AC coupling [RE-wrenches]

[Kirk Herander]

Chris,

I have a large ac coupled system - 

-3- SB6000US inverters controlling a combined 16.8 KWp array
w/ a quad stack of OB 3648 inverters

It actually works quite well. I have a 240 vac, 100a contactor which is
driven by the 12vdc OB aux signal to disconnect the SunnyBoy output from the
OB's when the batteries are charged during a power failure. But I am a
little concerned that if the aux signal ever failed, the batteries would
seriously fry if the Sunnyboys were left connected to the OB's. What can I
do for redundancy of the aux signal? Can I create a hardwired hierarchy of
all four inverter aux signals without frying the aux circuitry of any
respective inverter(i.e. via seperately derived 12 vdc power supplies wired
together)? Are external blocking diodes necessary?

Kirk Herander
Vermont Solar Engineering
802.863.1202
fax 802.863-7908
NABCEP(tm) Certified Solar PV Installer
Xantrex Certified Dealer Charter Member
NYSERDA-eligible installer
VT Solar Incentive Program Partner


-----Original Message-----
From: Christopher Freitas --- OutBack Power
[mailto:cfreitas at outbackpower.com] 
Sent: Friday, March 14, 2008 6:14 PM
To: RE-wrenches at topica.com
Subject: RE: AC coupling [RE-wrenches]


Drake - 

We (OutBack) have had good success with AC coupling our inverters with a 
wide variety of battery-less grid-tie inverters - including PV Powered.  
We are at the point where we are pretty comfortable with just saying 
that it will work fine - give it a try... 

The only issue I have seen on a PV Powered AC coupled system was the 
interaction of their anti-islanding scheme with the voltage regulation 
of the VFX inverter causing a slight flicker on some of the lights.  It 
was tolerable - and was less of an issue when other loads were 
operating.  The customer found it to be slightly irritating but 
acceptable. 

I am not sure if the newer PV Powered models still use the same old 
anti-islanding scheme they used before. With other inverters (SMA, 
Magnetic, Fronius, etc.) we did not see this problem occur.  

Like with all AC coupled systems utilizing OutBack inverters - you will 
need to provide an additional mechanical relay or solid state relay 
controlled by our AUX output to manage the power once the battery gets 
full.  This can be done in a variety of ways - let me know if you need 
any assistance with deciding what is best for your application.  

Christopher


Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com  
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030  


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