Ben Okopnik wrote: > On Sun, Nov 14, 2010 at 04:11:32PM -0500, Jim Lynch wrote: > >> To keep this on point I recall hearing a talk about modern electronics >> aboard boats. One of the devices discussed is a bilge pump that >> periodically turns on and if the pump senses it isn't pumping water, it >> turns off. I'm sure it's measuring the current draw to determine if >> water is flowing. >> > > They're made by Rule and are referred to as "Fully-Automatic" bilge > pumps. For some reason, they're very hard to find, even on the Net. > Here's an example from a UK shop: > > http://x.co/KGdb > > This one is listed as cycling every 20 seconds; in other places, they're > shown as cycling every 2.5 minutes for a couple of seconds. It may be > worth calling Rule to get the full story. > > >> My bilge is designed such that switches are quite >> impractical and I'd sure like to find on of those beasts. Before >> someone suggests an integrated switch/pump, I've had bad luck with those >> in the past. >> >> I've googled but I can't seem to find the right combo of search terms. >> >> I'm working on designing one of my own based on a microprocessor, a RTC >> and some other parts but I wouldn't mind having a commercial one foe >> backup. >> > > Can't see where you'd need a microprocessor; a timer chip, an op-amp > comparator, and a driver transistor should do it - maybe $10 worth of > components all together. Feed one side of the comparator from a shunt, > and drive the other input from a voltage divider driven by the timer on > one end and positive feedback from the output of the comparator on the > other. Set the divider so that when the pump is dry, there's not enough > drive to kick the comparator on - but when the pump is loaded, the > voltage from the shunt is enough to keep the comparator on. > > As they say, this is untested but should work. :) >
The processor I'm using is an $18 part (including a RTC) driving a $2 mosfet. The added flexibility of sensing when water might be coming in faster than usual might be worth the difference. Besides I might find other things for the processor to do like monitor battery condition, connect via a wireless connection to send me an email that things aren't right on the boat when I'm not around, etc. > > _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://liveaboardonline.com/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.liveaboardonline.com/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
