Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

how to Measure a 12v DC fan current

Not open for further replies.
May 21, 2015
Reaction score
Trophy points
Activity points
I have a few 12 volt computer fans but I don't know the current rating since the label has been rubbed off. I hooked up a 12 volt power supply but do I set the current limit to 1amp or do I need a series current limiting resistor to protect the 12 volt fan? I can use my DMM meter to measure the current draw of the fan to know how much current it need to turn on. How can you tell if the small fan is DC or AC volts if the label has been rubbed off or there is no label on the computer look type fans. I'm worried to turn on the power supply without knowing it needs AC or DC or it needs a current limiting resistor. Can you guys please help me.

In case you have any doubt, use a bulb light in series and watch if it turns.

All computer fans are 12Vdc. You can connect the 12V power supply that can supply more current from the value tha fan will draw, and the fan will draw the amount it required.
Do not worry about it.
A DMM could help or not to measure the current. The current may not be constant and some cheap DMM have problems with it. In that case you can add a 100uF electrolitic capacitor in parallel with the fan (after the DMM that should be connected in series).
Beware of the polarity of the electrolitic capacitors.

If it's a computer fan, it's a DC fan since it'll be run off the 12V DC power supply. It's likely (a standard small PC fan is) rated at about 150mA-300mA (although it could be more, depending on the fan). Hook it up to your 12V supply and measure the current draw.

Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to