DIY Manual

23 | P a g e 10-543-1 REV A

DIY Manual

3) Series-Parallel Circuit: A series-parallel configuration is basically like it sounds … PV

panels wired in series, and two or more PV strings wired in parallel.

To conclude, combining or paralleling is a wiring configuration to join multiple PV panels or strings

to create one common electrical output – PV positive and PV negative – while maintaining the

string voltage. Remember -- in parallel the voltage stays the same. The MidNite combiner box is

an excellent means of combining (paralleling) multiple PV panels or strings to achieve one PV

positive and PV negative output to the charge controller.

Reverse-Current Protection

A short circuit in a PV module, faulty wiring, or a related fault may cause reverse-current in PV

strings. This occurs if the open-circuit voltage of one string is significantly different from the open

voltage of parallel strings connected in the same PV array. The current flows from the healthy

strings to the faulty one instead of flowing to the inverter or charge controller. Reverse- current

can lead to dangerous temperature rises and fires in the PV module.

There is no risk of reverse current when there is only one PV string. When there are two strings

with the same number of PV modules connected in parallel, the reverse-current will be always

lower than the maximum reverse current. The National Electrical Code (NEC) Article 690.9

requires reverse-current protection when 3 or more PV strings are in parallel.

79Voc, 19.6A

(Isc)

158 Voc, 9.8A

9.8A + 9.8A = 19.6A

Panel Specs

39.5Voc, 9.8A Isc

Series-Parallel Circuit

158V, 9.8A

158V, 19.6A

158V, 9.8A