Updated 2020
Solar Regulators with Current Shunts

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

An RV magazine article once described a solution to a non-existent problem. That Australia’s sun can produce excess output that overheats solar regulators. It quoted a Plasmatronics PL 20 amp regulator as indicating 36 amps. And that from an 18 amp solar array. The article advised adding a cooling fan, That, it claimed, enabled the regulator to cope.

In reality the system’s was producing 16-18 amps. That current, however, was being 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. And equally mistaken ‘solutions’.

Ocasionally, your solar modules may briefly produce over their normal voltage. Their output current, is however, automatically limited. Your modules are thus not damaged by excess current. Your solar regulator likewise blocks excess current flow. There is thus no risk of overvoltage battery charging.

A cooling fan has merit in tropical areas. It may be advisable if air flow over the solar regulator is not feasible. A fan is otherwise not needed. Nor will a fan assist to increase your output.

Solar regulators with current shunts – return battery connection

When installing solar regulators with inbuilt monitoring, you must have the battery return path go directly to that battery. Furthermore, if a current shunt is used, it must by-pass that shunt. Moreover, details vary between solar regulators.

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

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