Well done Rufus, I think your idea may work. I am not on the boat now so I can't rig up a breadboard to try it out, but the idea looks good.
The only drawback is the need to have a double pole latching relay. I don't have a source for those yet. The other down side is that it won't work with the latching relay I want to use. I have a large single coil type SPST latching relay (where the state changes depending on the current flow direction through a single coil) I want to use as a house/start battery crossover switch for getting some extra juice for starting the main engine when needed. I thought of using a large starting solenoid type relay but I am concerned that if the batteries are low the relay might drop out when I hit the starter. As for just running two wires - most of the control wires I have are in multiple wire cables that connect centers of activity such as the engine room and the instrument panel. Many of the conductors are in use and there are a few spares. I wish, through clever design, to use these wires as economically as possible to allow for future expansion, thus the desire to use one wire where normally two would be used. In addition to operating the big SPST crossover latching relay using one wire, I would like to send the engine overheat signal and the oil pressure low signal from the engine room to the instrument panel over one wire using the same philosophy, that neutral condition would be a floating wire, one condition a positive 12 VDC and the other condition a Ground. There's gotta be a simple, elegant way to do these things. Norm S/V Bandersnatch Lying Julington Creek 30 07.695N 081 38.484W > [Original Message] > From: Rufus Laggren <[EMAIL PROTECTED]> > To: <[email protected]> > Date: 7/27/2008 6:51:51 PM > Subject: Re: [Liveaboard] 1 wire relay cntl - fr. 12 VDC buss > > Well, I considered a "floater" at first but lost it somewhere in my rigorous thought process...<g> Now I think about it some more if you used a single-coil relay, wouldn't a DPDT relay work with the floating signal on one coil terminal with the other coil terminal either grounded or hotted by the extra pole on the relay? That'd solve the oscillator problem, also; for any particular state the signal line would only carry current until it threw the relay - after that both ends would be at the same potential. > > The coil might need a little help to complete the latching process after the relay drops one side of its circuit - a hefty capacitor on the non-signal coil terminal? But maybe it'd work without it. Don't know what the trade-off between installing a good capacitor and installing a 2nd signal line looks like. I'd say the 2nd wire makes more sense because you lose the capacitor (and/or any other shaping circuitry) and you get to use SPST relays. I guess you could use solid state to flip the coil polarity at the relay but that would mean more futzing and also some kind of phantom load. A single twisted pair for the signal line is almost as simple a one wire. > > Rufus > > > ----- Original Message ----- > > From: "Norm of Bandersnatch" <[EMAIL PROTECTED]> > > To: [email protected] > > Subject: Re: [Liveaboard] 1 wire relay cntl - fr. 12 VDC buss > > Date: Sat, 26 Jul 2008 21:37:41 -0400 > > > > > > > > Notice I said "(system ground and system 12 VDC is available at both the > > switch(s) and the relay)". > > > > I imagine a system where the single line is normally floating with nothing > > on it. The control switch(s) would put the control line to 12 VDC or > > Ground when activated. Somehow at the latching realy the realy would flip > > from one state to the other depending whether the control line went to 12 > > VDC or to Ground. To save juice, no current should flow when the control > > switch(s) are not pressed. > > > -- > Be Yourself @ mail.com! > Choose From 200+ Email Addresses > Get a Free Account at www.mail.com > > > _______________________________________________ > 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
