How much power for my circuit?

Question

I'm an electronics newbie. Please don't hate on my question.
I'm wondering if there is a special rule for powering a circuit with many power consumers on it. For example, if I have a circuit with 10 5v motors...in order to power all the motors do I simply need one 50v power source?

Answer 1

What you are describing is one of the fundamental laws of electronics, called series and parallel circuits. There are many references for such topics, however Ibiblio has been hosting Tony Kuphaldt's excellent series, Lessons In Electric Circuits for nearly a decade. The first volume, 1-DC, will explain how this works and why.

The short answer is, you could try wiring each motor to each other motor, then power the entire string of them with 50V. This would be wiring them in "series." In theory this sounds logical, but in reality there are many issues with this method. The motors do not all start at the same time or rate, so one may "see" 3 volts while another "sees" 20 volts (and promptly burns out.) Instead, the better way is to connect each motor's red (+) and black (-) terminals together, otherwise known as parallel, and power all of them from one 5V source. Of course you'll need more "energy" to spin 10 motors all wired together this way, and the chapter about Ohm's Law will make this more clear.

Answer 2

Direct answer: no, you do not need a 50V supply. The voltage supply usually is selected according to the highest required voltage of a single component. Lets say you have 1 motor that needs 5V and one LED that needs 2V. You need to select a 5V supply and take care that all other elements that need less will see a lower voltage. This is accomplished by a voltage regulator or voltage divider. So in case of your 10 motors you will still select 5V as maximum voltage. What will multiply is the current capacity of your supply. Say each motors draws 1 Ampere. With 10 Motors your supply needs to provide 10 x 1 Amp = 10 Amps.

Answer 3

In the very unlikely circumstance that you intend to connect all the motors in series, so they will run simultaneously, you would theoretically need a 50 volt power supply. However, this is unlikely to work well, as the current required by each motor will depend on the load it is required to move.

However, you will more likely want the possibility of running the motors one at a time if needed, or several at once. In that case, you would want a 5 volt power supply with sufficient current capacity to run the number of motors you will want to run simultaneously.

For ease of calculation, assume a motor requires 1 Amp for normal operation. If you will only operate one motor at a time, the power supply just needs to supply 1 Amp, but if you might want to run all 10 at once, the supply must be capable of supplying 5 volts at 10 Amps or more.

Note that a larger (higher current) power supply than needed is no problem - the motors will only draw the current they need. The power supply does not force its maximum current through the load.