I have 12- 270 watt panels that are about 75ft from charge controller [outback 80]
What size of eather in line fuss or breaker should I have before the controller. I was also thinking of having
at my combiner box [ at the panels] a 15amp fuss for each of the 3 panel hook up . One more thing.
What size of breaker or fuss would I need from controller to battery bank. I'm using a Outback 3048 inverter and 8 golf cart 230amps 6 volt batteries in 48volt .series.
What would be a good size of fuss from bat to inverter. Thank you
Submitted
9 years 10 months ago
Comments
Hi Chad,
You have a couple of good questions here.
First, let's look at the PV source and PV output circuits. Assuming that your system is comprised of three strings of four modules each, you are required to install overcurrent protection in each of the PV source circuits (strings). The rating of your OCPD is calculated by multiplying the module Isc by 1.56 and choosing the next standard size fuse above this value. As you already mentioned, it would be good practice to install a 3-string fused combiner at the array to simplify the installation (allowing you to run a single set of conductors from the array to the charge controller). The size of the OCPD protecting the PV output circuit is calculated in a similar method as the PV source circuits. Take the PV output current (sum of all PV source circuit currents) and multiply by 1.25. If you are going to use a breaker rated for continuous load, no other calculations are needed - choose the next standard DC breaker size above what you just calculated. If you use a fuse, multiply what you just calculated by 1.25 (essentially multiplying the PV output circuit by 1.56) and choose the next standard fuse size above this value to protect the conductors.
Second, regarding the OCPD between the battery bank and the inverter, you must determine the maximum continuous current that the inverter would draw from the battery bank. Once you know the current you can choose the proper conductor and OCPD to protect the conductors. In your specific case, the Outback 3048 inverters (note, there are a few of them) have a 30-minute overload capacity of 3,200 watts AC. The lowest voltage of the battery bank the inverter will operate at is 42 V. Therefore, the continuous operating current in this situation would be 76 A. The conductor for this circuit would have to be able to handle 125% of this current resulting in a current carrying capacity of 95A. The next standard size DC breaker above this is 100A.
For further information, please refer to the Outback Installation Manuals for the Charge Controller and FX Series Inverter/Charger. All of the operating parameters were found in these documents.