I have a BT-153 bench power supply (0-15V, 0-3A, see https://www.conrad.com/p/basetech-bt-153-bench-psu-adjustable-voltage-0-15-v-dc-0-3-a-45-w-no-of-outputs-1-x-393647) which displays an incorrect output voltage when under load. I wonder if it is broken, just poor quality or if I am misunderstanding what this power supply is supposed to do or show me.
When measuring the output voltage without a connected load, the displayed voltage matches my multimeter measurement to within a few tens of mV, so all is good. When setting, for example, the voltage to 12V and setting the current limit to max, a 12V / 20W light bulb draws around 1.5A, and the power supply and my multimeter agree to within 10-20 mA.
However, after connecting the bulb, the power supply still displays a voltage of 12V, whereas my multimeter measures around 10.6V. When connecting another, identical bulb in parallel, the current increases to 2.93A (multimeter confirms), the power supply continues to show 12V, but the multimeter measures 9.4V.
I am confused as to what the power supply is doing: it appears to show the value of the desired voltage, and even though it should be able to deliver 12V and 1.6A, it can't, but refuses to inform me about this. I expected that (a) the power supply's voltmeter acts like a multimeter, showing the actual voltage, and (b) that the voltage will not break down when the supply is put under a load of 50% of its nominal capacity.
Is this simply poor quality or misguided expectations on my behalf or am I misunderstanding what is going on?
Best Answer
Oh no, how embarrassing. When I measure at the power supply's terminals all is good and as expected. It was indeed the resistance of the leads I hadn't accounted for. Thanks for your replies!