How To Install A Fixed 12V Solar Panel For Your Dual Battery System

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Last time, we looked at the details of our dual battery installation in our Isuzu NPS truck.

This time we’ll see how easily a fixed 12V solar panel can be wired into a REDARC Manager30.

Regulator-Free Zone

We had an old 60W solar panel that had given us faithful service for many years. This panel had done a lap of Oz for 12 months, being bashed and bounced from one side of Australia to the other.

It had a solar regulator and a long cable, terminating at alligator clips.

A tip for you:

If you have a 12V system and are powering the second battery from the cranking battery, always attach your portable solar panel to the cranking battery. Why? Alternators do not always fully charge the cranking battery.

However, a solar panel with a regulator will keep your cranking battery topped up, then any excess will automatically flow to your second battery as needed.

Charging starter & second batteries using 12V Solar Panel.
Charging starter & second batteries using 12V Solar Panel. This panel travelled all around Australia with us and is the same panel you’ll see mounted on our truck.

The plan was to temporarily mount the 12V solar panel to the top of our storage boxes. Eventually we would replace it with a 150W fixed panel. With an Anderson plug already in place for solar input to the Manager30, swapping panels would be easy.

Anderson plug for 12V Solar Panel input.
Solar panel input is the Anderson plug at top left.

The other advantage to having an Anderson plug is that we can use the solar panel off the Wedgetail Camper if we need to top up our second battery. And now we have a REDARC solar blanket, so we can connect that as well.

Now the REDARC Manager30 has a built-in solar regulator. So I disconnected all cabling and removed the regulator. Then I used 8AWG twin cable to connect directly into the solar panel’s terminal box. (For detailed information on sizing automotive wiring plus a Cable Size Calculator, go here).

Wiring our 12V Solar Panel.
Wiring our 12V solar panel directly to the terminal box. Regulator has already been removed.

Whenever you run cables, it’s worth protecting them from rubbing. The last thing you want is a cable’s insulation rubbing through and shorting out on the truck body. So we covered the cables with heat shrink, then cable tied them to the underside of the solar panel.

Neoprene isolators on 12V Solar Panel brackets.
Protecting the cables with heat shrink and fastening them to the underside of the panel. Note the closed cell neoprene strips on the angle brackets.

Keeping It In Place

Two lengths of aluminium angle served as mounting brackets. Using M6 stainless steel button head bolts and Nyloc nuts, we fixed the angles to the panel. Then we ran a couple of strips of adhesive-backed closed cell neoprene along the underside of each angle.

The closed cell neoprene prevents rubbing between the angle and the top of the storage box.

We drilled four holes through the top of the storage box, fitted the bolts and the solar panel was installed. Run some SikaFlex around each hole before fastening to prevent water leakage.

We had already fitted cable glands for the cables to run into the 12V dual battery panel. So it was just a matter of running the cables and terminating them at an Anderson plug.

12V Solar Panel mounted on our truck.
12V Solar Panel mounted on our truck storage boxes.
12V Solar Panel showing neoprene between bracket and top of storage box.
12V Solar Panel showing neoprene between bracket and top of storage box.

All cables were then covered with split corrugated tubing as further protection and the job was done.

How Effective Is It?

Keep in mind our dual battery system is running a 350W REDARC inverter, LED lights in the cab and storage boxes, a Cel-Fi GO mobile phone repeater in the cab and 2.4A USB outlets in the cab.

This might sound like a lot of equipment, however current draw is actually quite low.

The dual battery system is charged from the truck’s batteries when we’re on the move. Remember, the REDARC Manager30 prioritises solar inputs. So whatever charge the 60W panel can supply, is used to charge our second battery.

The 60W solar panel is doing the job. It’s ample for our application. So our temporary installation is now permanent.

Of course, if we’re stopped in one place for a while we can always use the Wedetail’s 200W solar panel or the 115W REDARC solar blanket to top up the second battery. However, we haven’t needed to do this yet.

Summing Up

So there you have it. A complete 12V second battery installation in a 24V truck.

Yes, it can be confusing. But if you’re handy and practical then you can do it. Just think it through and take a step-by-step approach. Good luck!

My Generator has a wide range of REDARC products… battery management systems, solar blankets, solar panels and more.

NOTE: REDARC send us products to review from time to time. (That said, we purchased the REDARC Manager30 mentioned in this article.)

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