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Possible Duplicate:
Choosing power supply, how to get the voltage and current ratings?

I need to power this fan which is rated at 12 V, 0.95 A, 11.4 W. I am unfortunately without a DC power supply, so I am wondering how I could power this fan using an AC adapter.

I am looking to purchase an AC adapter with variable voltage output, but I can only find ones at my local electronics store that are rated at 0.8 A or 1.2 A.

First question is: since I can't find one of these rated at 1 A, should I go with the 0.8 A or 1.2 A?

Second question is: where do I get Vdd and GND from a tip that looks something like this? I would like to have voltage and ground supplied to a breadboard so that I can supply the fan.

Thanks!

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  • \$\begingroup\$ Here are the adapters I was thinking of purchasing: 1.2 A and 0.8 A \$\endgroup\$
    – tomocafe
    Commented Nov 18, 2012 at 23:21
  • \$\begingroup\$ an old PC PSU can be useful for projects needing 12V. \$\endgroup\$
    – Tony Stewart EE since 1975
    Commented Nov 19, 2012 at 0:50

2 Answers 2

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  • You should always use a supply rated higher than your target load unless you really know what you are doing, so for your project, I recommend using the supply rated for 1.2A. Also, if you can look into what motor the fan uses, it may be possible to operate it at other nearby voltages safely.
  • There is no single standard to which conductor on the barrel connector corresponds to VDC or ground. However, generally the device is indicated to be Center Positive or Center Negative via a symbol embossed by the connector something like:
    this
    If your device lacks an indicator, you must take it apart and inspect the board/wiring to see which end is hooked up to ground to avoid damaging the device and power supply.
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You want to get a supply that is rated for .95A or higher, thus you should be fine with the 1.2A supply. However, you should make sure that it can supply enough current at all the voltages you'll be using.

As far as the connector goes, your best bet (while being non-destructive to the AC adapter) would be to buy a receptacle for that type of barrel plug, then use that receptacle as a breakout and wire it to a breadboard that way (obviously, you'll need to use a DMM to check which lead is + and which lead is -). If you don't care about preserving the tip of the AC adapter, I'd just cut the connector off, strip the wires, and plug them into the breadboard directly.

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