On Mon, 16 May 2005 01:18:55 GMT, "Roger Long"
wrote:

It's a diesel boat.

Would you please explain the snubber business? I'm sure a lot of us
besides myself would like to know what it's for.


An inductive element like a relay coil or a motor stator or rotor
has a predictable reaction to suddenly cutting off the current through
it: a back voltage which can rise to a fast peak of hundreds of volts,
making a spark that jumps the opening contacts for a little while.

This wears the contacts out. And ignites gasoline vapor too.

If something is arranged to let the current through a coil fall more
slowly, the voltage rise is much lower. If some resistance is in
circuit, the energy stored in the coil is used by the resistance -
which heats up a little.
This combination of a capacitor and series resistor is called a
snubber, because it snubs (or damps out) the spark.
The cap and resistor is placed across the coil.

Make sense?

Brian Whatcott Altus, OK

Like this, right?

http://home.maine.rr.com/rlma/Switch.jpg

I can appreciate the effect. I made a box in high school with a coil
in it and a switch made from a nail dangling in a ring. It had
textured aluminum foil sides wired to the coil and said "Mystery Box"
on top. It was a hoot when I left it in the faculty room.

Do you think I can get away with a single contact relay? The sealed
fog light relays that are readily available seem like they should be
sized and just right for this application.

--

Roger Long

"Roger Long" wrote in
:

Like this, right?


Oh, goody-goody! Let's all keep making the damned bilge pump more and more
complex, with lots more failure points so it can flood the damned boat and
put it on the bottom.....

Parallel two Rule float switches in series with EACH of two bilge pumps
hooked straight up to the batteries through a 3A fuse....

The boat will never sink.....until the flooding exceeds the combined
capacity of the pumps, of course.

SIMPLE IS ALWAYS BETTER!

On Mon, 16 May 2005 09:15:37 -0400, Larry W4CSC
wrote:

Oh, goody-goody! Let's all keep making the damned bilge pump more and more
complex, with lots more failure points so it can flood the damned boat and
put it on the bottom.....

Parallel two Rule float switches in series with EACH of two bilge pumps
hooked straight up to the batteries through a 3A fuse....

The boat will never sink.....until the flooding exceeds the combined
capacity of the pumps, of course.

SIMPLE IS ALWAYS BETTER!

Yeah, what he said.

__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at world wide wiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/

Larry W4CSC wrote:

"Roger Long" wrote in
:


Like this, right?



Oh, goody-goody! Let's all keep making the damned bilge pump more and more
complex, with lots more failure points so it can flood the damned boat and
put it on the bottom.....

Parallel two Rule float switches in series with EACH of two bilge pumps
hooked straight up to the batteries through a 3A fuse....

The boat will never sink.....until the flooding exceeds the combined
capacity of the pumps, of course.

Or, of course, the capacity of the batteries.



--
Stephen

-------

For any proposition there is always some sufficiently narrow
interpretation of its terms, such that it turns out true, and
some sufficiently wide interpretation such that it turns out
false...concept stretching will refute *any* statement, and will
leave no true statement whatsoever.
-- Imre Lakatos

"Stephen Trapani wrote:

Or, of course, the capacity of the batteries.

And, in this case, it would have had to be pretty impressive capacity.
After the fiasco with the oil sensing switches, I'm all for the
simplicity promoted above. What's driving this now is the fact that
the pumping capacity I want (enought to have a fighting chance of
surviving a burst stuffing box hose), combined with the hose lengths
forced by the design of the boat, means that any float switch on the
market will go into an endless cycle of pumping out the hose.

--

Roger Long

Roger Long wrote:

"Stephen Trapani wrote:


Or, of course, the capacity of the batteries.


And, in this case, it would have had to be pretty impressive capacity.
After the fiasco with the oil sensing switches, I'm all for the
simplicity promoted above. What's driving this now is the fact that
the pumping capacity I want (enought to have a fighting chance of
surviving a burst stuffing box hose), combined with the hose lengths
forced by the design of the boat, means that any float switch on the
market will go into an endless cycle of pumping out the hose.

****ing big centrifugal pump (or even two) with big hose with its float
switch mounted above that for a little, positive displacement diaphram
pump with a small hose?

The little pump doesn't affect the reliability of the big one but should
be enough to cope with the runback from the big hose.

Alternatively, back to the relay idea:
Take big pump and upper float switch (NO), wire in series, pump -ve to
batt -ve, other side of switch to +ve supply. Wire the relay (NO)
contacts accross the upper float switch. Wire a lower float switch (NO)
in series with the relay coil and feed it from the pump motor +ve.
Return the other side of the relay coil to the pump -ve (which is also
the battery -ve) Wire RC snubbers accross both the relay coil and the
motor as near as practical to them and a reasonably tolerable buzzer
accross the motor. Feed from an appropriate fuse directly off the
battery with a high dB output pizeo beeper accross the fuse. Put the
sounders and the relay (in a socket) somewhere where you can get at them
if you have to. e.g. back at the panel. You need four wires down to
the bilge, (Upper switch +ve, common junction of upper switch -ve &
lower switch +ve & motor +ve, lower switch -ve [to relay coil], motor -ve)

Now lets consider the possible failure modes:

1. Upper switch fails open: No alarm, bilge can flood silently till boat
sinks.

2. Upper switch fails closed: Continuous buzzer, bilge is emptied until
eventual flat battery or pump burnout

3. Motor OC: Continuous buzzer if enough water in bilge until the boat
sinks

4. Motor SC (or jammed so fuse blows): Continuous extremely loud
unignorable high pitched tone untill fault cleared and fuse replaced,
beeper smashed or disconnected :-) or boat sinks

All the above are the same as for a simple pump setup with one switch
and no relay. The only difference is you have two audiable alarms.

