Xantrex XW60 CC MPPT any feedback Yet ?

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Now, now, Niel... There is obviously a huge difference in how lightning behaves between when it strikes those wires that come in though the electric meter (or the TV antenna, or vent pipes, or phone lines, or cable TV, nearby trees, etc.) vs those wires that come in from solar panels...

I haven't figured out the difference yet--but obviously there is.

Honestly though, I have found that "Grounding" has become a religion among many engineers and others... Sometimes, when dealing with a "true believer", there is nothing you can say that will change their minds.

Its almost as though that Faraday never invented the Faraday Cage and showed that when everything is at equal potential, it is impossible to see a voltage difference anywhere (example of why all the ground leads should be wired together for common equipment/use).

-Bill

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Yep,

There is no reason to derate the charge controller's available power input via the NEC. As long as the device's specifications (max voltage, max available current limited by solar panel output and/or current interrupter device) are met too... At this point, I am going to assume a modern MPPT controller design. I don't know the details of the PWM controllers to know if they have a current limit (and it probably depends on a manufacturer and model basis).

The output current/voltage of the controller is limited by design (just like a computer power supply is limited by design--and believe it or not, one of the limiting options for a computer power supply is to "crowbar" the output--yep, put a dead short on the output if its output voltage is exceeded... Crowbars are perfectly OK because the power supply will current limit--or even fold back to near zero current--and in any case, because lots of current at near zero volts produces little heat and consumes little power from the input).

As long as the input current/voltage does not exceed the charge controller's specification (for normal Listed/Recognized equpment) its ability to safely manage device internal shorts and opens without catastrophic failures--either from internal failures or failures at the inputs from the solar panels.

Perhaps, that is the confusion here... We are typing about a wide variety of devices and capabilities here, but more or less, have been focusing on NEC connections to Grid Tie Inverters (not smaller PWM battery systems).

Older equipment and other designs that don't have to meet the same requirements very well could die if exposed to "over-sized" solar panels as they may not have the internal feedback control to limit output current/power.

And those inverters which have full control over their outputs (max current and voltage) and are designed to never exceed (under normal operation) the rated input current/power. And the inverters are designed and tested to "fail safely" (fail safely is my term--it drove my regulatory engineer nuts because they never want to say if anything fails safely--they just want to say it meets requirements--and there was even a rewrite in an older UL spec. that removed a statement in a later versions that talked about the safety of devices test under that code).

Just like the average computer power supply or inverter. You can connect any load to the device, but it will limit the total power through the device based on its specifications... And it does not matter what its available input current is (except in terms of upstream wiring/current interrupt ratings).

-Bill

Re: Xantrex XW60 CC MPPT any feedback Yet ?

And that is a very good question Jim (not being sarcastic).

There should be a spec. somewhere in the Xantrex documentation that talks about the maximum circuit rating that it can be connected too...

From the Xantrex GT 3.0 specifications (PDF), they list two ratings...

Maximum input is 22 amps (240 VAC connection) and Isc of array at 24 amps...

600 volts * 22 amps = 13,200 watt "solar array" for a 3kW inverter...

Or at minimum operation voltage of ~200 volts DC (round numbers) that would be:

200 volts * 22 amps = 4.4 kW PTC rated panels.

The maximum input wire size is either 6 or 4 awg--which certainly exceeds the 24 Amp maximum Isc--so that, from my guess, would be the result of Design/UL (and possibly NEC) limitations of the input "chamber" for the Xantrex GT... Technically, one could probably wave hands and argue that a 22-24 amp branch circuit breaker on a 1 MW solar array would also meet NRTL requirements too (my guess anyway)...

Jim, I have to go right know--so I will have to take some time and look up the new Xantrex product line. I did a quick post on the Xantrex GT 3.0 because I am familiar with that unit (installed at my home).

-Bill

Now, we can also start asking which xx Imp / xx Isc it is? STC, PTC, -40C/F, +77F, or Isc*125%*125% or whatever too...

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Niel,

I was referring the the Faraday Shield in terms that for everything that is at the same potential, there is no "problem" with arcing/high currents/etc...

However, by referencing different parts of a system (household wiring in this example) to different ground/circuit potentials--all bets are off.

I have gotten pretty good shocks by touching to ground references separated by ~100' (>60VAC) (was a dolphin exhibit and lots of water pumps, salt water, and bay fill).

