|
Wrenches: The situation: Two Grundfos SQFlex stand-alone pump systems, each with IO101 AC switch and CU200 controller in a remote application, filling a common tank two miles away for a community water supply. As a float switch can't be used to shut off the pump when the tank is full, the mainstream pump company doing the full community water supply installation (we have contracted only the pumps and PV power) has specified and supplied a pressure transducer-based system called P2Flow (www.p2flow.com) as a stand-alone way to control pump operation using a high-accuracy pressure transducer at the well outlet to signal a programmable controller. The P2Flow control unit draws 40mA when "on" and 30mA when "off", running on 10-30 VDC, which I am supplying with PV. As 40mA @24 hours is one Ahr/day, I have specified a 10W module and 7 Ahr sealed battery at each well. The problem: The float switch control Grundfos CU200 controller is preprogrammed to "close on rise" - that is, continuity between the terminals turns the pump off. The P2Flow system is "close on fall", as would be used to directly interrupt continuity of power to the pump when the tank is full. These are opposite logics. How can I reverse the action in the simplest (for reliability) and lowest-power way? I could add a second relay to reverse the action, but that would increase the power consumption beyond what this tiny power supply can produce: at 0.9 VA coil current rating, an ice-cube relay would draw double the current of the P2Flow unit itself. I have heard of using a 10K ohm "pull-up resistor" but have no idea how it works. Any good ideas, please? --
Allan Sindelar |
_______________________________________________ List sponsored by Home Power magazine
List Address: [email protected] 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
