eBay EMI line filters - Page 1
Forum section: electronics / projects

author: rhb
author_rank: Super Contributor
timestamp: April 19, 2018, 01:01:05 am
content: I got some eBay EMI filters and installed one in a 4' shop light converted to LEDs which had been causing a lot of noise. It did a very satisfactory job.Attached are sweeps with an 8560A w/ TG over the full BW and some more restricted sweeps.

author: rhb
author_rank: Super Contributor
timestamp: April 19, 2018, 01:04:03 am
content: And some more. Not bad for under $3. These were more because I wanted some sooner rather than later. I've got more on the way.

author: CopperCone
author_rank: Super Contributor
timestamp: April 19, 2018, 01:35:30 am
content: probably should get like, tdk lambda or some shit since its mains connected capacitors, instead of the rong brand.The filters not too hard to get right, considering what it is, but the transient survivability is the harder part (its your first line of defense and its gonna shunt any transients that go through it some what).also whats going on with those strands of wire in the top right crimp???also why is everything on that label crooked ? (tho I don't give a shit about this part, it looks like it has some style, like the old tektronix logo)kind of psychedelic actually, groovy baby

author: rhb
author_rank: Super Contributor
timestamp: April 19, 2018, 02:53:18 am
content: This is in a recycled shop light. The ballast had failed and it was headed for the trash when I discovered I could get LED tubes for it for $10 each. New lamps are cheaper than ballasts, so when the ballasts fail I would just buy a new light. Now I rewire the fixture and replace the FLs with LEDs.I don't care about protecting anything. I just want to suppress conducted EMI leaking into the power lines and getting radiated. My recent experience is that the SMPSUs in modern Chinese gear are *rather* noisy. $50 for EMI filters is a lot more palatable than $500. These also have the virtue of being small, so easy to stick inside a noisy instrument. I've got several Corcoms, but they won't fit in the light fixture.The wire ends are because to get a good crimp I had to fold the wire over. And in an effort minimize errors I cut the wires a bit too short. The wires are soldered to some BNC soldercup bulkhead connectors so I could connect it to my SA/TG. It's hard to see what I else I would use them for. So really a one time use.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2018, 03:28:45 am
content: Ah, so you did a sort of normal-mode 50-50 ohm insertion loss measurement?Yeah, that seems reasonable. I wouldn't expect a teeny one like that to be gangbusters below the low MHz, but still enough to take the edge off if that's what you need. Attenuation over 100MHz is largely a matter of wiring anyway, you'd need feedthrus and shielding to deal with that.Reminds me, I should measure my 24V charger supply; it's a variant of this design:https://www.seventransistorlabs.com/Images/100WPowerSupplies.jpgI put it in a metal box, with filtered IEC receptacle, in addition to the filtering that's already onboard (which does a good job, but not usually good enough to meet regs, based on the informal / precompliance setup I have here). I also put a line filter (just discrete parts) on the output terminals, so it should be pretty quiet now, in both directions.Not a big priority, because it lives in my lab, and I've got a bit of an ecosystem with pluggable headers, IEC cords and so on, hanging off my LISN (off an isolation transformer, off a variac), which is an effective absorber anyway.Tim

author: rhb
author_rank: Super Contributor
timestamp: April 19, 2018, 12:10:04 pm
content: I pondered the question of impedance match for about 30 seconds before deciding that was much more work than I wanted to do. Bodging the BNC-crimp terminal fixtures was pushing it. Things are quiet enough now I can use a bigger loop on my scope probe to hunt for the next offender on my hit list.I've been looking for cheap feed through capacitors, but have had a hard time finding them at reasonable prices and quantities. I want 100-200, but not 5000.