20V mod for Velleman/HQ Power PS1503SB

[mightyzen]

As Balaur stated in his review of this unit, it is possible to increase the output voltage to more than 15V.

By just turning the pot on the pcb I was able to go to 17.5V, which is less than the 18.5V Balaur was able to get.

The pot is about 200R and in series with a 910R resistor to the positive rail. By putting a 4k7 resistor in parallel with the 910R, I was able to go beyond 20V. However, at 20V the build-in volt meter overflows. With the 4k7 resistor in place, you can use the pot to set the max voltage to just under 20V.

See the photo's.

If you want to, try this at you own risk, and remember the unit was designed to handle 45W max.

BTW: the pcb is dated 2011.09.08 V3.0

[Tube_Dude]

Hi

Inspect if at 20 Volts output and supplying the rated current, you don't have ripple at the output.

Any regulated power supply need to have a minimal voltage difference between input and output, usually 3 to 5 Volts, to work properly, and usually the design team don't make that voltage too big, because it increase power dissipation and consequent increased expense in bigger heatsinks.

Maybe you are lucky and this issue don't apply... 

[mightyzen]

The input stage (behind the rectifier) is 29.3V, so there is plenty of room. Applying approx 7 ohm load at 19.179V yields a 3.00A (rated) current, dropping the voltage to 19.141V. Will hook up the scope later.

[Mint.]

HA!
Smart move!

[mightyzen]

Ripple is worst when current limiting kicks in. At 19V, with current limited to 3.26A, ripple is about 6mV RMS with peaks not exceeding 13mV. Without current limiting these values more than halve. Which I think is pretty good for such a cheap unit.