# How to determine DC Amperes required for Amplifier?

I'm trying to understand if there's any relationship between the rated wattage (RMS) of an audio amplifier and the corresponding power requirements on its power supply.

Practically, if I buy an amplifier that does not have its own power supply, is there any formula or inference I can make to help me determine the minimum wattage of the (bench) power supply I should purchase?

To provide an example, consider the following cheap amplifier and a power supply such as this one. Is it powerful enough? Not powerful enough? How can I tell?

your amplifier is capable of delivering 240 Watts of energy.

Power (Watts) = Voltage (volts) x Current (amps)

Therefore the current range is:

Power/Voltage = Current

• 240 W / 12 V = 20 A
• 240 W / 26 V = 9 A

So when powering the amplifier from a higher voltage, you are likely to require less overall current.

Maximum current drain at maximum power is 20A

The amplifier board indicates 90% efficiency, so you may well need to factor this in:

• (240/12)/0.9 = 22

So in order to deliver 240 Watts you may need to supply 22 Amps.

Looks like that PSU will probably be good enough to power that amplifier board.

• Thanks Mark, your caclulations seem straightfoward and easy to understand. I think, as in many things, these are all in a sense "worst case scenarios", in that the amplifier won't be delivering peak power 100% of the time, or for very long, so these are "safe" maximums, is that an accurate statement? Nov 21, 2018 at 16:25
• Yes. That is an accurate statement. Note in the specs the difference between "peak" output and "RMS" output. RMS is "square root of mean of squares of instantaneous values".
– Mark
Nov 22, 2018 at 2:53