RF Shielding on a Mains Inverter

Wednesday 19 September 2012

The mains inverter we have for our solar system generates a lot of RF interference on our ham radio transceivers and also across the entire HF spectrum.

The inverter body has plastic ends and very little filtering for the mains output and also on the DC input lines to stop it radiating unwanted frequencies.

To try to reduce the level of unwanted RF interference we decided to replace the plastic ended enclosure with a diecast aluminium box and add an additional mains filter to the output and also ferric rings on the DC inputs.

The photo below shows the inverter transformer and main circuit board. The old case can be seen at the top of the photo.

Mains Inverter Shielding Conversion

The new case was milled to add a fan hole and also exit hole for the cooling fan.

Mains Inverter Shielding Conversion

The components were fitted to the new case and the transistors on the top board fitted to a solid aluminium block with thermal paste and this was bolted to the main case.  The new mains filter was fitted along with new lenghs of 35 Amp DC cable for the inputs.

Mains Inverter Shielding Conversion

A large heat sink was then bolted to the top of the box (upside down on the photo) and this was also covered with a very thin layer of  thermal paste to aid heat transfer.

Mains Inverter Shielding Conversion

The box was then installed in the solar cupboard and after fitting the lid and reconnecting the power and mains output cables we found the level of RF interference had been greatly reduced.

Mains Inverter Shielding Conversion