I believe Allan's suggestion won't work because the utility AC is <always> present so the system cannot use PV unless there's a grid blackout on a sunny day.
Dan's suggestion sounds more likely: a "double pole double throw" DPDT relay which requires DC for the coil. Consider devoting a small 17v PV module to only drive the relay coil on/off in a sun synchronous manner. Depending on its wattage relative to the coil requirement, a 17v module may overheat a 12v coil but may be OK with a 24v coil. Setting up one mini-module just for the control function reduces the number of elements which otherwise add "fear uncertainty & doubt" to the equation. Jolliness, Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675 On Thu, May 20, 2010 at 2:38 PM, Allan Sindelar <al...@positiveenergysolar.com> wrote: > Kirpal, > I did this about 5 years ago, on an array-direct irrigation pump with the > ability for the client to run a generator when needed. Yes, it's all > automatic, and no additional relay is needed. When the IO101 senses AC it > automatically closes a contactor - AC coil, NO is the AC, NC is the PV. > Simple as that. The wiring diagram is a funky single page diagram that comes > with the IO101 - but it's accurate. > > Allan Sindelar > al...@positiveenergysolar.com > NABCEP Certified Photovoltaic Installer > EE98J Journeyman Electrician > Positive Energy, Inc. > 3201 Calle Marie > Santa Fe, New Mexico 87507 > 505 424-1112 > www.positiveenergysolar.com > > Exeltech wrote: > > Could be as simple as installing a DC relay of appropriate coil voltage and > contact configuration & ratings. Then, use the PV to power the relay and > the contacts to select your preferred power source. The necessary > hysteresis inherent in relays would be present. Select a relay for the > environment (enclosed is usually best), and wire it safely. This is just > one option - but it uses off-the-shelf parts and ought to be easy to > configure. > > > Dan > > > > --- On Thu, 5/20/10, Kirpal Khalsa <solarwo...@gmail.com> wrote: > > From: Kirpal Khalsa <solarwo...@gmail.com> > Subject: [RE-wrenches] Grundfos SQ FLEX AC/DC auto switching > To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org> > Date: Thursday, May 20, 2010, 2:28 PM > > Hi Folks.....I am working on putting together a domestic water pumping > system using a grundfos 11 - SQF - 2. This system will be connected to > a standard pressure tank and cistern and have a solar array providing > primary power. However at night and on cloudy days we would like the system > to switch back over to AC power from the grid. I know that the grundfos IO > 101 switch box allows the pump to use an AC source and when the AC source is > removed it automatically switches back to DC. What I am looking for is when > the DC source (solar) is not available it automatically switches over to AC > power (grid) ( the reverse of what the IO 101 switch does) and when the DC > becomes available again it again automatically switches back to the DC power > (solar). > Has anyone done this? Any recommendations for configuring this set up. We > are looking to provide solar water pumping during the day both when grid is > present and when their is a power outage and AC pumping at night or cloudy > weather all without battery back up. > Thanks in advance for any advice.!-- > > Sunny Regards, > Kirpal Khalsa > NABCEP Certified Solar PV Installer > Renewable Energy Systems > www.oregonsolarworks.com > > 541-218-0201 m > 541-592-3958 o > > > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
