I am needing a power inverter for something I am working on. I have a device that takes 12V AC @ 500mA according to its power brick. I want to power this guy off of a battery pack. I need to invert the DC to AC. I have seen several inverter circuits but most of them step up the voltage at the end with a transformer. Can I use one of these inverter circuits I have found to run the device and just leave the transformer out? I know I can buy a car inverter and hook it to a battery and just plug the device in but I am trying to minimize space and keep the whole thing portable. Thanks for the help.
At such a low power level you might be able to get away with a circuit that turns 12VDC to +/-12V square waves and filters the output to produce and approximate sine wave. Depends on how picky your device is.
If not, using a small AVR and an H-Bridge can be a fun little project to produce 12VAC sine waves.
Not knowing the device you are powering and not looking a schematic really limits what can be suggested. My first thought of using a wall-wart with an AC output is your device uses an internal split dc power supply, maybe a regulated +9v / -9v. Also some devices work best using an earth ground. If this ground is not needed one idea that might work for you is a UPS (Amazon) which has a built in battery. I use this UPS and it works perfect (clean) for what I suggest except it has slightly more than 2 hours of continuous service. It must be turned off to gain more time when using it remotely to save on its own operation battery drain. Outside of this approach what I think you want would be challenging to make. Use it on your computer and borrow it when needed.
Does this device realy operate with only AC power ? Does it not rectify to Dc as soon as the cable terminates into the case?
So the device is a plasma disk. It is one of those things that has “lightning” in it that will follow your finger when you touch it. I’m pretty sure AC is needed for generating the arc In the glass disk. I just don’t know how sensitive the thing is to the smoothness of the AC sine wave. If the square wave would work that would be sweet. It is sounding like building my own inverter is not a solution though the more info I get. At least not an easy solution.
A square wave will probably be fine. I don’t have time to draw a schematic, but an inverter is quite simple. You need a power source, obviously, an H-bridge (like the L293D) and a clock source such as a 555 oscillator or any of the numerous CMOS pulse generator circuits online. The clock needs to have normal and inverted outputs.
Power the circuit with 12V.
Hold the Enable inputs of the 293 high and toggle the half-bridge inputs on and off alternately. i.e., A low, B high, then A high, B low with the clock circuit. That will produce an output that is +/- 12VAC. Takes about $5 in parts maybe.
If the circuit will run on just a few mA, then you wouldn’t even need the L293 and could probably do it with a single CMOS inverter chip. Again, many circuits online for CMOS pulse generators.
I know that’s a somewhat cryptic explanation, but it’s all I can do right now.
My next guess if a plasma disk is the same as a plasma globe:
Now we have something to work around. If your wall-wart truly has a “12v-AC Output” then my guess is the device uses an internal full wave bridge to convert to dc.
Easy Solution: In the above case have you tried to connect a 12v battery to the device at the power jack? This could be done in either polarity direction if it is normally AC at the jack, as the internal bridge will direct the power in the proper direction. Use an 8 cell AA holder.
The plasma effect comes from high frequency energy inside a gas mixture (neon). A RF oscillator internally would generate the effect. Your fingers capacitively couple on contact at the surface of the device attracting the RF energy.
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Here’s another way to get about 12 VAC (pk-pk) from 12 VDC. It’s a basic RC phase shift oscillator w/an emitter follower tacked on to get the 500 mA needed. It’s a yucky sinewave but better than the MSW inverters you buy at Walmart. Two points; the output is not regulated, it’ll always have a peak voltage about 1.5 - 2.0 V less than the DC supply. It also has a DC offset of about 0.8 VDC (due to the emitter follower).
Here’s the circuit and it’s (LTspice) simulated output.
Here’s the .ASC file (posted as a .TXT) in case anyone wants to play with or optimize the circuit.