Lew,
You pays your money and you takes your choice. I understand why one would not want large industrial loads locked "on" after a power failure. Even so, when the power goes out in a storm, the utilities seem to have no difficulty turning on the power to whole neighborhoods full of refrigerator and air conditioner compressors at once. An industrial system has lots of juice to play with, whereas folks on a boat have a limited supply that they have to make themselves and some would consider it a waste of their supply to use some of it simply to hold a relay on. Using one line to operate two alarms can be done any number of ways, but I specifically stated using relays, diodes or other basic parts. I specified closing a contact to ground to send the signal because that is exactly how my Murphy gauges, and many other engine switches on our boats, operate. Safety is relative. Life is dangerous. We all die of it... Norm S/V Bandersnatch Lying Julington Creek 30 07.695N 081 38.484W > [Original Message] > From: Lew Hodgett <[EMAIL PROTECTED]> > To: <[email protected]> > Date: 7/24/2008 6:04:17 PM > Subject: Re: [Liveaboard] 12 VDC buss > > "Norm of Bandersnatch" wrote: > > > Arlid wrote to me suggesting several sources for latching relays to > > turn > > on/off loads connected to a buss using a remote switch. (see below) > > > >From a safety stand point, latching relays are a disaster waiting to > happen. > > As an ex control design engineer who spent a major part of my career > designing and selling control systems, I can tell you that every major > motor control user had as part of their electrical specifications, the > specific exclusion latching relays being allowed in their plants. > > The smaller users would say, if it is good enough for GM, FoMoCo, and > Chrysler, it is good enough for us. > > AS a result latching relays had almost universal exclusion. > > Why exclude latching relays? SAFETY. > > If you loose power, the only safe way is to reset every thing to the off > position and start over. > > A relay with a basic holding circuit accomplishes this by providing > under voltage protection. > > As far as trying to use a single circuit for oil and temp alarms for the > engine is concerned, it could be done with frequency shift technology; > however, you could by 10,000 ft of 14 AWG COPPER wire for less money. > > BTW, closing a contact from a device to ground is a less than desirable > way to do things. > > Again, it is a safety issue. > > Lew > _______________________________________________ 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
