improving "velleman" ps 613 - Page 1
Forum section: electronics / projects

author: conducteur
author_rank: Regular Contributor
timestamp: February 21, 2015, 08:11:26 pm
content: I have a velleman ps 613, and when i bought it, i was happy. Got my first power supply. Nowadays, my expectations are changed, and it doesn't meet my expectations.1) I could buy a new one (rigol dp 832?) but as a student, budget is limited so my idea is to hack my ps613. Is here someone who has done this before?things i want to do (don't really know if its feasible to do them, some are, others maybe harder to do)1) I want to change the potentiometers to 10 turn types (easy i think)2) hacking the display resolution (hard) : psu has 0-30v output. Maybe there's a way to set the decimal point in the 00,0-09,9 volts range so i can have a 0,00-9-99v readout? (hard)3) two similar to 2 but for current reading, now fixed two digits after period (eg 1,24A or 0,25A) (difficult to)4)mount switches to have common ground between fixed output supply voltages (12v and 5v fixed at 0,5A) with the adjustable readout.suggestions? comments? shoot!Or should i buy another psu, cheaper than the rigol but better than the ps613?

author: jimon
author_rank: Regular Contributor
timestamp: February 21, 2015, 08:33:52 pm
content: Hi, I have two similar units (LAB PS3003SM and LAB PS3005SM,http://www.velleman.eu/downloads/2/labps3005sma4v02.pdf).My plan now is to addhttps://www.eevblog.com/forum/projects/$5-voltmeter-with-5-digit-(0-1mv)-resolution/ as voltage display. I'm quite happy with coarse and fine 1 turn potentiometers, but maybe I'll replace coarse one to 10 turn's type when I'll be really desperate. Would be also nice to add output switch.But I've noticed issue with my units, they are unable to sustain voltage under load. If I set like 5.0000v (using my bench DMM) without load, and then connect 4 Ohm load, voltage gonna drop to ˜4.6v (I haven't done any logs or specific experiments, but voltage went down to some degree). Maybe this is a issue with my cabling (I'm using cheap cables, not even sure if they rated for 1A), or I just need 4 wire PSU, not really sure what is happening there yet, but would be nice to solve it =)

author: jimon
author_rank: Regular Contributor
timestamp: February 21, 2015, 11:07:48 pm
content: Quote from: jimon on February 21, 2015, 08:33:52 pmConfirmed, my wires where 2.5 OhmsSo PSU is ok.

author: chemary
author_rank: Contributor
timestamp: March 31, 2017, 12:01:29 pm
content: I have same unit and I'm planning to change the potentiometers, any recomendation about good multiturn ones and which value they must be?Also I'm concerned about slow over current limit, I have fried some LEDs I suppose because the although I set a secure current limit it is quite slow. Anybody know how to overcome this problem?

author: mikerj
author_rank: Super Contributor
timestamp: April 02, 2017, 10:03:15 pm
content: Check if there is a capacitor wired across the output connectors. There often is to improve transient response, but this means you will get a spike of current into a load before the CC circuit kicks in.

author: chemary
author_rank: Contributor
timestamp: April 02, 2017, 11:18:56 pm
content: Thanks @mikerj, there are four capacitors 100uF@50V in parallel at the output, next time I open the unit to replace the potentiometers I will try which is the effect in the output removing these capacitors.I have already ordered two 50Kohm Multiturn Potentiometers.

author: macboy
author_rank: Super Contributor
timestamp: April 04, 2017, 04:16:08 pm
content: Quote from: chemary on April 02, 2017, 11:18:56 pmDon't remove the output capacitor. It is often required for stability (it might break into oscillation without it) and is always required for good, fast, low-noise regulation. A constant voltage power supply ideally has "zero" output impedance. The capacitor helps to reduce output impedance especially at higher frequencies above the frequency response of the power supply's closed loop control. At low frequencies, the closed loop control provides apparently "zero" output impedance. Power supplies with remote sense terminals can even effectively remove the resistance of the connecting cables, a nice feature.A constant current power supply ideally has "infinite" output impedance. Purpose-built current sources (e.g. HP 6186C) have no output capacitor, in order to help achieve very high apparent output impedance. A typical lab power supply is intended to be a constant voltage supply with current limiting (not a 'true' current source like the 6186C), and it will always have an output capacitor. This does means that it can supply a surge of current when a low impedance load is connected.To help save your LEDs, use a small series resistance. Even just 10 to 22 ohms will reduce the short current spike to a level that most LEDs will survive, while providing minimal voltage drop.

author: chemary
author_rank: Contributor
timestamp: April 04, 2017, 07:10:11 pm
content: Hi @macboy, I have also though about using a series resistance to avoid burning diodes or other circuits.I was skeptical about removing the output capacitor, I know a little about power electronics, so that's why I said that I will try what happens when I remove them. This linear power supply is really simple, I only see a couple of operational amplifiers and some power transistors or MOSFETs, so little improvement can be done.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 04, 2017, 07:51:21 pm
content: Changing the capacitance at the output can be tricky. It is not only the capacitance that is important, but also ESR / ESL. With a wrong output capacitance it might not oscillate immediately, but only under certain load conditions.A good linear power supply does not need many parts. The difficult part is finding the balance so that supply is fast and still stable with any reasonable load.