DIY Manual

41 | P a g e 10-543-1 REV A
DIY Manual
Example – PV system with Voc = 90V, 48V battery bank, 30A PV input that is 50’ from the
charge controller.
1. If the highest battery charging voltage is 59.2V, for example, then the MPPT
charge controller needs an input minimum of 78.7Voc (59.2V x 133%).
2. A 3% voltage drop with #2 AWG wire means an effective Voc of 87.3V.
3. A 10% voltage drop with #10 AWG wire means an effective Voc of 81V.
4. If the MPPT charge controller needs a minimum of 78.7V and the #10 AWG wire is
giving you 81V, that does not leave much headroom for a decrease in sunlight
(early morning/evening), which means a drop in Voc. If Voc falls below the
minimum needed to charge the batteries, then your charge controller will go into
a resting mode until Voc rises.
CIRCUIT BREAKERS AND FUSES
Mounting Options
MidNite circuit breakers are available in DIN rail or panel mount configurations; our fuseholders
are available as DIN rail mount. Select the mounting option based on the enclosure you have or
intend to purchase. Figure 7 shows a DIN rail mount circuit breaker and Figure 8 shows a panel
mount circuit breaker.
Polarity Sensitive
Our DIN rail mount breakers (MNEPV series) are polarity sensitive, which refers to the orientation
of the breaker versus the flow of current. A correctly installed breaker will capture the DC arc
when the breaker is opened under load. An incorrectly installed breaker will trip at the rated
current, yet may suffer internal damage in the arc chute due to being incorrectly wired regarding
polarity.
Referencing Figure 9, the wire terminal marked “++” is connected to the highest current source.
So, between the PV array and the charge controller, ++ is electrically toward the array. Similarly,
between the battery bank and the charge controller, ++ is electrically toward the bank.
Figure 7
Figure 8