Positive ground with batteries? [RE-wrenches]

Geoff Greenfield Geoff at Third-Sun.Com
Fri Mar 17 07:04:17 PST 2006


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Thanks for the quick feedback!

Darryl - This is not a residence - so no GFCI... but it is a grid tie...
Chris F. hasn't chimed in yet, but I think that a positive ground on a GVFX
will let the smoke out (you weren't talking about an ungrounded system were
you?)

Chris - I thought of the Exeltec (or other telecom stuff) as an option but
this is for grid tie (and I don't believe they are listed for that
application (?))

John B. - Thank you for the response (and addressing the points I was
interested in!).  If we can work with 120 only (or put a dedicated T-former
on any specific loads) this might be easier than running a single SI with
T-former.

1) Your string sizer has the SRS modules but no options for SB2500 (just
checking).

2) If we do use a T-former (such as the outback X-240) will SI-SB
communication (for modulation) work?

3)Can you confirm that the US available SI can be paired up for split phase
(any special hardware/software? why did I think this was not doable?).  Can
this be done with an additional balancing transformer?

For a brighter energy future,

Geoff Greenfield
NABCEP Certified Energy Practitioner

THIRD SUN SOLAR & WIND POWER Ltd.
340 West State Street
Athens, OH 45701

www.third-sun.com
(740) 597-3111

------------------------------

Date: Thu, 16 Mar 2006 16:08:54 -0800 (PST)
From: Darryl Thayer <daryl_solar at yahoo.com>
Subject: Re: Positive ground with batteries? [RE-wrenches]



The chassis of the Outback MX60 is not connected to
the negative or positive.  The Chas is of the FX
series is not connected to positive or negative.  The
MX 60 can and does operate just fine with positive
ground because it is not connected.  Likewise the FX
will and does operate with either positive or negative
ground.  so go ahead and do it.  But the grounded
roofing panels can not be used on a residence. Because
the solid ground will defeat the ground fault detector
interrupter.

As for the sunny island or Outback Island, I am
proposing a system that uses an Outback Island, and I
am beginning to feel confortable. The reason I am is
solar modules on both a barn and the house, and the
desire for no trench and emergency power.

Darryl

Date: Thu, 16 Mar 2006 16:38:29 -0800
From: "Chris Worcester" <chris at solarwindworks.com>
Subject: RE: Positive ground with batteries? [RE-wrenches]



Hi Geoff,

I'd consider an Exeltech MX system if the OutBack can't go to positive
ground.

Sincerely,

Chris Worcester
NABCEP Certified PV Installer
USA Distributor of Proven Wind Turbines
Toll Free: 877-682-4503
Fax: 530-582-4603
www.solarwindworks.com
chris at solarwindworks.com
"Proven Energy Solutions"

------------------------------

Date: Thu, 16 Mar 2006 17:32:39 -0800
From: "John Berdner" <JBerdner at sma-america.com>
Subject: Re: Positive ground with batteries? [RE-wrenches]



Geoff:

In answer to your question:

The SI is presently configured for negative ground on the battery.

Yes, Ac coupling would work very will in this application since battery
ground and array ground polarity are decoupled and isolated.

You can order any of the SB's  with positive ground as special order.
If the loads are 120 only then you could use a single SI and one or
more 1800's without autoformer.
If you need 120/240 loads then you would add an autoformer (for a small
system).

For larger system you can run 2 SI's in split phase and then you can
use 240 Vac inverters.
The maximum pass through current for the SI's is 56 Amps continuous (70
amp thermal breaker).
This is the limiting factor for a grid tied system passing through the
isolation relay in the SI.
For larger arrays you there are other options with external xfer
relays.

Efficiency of the SI is about 95% peak at around 1200 Watts and around
93% at full power.
This is true in both charging and inverting mode.

The SB's vary, but the 3800 and 6000's are a little shy of 95 at full
power (all the test data is available on the CEC website).
In a grid backup system the SB's deliver power directly to the gird in
one conversion.
It is only when the grid fails that you have a dual conversion.
Even then the dual conversion is only true of the power that is
surplus, i.e. PV power - load power >> battery

Hope this helps.
Let me know if you have any questions.

Best Regards,

John Berdner

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