Updated May 2017

If connected incorrectly, solar regulators with current shunts can register twice the true solar input.  Here’s why – and how to fix it.

Some years ago a magazine article outlined a solution to a non-existent problem. That Australia’s sun can produce excess output that overheats solar regulators. It quoted a Plasmatronics 20 amps regulator as indicating 36 amps, but from an 18 amp solar array. The article suggests adding a cooling fan, This, it claims enables the regulator to cope.

In reality the system’s 16-18 amps is registered twice. Once as it flows through the PL 20 regulator. And again as it flows through the associated current shunt. (Forum members sometimes post similar examples.)

Under rare sun conditions, solar modules do briefly produce over their normal voltage. Their output current, however, automatically limits. They are thus not damaged by excess current. They block it. Solar regulators do likewise.

A cooling fan has merit where air flow is marginal. It is otherwise not needed. It will not, however assist to increase output.

Solar regulators with current shunts – return battery connection

Solar regulators with inbuilt monitoring must have the battery return path go directly to that battery. If a current shunt is used, it must by-pass that shunt. Details vary between solar regulators.

It is not feasible to show how do this in article form. I include full details however in Solar That Really Works! (for cabins and RVs) and Solar Success (for home and property systems). It is also covered in Caravan & Motorhome Electrics.

Our other books are the Caravan & Motorhome Book, the Camper Trailer Book. All are updated at least every second year. For information about the engineer/technical author please Click on Bio.