Thursday 04 September 2014
Radio and RF | Solar Power |
Following from the Mastervolt Soladin 600 Inverter RF Interference post about the major RF interference problems generated by the Mastervolt Soladin 600 tie-in mains inverter we have now resolved the RF interference by replacing the unscreened and unearthed plastic case on the inverter with an earthed metal case and installed filters on the DC input and AC outputs.
The Mastervolt Solardin inverter was housed in a plastic case and didn’t have any form of internal screening against RF interference being radiated from the unit so we thought that the best option would be to remove the circuit from the plastic case and install it in a metal box which could then be connected to the mains earth to limit any RF transmissions. We purchased a zinc coated steel case from RS Components (uk.rs-online.com/web/p/instrument-cases/0232024/) which has air vent holes to allow air circulation to cool the inverter.
We fitted a mains RF filter onto the output between the inverter and the connection to the mains electric and fitted this into the base of the case.
After fitting the new case on the wall and reconnecting the mains and solar DC input wires we ran tests using the Rigol Spectrum Analyser and found that the levels of RF interference had dropped from around -22db to -50db but when we moved the test antenna closer to the DC input wires we found that they were radiating a wide signal which peaked around 10Mhz with harmonics on higher frequencies.
The output mains wires didn’t have this RF signal radiating so the source of the interference was now confirmed as the cables going to the solar panels from the inverter. This was making a large radiating panel on the roof and swamping my Yaesu FTDX3000 transceiver which has a long wire antenna attached near the solar panels.
With the metal case fitted there wasn’t any reduction in the RF interference on my FTDX3000 so we had to find a way to block the RF from going back up the DC feed into the panels.
After researching a number of websites for both solar and ham radio we found references to EMC/EMI filters which are fitted on the on the DC side of PV inverters.
RS Components stock a Schaffner FN2200 Chassis Mount Power Line Filter (http://uk.rs-online.com/web/p/power-line-filters/7546064/) which is rated at 28 Amps and up to 1200 volts which is much higher than the output from our current panels but gives us plenty of room to expand in the future.
I ordered the filter which arrived today and after installing this we found a large improvement in the RF noise level but there was still a small signal radiating between the base of the inverter case and the filter inputs. To resolve this we installed a fine aluminium mesh behind the filter and inverters input cables and wrapped this around the cables creating a grounded faraday cage.
After running tests on the spectrum analyser to get a background RF noise base level we turned on the inverter and DC from the solar panels and found that the background RF levels around the house didn’t change.
I then tried all of the HF radio bands which had previously been unusable on my Yaesu FTDX3000 transceiver and found that the background noise and signal which was swamping the radio had gone!
Hopefully the installation of the additional filters and installing the feed in inverter in a metal case will not cause us any further problems.
The screen shots below are from the Rigol Spectrum Analyser (click to enlarge)
The circuit from the PV panels to mains consumer unit.