Here is a pic of my junction box showing the diodes.It's a 100 watt panel.My question is: Is the left one a bypass diode and the right one a blocking diode? Could either one cause low power output? diodes.JPG
bypass and blocking diodes
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If either has failed then the voltage and current output of that panel would be lower than nameplate rating.
More than likely a failed diode will create an open circuit and isolate a number of the pv cells depending on which one failed. -
Blocking diodes are seldom. if ever, used in a PV panel. Blocking function is nearly always performed in the Charge Controller
Bypass diodes are often found in the J-box of the panel. They should be a Schottky type of diode, lower loss and heat generation than a plain diode.
use conventional means to test them
Last edited by Mike90250; 05-06-2017, 07:14 PM. Reason: Blocking function is nearly always performed in the Charge ControllerPowerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-ListerComment
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were shadowed. The diodes should run completely cold in sunny operation, carrying no current. A meter would
show half the panel output voltage across each. If a blocking diode were in use, it would be in series, not parallel,
and show something like 1V forward drop when current was output.
If a bypass diode were to open, it would have no effect on sunny operation; an open blocking diode would stop all
current. A shorted bypass diode would run hot and eliminate about half your panel output voltage. A shorted
blocking diode wouldn't prevent operation, but would allow back (battery) current at night. Bruce RoeComment
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It's very odd that the Voc and Isc are within specs but under load I can only get about 30 watts out of this 100 watt panel.See my previous post : low solar panel output
Voltage under load is about 14V and 2A current The only thing I can think of might be a COLD solder joint on one or more of the tabbing wires or buss wires.Comment
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It's very odd that the Voc and Isc are within specs but under load I can only get about 30 watts out of this 100 watt panel.See my previous post : low solar panel output
Voltage under load is about 14V and 2A current The only thing I can think of might be a COLD solder joint on one or more of the tabbing wires or buss wires.
That might not show up on a simple OC/SC test. Bruce RoeComment
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OK It shows 10.6 across each diode, which is about right, but under load I still can't get over 31 watts .I guess I'll just give up on this panel.Anybody want it? May you will have better luck.Comment
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