Ferrite Choke questions

[NukeEngineer]

I got some 15mm ferrite chokes to try to filter the smart meter comms noise from my inverters, see my other thread.

I've got limited experience with these. So, is there is current limit on these? I'm clamping around the individual L1 and L2 lines, not both in the same choke. With a fairly small current, the bead I attached early this evening was buzzing. I'm worried that at 50 amps they might overheat or something.

[Mike90250]

They make choke material out of many different grades of Ferrite. You want a grade that ignores 120Hz, and becomes inductive around 60 KHz. DC current can saturate chokes, AC should not.

[NukeEngineer]

Well, bad news is it didn't work. Good news is, they didn't "do anything particularly bad". I was able to dig deeper and you should never attach these to a single load line, AC or DC. It should be both the supply and return, or both hots, or both hots and the neutral. In other words, the current through the choke should be 0 across all the wires going through it.

Here's an example of chokes on a single line. https://www.youtube.com/watch?v=cgP4B3_K8c8

Worth a try, but I doubted they could filter the strong signal the meter generates. Chokes are for relatively small, but disruptive EMI/RFI.

[kb58]

I'm a ham as well and will be facing this demon myself. From what I understand, microinverters/optimizers were never designed to be RFI shielded. Every single box, and its associated panel, and all the wiring, ends up forming a giant transmission antenna. Adding toroids way out at the end of one set of wires does nothing cutting down on the radiated energy. It's an big enough problem that I'm not sure that it is solvable short of moving away from microinverters/optimizers and replacing it with a traditional string converter.

[NukeEngineer]

I'm a ham as well and will be facing this demon myself. From what I understand, microinverters/optimizers were never designed to be RFI shielded. Every single box, and its associated panel, and all the wiring, ends up forming a giant transmission antenna. Adding toroids way out at the end of one set of wires does nothing cutting down on the radiated energy. It's an big enough problem that I'm not sure that it is solvable short of moving away from microinverters/optimizers and replacing it with a traditional string converter.

What I have is a string inverter, though not traditional since its DC optimized per panel. In my case, the source of the interference is known, and is literally coming down the AC lines. If it were RF radiated interference, then I wouldn't have expected the chokes to do anything.

[kb58]

What I have is a string inverter, though not traditional since its DC optimized per panel. In my case, the source of the interference is known, and is literally coming down the AC lines. If it were RF radiated interference, then I wouldn't have expected the chokes to do anything.

Wait, I'm confused, you say above that you wouldn't expect the chokes to do anything, yet earlier:

Well, bad news is it didn't work...

Which sounds like the RFI may be radiated instead of conducted - or both. How am I mixed up?

[bcroe]

You need to know the general frequency range of the interference, how strong it is, and how it is
propagating. Then an appropriate filter can be chosen. Throwing beads at it is just a shot in the dark.
Bruce Roe

[NukeEngineer]

Wait, I'm confused, you say above that you wouldn't expect the chokes to do anything, yet earlier:


Which sounds like the RFI may be radiated instead of conducted - or both. How am I mixed up?

If the interference was radiated and being picked up by the panels, wiring, etc. then chokes on the AC lines would be pointless. However, the interference is conductive, and being generated by the smart meter.

Analogy: The bad guys are coming in the front door of the house, so I tried a filter for front doors. If they were coming in the windows, then I would have expected a front door filter to be pointless.

[NukeEngineer]

You need to know the general frequency range of the interference, how strong it is, and how it is
propagating. Then an appropriate filter can be chosen. Throwing beads at it is just a shot in the dark.
Bruce Roe

100% agree, but was worth a low-priced shot. I'm having a hard time finding any info on what frequency and signal level meters tend to transmit on.

What's interesting is that the meter guy was surprised that you could hear the meter communicate audibly, just standing next to the meter and inverters. He indicated that he had never noticed this before.

He did mention that when the communications from the substation is generated, it IS audible and loud, and it's the kind of sound that makes you want to run. It supposedly sounds like shorting 277V to ground with a dirty conductor so that it's not a clean 60hz hum, but a sizzle sound. I would LOVE to find a video of this, but can't find anything yet.

[jflorey2]

I've got limited experience with these. So, is there is current limit on these? I'm clamping around the individual L1 and L2 lines, not both in the same choke. With a fairly small current, the bead I attached early this evening was buzzing. I'm worried that at 50 amps they might overheat or something.

Try both wires in the same choke. That makes it a common mode choke - and you are most likely seeing common mode noise that's re-radiating.

[kb58]

This may help, though of course they're trying to sell you something: http://palomar-engineers.com/rfi-kits/solar-system-rfi

[NukeEngineer]

I've got three chokes on each inverter this time, with both hots and neutral going thru them, so no overload worries. Let's see if this makes a difference...

[bcroe]

I'm a ham as well and will be facing this demon myself. From what I understand, microinverters/optimizers were never designed to be RFI shielded. Every single box, and its associated panel, and all the wiring, ends up forming a giant transmission antenna. Adding toroids way out at the end of one set of wires does nothing cutting down on the radiated energy. It's an big enough problem that I'm not sure that it is solvable short of moving away from microinverters/optimizers and replacing it with a traditional string converter.

If I had to use micro inverters, I would shield each one and filter all their wiring. No radiation to panels or
connecting wires. Bruce Roe K9MQG

[NukeEngineer]

I've got three chokes on each inverter this time, with both hots and neutral going thru them, so no overload worries. Let's see if this makes a difference...

Didn't help.

[kb58]

That's what I was afraid of. I suspect everything is radiating, including the micro inverters themselves, so they have to be placed in a shielded enclosure, their wires run through toroids, but worse, the noise is probably back-feeding into/onto the panels themselves. Not sure what can be done about that.