Power supply compatibility - 4.5v and 5v

Question

I am wanting to replace the power supply for my Dreamplug (too chunky for a power-board and requires a converter to an AU plug). I have another power supply, however I am unsure it will work (without letting the magic smoke escape).

The supplied power supply is rated at 5v @ 3A and outputs 5.16v - 5.18v when measured with a (cheap) multimeter. The other power supply is rated @ 2.5A for 4.5v,6v, 9v or 12v. It outputs 4.90v - 4.93v according to the same multimeter when on the 4.5v setting.

Can I use the other power supply (checking polarity and ensuring that the device does not exceed 2.5A of current)?

Answer 1

As long as you don't select the 6, 9, or 12V settings on replacement power supply, the magic smoke won't escape. However, 4.5V may not be high enough to power up the device, in which case it either won't turn on or won't function properly, although it shouldn't cause any damage.

The replacement power supply is rated for a lower current rating, meaning that if the device draws more than 2.5A, it will brown out. This again shouldn't cause any damage. Even the cheap power supplies today have some basic short-circuit/over-current protection.

One thing to note: When you're measuring 5.16-5.18V, you're probably doing this with "no load" (i.e. when the power supply isn't connected to the device). Since the power supply is not perfect voltage source but a Thevenin equivalent, the voltage reading will drop when you connect it to the device.

Another thing to note: Most digital devices today that run off 5V feed that rail directly into a voltage regulator which drops it to 3.3V or lower. Those devices need the input voltage to be a little higher than the target voltage, so maybe 3.6-3.9V at a minimum. Bottom line, you should be fine with the 4.5V supply.