Instructions / Assembly

MNPV6 Disco / -250 / AC Disco Installation Instructions Cont.
5 | P a g e 10- 1 8 3 - 1 R E V : B
Circuit breaker selection.
When selecting breakers for use with the MidNite combiners, first check with the PV manufacturer to determine
the proper “series fuse”. The term fuse is used even though you are probably using breakers. This is a carryover
from UL terminology. MidNite Solar offers PV combiner breakers rated at 150VDC, 300VDC and 240 VAC.
150V DC breakers come in these amperage ratings. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 30, 40, 50, 60 and 63.
Part numbers for breakers are as follows: MNEPV10, MNEPV15, MNEPV20 etc, the last 2 digits being the amperage
rating of the breaker.
300VDC breakers are twice as wide as the 150 volt versions. The wire input and output are located on the top side. These
breakers come in 7,10,12,15,20,30 and 50 amp sizes. Part numbers are MNEPV15-300 etc. Other sizes are available on
special order.
AC breakers come in 10, 15, 20, 30, 40, 50 and 60 amp sizes. Part numbers for AC breakers are as follows: MNEAC10,
MNEAC20-2P etc.
IMPORTANT! Polarity of the din rail DC breakers. The DC breakers supplied by MidNite Solar are custom
manufactured in Lesotho Africa by CBI. These breakers, like many other DC breakers are polarity sensitive. This
means that they need to be installed correctly in order to insure that they will be able to trip if called upon to do so.
In a PV combiner the + sign marked on the breaker connects to the PV positive output. The same breaker when
hooked up to the battery circuit (not in a PV combiner) hooks up a little different. The + sign hooks up to the
battery plus. This hook up is not obvious. The + sign designates the highest potential should be connected there.
This is an easy one to determine in a PV combiner. Follow the current path through the combiner, into the PV
input of a charge controller and out of the controller to an output breaker and then into the battery plus. You would
think that the end of the output breaker connected to the controller would be at a higher potential than the battery
plus. In normal operation this is true. The main job of this output breaker is to trip when and if there is a
catastrophic failure. (Any manufacturer of power electronics will tell you that power electronics can fail). If the
output breaker fails to trip, you are at risk of fire from the output wires burning up. When a charge controller fails,
they always short from positive output to negative output. Since these two terminals inside the charge controller
are normally connected up to a very large battery bank, you have a direct short across the battery bank if the
controller fails. During this condition, the controller is acting like a piece of wire. The battery positive terminal is
the highest potential! Make sure that the plus (line) of the breaker is connected to the battery plus terminal. If the
breaker is connected backwards, it can fuse in the closed position as it attempts to open. That could ruin your entire
day!
Combiner wiring.
There are numerous ways to hook up a PV array. There are no “best” or “correct” ways to accomplish this. They
all have merit. For instance if the battery bank is 24 volts and you have six 24 volt PV modules, what would be the
best way to wire them? For this installation we will assume a Classic 150 or similar charge controller that allows
the freedom to change PV array voltages.
1. This array could have all 6 panels hooked in parallel using the MNPV6 combiner and 6 MNEPV15 breakers.
This array would be ok if situated close to the battery bank. It requires larger wires than would a higher voltage
array, but has the advantage of being directly connected to the battery bank in case the controller fails. You can
also substitute a PWM controller for the MPPT in the event it becomes necessary.
2. The array could be wired in three strings of two panels in series for a 48 volt nominal array. This is a very
common installation and could be made with 3 breakers. This hook up is safe from a cold VOC standpoint, but you
cannot directly connect it to the battery bank. You cannot easily hook up a PWM controller either. If the PV array
is between 30 and 100 feet from the battery bank, this hook up may offer the best power production.
3. The array could also be hooked up in two strings of three modules in series. The MNPV6 disco / MNPV6-250
Disco and two breakers would accommodate this array. You have room to grow this system without adding