FY3200S - Safety Questions - Page 1
Forum section: electronics / testgear

author: CyclicUK
author_rank: Contributor
timestamp: January 20, 2018, 10:43:04 am
content: So I got one of these to help working through The Art of Electronics course (still a beginner). There's a lot of AC present on the BNC connectors (85V whilst off, 220V whilst on - UK mains). My DMM reckons there's 6.5uA of leakage current when on (nothing when off). It's a known issue with the power supply. I've read the main thread on here about it and watched a couple of YouTube vids.Here's a link to the main thread:https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/I want to do the easy fix (add 3 pin socket and connect the mains earth pin to the secondary DC GND). I'm assuming that essentially I'm draining that leakage current into the mains earth?Questions are:1. Will that contaminate my earth reference?2. Will I have created a GND loop which might damage my scope?3. I use an ESD strap (tied to mains earth), will I be safe? (Want to avoid Emporer Palpatine impersonations and inadvertant defibrillation where possible)Essentially, I don't want to blow my face off or blow my equipment up, I just want to make sure it's safe so I can mess about with it without damaging any components.Many thanks in advance.

author: JohnPen
author_rank: Regular Contributor
timestamp: January 20, 2018, 11:56:48 am
content: I used the easy fix on my FY3200S with no problems. It has been used for over a year now, without any signs of distress, coupled to my Rigol DS1054Z. It is worth checking with an AC voltmeter between the BNC outers of the generator to any other equipment just in case to give you more confidence. It should read zero volts!

author: Kleinstein
author_rank: Super Contributor
timestamp: January 20, 2018, 12:29:34 pm
content: The leakage current is just the allowed current through the normal EMC caps. So these 6.5 µA are not a problem. Many input side filters include such caps.Connecting the generator to PE through the plug might create a ground loop. However this would not damage a scope or other instrument of properly done and used. There is a chance to pick up some EMI however if low level signals are used. So it might be a good idea to have at least a small inductor / ferrite bead in the path.The anti ESD wrist band is usually connected to ground through a resistor of about 1 M Ohms. This is for protection, to limit the current in case you touch a live circuit. It also help a little to dissipate existing static charges a little slower.

author: CyclicUK
author_rank: Contributor
timestamp: January 20, 2018, 03:10:01 pm
content: It sounds like I'm safe (I just lack confidence). Thank you so much.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 20, 2018, 03:37:53 pm
content: I wouldn't want any test gear to have floating AC on it, and most stuff has the output grounded to mains earth, with the exception of PSUs, where you generally don't want it.To reduce ground loops, and in the case of PSUs, a 100nf cap from mains earth to DC GND, and maybe 1M across it to discharge any DC can be a good option to reduce any floating AC while avoiding a DC path.

author: CyclicUK
author_rank: Contributor
timestamp: January 20, 2018, 06:02:06 pm
content: Roger that. That makes good sense. Would they have to be rated for 400v or would I get away with a ceramic capacitor and a 1/4 watt resistor? (big fan of your YouTube channel by the way).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 20, 2018, 08:25:30 pm
content: You want it mains rated as a low-voltage one may fail short. A 275vac (or more) snubbber cap is a good choice

author: CyclicUK
author_rank: Contributor
timestamp: January 21, 2018, 06:56:18 am
content: (Googles snubber cap). Ah, that would be what that cap and resistor were doing that I cut off from the 3 pronged socket I robbed from my old PC power supply. I was wondering what the hell that was for! Learnt something, thanks Mike! The one I cut off is a 0.33uF 275V one and it's got a 1M ohm 1/4 watt resistor over it - can I use that one?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 21, 2018, 09:13:50 am
content: Yes that would be fine

author: CyclicUK
author_rank: Contributor
timestamp: January 21, 2018, 05:33:45 pm
content: OK, I'll be busy soldering. Thanks for helping a noob to be less scared of AC, much appreciated!

author: cowasaki
author_rank: Frequent Contributor
timestamp: January 23, 2018, 09:58:15 pm
content: I have made PCBs to isolate this device. I have LOTS of spare onesMy board isolate both the power and the USB.The power is working and I am waiting for the IC to test the USB but it should work no problem at all.Note in the schematic for the power the large caps should be 2200uF rather than 3300uF and the IC is the ADuM

author: Dr. Bogger
author_rank: Newbie
timestamp: September 10, 2018, 12:40:24 pm
content: Quote from: cowasaki on January 23, 2018, 09:58:15 pmAre you selling these PCB's? If so, how much?

author: eitriv
author_rank: Newbie
timestamp: April 13, 2020, 12:30:33 pm
content: A (nother) simple solution to the power supply isolation problem.I just added an isolation transformer 220v to 220v between the power socket and the power supply circuit. No need to change or even move the original power supply circuit. There is a lot of room and the 10W transformer is not expensive, took about half an hour to complete. The USB is still not isolated but I do not use it much and if you connect a laptop there is no problem.Attached a photo of the complete modification.