Electronic – Best way to power 2 motors with 1 power supply

Your calculations are correct. 354 LEDs at 20mA each is 7.08 A (354 * 0.02).

The thing to be careful about with LED strips is the voltage drop. The copper thickness on strips like the 5 meter one you have tends to be 0.5 to 1.0 oz, and the voltage drop is quite noticeable. In other words, if you supply voltage to one end of the strip (12V), the opposite end will only receive 10-11V. The instructions may indicate that you should supply power at both ends of the strip, which is a good idea. Personally, in my projects, I do not run strips longer than 2 meters with that type of copper.

Edit:

Looking at the datasheet for the LED strip, it is a 5 meter strip with 60 LEDs per meter. Each "LED" is actually a 5060 package SMD RGB assembly, which means there are three LEDs per package. The datasheet specifies the maximum I_f at 30mA (not 20) for each color, R, G, and B. (The characteristics are derived using a test I_f of 20mA, but the absolute maximum value is a worst-case scenario, which you should use in calculating power supply size.)

Unless I am reading it incorrectly, this means to light the strip at 100% brightness at white (all three colors), it will need 90mA per LED. That works out to 5.4A per meter, or 27A total.

Comments on the product page suggest that the strip only requires 6A. I suggest measuring to be sure. (Strips that I have require about 20mA per color, which is what made me think to come back and add this addendum.)

You are correct in the power calculation, however that's not directly useful in specifying a power supply (except that you can remove all supplies with less than that supply rating from consideration).

Each output of the supply must be capable of supplying the maximum possible current draw. In this case you need a supply with at least two outputs, one 30V at 14A or better rating (in a real situation you'd have to look at the stall current of the motors and other possible conditions that could cause the motor to draw more than the stated current). In a real situation you might not want to share the same supply between the electrically noisy motors and whatever those peripherals are, so you might want two outputs for 30V or even two separate supplies.

Generally speaking, under no conditions should you exceed the maximum current rating of the supply on each output.

So, in theory, from the numbers you give, a supply with two outputs, 30V rated at 14A or better and 5V rated at 0.5A or better would fill the need. In some cases there may be a constraint on the total power, in which case you would check that the total power of 422.5W does not exceed the rated total power.

In real situations you must look more deeply at the datasheet and applications data because the top-line specifications often must be derated for elevated temperature or if you want long lifetime. You might find you need a 600W 30V supply, for example.