Balancing Two SW Inverters on the head of a pin [RE-wrenches]

Todd Cory, Mt. Shasta Energy Services toddcory at finestplanet.com
Thu Jun 10 07:25:43 PDT 2004


 

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Hello wrenches,

I dug through the archives and found this posting on balancing stacked
sinewaves, selling power to the grid. This  dated (9-26-01) post 
suggests setting max. charge amps to 1, however if the max. charge 
amps are set to 1, and if the grid is down with the genny on feeding 
the house loads, the batteries will not charge very much. What do 
people suggest for that situation? If I raise the charge amps will 
one inverter charge the batteries while the other one sells that power?

I usually see only one of the two inverters doing most of the selling
(with fans roaring away). I believe the DC calibration is off between
the two units so tweaking the float/sell voltage should help compensate
for that, right? Unplugging the temp sensors will probably help too as
they seem to be inaccurate with respect to each other and they are not 
on the batteries anyway. (The original installer just stuck them inside 
the DC250.)

If people have any other tricks to make stacked SW's best sell, please
pass them on. 

Thanks for the feedback,

Todd



Bill Brooks wrote:

> William, Marco, and Jeff C.,
>
> Here is the method I found to be most effective:
>
> INVERTER SETUP (MENU 9)
> set to SELL
>
> BATTERY CHARGING (MENU 10)
> set ABSORPTION TIME to 0:00 on both machines.
> set MAX CHARGE AMPS to 1 amp on both machines.
>
> BATTERY SELLING (MENU 17)
> set MAX SELL AMPS to X amps on both machines. (where 2X is the Max AC amps
> that the PV array can produce. (e.g. 4000 Watts should set both to 18
> amps --18A*120V=2160Watts)
>
> Both temp comp probes must be installed so as to operate at the same
> temperature. I have tried adjusting the float setting and that also works
> particularly for an inverter that is out of DC calibration. They still get
> out of wack at times at different temperatures because the slope of the temp
> comp probes are usually not the same. This should keep both machines selling
> as evenly as they can and limit each machine to a maximum of half the AC
> Watts output. The one amp MAX charge amps keeps one unit from charging while
> the other one sells.
>
> Try it and see how you like it.
>
> Bill.
>
> -----Original Message-----
> From: William Miller [mailto:wrmiller at slonet.org]
> Sent: Wednesday, September 26, 2001 6:19 PM
> To: RE-wrenches at topica.com
> Subject: RE: system output honesty [RE-wrenches]
>
> Marco:
>
> I must not have been very clear, but you don't necessarily end up with the
> same numeric float voltage setting.  Take the inverter with the lower
> output and increase it's float voltage one increment at a time (I think it
> adjusts in 0.2 volt increments)  while checking sell amps.  The change
> should be immediate and obvious.  (If it doesn't improve, try decreasing
> float voltage because my memory may not be accurate.)
>
> William
>
> At 01:09 AM 9/26/01 -1000, you wrote:
> >William,
> >
> >Maybe you have the magic touch with your dual SWs, but my dual SWs are set
> >at the same float voltage and, as Bill B. noted, they don't "share" those
> >incoming PV electrons very equitably.
> >
> >On another note, has anyone received an AEI MM5 or MM3 yet?
> >
> >marco
> >ProVision Technologies
> >Hilo, land of declining tourism Hawai'i
> >
> >Friends:
> >With dual SW inverters (I believe, if memory serves me right) I finally
> >discovered that adjusting the float voltage until they both sell more or
> >less equally does the job of balancing.
> >William
> >
> >
> >
> >
> >
> >
> >At 05:04 PM 9/25/01 -0700, you wrote:
> >>Jeff C.,
> >>
> >>It is less important with a small array, but it still will work slightly
> >>better. The much bigger issue with dual inverters in sell mode is that
> they
> >
> >>don't behave nicely with each other (they don't know how to share). One
> >>inverter invariably wins the conversion battle and the other inverter sits
> >>idle, or more likely, starts drawing power from the grid to fight the
> other
> >
> >>inverter.
> >>
> >>I have yet to see a dual SW system on the grid the worked really well. You
> >>can trick them into working with various settings. I have a set of
> settings
> >
> >>that has worked well for me, others on the list may have their own
> methods.
> >
> >>If people are interested, we can do this onlist. If not, email me and I'll
> >>send them offlist.
> >>
> >>Bill.
> >>
> >>
>
> __________________________________________________________________
> William Miller
> SLO Communications: Communications and Power Systems Consulting
> PO Box 50, Santa Margarita, CA 93453
> Voice :805-438-5600             Fax: 805-438-4607       VMail: 805-546-4875
> email: wrmiller at slonet.org
> License No. C-10-773985
> _____________________________________________________________
> Compatibility:
> Word processor: WP7
> Spreadsheet: Quatro Pro 7
> CAD: Microstation 95, DXF, Visio 4.1T
> _____________________________________________________________
> "I stand by all the misstatements that I've made." Dan Quayle
> __________________________________________________________________
>

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