DC Bench power supply - basics

Thread Starter

Mark Flint

Joined Jun 11, 2017
I'm wanting to know if my PSU is operating "normally" or if there is a problem with it.
I'm powering a 12v motor - the heater-blower type from a car. This can draw over 10 amps at 12v, but I only need this powered at about 4A at 12v.

When I allow max amps from the supply (5A) the voltage will only get to 3.95v. The supply is rated at 150w (30v @ 5A). So why will it stop at about 12w maximum?

Am I using the power supply (pictured below) incorrectly?




Joined Apr 11, 2010
Your power supply appears to be working as expected. You have set it to control both current and voltage. You know (or should) that according to ohms law, this is impossible. The way a power supply handles that situation is when the maximum current you’ve set is exceeded, it reduces the voltage.


Joined Oct 2, 2009
Ohm's Law applies.
Let's assume that the heater takes about 150W. Hence the resistance is about 1Ω.
Power P = V x V / R = 12 x 12 / 1 = 144W
(According to the PSU reading, the heater is about 4V/5A = 0.8Ω)

You cannot have both 4A @ 12V at the same time going into 1Ω.
The PSU reaches a limit of 5A first and holds it there.
If you want about 48W output then you need a PSU that can deliver at least 7A.


Joined Jun 5, 2013
Trying to run a device requiring 10A at 12V with 4A at 12V is sort of like trying to fill a gallon milk jug with 1/2 gallon of milk.


Audioguru again

Joined Oct 21, 2019
The Chinese power supply is missing a safety certification label. Then it might catch on fire or electrocute you.
It does not say 10A continuous, it might produce 10A only for a moment.