Owon HDS272S Scoping Mains Voltage - Page 1
Forum section: electronics / beginners

author: sijmen
author_rank: Contributor
timestamp: August 09, 2021, 07:29:43 am
content: Hi,I have a Salt Water Pool chlorinator, and the Control Board failed. I have already replaced the controller with a new one, and kept the old one. In the interest of learning electronics, I wanted to design a new control board for the old chlorinator and add some new features to it. Other than the control board, everything else works (Transformer, SCRS, Timer, etc)Now I know there is mains power running through all this, and I'm quite versed in the dangers of working with mains power. What I'm not versed with is using an oscilloscope with mains. I know I should be using an active oscilloscope probe to insulate the mains from my scope, but I don't have one.Instead of using my main oscilloscope, I have a battery Owon HDS272S portable scope, which I was planning to use for initially for this project.What I'd like to know, is the following:1. Can I use the scope and supplied probe to read the mains input to the transformer, without damaging the scope, and how could I damage it?2. Can I then place the second channel on the output side of the transformer to read the output of the transformer at the same time?These are my initial requirement. I'll then use the scope to monitor the power to the Salt Cell as the control is adjusted, so I can work out the requirements of the what I'd like to build.Regards,Sijmen

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2021, 08:03:08 am
content: The general advice is don't float the 'scope!Connect the device under teast to the mains, via an isolation transformer. Note that if you do this, once the oscilloscope is connected, the rest of the circuit will become live, with respect to ground and you will lose the protection of and GFCI/RCDs in the circuit.The two channels on an oscilloscope share a common ground connection, so the ground clips must be at the same voltage.

author: Ian.M
author_rank: Super Contributor
timestamp: August 09, 2021, 08:09:04 am
content: See section 2 'Safety Information' of its user manual.Your scope *can* be used with Cat II rated probes to monitor mains circuits, provided it not connected to its AC adaptor or to a PC, but the probe ground clips are internally connected, common to both channels so *MUST* only be connected to the same node of the circuit. I would *NOT* recommend using it in such a way as the BNC connectors will be a mains live safety hazard. Also if the cover over the USB port isn't firmly in place that also becomes a shock hazard.You absolutely must *NOT* connect one probe + its ground clip on the primary side of a transformer and the other + its ground clip on the secondary side. The two ground clips will bridge from primary to secondary through the scope, removing the isolation the transformer was designed to provide, risking damaging or destroying the circuit, the scope, and possibly electrocuting you as well.Furthermore, I would not care to work on such a circuit in a wet area. The personal risk is just too high. If you can get it on the bench with the wet section entirely contained in a polypropylene storage tote, covered to prevent any splashes escaping, the risk becomes much more manageable.

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2021, 08:21:42 am
content: Sorry, I should have Googled the Owon HDS272S. Yes that can be safely floated, providing the correct safety precautions are taken. You should use RCD/GFCI with all the mains equipment.

author: Ian.M
author_rank: Super Contributor
timestamp: August 09, 2021, 08:33:25 am
content: I wouldn't say "safely floated", rather, with appropriate training, and appropriate choice of probes, the risk of using it for a floating measurement can be made manageable. There is nothing *SAFE* about any device that could let you come in to contact with a live BNC connector!

author: sijmen
author_rank: Contributor
timestamp: August 10, 2021, 06:54:30 am
content: Thank your for your responses.I've decided to invest in a differential probe, which would also then allow me to play around with SMPS's. Now to figure out which one.Regards,Sijmen.

author: SteveyG
author_rank: Unknown
timestamp: August 10, 2021, 08:50:03 am
content: The Micsig is good for the money. I'd recommend the DP20003 though as the ranges are a bit more useful.I did a review a while back on YouTube (Video #081)