Q&A for How to Convert a Computer ATX Power Supply to a Lab Power Supply

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I actually want to remove and replace just the plug on one of my power cords—how do I do that?

Marvin Woo
Licensed Electrician
Marvin Woo is a licensed electrician and the Owner of Woo's Electrical & Appliance based in East O’ahu. With over two decades of experience, he specializes in troubleshooting issues and maintaining residential electrical systems. Marvin is both licensed and insured to complete electrical work in the state of Hawaii.

Marvin Woo

Licensed Electrician

Expert Answer

Disconnect from the power cord from the power supply and cut off the old plug. Strip away any excess length from the bundle sheathing and conductor insulation of your power cord so they'll fit into your replacement plug. Reconnect the wires one at a time to match the original polarity and ground.

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Question

How do I check the wattage of my AC circuit using a multimeter?

Marvin Woo
Licensed Electrician
Marvin Woo is a licensed electrician and the Owner of Woo's Electrical & Appliance based in East O’ahu. With over two decades of experience, he specializes in troubleshooting issues and maintaining residential electrical systems. Marvin is both licensed and insured to complete electrical work in the state of Hawaii.

Marvin Woo

Licensed Electrician

Expert Answer

When checking wattage for an AC circuit, I prefer to use a clamp on multimeter. Clamp onto one line of wire and take your reading (which will usually be in amps). Multiply that figure by the voltage of the circuit to determine the wattage.

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Question

Can I convert a computer ATX power supply to use for a ham radio?

Community Answer

Yes, except that your radio may need 13.8 volts which will require a specific power supply but may still function. Check your manual for input voltage range (11.5 - 14v) for example so 12 v will work in this case.

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Question

Can I combine the +12V and +5V wires onto one output port?

Community Answer

No, that would make voltage unstable and potentially damage the power supply. The power supply is more useful with the ability to tap into either voltage, and each is regulated separately by the power supply.

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Question

How many amps can I expect from this power supply?

Community Answer

It depends on the model. The label should tell you.

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Question

If I connect the orange (3.3v) wire as Negative (ground) and the yellow (12v) wire as Positive, the output voltage will be 8.6v. Is it safe to use on a device that requires 8.5-9v?

Community Answer

Yes, it is safe. Be careful if the ground from the power supply connected to your device will damage the power supply, as this means you made a short circuit for the 3.3 v.

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Question

Can I connect 12v from two PSU in a series to get 24v?

Community Answer

No, they are both +12 v referenced to ground so both are equivalent to each other so if you measure between them it's 0 volts.

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Question

Can I use the power supply with a charged battery without connecting it to the AC?

Community Answer

No, not unless you connect a DC power inverter to the battery. A car battery only puts out DC power. A PC power supply (PSU) requires AC power.

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Question

How do I know what type of voltage I can use as a power supply?

Community Answer

Simply check the "input power" of the devices you wish to power. Most mobile/portable devices will use DC power. Most PSUs will clearly list the max. amps of each power rail on a sticker on the PSU. +12V and +5V will usually always cover most devices you'd want to power, as long as they put out high enough amps!

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Question

Can I connect a 12 V to a 3.3 V to obtain 15.3 V?

Community Answer

Only using two different PSUs. Connect the ground wire (black) of one PCU to the 3.3v wire (orange) of the other PCU. Use the 12v wire of the first PCU and the ground wire of the second one.

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Question

How do I create a 17 volt ATX power supply?

Community Answer

-5v to neg +12v to positive = +17VDC Be careful as above to not short the negative ground to chassis ground or you may fry your -5v section. Also, never, ever use a negative ground on a ham radio, even if it runs on DC. When you key the radio, it will pull earth ground through the antenna and fry the main board.

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Question

Can I connect a USB port using the purple wire?

Community Answer

In short, yes. The standby power is typically +5vdc, however some are +12vdc. Be sure to check the label. Also, note that the standby power is always on while the power supply is plugged in. The reason for that is so USB devices still receive power even when the PC is turned off (exactly what you want to do).

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Question

How can I get 12V of AC on the output and not DC?

Frank Merenda

Community Answer

You can't do that from this device. This takes 120-220v of A/C and converts it to various DC outputs. If you are looking to go from, say, 120v AC to 12v AC you'll just need a transformer. You can research AC to AC converters for examples.

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