Radio Noise from PV System

[daniel]

Hello Bob:

Well if you wanted to use an a ferrite that was large enough to work with 44 amps of power, like I have on my MX60, I think it would be quite large. A electronic design engineer informed me that any ferrite put on the wire would change the inductance on the wire and it would directly affect the opening and closing of the FETs. His advice was to talk to Outback and see what they recommend. I think when you twist the wires this also increases the inductance and I am going to ask Outback about this as well.

When I put a ferrite on either the input or the output lines to the MX60, the signal causes the ferrite to become magnetized and I didn't expect this to happen. It does sound logical. Also when I put the probe of my scope on the ferrite I get a really good signal so the ferrite is absorbing rf from the line.

My electronic design engineer friend likes Bill's idea about using a donut choke and having both wires go through the donut. This is as opposed of having individual ferrites on each wire.

Measuring the interference isn't easy. It seems easier to measure it with a radio as opposed to a scope or spectrum analyzer.

Best Regards,

Daniel

[boB]

It will be interesting to see what Outback has to say about this.

[inetdog]

I am disappointed by not surprised that I have RFI noise on amateur radio. I find a "birdie" about every 24 khz on all the amateur bands. I am using an Outback Flex 80. If I shut the breaker off to the four 205 watt 24 volt panels the "birdies" go away other than on 80 meters
I can still barely hear them and if I shut the Flex 80 off then they go away. When the controller goes to "sleep" I of course do not have them.

I have twisted the wires out of the controller going to the battery and I have tried ferrite all to no avail. I did some "sniffing" with my HT on two
meters and I find the lines with about 50-60 volts coming in from the panel are radiating as well as those going to the battery bank. It would
not be real hard to put the wires going to the battery bank in conduit but I wonder if anyone has had success doing this. I would assume you would have to bypass each end of the conduit to ground? It would be a lot more difficult to put the wire coming in from the panels in conduit. I have the first 25 feet buried.

It is coming in over the antenna's as I can use antenna's farther away and the "birdies" are weaker and I can point my beans away and they
get weaker.

Another question? I note that the Xantrex MPPT controller has an FCC Class B rating. Is there anyone here that has this unit and could tune the ham bands and tell me if they have "birdies" They are very loud and are, not problem to hear from the Flex 80.

Ed W0SD

If you are seeing a birdie about every 24 KHz, it is an indication that it is related to a 24 KHz switching frequency in the DC to DC convertor of MPPT or the current regulation of PWM, with a very sharp edge that is generating lots of high harmonics.
Some additional filtering inside the CC would be the best attack, but not really feasible without cooperation from the inverter or CC manufacturer. It is always easier to eliminate/reduce the source of the interference than to try to filter it out later. There is a tradeoff between a fast switching waveform to minimize losses in the switching element and a slower switching waveform to minimize harmonics.

[niel]

this is interesting as to what this installer is saying, but i think he over thought it or he may have been misinformed. now longer wires will also increase inductance and nobody puts up warnings about not having wires too long due to the fets not switching properly. overcoming the resistive losses is a factor in long wire runs though. the inductance that is added is to affect frequencies far beyond what the desired frequency is (0hz) and the power content of those harmonics are much lower, especially in the rf spectrum range of things, so it will not have an adverse effect to the controller imo. we are NOT talking of very large amounts of inductance in the suppressing emi/rfi.

[inetdog]

the inductance that is added is to affect frequencies far beyond what the desired frequency is (0hz) and the power content of those harmonics are much lower, especially in the rf spectrum range of things, so it will not have an adverse effect to the controller imo. we are NOT talking of very large amounts of inductance in the suppressing emi/rfi.

Right, and since the goal is to stop harmonics from leaving the box at all, two measures to accomplish this would be:

1. Use a co-axial capacitor (available for filtering automotive alternator noise) on both leads on the DC side, and
2. A combination of a parallel capacitor to ground and a series inductor on AC leads. The inductor should be closest to the wire exiting the case and the capacitor should to from the outside end of the inductor to the neutral (not to the case ground.)

Either of these should not be done except by a qualified electrician. A ferrite (with both hot and neutral or both + and - leads wound in the same direction though the same ferrite toroid if possible) is the only remedy which does not involve making a direct connection to any wires and is therefore DIY-safe.

[niel]

a cap is one possibility and i agree some may lack the skills to wire up this simple part.

as to adding the inductance, this is quite easy to do for any diy person. they don't have to use the donut types as any of these would suffice too,
http://www.solar-electric.com/nosufefi.html
also, it is possible to wind a coil out of insulated wire that would also add some inductance and this could be some of the wire already inline going to or from the cc. the thicker the wire the more difficult it may be to wind a tight coil, but larger coils can still add a tad of inductance. there's no law saying you can't run the + and - together in the same ferrite core either, be it a donut or otherwise, and if one can fit more turns of the wires to loop back through the ferrite material then they will gain even more inductance. in the case of just a couple of turns of wire and no ferrite material involved then the inductance produced by this will likely be too small to be effective at radio frequencies.