The power supply is too big and is in the unit. All we'd like is a power cord with at least a CM choke inside the wall plug. Much more than a molded-on toroid can do. We could of course have it custom made but it would be better if available COTS because there will have to be many international versions.
-- Regards, Joerg http://www.analogconsultants.com/
Radiated onto the cord and the conducted ot. Has to be muffled off at the wall plug because any other place would not allow feed-forward (too much variation in the setup possible). I know this works well but just can't find a cable with a CM choke built in. 10uH would do fine, doesn't have to be as high as usual. But a toroid slipped on does not provide enough.
-- Regards, Joerg http://www.analogconsultants.com/
How about contacting a supplier for a custom cable with cm inductor?
If you can live with an eastern supplier it can be very low price
Just don't choose the cheapest Chinese guy, find a good one from Thailand or whatever
Cheers
Klaus
If necessary we will have to do that but it will be expensive because the quantities aren't very high. A cost adder is that it has to be medical grade.
-- Regards, Joerg http://www.analogconsultants.com/
Some time ago, I remember having seen a similar item... But it wasn't exactly what you're looking for either. Sure, it was a mains cord with inductors in the plug, but it came fixed with some household electronic device, there was no IEC "back-end". I'm not sure any more what device it belonged to, most likely a TV. The device was class II, there was no earth ground, the plug was a 2-prong euro type.
But there were some obvious caveats: it did not seem to be designed to be universal in any reasonable sense. It was rated for 2A only, and given the thin wire in the coils, that was for a good reason. It was not fused internally, which would probably be considered unacceptable and rather appalling by today's safety standards.
The coils were not rated to carry currents up to the trip rating of any common circuit breaker and the likely failure mode under a limited current fault (test case: set the current just below the trip current of the over-current protective device and wait until either something blows up or the EUT attains thermal equilibrium) would have been the meltdown of the plug, fire included, in a rather catastrophic way.
In the case of that appliance, they must have relied on fuses in the appliance, but these are "after" the coils, and while that may have been ok some 20 years ago, who knows what stance any certification agency would have nowadays.
For something with an IEC connector, there's no way to ensure external fusing, the user could just plug it anywhere. It would have to be internally fused instead. If the plug were polarized, ok, but with unpolarized plugs it would mean either fusing both lines or rating the coils to sustain potentially large fault currents.
You'd probably need something either with beefy inductors or with appropriate fuses in the plug before the coils. Also you didn't say what to do with protective earth. Would it also need a coil? If so, fault current capability and PE impedance would get tricky. It may be doable, with a very thick wire on a gap-less toroid designed for fast saturation at low currents, but how big is the plug supposed to be?
In all, I would be surprised to see something like this as an off the shelf generic solution, but if you find one, please let us here know.
Dimitrij
It's bulky, but could you get by with a COTS isolation transformer? At the RF frequency of interest, it's a very lossy choke.
It ha to be small. A CM choke embedded inside a NEMA connector would be great. But it has to be molded and hospital-grade.
-- Regards, Joerg http://www.analogconsultants.com/
The company was probably somewhere in Outer Podunkia so they can't easily be sued and in case things really hit the fan they'd go "bankrupt" and pop back up under another name :-)
It can be done, with a CM choke and even individual ones. I've done it before but we had an enclosure down there. Dale IH series and such. Also, in case of individual chokes it's ok if the core saturates are a few amps as long as the wire is 12AWG or at least 14AWG. Hospital-grade plugs are huge and customers are used to that. Lots of room in there.
A CM choke would be acceptable and PE does not go through it, PE doesn't need to be choked. Hospital grade NEMA plugs are usually about 1" diameter and 2" long.
I will but it's all pointing to a custom run :-(
-- Regards, Joerg http://www.analogconsultants.com/
Those Dale coils are big. Ok, I did not know about hospital-grad plugs and their sizes. Looks like 2 / 3 of them may fit well enough though.
