Updated 2020

Solar Regulators with Current Shunts

If connected incorrectly, solar regulators with current shunts can register twice your true solar input. This article explains why. Moreover, how you can 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. And that overheats solar regulators. It quoted a Plasmatronics 20 amps regulator as indicating 36 amps. The solar array, however was only half that. It was 18 amp.

The article misrepresented that actually happening. It wrongly assumed that 36 amps was feasible. It advised that adding a cooling fan would enables the regulator to cope.

In reality that system’s 16-18 amps is being registered twice. It is being registered once as it flows through the solar regulator. It is then being registered again as it flows through a current shunt. Caravanner’s forum members sometimes post generally similar examples.

Solar modules may briefly produce over their normal voltage. Their output current, however, automatically limits. Solar modules are thus not damaged by excess current.

Solar regulators programs can likewise block excess current. You do not, however, need to do that for most batteries. One exception is small capacity lead-acid batteries. AGM and lithium batteries accept high currents without harm.

A cooling fan has merit where air flow is marginal. You not otherwise need one. Moreover it will not increase your output.

Return battery connection

If your regulator has inbuilt monitoring your battery return must be directly to that battery. If you include a current shunt, you battery return must bypass that shunt. Unless you do, solar current is recorded twice. 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). I explained it in Solar Success(for home and property systems). Furthermore, I also covered it 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.