Originally Posted by MapleSugarMan
Thanks so much for taking the time to write your responses.
A few other details that folks have asked for:
The controller is a Solar
'n Play rated for 21 amps max.
are 140 watt Nature Power brand by RDK.
Wire from the panels
to the controller is 20 feet @ #8 (Recommended by the manufacturer of the controller.)
Wire from the controller to the master switch is 2 feet @ # 10 or 12 (permanently installed by the manufacturer.)
Wire from the switch to the batteries is (I think) # 4 or 6 battery cable. :
Wires are fine, only subject to checking voltage drop in the #4/6 that we do not know the length of.
Do you have the controller described in the attachment? That seems to be a basic cheap
1-stage "cut-out" controller. This even more basic that a PWM controller. Forget my suggestion of connecting in series; that will not help with this controller.
If/when you want to get a better controller, consider spending US$107 in a Victron MPPT
75/15 that is much better for what you have. It will let you run both panels in series; it will extract more Ah per day from those panels; and it will keep batteries at absorption voltage for a reasonable time.
Do not assume that the controller needs a 20 amp fuse to protect itself. Many controllers specify a fuse with a rating that is bigger than the published rating of the controller (at which the fuse should not blow). For example, the Victron 75/15 MPPT
controller is rated to handle 15 amps of current
to the battery but the internal fuse is a 20A fuse.
If you replace fuseholder and install 25A or 30A fuse close to the switch end of the #12 wire that will protect that wire (ampacity 31.2A asumming 105°C insulation
space, per table VI-B of ABYC E-11) from current
coming fro the battery, which is the big issue. The question is whether that is fine with the controller, but that is not very likely to be an issue.
If I guess correctly from the manual that this is a "cut out" controller that cuts out (instead of keeping voltage constant) when the battery reaches absorption voltage, then your batteries will not charge in full. I suggest that you check voltage at the battery terminals over time before and 30 miniutes after the moment when the LED turns green. If voltage stays at 14.4V then you have a 2-stage controller. If it drops to below 13V then it is a basic cutout controller that is not good for the batteries.
Ignore the fuse at battery end (sized for the fat wires it protects or smaller) at your own peril. MRBF fuse blocks are cheap