Of course, Ground Loops and high frequency effects (light lightning), do have various strange things that they can do and cause problems... It is not really an easy problem to address--and it is even harder to test different grounding systems (G*d--please strike here at 8am Monday...).

-Bill

Re: Xantrex XW60 CC MPPT any feedback Yet ?

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.

Any derating of the controller is defined by the manufacturer and "inspected" by the NRTL. They are the ones that should/will define their operating parameters.

Now, when we design the equipment, we too use the NEC to define, rate, and derate the components (like wiring, chemical/sunlight resistance, ambient temperatures, and input connector box volume).

When NEC derates (in general) it is based on the specifications of the components (like wire insulation). And the wire manufacturers design and "certify" their product to meet the NEC requirements (using a NRTL).

Perhaps a bit of the confusion is the chicken and egg appearance of NEC derating wiring, and then buying wire that meets the specifications.

I would guess (since I was not involved in NEC and how new wire types are added to it) that when a new material/feature/compound of wire insulation is created, the inventor/vendor/NRTL work with NEC to define its particular characteristics. So, when NEC says to derate Type XYZ wire by 30% for 40-50C applications, that should have been based on the performance of the insulation that is defined by NEC/NRTL/Mfg.

And those specifications for "raw" components are now defined and approved for field installations via the NEC.

However, that charge controller is not a component. It is a complete device that has been designed/defined/manufactured with a specification sheet. And if it is installed per that specification sheet--then it meets the requirements of UL1950, IEC1950, etc... And NEC should state that all devices will meet the respective NRTL requirements.

Now, what I have seen in years past was checking for the NRTL mark (was originally only the UL mark)--much of this was done during fire inspections by local cities/agencies. And, for example, if the coffee maker in the lunch room was not "UL" marked--the fire marshal could have the device tossed or the business shut down.

Regarding the maximum practical array--that would not be a "code issue" but an installer/owner issue. The NEC/NRTL/Safety question is what is the Maximum Array (voltage/current) that may be safely installed. And under what conditions will those be (circuit interrupters, wire gauge, insulation type, conduit type, etc.).

Generally, if a Mfg. is smart, their requirements for facility wiring terminating into their equipment will meet NEC (wire awg, insulation, box cubic inches, appropriate termination, grounding, protection against prying fingers, markings, voltage/amperage ranges, etc.).

But, in the end, past the input termination box/cord/etc., NEC has pretty much ZERO responsibility/control about how the box is defined, NRTL Listed/Recognized, mfg. inspected, etc.--that is all the responsibility of the NRTL.

So, whether or not that 4,000 kW array connected to a 60 amp charge controller is defined/tested/listed by UL/NRTL under certain specifications. If that is 100% up to 95F, and derate by 1% per degree F rise to 135 F, or whatever, this is done per the NRTL written/controlled standard. Not by NEC.

And if the unit fails if you run it on a 61 volt battery--NEC does not care other than the wiring to the device will not fail "unsafely". And the NRTL does not care one bit about the reliability of the device other than it fail "safely" too. (I have seen times past that Europe has tried to put quality requirements in some of their specifications through the CE process--but I am not sure that will go anywhere--other than may be to provide some standards against which quality/performance could be defined--kind of like STC and PTC for solar arrays today).

-Bill

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Jim,

Just for clarification, is the 60Amps Charge Controller Input current rating or Output current rating? And what make/model specifically are you referring to?

Because, as an example, the Xantrex GT 3.0 is rated at Imp=22amps and Isc=24 amps (a bit too close together IMHO--unless that is STC rating and it has been taken into account that these panels could be installed in a -40C/F environment--but that should have been taken into account when the panels themselves have been NRTL tagged too)--that at maximum rated voltage Imp gives 13,200 watts of available power for 3kW grid tied inverter.

If, Isc is the concern, then the device should be rated for Imp=60amps, and be "safe" to connect to an array with Isc of (example) =75amps (at a defined temperature--or give the requirements for on-site calculations) or a branch circuit protected by a 75 amp maximum circuit breaker. And the "person" would have the choice to either install Isc=75 amps, or install a 75 amp Circuit Breaker (and associated wiring).

As I added the "marking the UL on the panels too) Isc rating... That kind of gets back to the "problem" with NEC derating the inverter/charge controller...

