Simple AC generator for testing devices?

[Zeitkind]

When repairing or checking stuff, I often come across AC parts like (small) transformers. Testing a transformer with DC isn't working that well, testing for shortages is difficult if you have no idea and information about what resistance to expect. So having a small AC power supply (like 6V or 9V) is a good idea, but this damn thing is for sure missing every time I need it  . Another thing: testing 50Hz and 60Hz.

Hobbyists like me normally have a bunch of cheap DC power supplies. I have a cheap Chinese one, a BK Precision dumpster dive (wrong AC input selected and a blown fuse..) and this well-known Riden one - but no AC supply. I rarely need a big variable voltage AC transformer (although it is nice to have one when testing unknown devices), so I don't want to buy one - have not really the place anyway. Also, I often work with young people and keeping them away from 230V as far as possible is a must anyway. I could grab one of the multiple transformers I have lying on the shelf and build me a power supply with one or more fixed outputs or a voltage divider, but hmmm...
So, my idea was a small "black box" (then fixed onto one of my DC power supplies) which takes a variable DC input and outputs something like a sinusoidal wave. I don't need 10 amps, I don't need "real sinus", I don't need 230V and I don't want to power my house with it. I just want to feed 6V DC and get something like 4-6V AC with 2A max. so that I can test a transformer or those small AC->DC-converters. And testing a flyback from an old CRT or testing a 1:10 microwave transformer just feels safer with only 3v input...
Google gives me H-bridges controlled by a MCU or similar complicated stuff but no simple convenient components. Do they exist? Or are there prebuilt parts to give out 50Hz and 60Hz by just feeding them with DC? YT'er GreatScott! made a video some years ago about an EGS002 controller from China, but his video is also far from just taking some simple parts and components (yt /watch?v=Dn2PFebi2ww). I mean, c'mon, there are for sure dozens of special controllers for feeding cats but not one simple chip for generating 50Hz AC?

[IanB]

I mean, c'mon, there are for sure dozens of special controllers for feeding cats but not one simple chip for generating 50Hz AC?

I think it is not simple.

One way you could consider is with a simple audio amplifier. Most amps are specified for 20 Hz to 20 kHz, so one should be able to do 50 or 60 Hz. Just take an audio amplifier and feed a 50 Hz sine wave at its input (maybe generate from the audio output of a computer), then use its output as a power supply.

If an amp is, for example, to deliver 20 W into an 8 Ω load, then it would need an RMS output voltage of about √(20∙8) = ~12 V.

Traditional analog amplifiers would be somewhat big and wasteful, but modern class D amps should be much more compact and efficient. I do not know what kind of load an amplifier can deal with, but considering that loudspeakers and cross-over networks are not simple loads, you might get it to work without blowing up the amplifier.

[NiHaoMike]

Just use a motor H bridge shield and an Arduino.

[IanB]

Just use a motor H bridge shield and an Arduino.

Wouldn't that produce a square wave? How could you get a sine wave out of it?

[nightfire]

On ebay and other sites you can find some small inverter modules, that are in some cases configurable to do 50Hz or 60Hz.
If you simply want to test some transformer, it should not matter if you use 50 or 60 Hz, at least nor for basic tests.

Another idea: You could get some used industry power supply like those used in machines etc, as 12VAC or 24VAC is a common control voltage in the industry.
Another idea: At least in germany, you can get some so called "Klingeltrafo", to provide isolation and overload protection to doorbells. (DIN EN 61558-2-8)
https://www.ebay.de/itm/132967317385

Depending on the config (earthing) you have some characteristics of an isolation transformer when testing.

[NiHaoMike]

Wouldn't that produce a square wave? How could you get a sine wave out of it?

PWM.

[themadhippy]

DC motor-gearbox-pushbike dynohub

[tszaboo]

You could use a variable autotransformer, if you know how to do that safely.
Otherwise a few watt audio amplifier plugged into your sound card would be a very easy to make this.

[David Hess]

For small signal tests of power transformers, I just use my function generator.  For higher power, I would add an amplifier to the output of the function generator.