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Re-wire suitcase panels in serial

mptx

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I have 2 Renogy Eclipse suitcase panels; one is 100 Watts (2X 50 watt panels) and the other is 200 Watts (2X 100 watt panels). I want the option to connect both together serially which means rewiring the 200 Watt suitcase panels in serial. What’s the best way to do this? My plan so far is to cut the connecting PV wire and swap 2 of the strands serially which then leaves a positive and negative free. These remaining 2 strands (one from each panel will then be the serial connections; one to the 100W suitcase and the other to the charge controller.

Questions: Does it matter which panel provides the positive wire and which the negative assuming I continue that sequence to the 2nd suitcase? Do the diodes in each box somehow dictate the direction of the wire connection? Not sure if this will make total sense so let me know what questions you have back to me.
 
The diodes fo not force polarity, they just truncate feedback of voltage for three, maybe four reasons depending on how you describe it. The diodes protect the panel (ish), keep the battery bank from discharging/powering the panel, and have a beneficial effect in shady conditions. All the same root electrical principle.

You might want to do the 50W panels in series and parallel them with the 100W panels to get them to play well together. Some would say series a fifty-watt with each 100W panel for 2S2P but I don’t think that’s preferred though I can’t recall why I think that.
 
So, I think you are saying to leave the 2 50W panels in parallel as they are now and connect that combination in series to the other 2 100W panels. Result is 3 100W panels connected in series with Imp within 1 Amp of each other. Sound right?
 
No

One way of using your mismatched panels is connecting the two 50W panels in series to make 100W, and parallel those with the two 100W panels- which should minimize reducing output. You sorta have three 100W ‘strings’ in parallel, though two of the strings(that really are not strings) are single 100W panels.
 
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I didn’t think this made sence until just now I took a closer look at that 100W suitcase. It is wired in series. I only looked closely at the 200W suitcase wiring and assumed they were both parallel, but no. Thanks for pointing out my mistake.
 
In my signature block, there’s a ink for mismatched panels that have math.

Whether or not this works in series or parallel will really depend on the voltage of the panels. My guess is the 50 watt panels have a voltage different enough to skew that output so that this will not be 300 watts in parallel or 300 watts in series. A couple volts will get you close, like a theoretical limit of 280 watts, but a 33 Volt panel 100 watt panel to a 16 volt 50 watt panel will get you a lot less.

Sometimes its easier and cheaper to get a second PWM. Whether you do or not depends on how closely the voltage matches.
 
I’m doing the math now and it looks like the 100W suitcase won’t work here. I need to stay under the 15A cap of the AC200MAX and connecting the 3 panels parallel will blow through that. Time to get a couple more ridged 100W Rich Solar panels I think, and use the 100W suitcase for the travel trailer. (y)
 
Whether or not this works in series or parallel will really depend on the voltage of the panels. My guess is the 50 watt panels have a voltage different enough to skew that output so that this will not be 300 watts in parallel or 300 watts in series. A couple volts will get you close, like a theoretical limit of 280 watts, but a 33 Volt panel 100 watt panel to a 16 volt 50 watt panel will get you a lot less.
Much better explanation

FWIW I’ve come to the conclusion- as OP has- that just buying matched or nearly matched panels (or another SCC) is worth more than the money that might be saved cobbling things together. $200 for panels is way different today- not that much money- than it was when you could still buy a decent 1- or 2-year usable used car for $500. Now that’s $5000+ which makes the panels $20…:rolleyes:
 
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