On Sat, Mar 05, 2011 at 09:52:52PM -0800, James Maynard wrote:
> Simpler yet, how about an AC source selector switch - 2P3T, two poles,
> three throw (two positions plus center OFF) for 120 VAC sources, or
> 3P3T, three poles, three throw (two positions plus center OFF) for a
> 120/240 VAC sources. You switch both the hot and neutral wires (black
> and white in a 120 VAC system, black, red and white in a 120/240 VAC
> system). The boat's AC system is connected to the movable contact, the
> shore power inlet to position 1 of the fixed contacts, nothing is
> connected to position 2 of the fixed contacts, and the inverter output
> (or on-board generator output) is connected to position 3 of the fixed
> contacts.
>
> With this setup, the inverter output is never connected to the shore
> power cord.
>
> Blue Seas Systems sells switches and switch panels for just this
> purpose. The switch panels come with reverse polarity indicators, too.
> They offer them in 20-amp and 65-amp current ratings, and in 2, 3, and 4
> poles.
>
> See <http://bluesea.com/category/4/productline/221> for the Blue Seas
> selection of AC source selector switches and switch panels.
Jim, thank you for the idea; I appreciate it. However, I think I'm going
to go with a $14 commercial-grade relay that does this automatically
rather than an $80 switch which I have to remember to throw (and if I
forget, will mean that I "invisibly" continue using ship's power while
the plugged-in dock cable remains disconnected. That's a really bad
failure mode, exactly the kind of thing I'm trying to eliminate. :)
Hmmm. I'm noodling on a circuit that would detect that situation, in
either case. Let's see... a pair of neon bulbs (with appropriate
resistors, of course) between the "hot" center terminal and the two
poles that connect to it should do it. The side of the switch/relay
that's active will short across one bulb, so that it won't light up -
and the other one isn't supposed to be powered up at those times (i.e.,
the inverter should be off when the switch/relay is in the "dock power"
position, and dock power should be disconnected when the inverter is
on.) So, the only time when one of the bulbs will light is when either
a) the inverter is on while you've got dock power connected, or b) if
dock power is on but the relay has failed (or the switch is in the wrong
position.) Bingo.
The power to light up the bulb comes from the fact that 1) the two power
sources are always going to be out of sync with each other and 2) neon
bulbs require almost no current to operate. I'm not at a dock right now,
and probably won't be for a long time, so I can't test it, but it should
work fine.
Ben
--
OKOPNIK CONSULTING
Custom Computing Solutions For Your Business
Expert-led Training | Dynamic, vital websites | Custom programming
443-250-7895 http://okopnik.com http://twitter.com/okopnik
_______________________________________________
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
