[RE-wrenches] Grundfos SQ FLEX AC/DC auto switching

R Ray Walters ray at solarray.com
Thu May 20 14:52:07 PDT 2010


I think you're going to have trouble with the array direct to the relay coil. a 12 v relay may burn long term, as suspected, but the 24 v relay probably won't close reliably at the lower voltage.

R. Walters
ray at solarray.com
Solar Engineer




On May 20, 2010, at 3:37 PM, Mick Abraham wrote:

> 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
> <allan at 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
>> Allan at 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 <solarworks at gmail.com> wrote:
>> 
>> From: Kirpal Khalsa <solarworks at gmail.com>
>> Subject: [RE-wrenches] Grundfos SQ FLEX AC/DC auto switching
>> To: "RE-wrenches" <re-wrenches at 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
>> 
>> 
>> 
>> 
>> 
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