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Old 08-20-2018, 09:37 PM   #1
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Daisy chaining solar panels

I have a Renogy solar suitcase 100 watt kit which consists of two 50w panels, which I bought to experiment with solar.

I recently bought another used Renogy 100 watt suitcase panel without a controller to daisy chain to my current one, and made sure they were both the same model number. I also bought a kit to crimp on some MC4 connectors, and an adaptor that takes two MC4 inputs into one MC4 output, and 30 feet of 10 gauge solar wire to make an extension cord.

In looking at the junction boxes for both of the panel kits, they appear to be different. In Panel A, the panels appear to be wired in series (negative wire on one of the 50w panels is wired to the positive of the second panel, and visa versa. There is a resistor across the positive and negative posts in the junction box. Here is a pic:

On the extension panel kit (Panel B), the two 50 watt panels appear to be wired in parallel: positive to positive, negative to negative. There is also a resistor across the positive and negative posts: Here is a pic:

Here is a closeup of the junction box:

So for a solar newbie, what's the best way to resolve this? Ultimately I want the positive leads from each of the kits to join at the MC4 2into1 adaptor to feed the solar controller. I don't mind monkeying with the extension panel since it is used and not under warranty.

Do I need to resolder the connections at the junction box of the extension panel to wire the two 50w panels in series? And what is the purpose of the resistor that is used on the main panel (A)?

Or, can I just combine the positive lead on Panel A with the Positive Lead on Panel B using the 2 into 1 MC4 adaptor (same with negative wires)?

Note, the Controller is a 20a PWM controller. I have handy a Victron 20a MPPT controller too, if that makes any difference.

Thanks in advance to the solar experts here.

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Old 08-20-2018, 10:42 PM   #2
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First off, that's a diode, not a resistor.

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Old 08-20-2018, 10:51 PM   #3
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Thanks. Again, noob here.

This video seems to suggest an option where I take the positive leads from Kit 1 (composed of two 50w panels in series) and couple them using an adaptor to the positive lead from Kit 2 (composed of two 50w panels wired in parallel), and repeat for both negative leads, and send the output into an MPPT controller, which will do its magic. Iíll have to use the Victron, not the PWM controller that came with the kit A.

Did I get this wrong?
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Old 08-21-2018, 12:19 PM   #4
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I still have a lot to learn about solar, but let me take a stab here since you're not getting any other answers. I have a Renogy 100w suitcase w/o a controller. The one you show without the controller is exactly like mine (parallel connection between the panel). It would appear to me that someone has rewired your panel shown with the controller.

Have you measured the voltage coming from the panels? Not sure why you would want a pair wired in series, which doubles the voltage out. That looks like a Voyager controller on Panel A, which is a PWM controller and doesn't convert 24v down to 12v; only an MPPT controller would do that. I realize you said you have an MPPT controller, but I still question any advantage with having one set in parallel and one set in series. I believe with an MPPT controller you want to have all panels as close to the same voltage as possible, and then let it convert it to 12v.

What are you trying to accomplish here? Just use both panels? I'd rewire Panel A to parallel and use a "Y" connector to run them into a controller. Either of your controllers should work in that case.

If I'm wrong, I'm sure someone will chime in. Hope I'm of some help here and not just showing my ignorance.

Happy trails,
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Old 08-21-2018, 02:37 PM   #5
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Thanks Mike. I wondered the same thing. Iíll experiment and report back.
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Old 08-21-2018, 07:24 PM   #6
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The diode you see is a bypass diode in the event you connect the panels in series and one of the panels gets shaded it will act as a high resistance and the diode would let the current from the other panel through. Connecting in series would increase your voltage but not your current. Connecting in parallel will increase your current but not your voltage assuming that the panels are equal. If you have different panels then one wins out over the other and there are some advantages to both approaches assuming you know what you're doing. For basic solar you are better to stick to the parallel approach. There are all sorts of calculations you need to do if you want to mix and match different panels and different configurations which would take pages to explain. You can connect your panel directly to the batteries without a controller but it is not advisable. For one you would need a blocking diode in series. If you're connecting in parallel you can use either the PWM or MPPT. The MPPT would give you more charging current.

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