crewzer wrote: »
Actually, I've been semi-automatically focusing on off-grid systems.
OK... but, allowing for the "60 A" controller's input voltage limit (~140 Voc), what should be the limit for the array's STC power spec?
Jim / cewzer
boB wrote: »
If the controllers' output current limit is working properly, the input current will be limited to no more than the output current. There may be some overshoot though that lets the input (and output) current go high for a few moments.
I wouldn't (personally) have a problem hooking up a 10,000 Watt array to the input of an MPPT controller, except it would be a waste of money a lot of times (but certainly not always up here in Washington AC). A regular PWM controller (C40 etc) would have very high peak currents though, but average or RMS current would be limited to the output current.
How about a failsafe PV array shading current limit thingie operated by a linear actuator that shades the "too-big" array when the sun is shining too much to limit current ? New product.
crewzer wrote: »
Therefore, as a practical matter, a "60 A" controller should be able to deliver ~60 V x 60 A = 3,600 W all day long. Allowing for "typical" conditions of use, a 90% array derating might be a functional and fair compromise.
Accordingly, it seems the practical maximum array size for a 48 V system with a 60 A controller would be ~4,000 W STC.
For PV array sizing guidelines, use the XW Solar Charge Controller PV array sizing tool accessible from www.xantrex.com/support.
Although the Solar Charge Controller can harvest a maximum of 3500 W, the PV array size can be as large as 6720 W (based on 48A×140Vdc=W).
Panels rated up to 48 A at 25 °C (77 °F) are recommended to allow for increases in Isc at low panel temperatures and at solar noon. Ensure that the Isc rating under all conditions does not exceed 60 A. A factor of 1.25 is applied to the rated Isc at 25 °C (77 °F) when the panel is colder than -21 °C (70 °F).
Battery CircuitThe DC-rated fuse or circuit breaker between the battery and the XW Solar Charge Controller must have a maximum size of 1.25 × 60 A (the maximum current rating of the XW Solar Charge Controller). That is, the fuse or circuit breaker must be rated equal to or above 75 A.
crewzer wrote: »
1) I don’t think that PV modules need to be derated. Without intending to be flippant, the CEC already derates PV modules’ power specs, and the NEC already requires “uprating” module voltage (690-7) and current (690.8 ).
2) The “60 A” rating of the TriStar-60 (PWM), MX60 and the XW-60-150 (both MPPT) is the continuous output current rating, subject to ambient temp conditions. It’s also possible to make the MX60 overheat and shutdown by operating it in conditions of high input voltage (i.e., ~114 V) and max output current.
3a) The array size comments you found in the XW manual are the very ones that are to be changed based on SG’s comments early in this thread.
3b) Check the XW’s online sizing tool. It includes a note re the NEC and the 48 A Isc limitation. It’s easy to update web pages these days.
4) The 60 A controllers output circuit breaker would normally be sized at 60 ADC x 125% = 75 A per NEC 690.8(B)(1). However, 690.8(B)(2) provides an exception and allows for an overcurrent device in an assembly listed for continuous operation at 100% of its rating shall be permitted to be utilized at 100% of its rating. OutBack and Midnite Solar both sell DC circuit breakers rated for 100% continuous duty, so it’s OK to use their ~60 A breaker on the output of a 60 A controller. For example, I use MidNite’s 63 ADC 100% duty breaker on the output of my MX60.
5) Part of the reason why an OCD is required on the input of the controller is because of the battery. Note that OCD's are not required between the PV array and the controller/inverter for battery-less utility-interactive installations per NEC 690.9(A).
My head still hurts…
Jim / crewzer
boB wrote: »
I believe that the "intent" of this NEC overcurrent ratings stuff is to protect the WIRES from overheating, not the unit itself, which is why the wiring must be sized higher amperage for a given wire temperature.
If 48A is Isc, then you can't have 48A * 140V = 6720 W because that would be comparing apples and moon rocks. They just don't taste the same and can't be had at the same time.
blwncrewchief wrote: »
And as my local inspector told me, the only interpretation I need to follow is his as he is the "authority having jurisdiction" I do not know how it applies to a equipment manufacturer?