Roy is correct; there is a voltage drop across a blocking diode.
This was one of my concerns when I first decided to add a blocking diode to my panel wiring. I still ordered a 30Amp blocking diode, with the intent to test it prior to installing it. I sat down at the test bench and tried 3 different voltages to see how much the loss would actually be.
Here are the results of my original test (kept them in my Solar note book):
0.18VDC loss @ 12VDC supply voltage (12.33VDC Before, 12.15VDC After diode)
0.2VDC loss @ 24VDC supply voltage (24.5VDC Before, 24.3VDC After diode)
0.3VDC loss @ 31VDC Supply voltage (31.7VDC Before, 31.4VDC After) Actual Solar Panel
I was anticipating a much larger loss based on my research, but since the actual loss was well below what I read, I installed it anyway. Since my solar panel is a high voltage panel (31VDC) I needed to use an MPPT controller, which also gives me an extra 42% of charging power.
The batteries are usually in the “FLOAT” stage by 2PM each (sunny) day. If you do decide to add a blocking diode, be forewarned that they need to be mounted on a heat sink as the do get hot.
Originally Posted by RoyBraddy
Blocking DIODES like in MUSTANG65s solar block diagram is a two edged sword. The Blocking DIODE will BLOCK your DC VOLTAGE coming from the load side from getting back into the solar panels as stated. The DIODE will also drop your DC VOLTAGE going the other way being produced by the SOLAR PANEL by .7VDC.
2013 Jayco Eagle 284BHS
250Watt Grape Solar Panel, MorningStar MPPT 60 Charge Controller
1500 Watt Ramsond PSI, 2 Trojan T145 Batteries (260Ah)
2 - AirSight Wireless IP Cameras (used as rear view cameras)
EnGenius WI-FI extender, D-Link wireless (n) modem
MagicJack Internet Phone
2012 Ford F150XLT, EcoBoost w/3.73
157" Wheel base, HD Towing Package
Our Solar Album http://www.jaycoowners.com/album.php?albumid=329