Yep, and they kill the noise dead, as John Wayne would have put it. But it'll be a custom cable.
-- Regards, Joerg http://www.analogconsultants.com/
I already know they are enough. My question is just whether a cable with them already in there is available off-the-shelf. Looks like it ain't.
They don't make a difference up there. Stuff gets coupled into the cable.
They are effective but too big down at the power plug. One lone CM choke would do and they aren't large if you only need tens of uH. It's just not common inside molded-on NEMA plugs.
-- Regards, Joerg http://www.analogconsultants.com/
If you can see the choke effect, it was dominating before chokes were present. Find what is the next dominant factor - then chokes might be 'enough'.
What's the ground wire doing. Has it got an impedance, in series? Balanced output? What happens when you disconnect output structure from box 'shield' (expected in medical applied part),or vice versa (if not 'applied part')?
Where are the (minimal) Y caps located in the circuit? Should be on converter side of CM/DM internal line filtering.
Biomedical grade canned filters for IEC line sockets should be effective at 30MHz, if they don't interfere elsewhere (150K).
RL
and you'll probably want a funny connecter on the appliance end so that a different cord doesn't get substituted...
-- \_(?)_
Too late to patent the concept in 2013. In use pre-1985. Method a possibility, but unlikely. detection - no coupling - no differentiation - no processing linear - no physical shape - maybe nomenclature - always
RL
In that environment people don't do that, especially if it says "XYZ power cord must be used".
-- Regards, Joerg http://www.analogconsultants.com/
Ever ran across some stuff like this?
It doesn't look like it has all that much inductance per length, but the upside is that you could simply specify an erroneously long cable for it, like 10 meters or something.
Oh also, that cable probably has to be "integral", not a regular unpluggable IEC, no? Since, if it's user-replaceable, and EMC critical...
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:
Got an EMC challenge, fairly large RF power under 30MHz so conducted is a problem. Medical, meaning no or very small Y-capacitors. Long story short some of the stuff inevitably and unavoidably gets coupled onto the power cord and that makes it tough to reach the limit on conducted no matter what we do to the system.
What will work is inductors but only if they arr right at the mains power plug (the NEMA, Schuko or whatever the target market is). Need medical grade. So ... is there a med-grade power cable that has a universal IEC at the system side, the various domestic and international mains plugs and then inductors in line with L and N?
10uH would be needed. More is fine as well as long as it won't resonate below 30MHz. Shielded dna doubly-shielded cables help but that has its limits.One way to do it is use those GFCI attachments that hotel hair dryers have and mount the chokes in there instead of the GFCI. But that is a not so elegant solution.
-- Regards, Joerg
It is not when it causes you to pass EMC. I know the mechanism, there is nothing that can be done about what's happening in the room. If the wiring in the walls picks up stuff that is the building owner's problem.
-- Regards, Joerg http://www.analogconsultants.com/
I know Eupen wire but I don't know anyone who builds flexible power cords with it.
IEC. It is a professional application where people adhere to instructions in manuals and on the back of machines. They have to, out of liability concerns and also because their boss or auditor might read them the riot act if they don't. It's not in grandma Miller's kitchen :-)
-- Regards, Joerg http://www.analogconsultants.com/
It sounds like you are not trying to address a real problem. Device compliance to EMC directives does not guarantee that in the final application, the device and its line cord will not act as a reciever for local radiators. It can only ensure that any conducted interference in the line cord does not originate inside the device.
The test setup controls this by directing the orientation of the line cord and LISN in the test site.
If the wall socket sees objectionable conducted interference from any line cord plugged into it, then it will also see similar interference picked up by the wall's distribution wiring connections. Blocking one set of (~passive) wires is pointless.
RL
You should ask your UL guy if the Tripplite Spikecube can work. I't got an EMI filter in it. I'm not sure if the leakage will meet your specs but.... As long as it filters out you RF hash it's along the lines of what your looking for.
Cheers
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