5. Relay fails open or lower switch fails open: Circuit reduced to
simple switch and pump, you hear a double (or more) buzz due to runback
restarting the pump, boat does not sink.

6. Relay fails closed or lower switch fails closed: Continuous buzzer,
bilge is emptied until eventual flat battery or pump burnout or untill
you pull the relay out of its socket which puts it back to the simple
single switch case.
**** This is the only increased risk ****

The snubbers have a resistor + a capacitor in the same package.
Resistors almost always fail by going open circuit which would make the
snubber ineffective but not cause an immediate circuit failure or the
capacitor might short, in which case the resistor would limit the
current until it went open and the circuit would keep working. If you
are fairly (justifiably?) paranoid, you might use two snubbers in
parallel in place of a single one in each circuit position.

Finally for backup security fit the second pump which only needs a
simple switch a little higher in the bilge than the first pump's upper
switch with pizeo sounder accross its fuse and another accross the pump
(+ another RC snubber) off your other battery. This catches any fault
with the first pump that haven't sounded its alarm.

(NO stands for Normally Open contacts)

N.B. *DONT* PUT THE LOWER SWITCH FOR THE FIRST PUMP IN SERIES WITH ITS
MOTOR (as per your JPEG) OR YOU DOUBLE THE CHANCE OF A FAILED SWITCH
STOPPING THE PUMP WORKING WITH NO ALARM.

Hope that helps, Roger.
Have I missed anything Larry?
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL:
'Stingo' Albacore #1554 - 15' Early 60's, Uffa Fox designed,
All varnished hot moulded wooden racing dinghy.

On Mon, 16 May 2005 10:30:55 GMT, "Roger Long"
wrote:

Like this, right?

http://home.maine.rr.com/rlma/Switch.jpg

I can appreciate the effect. I made a box in high school with a coil
in it and a switch made from a nail dangling in a ring. It had
textured aluminum foil sides wired to the coil and said "Mystery Box"
on top. It was a hoot when I left it in the faculty room.

Do you think I can get away with a single contact relay? The sealed
fog light relays that are readily available seem like they should be
sized and just right for this application.


I am sure you can get away with the one pole switch relay - but the
float switch then takes the motor current make and break and I suspect
the usual float switch won't feature 20 Amp contacts - but an auto
relay will. So there's a life trade-off.
If you can source a two pole relay, let the float switches handle the
modest relay current, and the second relay switch then handles any
reasonable - even unreasonable - bilge pump load.

Brian Whatcott Altus OK

I found LD1A-12F headlight/horn relays for six bucks at the auto
store and available here for less:

http://www.jameco.com/Jameco/catalogs/c252/P138.pdf

where I've ordered sockets with coil suppression diodes. The relays
are completely sealed and appear to be as watertight and ignition safe
as any marine unit. 30 Amp, 220 watts. It'll be a simple matter to
carry a spare and they can serve as the shut off switches if the pump
jambs.

I got the parts for the snubbers. Does the presence of the diode in
the socket change anything?

Many thanks for your help on this. It's what this group should be for
instead of worrying about who's pretending to be Peggie.

--

Roger Long

I'm not sure that there needs to be any snubbing in this arrangement.
For one thing, a 30 amp contact should easily handle the surge of 12 volt
bilge pump circuit being broken.
But mainly:
the relay connects across the hi level switch (after that switch has closed)
then when the hi level switch opens, the relay stays closed
and after the lo level switch opens (stopping the pump)
the relay opens.
So the relay never sees any starting or stopping load.

wot sort of switches are you using? I've had a terrible run with Rule. The
most reliable one I have sounds like it has a ball inside that runs along
and makes contact when the body tilts.

"Roger Long" wrote in message
...
I found LD1A-12F headlight/horn relays for six bucks at the auto
store and available here for less:

http://www.jameco.com/Jameco/catalogs/c252/P138.pdf

where I've ordered sockets with coil suppression diodes. The relays
are completely sealed and appear to be as watertight and ignition safe
as any marine unit. 30 Amp, 220 watts. It'll be a simple matter to
carry a spare and they can serve as the shut off switches if the pump
jambs.

I got the parts for the snubbers. Does the presence of the diode in
the socket change anything?

Many thanks for your help on this. It's what this group should be for
instead of worrying about who's pretending to be Peggie.

--

Roger Long