2 solar panel one not working when connected to system. (1 Viewer)

Jul 14, 2021
14
4
Funster No
82,685
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rollerteam
Hi Im very confused, with the sun being out I thought I check my solar panel on my Swift Select 184, setup is the 40watt factory fitted panel and one after market 100w panel connected using mc4 y connector to factory fitted cables to the Sargent system via a victron http.
having noticed that lately with the beautiful Scottish sunshine lately my controller is getting about 47watts 2.7-3 amps so I checked my panel separately and it looks like the 100w panel is only one powering the system, however both panel tested are outputting watts etc when unconnected from the system. Please help or explain if I being stupid and shouldn't be near electrical stuff.
 
Sep 17, 2017
5,660
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Birmingham, UK
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When panels are mismatched, they produce different currents and voltages at different loads. One will drag down the other. You might find they're both working, but in some conditions, the combined efficiency is so bad that you're better off with one. Also, if it's a PWM charger (not the more modern MPPT) it'll make it worse.

Although at this time of year in Scotland, you're probably only getting about 50% max power in the middle of the day anyway.
 

Stealaway

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Jan 8, 2013
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Have you checked the connection between the two panels. I've had problems with those MC 4 connector's
 
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OP
stevenmac08
Jul 14, 2021
14
4
Funster No
82,685
MH
rollerteam
Yes disconnected both panels and test separately both panel were banging out over 2 amps for 40w over 2.9 amps for the 100w. however it looks like the 40w panel isn't doing much when connected up

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Sep 17, 2017
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If they're connected in series, the maximum current will be the current of the lowest panel (but you can add voltage).

If you connect them in parallel, the voltage from the lowest panel will limit the voltage on the other panel (but you add current).

Mismatched panels often mean you get quite a bit less than the sum rating of the individual panels.
 
Sep 17, 2017
5,660
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Birmingham, UK
Funster No
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So if the 100w panel is designed to be higher voltage, it'll be dragged down to whatever the 40w is generating. So it might be seriously hobbled. In some scenarios, you could be losing nearly as much as the 40w panel is providing.
 

Lenny HB

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Oct 18, 2007
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The Sargent controller has a max of either 100 or 120 watts depending on the model but that won't make any odds at this time of year.
Try connecting each panel separately to the controller to make sure they are both working.
 

Lenny HB

LIFE MEMBER
Oct 18, 2007
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On the coast in West Sussex
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So if the 100w panel is designed to be higher voltage, it'll be dragged down to whatever the 40w is generating. So it might be seriously hobbled. In some scenarios, you could be losing nearly as much as the 40w panel is providing.
Assuming the panels are similar the loss will only be small.

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