How To Connect Two Solar Panels To One Battery

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We have a Wedgetail Camper with a REDARC Manager30 and a 100Ah Revolution Power Lithium battery. We figured out a way to connect two solar panels to the camper at the same time.


It’s All In The Wiring

The Wedgetail Camper has two solar inputs via red Anderson plugs. The first is on the roof. This is used when the solar panel is stored for travelling.

When the Wedgie is open, the roof hinges over 180 degrees and becomes the base of our bed. It doubles as an awning over the outside kitchen. The solar panel can be removed and used as a portable panel with a 10 metre extension lead.

Our Wedgetail Camper has 2 solar inputs, allowing us to connect two solar panels at once.
This solar input is used when the solar panel is stored for transport. We use this to plug in our solar blanket.

The panel is mono crystalline, 200W maximum output.

When used as a portable panel, there’s a second red Anderson plug on the front right corner of the Wedgie. This is where you plug in the extension lead when the panel’s being used as a portable unit.

The 2nd solar input on our Wedgetail Camper. By using both inputs, we can connect two solar panels to our REDARC BMS.
The second solar input on the front right hand side. We plug the portable solar panel into this.

In this configuration the red Anderson plug on the roof (now on the underside of the outside kitchen awning) is not used. I’ve always wondered if it’s possible to use both red Anderson plugs at the same time… have one panel connected to each.

We also have a REDARC 115W SunPower mono crystalline solar blanket. It was supplied with a 10 metre extension lead. REDARC use standard grey Anderson plugs, so I had to make a short adapter lead with a red Anderson plug on one end and a grey one on the other.


Note: For a 12 month review of our REDARC solar blanket, go here.

Why did I need the adaptor plug?

Our adaptor cable allows us to use red and grey Anderson plugs interchangeably.
Our red to grey Anderson plug adaptor.

Well we often leave the solar panel on the roof and use the solar blanket instead. It’s just easier to get out and set up compared to wrestling with the large panel. And interestingly the 115W solar blanket’s output is consistently lineball with the 200W solar panel’s output. You simply can’t beat quality…

But sometimes it would be handy to use the blanket and the panel at the same time… especially on cloudy days.


Ask The Experts!

I spoke to the people at Wedgetail Campers about how the two solar inputs were wired. They assured me they’re individually wired to the REDARC Manager30 solar input, with no tricky devices in between.

The terminal strip on top of our REDARC BMS. The solar inputs are individually wired, so we can connect two solar panels to one charge controller.
Double-checking the wiring on the Wedgetail Camper’s REDARC BMS.

All good so far.

The next step was to contact REDARC. I gave them two important pieces of information:

  1. how the solar inputs to the BMS were wired, and
  1. what type and size both the solar panel and solar blanket were.

They confirmed there would be no issues running these simultaneously. Thanks to Jessica and the tech team at REDARC for your help.


A Good Result

So now we can use the portable panel and blanket together. With both panels connected we push about 12A into the system. This is about double compared to when just one panel is connected.

How to connect two solar panels into one battery system.
Our panel and blanket working together.

Here’s a few figures for you:

Conditions:

  • Solar blanket flat on the ground.
  • Solar panel angled perpendicular to the sun.
  • Sunny day, no clouds, January (perfect conditions!)
  • The individual contributions of each panel/blanket were measured by disconnecting the blanket and checking the revised current.

Result 1:

  • Input voltage = 14.2V
  • BMS output to 2nd battery system = 11.5A total
  • Power (14.2 x 11.5) = 163W
  • BMS output, Panel connected = 6.4A (or 56% of total)
  • BMS output, Blanket connected (11.5 – 6.4) = 5.1A (or 44% of total)

Result 2:

  • Input voltage = 14.4V
  • BMS output to 2nd battery system = 12.0A total
  • Power (14.4 x 12.0) = 173W
  • BMS output, Panel connected = 6.6A (or 55% of total)
  • BMS output, Blanket connected (12.0 – 6.6) = 5.4A (or 45% of total)
The REDARC battery monitor showing the input voltage with two solar panels connected.
The REDARC battery monitor showing the input voltage with two solar panels connected.
The REDARC battery monitor showing current output to battery with 2 solar panels connected.
The REDARC battery monitor showing current output to battery and loads with two solar panels connected.

A couple of comments on these results:

  • The solar blanket’s maximum output is only 58% of our solar panel (115W vs 200W).
  • The solar panel was angled at the optimum angle to the sun, whereas the blanket was simply laid flat on the ground.
  • Yet the REDARC solar blanket consistently contributed 45% of the total input power. You could say it’s punching above its weight!


Some Considerations

You too can connect two solar panels into one system, just like we do. REDARC sell a ready-made cordset with grey Anderson plugs. It allows you to connect two panels, then connect them into one solar input.

Just check a few things first:


Are the solar panels compatible?

The best way to find out is to contact your solar panel supplier. I contacted REDARC because the solar blanket was their product.


What is the maximum rated input power of your BMS?

The REDARC Manager30 has a maximum solar input rating of 520W. Our panels are rated at 115W and 200W for a total of 315W. So we’re well within allowable range.


Is the solar input cable heavy enough to handle the higher current?

If your BMS has been wired correctly, the solar input cable should be large enough to handle the maximum input current that the BMS is rated to. You can ask the manufacturer of your camper or caravan to confirm this. The last thing you want is to melt the cable and start a fire.

Alternatively, you can check it yourself. Use this handy calculator to check the required cable size.


Do either of the panels have a built-in regulator?

If so, you might not be able to connect them. Alternatively you might have to remove the regulator. Contact the supplier of your battery management system.


In Summary

We now have the ability to re-charge our second battery system quickly and efficiently. On clear sunny days, one panel is more than enough. But on those cloudy days, you need every bit of solar power you can find.

With some simple investigation, you might find you can do the same thing…


If you’re looking to buy, My Generator have some good deals on REDARC Solar Blankets and Battery Management Systems.


 

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Any errors or omissions are mine alone.


NOTE: The REDARC solar blanket was supplied to us free, in return for a review. (That said, our reviews are always honest and authentic – we tell it how it is).


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