Ken, Four relays to control a latching relay. It may work, for some time, but I promise a well protected 74C73 would be more reliable. The absolute requirement that there be zero current when not in use is something I just do not understand. Even if a voltage regulator chip was used to provide additional protection for the CMOS chip the power used would still be a lot less than the self discharge rate of even the best AGM batteries. Oh well. I guess I can never change Norm's requirements. After all it is his boat...
Eric Thompson S/V Procrastinator South San Francisco [EMAIL PROTECTED] ----- Original Message ----- From: "Ken James" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Wednesday, July 30, 2008 9:26 PM Subject: Re: [Liveaboard] Latching relay control > Always the same problem...(sigh). > > The real issue is that the normal methods of doing > this use a small amount of sensing current, like a > voltage divider, ect. and/or they involve > semiconductors such as transistors and IC's. > > But I think I may know of a method that might work. > > It uses only very simple components, but it is a > bit tricky. > > It involves using a sensitive polarity sensing > reed relay with two N.O. point sets, one set > closes with one coil polarity the other closes > with the other polarity. The coil is connected to > a set of (prob in this case good sized) > capacitors, connected like a voltage divider with > one caps end at pos the others at neg and the two > tied together at the other ends. > > (If needed two reed relays could be connected to > the caps if a single polarity sensitive relay of > the correct type cannot be had cheaply.) > > This middle point where the caps are connected > together is connected through a resistor (to > control the charge/discharge time of the caps)to > the coil of the reed relay. > > The other end of this coil is connected to the > input single wire control. > > When the input goes either pos or neg one of the > caps charges pos and the other charges neg. > Current flows through the reed relays coils as the > caps do this, causing one set or the other of the > N.O. points to close depending on the polarity of > the single wire input. > > The points of the reed relay supplies power to one > or the other of either of two further relay coils. > These are small relays that do not use much power > in their coils, necessary since the reed relays > points cannot handle much current. > > These relays points are used to control the coils > of the latching relays. > > So the reed relay senses the polarity of power as > the capacitors charge in response to the single > wire input voltage, and one set or the other of > its points close in response. > > These points in turn energize another set of > relays that can handle enough power to drive the > latching relays. > > With no power on the single input wire, no current > flows anywhere. > When there is voltage of either polarity, only one > set of latching relays driver coils is energized > at a time and so only one set latching relay coils > are energized at a time. > > No current flows between any of these coils at any > time. > > Again, when the single wire input 'floats' there > is no current flow anywhere. > > I will send a schematic. -Ken > > > > > _______________________________________________ > Liveaboard mailing list > [email protected] > To adjust your membership settings over the web > http://www.liveaboardnow.org/mailman/listinfo/liveaboard > To subscribe send an email to [EMAIL PROTECTED] > > To unsubscribe send an email to [EMAIL PROTECTED] > The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ > > To search the archives > http://www.mail-archive.com/[email protected] > > The Mailman Users Guide can be found here > http://www.gnu.org/software/mailman/mailman-member/index.html _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [EMAIL PROTECTED] To unsubscribe send an email to [EMAIL PROTECTED] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
