Korad KA3005D On/Off spike measurement - Page 1
Forum section: electronics / beginners

author: nubinstanley
author_rank: Regular Contributor
timestamp: April 27, 2022, 12:27:54 pm
content: Hi AllI recently bought a Korad KA3005D. I wanted to measure its power ON/OFF output spike. I am not sure if I used the right methodology to do it - kindly comment.I had a5Ohm/5W resistor across the output terminals and used my scope to measure across the resistor. Output was set to5V/1A.Observations:1) Power ON (not output ON)2) Power OFF (not output OFF)3) Output ON4) Output OFFA few queries:The PSU power cord does not have a ground pin. Looks like I have the option to attach one. Should I ?Output ON/OFF looks OK ?Power ON/OFF shows big spikes. I'll be careful, not to turn ON/OFF the PSU with something connected. Even so, what kind of devices can be affected by these spikes that last for such short duration ?

author: xavier60
author_rank: Super Contributor
timestamp: April 27, 2022, 01:01:30 pm
content: The first 2 look like switch contact bounce and a arcing. Test again with the probe connected to the negative side of the resistor as well as the ground clip.

author: ledtester
author_rank: Super Contributor
timestamp: April 27, 2022, 05:15:50 pm
content: Quote from: nubinstanley on April 27, 2022, 12:27:54 pmFrom this tear down video at 5:00 you can see that the chassis is connected to the ground pin of in the IEC inlet:https://youtu.be/-PaYVGFTxOY?t=5mIt's a protection feature so I would use a 3-prong IEC power cord.The video also points out the earth connections at around 6:50.

author: nubinstanley
author_rank: Regular Contributor
timestamp: April 28, 2022, 01:38:03 pm
content: Quote from: ledtester on April 27, 2022, 05:15:50 pm

author: nubinstanley
author_rank: Regular Contributor
timestamp: April 28, 2022, 01:41:35 pm
content: Quote from: xavier60 on April 27, 2022, 01:01:30 pmI hope I understood you correctly : Probe tip to the negative side of the resistor; Probe ground clip to the ground of the PSU ?

author: nubinstanley
author_rank: Regular Contributor
timestamp: April 30, 2022, 08:44:30 am
content: Quote from: xavier60 on April 27, 2022, 01:01:30 pmI repeated the test with the probe connected to the negative side of the resistor and the ground clip to:1) Positive of PSU2) GND of PSU3) Negative of the resistorIn all cases, the same spikes could be seen. What does that mean ?Now a dumb question...If I just connect the probe tip to one of the output posts of the PSU (GND clip not connected), I see a 100+V 50Hz signal. Some kinda mains interference... ? 100+V ?

author: xavier60
author_rank: Super Contributor
timestamp: April 30, 2022, 08:55:15 am
content: Quote from: nubinstanley on April 30, 2022, 08:44:30 amThings that arc generally create large amounts of common mode EMI. What you are seeing is voltage drop across your probe's ground lead caused by the EMI's current flow.The ~100VAC is likely caused by a missing mains earth connection.

author: nubinstanley
author_rank: Regular Contributor
timestamp: April 30, 2022, 01:31:40 pm
content: Quote from: xavier60 on April 30, 2022, 08:55:15 amOk, thanks for this!Just out of curiosity, this can also induce a current in, say, a nearby breadboard circuit? Can it generate enough energy to damage something?

author: xavier60
author_rank: Super Contributor
timestamp: April 30, 2022, 01:40:34 pm
content: Quote from: nubinstanley on April 30, 2022, 01:31:40 pmYes, a small chance, depending on what and how other connections are made to the outside world. It's difficult to be specific.It's better to use the PSU's output enable switch rather than its mains switch.

author: nubinstanley
author_rank: Regular Contributor
timestamp: April 30, 2022, 01:47:09 pm
content: Quote from: xavier60 on April 30, 2022, 01:40:34 pm