# Trying to convert 12V DC to 120V AC

Discussion in 'General Electronics Discussion' started by kyij, Nov 20, 2011.

1. ### kyij

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Nov 20, 2011
I have a PC atx psu and I am trying to convert a 12V rail to to 120V AC current. I need the psu for other voltages at the same time, that's why I simply can not use the original 120V from the wall...

The converter I just bought at wall-mart, hoping it would work for my use (just a car converter from 12 to 120v). Which I do not see why not..

But every time I try to close the circuit I just get a spark and the psu automatically turns off.

Thanks for any help!

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
That inverter sounds like it is overloading your power supply (which then shuts down to protect itself).

3. ### kyij

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Nov 20, 2011
Sorry I am new to electronics, will amps overload it? Or watts / both as it draws 140ish watts and the psu should be 200 or 250 watts.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
The power supply can probably supply less than 100W on the 12V rails -- check it.

If the power supply says that the 12V rail is under 12A then you *will* overload it.

Even if it can supply more than 12A you *may* overload it (it may require more current at startup than when it is operating). In addition the 140W may refer to the output power, not the input power (losses mean that it requires a bit more power input than it can output).

The voltage rating of the power supply is what the voltage will be. The current rating is the *maximum* it can supply. The load determines the actual current supplied -- up to the maximum. If the load demands more current than the power supply can provide, the power supply is overloaded and bad things will happen. In this case it's simply the power supply shutting down to protect itself.

Power (watts) is volts times amps. However, while the power supply may be rated at 250 watts, this is spread over all the outputs (+5V, 12V, -12V, 3.3V, and possibly others) There are seperate limits for each voltage rail.

5. ### kyij

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Nov 20, 2011
If it is less then 100w how do i get the full 200?

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
You can't easily.

You could find a bigger power supply which can provide more current on the 12V rail.

But you have to remember tha tthe compuer will (presumably) be using some power also.

This seems to be a really unusual thing to try to do. Can you explain why you can't get the 120V from the mains?

7. ### kyij

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Nov 20, 2011
Actually I am not powering a pc at the same time. I am trying to power a light bulb (led) and run other dc currents (for like computer fans) at the same time.

Last edited: Nov 20, 2011
8. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Why not run the bulb and the power supply from 120V?

Last edited: Nov 20, 2011
9. ### kyij

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Nov 20, 2011
how both? I need the power to come from the psu / or at least look like it. I looked, and I think I could connect a few wires from the ac source before getting to the board (just solder to the leads). But my soldering skills are not great and idk ... I do not really want to ruin a second psu

Last edited: Nov 20, 2011
10. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
The power supply is plugged into 120V, right?

Plug the lamp in there too.

If you want the lamp to *look* like it's being powered from the PSU, go to a store that sells stuff for caravans and look at their 12 volt globes. You may find something that looks like a 120V globe, and probably some that fit in the same sockets.

But 140 Watts -- that's a lot. can't you get away with less? (like under 20W)

11. ### kyij

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Nov 20, 2011
Ahhh, I had given up... I tried to connect to source that came into the psu (the 120v) but it did not work, I am sure I had a bad lead in one of them.

But instead I just took another plug from a computer and ran it through the psu and into the computer, not exactly what I was going for as having two plugs, one powering 2 12V rails and another plug just powering the light!!

So, well thanks for the help, gave me a few ideas but just had to get it done today.

12. ### kyij

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Nov 20, 2011
How do I mark threads as solved? Sorry for bad question but I can not find it anywhere...