor
timestamp: November 18, 2017, 11:11:46 pm
content: I have a small variac supplied by the mains feeding a transformer with multiple windings and multiple taps. The variac is just to trim the voltage a bit but the transformer gives true isolation.

author: iainwhite
author_rank: Unknown
timestamp: November 18, 2017, 11:26:17 pm
content: In the US you can buy an AC-AC wall adapter :e.g.https://www.jameco.com/z/ACU120100D0531-AC-AC-Wall-Transformer-12-VAC-1A-2-5mm-Plug_100167.htmlmaybe similar is available in the UK? How about:http://uk.farnell.com/c/power-line-protection/power-supplies/wall-plug-in-power-supplies-ac-ac

author: Brumby
author_rank: Unknown
timestamp: November 19, 2017, 01:10:15 am
content: AC is a generic term. It applies to a variety of circuits that range from signal levels to power circuits. Voltage levels and current levels can be just as diverse DC - and it is the range of these that you want to explore that will dictate the sort of solutions you will need to consider.The one parameter common to AC circuits (that you don't get with DC) is frequency. It gets interesting when there is more than one frequency involved.Quote from: paulca on November 18, 2017, 08:18:49 pmI won't say you are missing the point - you have basically got it right - but there is a little more to it.All voltages are expressed as a valuereferenced toa specific point. This is often called the 'ground' - but that is, strictly speaking, misleading. It's just the zero volt reference point.To have 'positive' voltage and 'negative' voltage, you need 1 reference point, one 'positive' point and 1 'negative' point. 3 points in total. The typical way to achieve this from a mains supply, is to have a transformer with a centre-tapped secondary or one with two identical secondaries. Wired appropriately, with the rectification circuits, these produce the 3 points you need.With a single secondary with only 2 wires, you can still create positive and negative power rails - but you have to create your zero volt reference point ... and there are a few ways of doing that.The most important thing to remember about 'positive' and 'negative' voltage is that the ONLY difference is where you put your meter leads! The black one is typically on the 0V reference point - and that's the ONLY difference in this diagram:

author: IanB
author_rank: Super Contributor
timestamp: November 19, 2017, 01:16:32 am
content: Quote from: paulca on November 18, 2017, 02:42:41 pmI don't get this question. If what you mean is a simple mains frequency 50 Hz low voltage AC supply, then just buy/salvage a transformer. I had a box full of them when I was a kid, and these days I have a few modern ones from the local electronics store. Really cheap, really simple.It only gets complicated if you need a continuously variable voltage (power the transformer from a variac), or variable frequency (get a signal generator).

author: Old Don
author_rank: Regular Contributor
timestamp: November 19, 2017, 04:44:00 am
content: I seem to remember the old "O" gauge trains ran on AC voltage, I think, and maybe searching eBay for one would allow you to have a variable voltage AC power supply for a few bucks/euros or pounds.

author: Shock
author_rank: Super Contributor
timestamp: November 20, 2017, 03:22:40 am
content: Quote from: Old Don on November 19, 2017, 04:44:00 am