An article in the March issue of The Wanderer suggests a “solution to over heating in Solar Controllers, due to the high amperage input from the Australian sun.” It goes on to suggest the use of thermostatically-controlled fan cooling for this purpose - and indirectly that the input of a solar regulator may be safely increased by so doing.

The article is seemingly predicated on four Sharp 80-watt solar modules whose output current has been ascertained from the readout of a Plasmatronics PL20 regulator and current shunt. These components have perhaps been incorrectly installed as the current indicated is massively too high.

The incoming current is possibly being recorded twice: once as it passes through the regulator and again it as passes through the shunt; or the indicated load current and charge current is possibly being shown as combined. But whatever the cause, the current input cannot possibly be the 45 amps quoted in the article and upon which the assumption of “abnormal heat build up as a result of 43 amps going through a 20-amp controller” is seemingly based.

Firstly, an input current exceeding 40 amps is more than twice the maximum typically achievable from four paralleled (conventional) 80-watt modules regardless of brand. Secondly, a PL20 regulator is automatically current limited to 20 amps. It cannot and will not accept a charge rate higher than 20 amps.

It appears likely that the PL20 in question actually is also working within its intended temperature range. The readout of a PL progressively blackens to invisibility as it approaches maximum input current, increasingly reducing its ability to be read. That it obviously can be read suggests the input current is somewhat less than 20 amps.

Plasmatronics is concerned that this article may inadvertently lead to a misunderstanding of the operation of its regulators and has contacted the CMCA seeking an opportunity to respond.

I have prepared the following ‘interim note' after telephone discussions with Plasmatronics and senior CMCA Management. A comment is expected to follow from Plasmatronics (and will be published in the Letters section of the April issue of The Wanderer ) as well as on this website.

Collyn Rivers W8054

Interim Note to Members

It is not possible for a Plasmatronics PL series regulator to accept input current greater than its designated rating: e.g. a PL 20 regulator will limit input to 20 amps. There cannot thus be 'abnormal heat build up' as a result of '43 amps going through a 20-amp (PL20) regulator.'

The above is not true of all regulators. Attempting to exceed the rated output of an unprotected regulator by fan cooling may result in such a regulator being damaged or destroyed.

The suggested method of fan cooling may have merit in installations where normal air flow is marginal but damage is likely to follow if that fan were to stop or fail. Improved natural ventilation seems a safer approach.

Whilst it is common to derate regulators where air temperature around the regulator exceeds 40 degrees C or so, the current output of most solar modules has typically decreased by 25%-27.5% at that (ambient) temperature anyway. This decrease may be more than the recommended input current derating, however derating is likely to involve limiting various combinations of input and load currents).

Heat by and large reduces the output from solar modules. It is light, not heat, that results in their generation of electricity.

I confirm that Plasmatronics and/or myself will assist in advising on resolving what appears to be an incorrect implementation.

Collyn Rivers W8054

UPDATE

Following a check by Plasmatronics, the PL20 had in fact been installed such that it was recording the incoming solar charge twice. Plasmatronics' response (Letters, next issue) explains what was happening and why.

Collyn Rivers