Solar regulators with current shunts – how to fix misleading readings

Oct 2, 2019

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 fix it.

Some years ago a magazine article outlined a solution to a non-existent problem. The article claimed that Australia’s sun may produce excess output. Furthermore that it can overheat solar regulators. It quoted a Plasmatronics 20 amps regulator as indicating 36 amps. The solar array, however, was only 18 amps.

The article misrepresented that happening. It wrongly assumed 36 amps output was feasible. It also advised adding a fan to cool the regulator. In reality, that system’s actual 16-18 amps were registered twice. Once as it flowed through the solar regulator. Then again. It flowed through a current shunt. That shunt’s output also, was to that regulator.

Solar in areas close to a large expanse of water or sand may produce freak high voltages. This happens if direct irradiation is reflected back to light scattered clouds. Then down again. Solar voltage may thus briefly escalate. Their output current, however, is limited automatically.

Solar regulators likewise block excess current. That is necessary for small capacity lead-acid batteries. AGM and lithium batteries, however, accept high currents without harm.

RB Books advises you to use a cooling fan for a solar regulator in tropical areas where airflow is also limited. You do not need one otherwise.

Battery return connection

For solar regulators with inbuilt monitoring, battery positive and negative returns must be direct to that battery. If you include a current shunt, your battery return must bypass that shunt. Unless you do, the solar current is recorded twice. Details vary between regulators.

It is not feasible to show how to do this in article form. Full details, however, are in Solar That Really Works! (for cabins and RVs). Also in Solar Success (for home and property systems). Furthermore, 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. 

Caravan & Motorhome Electrics

The essential handbook for anyone with an RV of any kind.  Everything you need to know to make the electrics in your rig work for you.

eBook versions

Paperback version

The book retailers set their own prices which can vary substantially. We'll aim to keep a selection of the better prices above.

Any bookshop, whether online or bricks and mortar, can order copies of Caravan & Motorhome Electrics.  Just ask.
ISBN: 978-0-6483190-8-5

Solar That Really Works!

Solar that Really Works! covers the design, installation and use of solar in cabins, camper trailers, caravans, fifth wheelers, campervans and motor homes.

eBook versions

Paperback version

The book retailers set their own prices which can vary substantially. We'll aim to keep a selection of the better prices above.

Any bookshop, whether online or bricks and mortar, can order copies of Solar That Really Works!  Just ask.
ISBN: 978-0-6483190-3-0

Caravan & Motorhome Electrics

The essential handbook for anyone with an RV of any kind.  Everything you need to know to make the electrics in your rig work for you.

eBook versions

Paperback version

The book retailers set their own prices which can vary substantially. We'll aim to keep a selection of the better prices above.

Any bookshop, whether online or bricks and mortar, can order copies of Caravan & Motorhome Electrics.  Just ask.
ISBN: 978-0-6483190-8-5

Solar That Really Works!

Solar that Really Works! covers the design, installation and use of solar in cabins, camper trailers, caravans, fifth wheelers, campervans and motor homes.

eBook versions

Paperback version

The book retailers set their own prices which can vary substantially. We'll aim to keep a selection of the better prices above.

Any bookshop, whether online or bricks and mortar, can order copies of Solar That Really Works!  Just ask.
ISBN: 978-0-6483190-3-0