Single DC Source - Multiple Inverters [RE-wrenches]

[jberdner at sma-america.com]

David:

Yes, UL does prohibit parallel sources on one inverter but there is a
simple solution.
UL evaluates inverters with a supply capable of 2.0 times the maximum DC
circuit input current (specified by the inverter manufacturer).
UL forces failures and then tests to be sure the fire and electricity
stay inside the inverter enclosure.
If you connect the inverter to a source capable of higher dc input
currents then UL has not really verified the fire and electricity will
stay inside the box at the higher current.

Solution: Install a fused disconnect between the higher current source
and the inverter.  Each inverter can be protected with a fuse that has a
rating low enough to protect the inverter and maintain the UL Listing.
For the 2500U the max input current is 11.2 Amps so fuse should be sized
at 12.5 Amps (I think this is the standard fuse size in this range).

If you have any questions, or if I can be of any further assistance,
please do not hesitate to contact me.

Best Regards,

John Berdner

SMA America, Inc.
20830 Red Dog Road
Grass Valley, CA  95945
530.273.4595 (voice)
530.274.7271 (fax) 


-----Original Message-----
From: David Blecker [mailto:blecker at earthsys.org] 
Sent: Tuesday, September 17, 2002 6:29 AM
To: RE-wrenches at topica.com
Subject: Single DC Source - Multiple Inverters [RE-wrenches]

Folks,

I'm working on a Proven 6kW wind turbine installation with parallel
WindyBoy 2500W inverters (grid-tied battery free.)  A question came up
that I hope one of you know the answer to.  Does either NEC or UL
prohibit a single DC source (e.g., 300 VDC from the Proven controller)
from supplying two inverters in parallel?  Stated another way, is each
inverter required to have a seperate DC source.

Hoping the answer is no,
David

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