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Solar Power RFI

Discussion in 'General Technical Questions and Answers' started by KG4PID, Jul 3, 2021.

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  1. KG4PID

    KG4PID Ham Member QRZ Page

    I'm having issues with RFI from my small solar powered station. This consists of four 100 watt panels, a 40 amp MPPT charge controller sold by Rich Solar and a 100 ah battery. Every thing is fine until the sun comes up and the system starts charging the battery. Then I get RFI that sounds like it is constantly changing and sweeping back and forth.

    Any one here familiar with the noise the these MPPT controllers produce? How should I go about trying to quieten this thing down?

    Thanks, Max KG4PID
  2. G3YRO

    G3YRO Ham Member QRZ Page

    Usually it's the poor actual design of a Controller (Inverter or Switch-mode power supply/charger etc) that causes RFI . . .

    Fitting external chokes, capacitors etc usually only makes a marginal improvement (like shutting te door after the horse has bolted!)

    Roger G3YRO
    K0UO likes this.
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    Shielding, grounding & ferrites should help. You may need to encase the controller in a faraday enclosure.

  4. KP4SX

    KP4SX Premium Subscriber QRZ Page

    I was pretty successful in taming the noise from my Outback 60 controller. Big ferrite toroids on both the input and output. With #2 wire on the battery connection I couldn't get but a couple of turns so I put two in series.
    The Outback has a pretty tight molded metal case.
  5. VE7BPB

    VE7BPB Ham Member QRZ Page

    Your description of a sweeping noise is exactly correct. I also have an mppt controller and on my SDR covering from 1.8 Mhz to 8 Mhz I can see the noise sweeping back and forth as the controller attempts to optimize it's output. It does mostly affect the lower part up to about 5 Mhz but still has spikes up into 40m.

    I have put FT240-43 ferrites on all the leads in and out of the controller and also put some .1 uf ceramic caps across the leads at the controller and have managed to reduce the noise somewhat, but because of my location I can't ground the body of the controller to a good physical ground, which might help.

    I have tried other solutions, like making my own very basic linear controller, and that does indeed fix the problem. I have also tried just using a buck converter set to limit the maximum voltage from the panels and that also works, but neither solution is as efficient as the mppt unit.

    Also, make sure you have good current mode balun chokes on your coax feedlines; no point in letting the coax pick up any local RFI if you can avoid it.

    Good luck.

    regards, Roy
  6. SM0AOM

    SM0AOM Ham Member QRZ Page

    Solar power EMI is a reality.

    Currently, there are several investigations going on here about the impact on air traffic control, public safety communications and military tactical communications in the HF and lower VHF spectrum.

    The preliminary results here are that the RFI levels vary considerably depending on which technologies are used.
    Worst are the units using "optimisers" either distributed at the panels or integrated into the panels.

    RFI propagates from the optimisers by the connecting leads, and by twisting them the equivalent apertures are reduced.

    There have been reported some limited improvements using ferrites and shielding but it is seldom sufficient to permit weak-signal operations.

    Some designs use no optimisers, and use inverters with well controlled EMC characteristics, and these become free from RFI emissions as far as can be determined.

    There is a measurement campaign "in the works" where comparisons between "good" and "bad" solar power installations are to be made.

    The measurements are intended to find out how good EMC performance that can be attained by choosing the right components and by attention to detail in the installation process.

    SM0GLD likes this.
  7. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    I agree totally with that/ he is probably wasting time and money trying to fix it FT240-43 ferrites cost $$$$. The Cheap Chinese parts even the good manufacturers are having trouble maintaining quality control. RFI is getting worse every day from all different types of inverters controllers. Not to mention unskilled people installing them. I talked to a guy the other day that had been installed in for a couple of years he didn't even know what I was talking about when I said noise or radio interference/EMC
    K8XG likes this.
  8. W9KEY

    W9KEY XML Subscriber QRZ Page

    This thread might be a good place for those with past experience to list solar controllers (by Manufacturer and Model Number) that both DO and DO NOT emit excessive RFI.

    That way anyone considering a new purchase - perhaps for portable operation - would have at least some chance of picking a "better" unit.
  9. KV4PD

    KV4PD Ham Member QRZ Page

    Been using one of these (45 amp version) with four 135 watt Kyocera panels for the last ten years and have had zero issues with RFI. Runs the whole house - most of the time (HVAC excluded). Radio room is happy.
  10. SM0AOM

    SM0AOM Ham Member QRZ Page

    Last year, I wrote a "design handbook" for a trade association of municipal airports which have demands placed on them from the agencies responsible for air navigation safety not to create RFI problems for ATC communications.

    It ended with "checklist" of items that should be included in a procurement specification for solar power installations at airports.

    The major items were:
    • Use no optimisers
    • Use twisted pair wiring from the panels
    • Use the inherent shielding properties of metal
    • Use inverters with demonstrated good EMC properties
    • Use shielded wiring for the connections to the power entrance panel
    • Make room in connection boxes for additional ferrite chokes and feed-through filters if needed
    • Make follow-up measurements of both conducted and radiated EMC
    A radio amateur friend of mine purchased solar power installations this Spring together with a neighbour.

    They included the checklist in the contracts, and consequently received installations which did not cause RFI.

    Last edited: Jul 3, 2021
    KG4RRH, W0PV and K0UO like this.

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