My Solar Install
Summary of parts/pieces. Tristar mppt-45 controller 250w Conergy 250p 24v panel 10awg mc4 connector wire from roof to controller, wanted 8awg, but couldn't get them locally and shipping was ludic...
Forum Discussion
Almot wrote:AlbertaNewbie wrote:
my single panel is putting out over 16amps, so 3 would put me over the allowable rating of 36amps Isc per the tristar manual. Current rating of the controller must be 125% at or greater than solar arrays short circuit current output (Isc).
Correct estimate though achieved with incorrect methods :)...
The panel is putting out 8.5 Isc, period. 45/8.5/125%= 4-something panels in parallel with 8.5 Isc each.
There is also input Voc limit - 150V? for this unit, don't remember - which means that in series you can't have more than 4-something panels again, because Voc is probably around 30.
But you can't really have 4, here is why. With charging voltage as low as say, 13V, and controller efficiency 5%, and wire losses 2%, the controller will clip the amps when array WORKING wattage (not name plate wattage) hits 45*13*107% = 625W, i.e. 750W will be an oversizing. This is what the Morningstar calculator was trying to tell you.
Now, oversizing isn't necessarily a bad thing. MPPT 45 clipping results in diminishing returns of daily AH when arrays are getting progressively larger than total 45A post-MPPT. But such installs are still possible and often useful, see what Morningstar and other sources say about oversizing the array wattage. This was discussed here a few days ago. My guestimate for safe oversizing with MPPT controllers and flat installs is at least ~10-15% at sea level, i.e. about 720W in your case. Smkettner here has 700W flat array and 60A MPPT, ask if he ever saw more than 40A post-controller ;)
Btw, 10 AWG wire will force you to do series wiring when adding more panels. Otherwise you'll lose some amp-hours.
Alright, off the soap box. A question: how did you attach big plastic nut on strain-relief cable grips (it can't be seen on the photos) INSIDE the crate of the fridge vent?
Thanks for this. In regard to the plastic nut in the fridge vent, I didn't use it, I sized the hole small and threaded the keeper in then used pvc glue to bond the 2 together. After all was done I dicored it as well. Should have just ripped the screen off and used the nut after I dropped the screwdriver through but didn't have any expanded mesh that was light enough to repair.
