Kirpal, The IOTA ITS-30R automatic transfer switch has two 30A DPDT relays in it. You could use one relay with the 200VDC positive line wired in series across the two poles of the NC terminals, and the 240VAC hot lines on the NO terminals. The second relay could have the DC negative line in series between the two NC poles, and the AC neutral on the NO pole. That way, the DC circuit would have four breaks in it when disconnecting, which I imagine would be enough to break the circuit and extinguish the arcs at 200VDC.
The grid AC would hold the NO poles closed, but during a grid failure, it would automatically switch to the PV array. If you want to always run off of PV during the day, you could put a timer in the AC line and only turn o the AC at night. I don't know what an inspector would say about all this (live 200VDC and 240VAC in one box?), but I think that it would work. It would at least be an interesting experiment, and not very expensive. Brian Teitelbaum AEE Solar From: [email protected] [mailto:[email protected]] On Behalf Of Kirpal Khalsa Sent: Tuesday, May 25, 2010 4:07 PM To: RE-wrenches Subject: Re: [RE-wrenches] Grundfos SQ FLEX AC/DC auto switching Hi All....thanks for the good feedback on this water pumping system. Many good ideas....It looks like this is a system which can be done. I will be looking for a relay that will have the necessary voltage characteristics which will have ~200VDC on one side being normally closed and 240VAC on the other side, normally open. Mark, Allan.....I am looking at the Grundfos SQFlex Battery Back up system brochure and it shows a SQFlex system running with a pressure tank in their example system. Additionally they brochure goes on to say that "the CU 200 Controller has terminals for a pressure switch, which will control the pump's on/off operation via the pressure in the storage tank. The pressure switch should be of a normally open configuration, where the contacts within the switch are in the open position when the pressure is below the maximum set-point. When the pressure in the system rises to the maximum desired pressure, the contacts will close signaling the pump to shut off." In researching further it looks like the float terminals in the CU 200 controller are able to be used for either a float switch or pressure switch. I don't have any experience running a pressure tank in line with the output of the system but I can't see why as Allan pointed out that it would know the difference between 40PSI in a pressure tank or an additional 100' of head. I think that it is important to recognize the additional head ( due to the pressure tank) that will be present and to take that into consideration when sizing the array for the desired amount of gpm production. If anyone has any recommendations for a relay or other switch which can handle 200VDC and 240VAC I would be grateful..... Cheers, -- Sunny Regards, Kirpal Khalsa NABCEP Certified Solar PV Installer Renewable Energy Systems www.oregonsolarworks.com<http://www.oregonsolarworks.com> 541-218-0201 m 541-592-3958 o On Mon, May 24, 2010 at 2:42 PM, Mark Dickson <[email protected]<mailto:[email protected]>> wrote: Allan, This is all Dwight at Genpro could tell me. . .sorry to be vague! I agree, it seems like it would not know the difference. I would love to shed some light, however this was shared with us at the NGWA show by a Grundfos Engineer. It has brochursomething to do with the thrust load bearing on a them. Lorentz has two I believe Grundfos has one. Best regards, Mark Dickson, NABCEP Certified Solar PV Installer (tm) Oasis Montana Inc. ________________________________ From: [email protected]<mailto:[email protected]> [mailto:[email protected]<mailto:[email protected]>] On Behalf Of Allan Sindelar Sent: Monday, May 24, 2010 2:39 PM To: RE-wrenches Subject: Re: [RE-wrenches] Grundfos SQ FLEX AC/DC auto switching Mark, Your message gave me pause, as I just last week specified this setup, so I checked into it with our Grundfos rep. He said he had never heard anything recommending against the flex in a pressure system. He said the SQF doesn't know the difference between 40 psi and 100' of head. At the end of the day the pump just stops. He did make a point of emphasizing the need for pressure relief valves, as the helical rotor models can overpressure a system. Could you check with your distributor about this and post the reason you're given, please? Allan Allan Sindelar [email protected]<mailto:[email protected]> NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com<http://www.positiveenergysolar.com/> Mark Dickson wrote: Our Grundfos pump distributor has always warned against using the SQF pumps in pressure pumping situations. I can't quite remember why, but you may want to check into that. The Lorentz HR's have been the choice in these situations. Best regards, Mark Dickson, NABCEP Certified Solar PV Installer (tm) Oasis Montana Inc.
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