Electronic – Replacing a 1.5V with a 5V power source

basic

I've got a motor that's driven by a 1.5V battery. The shaft turns slowly and that's the way I'd like after replacing with a USB cable (5V) source.

In the current circuit there's no resisters (just a diode) – so using ohms law – not sure what the current draw is. It's V/0 right? Infinity?

If I can find the current draw – I plan to use 5/I to add an appropriate resistor and I should be good to go – right?

Please help the nube boob.

Best Answer

Just adding a resistor is not the right way to go. The current draw of a simple DC motor changes depending on the load. In an unloaded condition the current will be at a minimum. In a stalled condition it will reach a maximun. To run a 1.5V motor from a 5V source you should step down the voltage with a regulator IC or a string of 4 or 5 silicon diodes, (the diodes will need to be rated for at least the maximum motor current, or best guess in this case). Using a USB from a PC might be risky if you do not know the motor's current draw, best to test out the idea using a USB wall adapter first.