Xantrex SW and battery configuration [RE-wrenches]

Rick Cullen - Blue Sky Energy rick at blueskyenergyinc.com
Wed Jan 25 10:13:56 PST 2006


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The short answer is no, nominal 72VDC input is not recommended for the
SB3048L and SB6024HL.

Both the SB3048L and SB6024HL have a maximum input voltage specification of
140VDC. This is a hard DC voltage limit above which transient voltage
protection devices which protect against lightning or other transient
voltage spikes will be damaged. I assume by 72V you mean 6 12V modules in
series. The basic NEC rule and our recommendation is to not apply more total
Voc at STC than the controller rating (140VDC) divided by 1.25, or 112VDC. 6
typical modules with ~22Voc would be 132VDC at 25degC or much too high. A
voltage derating factor less than 1.25 can be used in warm climates but this
must be done very carefully to assure DC voltage will never exceed 140VDC.

Richard A. Cullen
Blue Sky Energy, Inc.
760-597-1642 x102
Fax 760-597-1731
mail; rick at blueskyenergyinc.com
www.blueskyenergyinc.com


----- Original Message -----
From: "William Miller" <wrmiller at charter.net>
To: <RE-wrenches at topica.com>
Sent: Tuesday, January 24, 2006 12:04 PM
Subject: Re: Xantrex SW and battery configuration [RE-wrenches]


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Marco:

In the 1990s when MPPT controllers were not available, this might have made
sense.  Now there here, why not stick with a 48 VDC battery bank and
configure your PV for 72VDC with a Blue Sky or MX60?  (Will the Blue Sky do
72 VDC PV array?)

William Miller









>I don't know how many of you tried this back in the olden daze of the late
>1990s, but I remember being convinced by a Trace tech to try a 54 volt
>battery bank with a 4048 or 5548 in order to allow the nominal 48V array to
>spend more time at its MPP.  (This assumes the use of a non-MPPT charge
>controller.)  So, I did several systems with a 54V battery bank.  Well, for
>the first time in years, I'm doing a SW4048 NEM system here in Hawai'i and
>am wondering if it will make much of an appreciable difference in terms of
>overall system output over time if I go with a 54V battery rather than 48V.
>
>
>Any thoughts or actual experience comparing output between the two
>configurations?
>
>aloha,
>marco

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