Xantrex MPPT 60 150 OK for 2450 Watts at 48 V ?

[Windpower]

The way I read the spec it seems that this should be at least 9 A under the max for this controller (2450/48VDC= 51 A) or 85% of rated 60 A

Is that OK on a cold day in Wisconsin --0ne person I talked to did not think so --- Several months ago they said OK  (of course now they have the 80 A high voltage one for twice the price)

I have 12  Sunelctric 205 watt panels going into a bank of 750 A- Hr 48 VDC battery bank

I would rather not have to go to the 200 VDC input required on the new model

[Windpower]

I forgot the panel numbers

Pmp   205 W
Vmp    18.4 V
Imp   11.15
Voc    22.8
Ioc    12.1

[MountainDon]

How exactly are the modules configured?  How many parallel, how many in series?

[Windpower]

Thanks Don, I knew I was missing some info

3 groups of 4 panel each for a total of twelve 205 watt panels

Here is a relevent section from the controller manual

PV Array Requirements
Each XW Solar Charge Controller (XW SCC) must be connected to its own PV
array. Although the XW SCC can harvest a maximum of 3500 W, the PV array
size can be as high as 6720 W (based on 48 A × 140 Voc = 6720 W).


CAUTION: Equipment damage
The PV array voltage must never exceed 150 Voc (open circuit voltage) under any
conditions. The array Isc (short circuit current) must not exceed the 60 A input current
rating of the XW SCC at any time.

Panels rated up to 48 A at 77 °F (25 °C) are recommended to allow for increases
in Isc caused by irradiance enhancement under certain conditions (reflection from
snow, for example).

[MountainDon]

3 groups of 4 panel each for a total of twelve 205 watt panels

I interpret that as 3 groups consisting of 4 series connected modules. Each of the three groups of 4 then connected in parallel.  Here's how I calculate the numbers....

The Voc of each module is 22.8 volts x 4 = 91.2 volts for the series string
Apply NEC and cold weather safety factor;  91.2 x 1.25 x 1.25 = 142 volts
That's within the absolute max of 150 VDC for the CC. So that's okay, though close.

Ioc (Isc?) of 12.1 amps per module and series string x 3 = 36.3 amps
Apply the irradiance safety factor 1.25 x 36.3 = 45 amps
That is within the 48 amps the manual suggests. So that's okay, though again close.

And then taking the 142 volts max. x 45 amps max. = 6390 watts which is within their figure of 6720 watts.

So it would appear the numbers are getting close to maximum with all the safety factors applied.

It's too bad the Xantrex Sizing Tool does not include the SunElec modules in its available selections, and they don't seem to allow manual entry for non listed modules. 
http://www.se-renbu.com/support/xwsizing/Default_SE.aspx

Outback's String Sizing Tool does permit manual entry
http://outbackpower.com/resources/string_sizing_tool/
I plugged your values into the Outback Tool as it does permit manual entries.
That tool also says 4 series x 3 parallel is okay. (I used the FM60 which has the same maximum voltage and amperage limits as the Xantrex XW MPPT60-150

I like the Outback tool as they include minimum and maximum environmental temperature sliders and a graphical display or what module combinations work. Fun to play with. The bottom left corner indicates one module, going up adds modules in series and across to the left adds series strings in parallel.

[Windpower]

Don thanks

How about two six series strings @ 136.8 Voc

would also be within max values ....



why isn't this stuff easy

[MountainDon]

How about two six series strings @ 136.8 Voc

would also be within max values ....

Within values? maybe not. 

The Voc values must have the NEC (for electrical safety) correction and the cold weather corrections applied.
Each is 1.25
So always multiply the Voc x 1.5 and then by 1.25 again. (or simply multiply the Voc by 1.56.
So 22.8 x 6 = 136.8  call it 137
137 x 1.25 = 171   so we're already over the maximum voltage the Xantrex CC will tolerate.
BTW, I know the Outback has a recorder inside, probably the Xantrex does too. It records the peak voltage and 'they' look for that on warranty claims.

The results from using the Outback String Sizing Tool are interesting.  The 6 modules in series configuration works as long as the minimum environment temperature never falls below 64 F     and a 5 series string works until the temperature drops below -19 F.  Not gonna work in your backyard, I think.   

[Windpower]

Don, thank you for the link

I found the panels in the drop down --they are the same as Evergreen ES-A 205 fa3

looks like everything works between -20 F and 79 F for 4 panels in 3 strings

might loose some energy on very hot days -- not a serious problem I don't think

BTW Sunelec has panels for $ .98 and $ .88 per watt on similar panels now --minimum 20 panels ( I paid almost twice that for the ones I have)

[Windpower]

Actually the ES-A 205 evergreens are an exact fit for the numbers
typed in -40 F to 80 F

and everthing looks ok except for a few really hot days above 80 F (not sure what "Average High Temp" means  --- average temp or what --) that shows the VMP at max temp may be marginal at 60VDC

I understand the low temp is in case of a really cold sunny day -- but even then in da north the sun angle makes the intensity significantly less and the array only puts out 44 A (max recomended 48 A almost a 10% margin)

Thanks again, Don, for the help