What is the best (and safest) way for a newbie to play with AC? - Page 1
Forum section: electronics / beginners

author: Dan123456
author_rank: Regular Contributor
timestamp: September 08, 2023, 02:03:54 pm
content: Hey allJust wondering if you all have any thoughts on the the best (and safest) way for a newbie to play with AC?I have always steered clear of AC unless I had researched the shit outta what I was doing as have always believed DC kills components, AC kills people (I’m aware that isn’t entirely true but works well enough for every day life :p)!However, I would like to start to mess around with it in a safe way just to get my feet wet (I.e. not to do anything “useful” with it but more just poke at it with a scope to see the pretty line go up and down and to feed it into random components just to see what they do etc. :p)I was thinking maybe just a crystal oscillator circuit? Or maybe a 5v DC to 5v AC inverter?Are those good options or do you all have some better ideas?Please no mains stuff! I am really looking for an option/s with virtually no consequences if I mess up so I can just screw around and learnThanks so much in advance!

author: langwadt
author_rank: Super Contributor
timestamp: September 08, 2023, 02:13:48 pm
content: find someone with a pile of old wall wart powersupplies, 12VAC was common for modems

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 08, 2023, 02:25:16 pm
content: An acquaintance of mine, wanted to learn to control DC motors via thyristors which were supplied from a three phase voltage.I told him exactly the same thing, use 230 to 12 volts transformers, and do all the control and power stuff on the low voltage side. He powered an automotive fan with the resulting DC.Worked beautifully.

author: Dan123456
author_rank: Regular Contributor
timestamp: September 08, 2023, 02:32:05 pm
content: Quote from: langwadt on September 08, 2023, 02:13:48 pmAh damn! I literally just chucked out about 50 old power bricks the other dayI’ll have to have a look through the 2 dozen or so ones I kept just incase any of them are AC out!That is a good point though! I hadn’t thought of that and I might check eBay to see if I can find any cheap

author: Infraviolet
author_rank: Super Contributor
timestamp: September 08, 2023, 05:36:58 pm
content: For the most part, weird cirumstances aside, it is high voltages (due to their ability to drive currents of even just a few mA through the resistance of human skin) which shock people. AC vs DC has some effect, with debates about which is worse, likely being circumstance dependent, but it isn't anywhere like as important as the voltage in the first place.I must say, the idea of seeing whether each of the various different types of AC motor could be driven from low voltage AC supplies is interesting. You might do best to build your own inverter circuit to convert from a 12V or 24V DC supply wall wart or laptop-style power brick (these devices should almost always have transformers inside and therfore have outputs fully isolated from the mains supply side), to provide AC at a variable voltage and frequency, could also then have multiple units working together with some sort of synchronising signals to provide multiple supplies with different relative phases. You'd built a supply which would have your variable voltage/frequency AC centred about half the voltage of the DC supply. To avoid having high voltages you'd just make sure not to power any step-up transformers with your AC supply.

author: rstofer
author_rank: Super Contributor
timestamp: September 08, 2023, 11:36:35 pm
content: A wall wart with AC output or a transformer will put out a fixed frequency - boring...AC of variable frequency and very low voltage (<=5V) can be had by using the tone() function on an Arduino uC.If you want bipolar output, put a 100 ufd capacitor in series with the output pin to eliminate the DC bias.You're going to wind up with an Arduino UNO R3 anyway, it might as well be now. There are some great starter kits on Amazon.https://www.amazon.com/s?k=arduino+starter+kithttps://www.amazon.com/ELEGOO-Board-ATmega328P-ATMEGA16U2-Compliant/dp/B01EWOE0UU--- a clone board

author: rstofer
author_rank: Super Contributor
timestamp: September 08, 2023, 11:50:42 pm
content: I have never used a sound card signal generator but they are fairly popular as an entry level signal sourcehttps://dinotechno.com/list-best-free-signal-generator-software-for-pc/I was always worried that I would do something to destroy the sound card (or motherboard) but I might do it with an old unused PC.Or, I could be careful...

author: MrAl
author_rank: Super Contributor
timestamp: September 09, 2023, 12:05:17 am
content: Quote from: Dan123456 on September 08, 2023, 02:03:54 pmHi,Simplest way is to get an AC transformer that puts out maybe 12vac.If you have an old wall wart that puts out DC you can convert it to AC if you have the tools to take it apart and just tap the output of the transformer. This only works with the older heavier ones. The new ones have regulated voltage and the transformer is high frequency so you cant use that.The nicest way to start out is to puchase a small audio generator from the web like from Amazon or something. They are sort of cheaper and you can get a range of frequencies and amplitudes, from 0 to maybe 5vac and from 0 to around 20kHz. A good range to start with and very safe. They can run on batteries usually.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 09, 2023, 02:22:05 pm
content: Quote from: Dan123456 on September 08, 2023, 02:03:54 pmThis is just silly.In fact, high DC voltages are far more dangerous then high AC voltages. Just go watch some youtube video's of unplugging wires from live solar installations.Electricity becomes dangerous when there is a relatively high current through flesh or nerves. You can put two forks in a hotdog and cook it quicky by sticking it in a mains socket (plenty of video's on youtube about that too) and the same will happen if you put to forks in your arm.In general, everything below 48V is considered safe, and voltages above 48V are still quite safe if the current (and thus energy) is limited enough.So getting some old fashioned mains power transformers is a nice way to experiment with electronics. Before LED's became common, I designed a uC controlled phase control for mains voltage, And I did most of the testing of the software by controlling 12V light bulbs with the triac's.When working with mains transformers, there are just a few things to be cautious about.1. Make sure you have the correct fuse in the primary circuit.2. Make sure the wiring is made sturdy. Use solder connections, ferrules or Wago 222 or similar.3. When soldering wires, put shrink wrap around it to isolate it.4. Add an extra layer of insulation, so it is double isolated. This can be as simple as a cardbord box around the transformer, but I recommend something more elegant.Also note that not all transformers are double isolated themselves. You can recognize double isolated transformers with an icon of two squares drawn inside each other.