Should not have NEC derated the solar panel Isc too? I mean, that 8 amp panel be derated to Isc=6.4 amps maximum?

No?--is this because the panel is self regulating (based on the physics of the panel)? Or should this panel have a 8 amp fuse on the output so that we have random trips and that well will teach those inverters not to draw so much power?

Or, is has it been assumed that the panel output current cannot be managed by NEC (only by UL/NRTL) and so they focused on the unit that self regulates based on actual measured current and voltage?

If the physics of the inverters/controllers was such that you could not "derate" them by cutting down on the number of solar panels--but instead the devices would not work if the exact number of panels required were connected...

Bet that NEC would have just ignored the whole issue--just like they have on the Solar Panel Isc derating today...

I just cruzed through the XW solar charge controller installation chapter (XW installation guide) and:

Array Size:

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).

But yet, the battery output of the same controller is rated:

Battery Circuit

The 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.

A bit of confusion in the manual... Maximum would be never exceed 75 amps. Equal or above would mean how high? 80A? 100A? This is where one needs to read the NEC (don't have) and see what it requires (round up? round down? use a higher temperated insulation to allow larger breaker?)

Well... Back on topic, here we have the input connected to a relatively low current source (solar panels) that is designed for 60 amps, limited by panel installation down to 48 amps.

But, we also have the same terminal/box connected to a 60 amp rated minimum circuit--which is really x 125% or 75-80 amp breaker.

Should not the 60 amp output also been derated to 48 amps somehow?

Why could not allow the solar panel input have Isc=60 amps or even Isc>75 amps and protected by a 75-80 amp breaker? Why is derating the only allowed option. The charge controller will not draw more power than it has been designed/approved for by NRTL/UL.

Or could the the Xantrex Solar Panel input be rated for connected to a 75-80 amp capable branch circuit and then use Isc calculation rules and/or a 75-80 amp rated breaker...

This is typical from what I have seen from regulatory agencies sometimes. Focus like a laser on one piece (input solar panel Isc rating for a charge controller/inverter) and completely ignore the implications (derating somehow the solar panels themselves is ignored because it can't be done and is obviously stupid) to ignoring the 8,000lb gorilla (battery bank with tens of thousands of short circuit amperes available).

What is the maximum interruptible current for the 80A, 160 Vdc, Panel Mount, UL/CSA breakers? I bet the short circuit capacity of a 2,000 AmpHour 48 VDC battery bank (max suggested/rated for XW system) could make one of these beakers go up in a cloud of plasma.

-Bill

Re: Xantrex XW60 CC MPPT any feedback Yet ?

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.

boB

I agree with boB on the first statment (can't get in trouble with agreeing with an expert--can you )

The second paragraph sort of explains why I think NEC is all wet on the issue... The MPPT charge controller can certainly output 672 amps into a 10 volt ("dead") 12 volt battery bank based on a 6,720 watt panel (on a cold day-- see note)... So even derating this by 25% doesn't change the output current to any where near 60 amps maximum.

So this just limits the input current--and they could have chosen wire awg/insulation/packing ratio/ambient temperatures to support 60 amps on the input + 125% branch circuit rating buffer with no problem at all...

In fact, I can argue that since the "cold" Isc is higher, then the cold Isc ambient temperatures are lower... So what does NEC (up) rate a branch circuit with an ambient of 0 degrees F? Seems to me the colder weather should support higher short circuit currents as the system cools. And once the panels warm up to 77F--then can used the standard ambient temperature ratings of the wiring--Right? :cool:

-Bill

Note: I realize that the 60 amp MPPT controller will not output more than 60 amps unless there is a weired falure... And no failure on earth would allow it to output 10x is rated current in any fault condition (this is different than a shorted output stage where a battery can certainly output 10,000x rated current back into the inverter if installed incorrectly or an interrupt device fails).

Re: Xantrex XW60 CC MPPT any feedback Yet ?

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?

And the local inspector has no legal liability for his interpretations--as far as I know--which isn't very far (or even lack of performing his/her duty--as was found decades ago by some condo owners in the town I grew up in where it appeared the inspector never even bothered to inspect the grading/compacting/foundations for a 10-20 unit development and the foundations began failing only a few years later).

And, from what I could tell--as a designer/mfg--it only applies in that we get the "mark" and how we do it is our (and our NRTL's) business.

-Bill