system output honesty [RE-wrenches]

Tue Sep 4 14:01:11 PDT 2001

David,

Even with a big array it will wander off max power in the middle of the day.
It is hard to detect unless you are monitoring dc voltage constantly.
Nothing you can do to fix that so its hard to worry about it. The bigger the
array, the better it track because it is looking for too large of a change
in output current when it does the sweeps. A good example of how not to do
max power tracking.

Bill.

> -----Original Message-----
> From: David Blittersdorf [mailto:davidb at nrgsystems.com]
> Sent: Tuesday, September 04, 2001 2:34 PM
> To: RE-wrenches at topica.com
> Subject: RE: system output honesty [RE-wrenches]
>
>
> Bill,
>
> I have figured out the MPPT problem. It seems to only work well
> if the inverter
> has lots of incoming PV. I installed 5500 watts of PV and it
> works fine. When
> I only had 1500 watts installed it would not work at all on hot
> days. On a hot
> summer day with 1500 watts of PV, it would not put any power to the grid
> because the inverter seems to have needed an input voltage above about 55
> volts to start working (I have sets of 3 PV in series). I put in
> a 12v battery to
> keep the inverter "alive" and ran the inverter in manual mode
> until the full
> amount of PV was installed.
>
> Another problem: The ripple cap. on the DC input shorted. Finally a Trace
> tech. gave me the real skinny and said that I should not try to
> get more than
> 4000 watts AC out of the inverter as the cap. will not take the DC ripple
> current. Suggested that I add caps. and I added 1.5 times the
> original value.
> Works fine now and I tripped the 110 amp DC breaker only one time
> on a hot
> sunny VT day this summer.
>
> Any other major problems I should be aware of?
>
> David Blittersdorf
>
> On 4 Sep 01, at 12:06, Bill Brooks wrote:
> > David,
> >
> > The UPV does not seem to have the same problem--It has it's own set of
> > problems like not being about to max power track. You are
> correct that any
> > changes you make would be lost anyway.
> >
> > Bill.
> >
> >
> > > -----Original Message-----
> > > From: David Blittersdorf [mailto:davidb at nrgsystems.com]
> > > Sent: Tuesday, September 04, 2001 12:58 PM
> > > To: RE-wrenches at topica.com
> > > Subject: RE: system output honesty [RE-wrenches]
> > >
> > >
> > > I have a UPV 5548 grid-tie only Trace inverter (ETL-listed) built
> > > in 1999. Does
> > > this same problem occur with this inverter? I have noticed that
> > > above about
> > > 1.5kw AC out that the fans do run all the time. Problem with this
> > > inverter is
> > > that it shuts down every night so any none firmware settings reset.
> > >
> > > David Blittersdorf
> > >
> > > On 4 Sep 01, at 9:00, Bill Brooks wrote:
> > > > Todd and all wrenches with ETL-listed, grid-connected SW-series
> > > inverters,
> > > >
> > > > I thought you'd never ask. Actually, this is fairly
> > > straight-forward as long as
> > > > you don't screw around with any other settings. Don't call
> > > Trace if you screw
> > > > everything up in the tech menus--just kill the voltage and
> start over.
> > > >
> > > > The tech menu is the third level (go to menu 20, then push the
> > > red and green
> > > > buttons). Go to menu 22 (Sync) and then push the down menu
> > > arrow until you get
> > > > to "Set PWM Angle". The factory default is 129---push the down
> > > arrow until it
> > > > reads 126 (minimum setting). Then make sure you return the unit
> > > to meters (or
> > > > wherever you leave it) so that the owner doesn't screw up
> the settings.
> > > >
> > > > I make no guarantees on whether or not the unit will blow up in
> > > your face
> > > > (just kidding), but if you try this out on a good size
> array (3-5 kWstc)
> > > > during the middle of the day, you will see a very pronounced
> > > reduction in
> > > > heat of the SW unit.
> > > >
> > > > The first time I did this on my unit, the inverter was
> > > producing 2000 Watts AC
> > > > but was sloshing around 3000 Volt-amps AC. The fans were
> > > running full blast, the
> > > > unit was burning hot to the touch which caused me to inquire
> > > what the problem
> > > > was. After finally getting hold of the SW designer and
> > > describing what I was
> > > > seeing on the oscilloscope, he suggested the above fix. After
> > > doing this, the
> > > > volt-amps dropped dramatically and the unit cooled down and the
> > > fans started
> > > > cycling. It would be a miracle for the efficiency of the unit
> > > to be above 80%
> > > > under the unadjusted condition.
> > > >
> > > > This ONLY applies to SELL mode operations. Off-grid units will not
> > > > experience this problem because they are not syncing to the grid.
> > > >
> > > > Bill.
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Todd Cory, Bald Mtn. Solar [mailto:toddcory at jps.net]
> > > > > Sent: Tuesday, September 04, 2001 8:38 AM
> > > > > To: RE-wrenches at topica.com
> > > > > Subject: Re: system output honesty [RE-wrenches]
> > > > >
> > > > >
> > > > > Ok Bill, spill the beans and tell us all what adjustments to make
> > > > > in the tech
> > > > > menu.
> > > > >
> > > > > Todd
> > > > >
> > > > > Bill Brooks wrote:
> > > > >
> > > > > > This mis-timing was causing substantial
> > > > > > effeciency reduction. Once the error was corrected, the
> > > unit cooled down
> > > > > > substantially and I was able to see efficiencies in the
> > > mid-to-upper 80s
> > > > > > using very accurate equipment. All ETL-listed SW series
> > > > > inverters have this
> > > > > > problem and it can only be corrected by going into the tech
> > > > > menu and making
> > > > > > the adjustment.
> > > > > >
> > > > > > The new UL-listed units were supposed to solve this problem,
> > > > > but I haven't
> > > > > > had the time to do the detailed testing to prove it.
> > > > > >
> > > > > > Bill.
> > > > > >
> > > > >
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> > >
> > > David Blittersdorf
> > > NRG Systems, Inc.
> > > 110 Commerce Street
> > > Hinesburg, VT 05461 USA
> > > Tel: 802-482-2255
> > > Fax: 802-482-2272
> > > email: davidb at nrgsystems.com
> > > Web:http://www.nrgsystems.com
> > >
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>
>
> David Blittersdorf
> NRG Systems, Inc.
> 110 Commerce Street
> Hinesburg, VT 05461 USA
> Tel: 802-482-2255
> Fax: 802-482-2272
> email: davidb at nrgsystems.com
> Web:http://www.nrgsystems.com
>
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