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Do you add amps together? Answered

I guess I don't understand how amp ratings work. I want to use a 12v 5a power supply for a peltier plate. I am using a 2" cpu heatsink with a small fan attached to cool it properly. I tried it with a 9v battery and it worked but I want to use an AC to DC wall psu. The fan is 12v 0.12a. Do you add the amps together (5.12a) for the total? If so, does that mean a 5a psu is not enough? I don't want it to be too low and draw too many amps and damage something.


If the peltier plate is 5 amps and the fan is .12 amps then the total is 5.12 amps.

However if the peltier plate is 4 amps and the fan is .12 amps then the total is 4.12 amps and the 5 amp power supply is powerful enough to run it.

So the question is your peltier plate 5 amps or is the power supply 5 amps?


I know that my peltier is 5 amps and fan is 0.12 amps so together they are 5.12 amps. I want to know if it is better to have a 6 amp psu than a 5 amp one because it is slightly over 5 amps combined.

You add the amps of the loads together to find what you need for the power supply. If you used a 9 volt battery and it worked, you were only using about 900 mA, or 0.9 amps max. All batteries have an 'internal' resistance which limits their current output, and at max they'll even get hot. Anyway, the load amps are the concern, so if the peltier uses 3 amps, and the fan uses .12 amps, then your circuit will pull 3.12 amps total.

Since the peltier and fan together are 5.12A, would a 6 amp psu be a better choice?

The amperage _rating_ on the power supply tells you the maximum current which it can supply. The fan only draws (pulls) 0.12 A (the abbreviation is upper case), so your power supply is plenty large enough.

Even though the peltier plate draws 5 amps?