author: Infraviolet
author_rank: Super Contributor
timestamp: September 09, 2023, 03:18:30 pm
content: rstofer "AC of variable frequency and very low voltage (<=5V) can be had by using the tone() function on an Arduino uC."My thoughts would be one would be better building an analogue sine wave generating oscillator, use a digital potentiometer as a way of varying the frequency perhaps, the amplify the current, if necessary, with a voltage follower transistor. An arduino, or 555, would give a digital square wave, unless put through a series of low pass filters, in which case it would approximate a sine pretty well.Doctorandus_P "4. Add an extra layer of insulation, so it is double isolated. This can be as simple as a cardbord box around the transformer, but I recommend something more elegant."My guess for anything self-built and mains AC powered would be to encase it in two concentric shells, in either order I'd think could be ok(?), one to provide insulation made of plastic, a plastic project box or perhaps a 3d printed form, and one to provide some level of fire resistance made of metal. Cardboard could burn all too easily, and infact could conduct and crumble if it got wet. I'm thinking that would be the wisest way for anyone wanting toconstruct something mains powered to set it up, so long as it wasn't something which generates enough heat during operation that such layering ofprotection would be problematic, then safe design would get rather trickier in terms of having to have vents. To the original poster Dan123456, I'm making some speculations about mains powered devices here, none of this paragraph's compexities apply to your needs at low voltages and low currents, you don't need to worry about shocks at all from low voltage AC, and it would be very difficult for anything at low voltage AC to catch fire unless large currents were involved, which they can't be unless your initial supply (the DC wall wartpowering your AC inverter or the AC wall wart) has a high current limit, or unless you dumped appreciable currents in to a tiny resistance (whole 12V across a 50 ohm resistor or something, Power=V^2/R).

author: EPAIII
author_rank: Super Contributor
timestamp: September 10, 2023, 07:46:13 am
content: 6 Volts, 12 Volts, even 24 Volts AC just isn't gonna hurt you. At those low levels you can even wet your fingers and try to feel it if you want. Even 48 VAC won't harm you unless you go to extraordinary means to help it to do so. But it will may tickle a bit - or not. 48 (or 50) VAC is considered somewhat of a dividing line between safe and dangerous AC Voltages. And YES, DC can hurt you as well. But the dividing line is probably more like 70 or 80 or even 90 or 100 Volts DC.I have been "bit" by 115 VAC power mains a time or two and survived. It wasn't pleasant, but I was fortunate to be in a position where I jerked away from it. And I probably wasn't well grounded. I don't recommend it.For 6 or 12 Volts AC I would say you are almost completely safe. At 24 VAC, you may be able to feel some effects if you try hard. I would not hesitate in the slightest to work with those, low AC Voltages.At 48 VAC, the peak becomes 1.414 times that value or about 68 VDC and you are starting to get into the range where it can penetrate dry skin. But there is probably more danger from an unexpected jerking motion induced by the slight shock than from the shock itself. Of course, don't do something like connecting the wires to your skull or chest. And there is a "one hand in the pocket" precaution, probably because the human heart is BETWEEN the two arms.I do take and recommend that others take serious precautions when working with 115 VAC and even more so with 230 VAC. Of course, here in the States, 230 VAC is supplied to every house as two, out of phase 115 VAC lines so touching one of them is the same as touching 115 VAC. Only if you touch BOTH sides of a 230 VAC circuit do you get that full Voltage.When working with 115 and 230 VAC the very first rule is to DISCONNECT the apparatus BEFORE doing anything with the wires. Another good idea is to touch all points of the circuit with a ground strap before touching with your body. I learned that one while working with HV DC systems in transmitters. I like to be careful to only come in contact with one hand at a time, even after disconnecting things. Insulated gloves and tools can be used when it is absolutely necessary to work on live circuits.One great way to work on both AC and DC circuits is to set up a test with power OFF and then turn it on to observe the results. Then turn it OFF again, before setting up the next test. After some time working with electric and electronic devices you will develop a sense of what precautions to take with each kind of circuit.And some work you just DO NOT DO unless there is a second person present to serve as a safety person. This includes things like HV AC power and how powered transmitters that I worked with in the TV and radio field.In 45+ years of professional work on all kinds of AC and DC circuits, the worst shock I ever got was from a TV HV supply which was around 40,000 VDC. That had me feeling dizzy for several hours. It jumped through both an insulated probe I was holding and through the soles of my shoes. As well as through almost all of me. In spite of being careful, I managed to get on the wrong wire. No joy there. But that was at least 50 years ago and I am still here.

author: rstofer
author_rank: Super Contributor
timestamp: September 10, 2023, 04:30:19 pm
content: Quote from: Infraviolet on September 09, 2023, 03:18:30 pmIndeed, that would be better but even better would be a commercial Arbitrary Waveform Generator. I would also consider the Digilent Analog Discovery (any version). Costs vary as do needs.Google for 'low cost sine wave generator', there are a bunch of low cost alternatives.To be fair, using the Arduino tone() function results in a square wave output, not an actual sine wave. A low pass filter on the output may help but it might not matter.Avoiding mains exposure at this level of experience is a really good idea. I tend to do projects that are USB powered or even battery powered. I also have a proper lab supply for those dual rail Op Amp projects but it isn't nearly as portable as a USB battery pack.