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

Sorry to hear about your experience with Rule since I have two of
them. I'm whipping myself soundly for buying mercury switches after
preaching against them but they didn't have any clean ones in the
store. I'm glad to hear that the rolling ball ones are reliable.
Johnson makes one which I'll try to get a pair of them for the bottom
set.

I understand that the Rule's go because the repeated flexing breaks
the wires going to the switch. Is that consistent with your
experience?

I really appreciate the advice on the snubbing because incorporating
it was going to required a whole enclosure for the switch set up.

--

Roger Long



"barry lawson" wrote in message
...
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

Roger Long wrote:

I really appreciate the advice on the snubbing because incorporating
it was going to required a whole enclosure for the switch set up.

Minimum Snubbing, put a snubber across the pump motor. If you solder
stranded wires onto the resistor and the capacitor and twist and solder
the two components in series then put in a n old 35mm film canister and
pour in epoxy resin (glass microbubbles would be fine as a filler), you
will have a sealed unit you can connect to the motor terminals.

Why not post a link to the new circuit diagram for some peer review of
the final design?


--
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.

Why would the pump motor need snubbing in this design more than in the
usual set up? Or, is snubbing one of those things that is always a
good idea but seldom done?

Good idea on the potting.

I've been constantly updating the jpg behind the original link which
is:

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

The socket I'm getting for the relay has a "coil suppression diode".
I assume that is intended to do the same sort of thing by preventing
current from flowing in reverse when the field collapses through the
coil.

--

Roger Long



"Ian Malcolm" wrote in
message ...
Roger Long wrote:

I really appreciate the advice on the snubbing because
incorporating it was going to required a whole enclosure for the
switch set up.

Minimum Snubbing, put a snubber across the pump motor. If you
solder stranded wires onto the resistor and the capacitor and twist
and solder the two components in series then put in a n old 35mm
film canister and pour in epoxy resin (glass microbubbles would be
fine as a filler), you will have a sealed unit you can connect to
the motor terminals.

Why not post a link to the new circuit diagram for some peer review
of the final design?


--
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.

Roger Long wrote:
Why would the pump motor need snubbing in this design more than in the
usual set up? Or, is snubbing one of those things that is always a
good idea but seldom done?
Snubbing provides a path for the current flowing in a coil to decay into
rather than sparking accross the opening switch contacts. The bigger
the coil the more it needs snubbing. Worst case, the arc can actuallly
weld the contacts so they dont switch no more. Lack of snubbing on
motor loads is probably a major factor in the notorious poor reliability
of float switches.



Good idea on the potting.

I've been constantly updating the jpg behind the original link which
is:

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

Hmm, if EITHER switch fails open, you loose the pump. If you move the
pump +ve to the JUNCTION of the two switches (dont change anything
else), then only the top switch is critical. Also you could then
manually override the switches to run the pump by pulling the relay and
stuffing a (pre prepared?) jumper wire down the appropriate contacts of
the socket. Otherwise it WILL work the way its ment to, the discussion
is now just "Can we 'gold plate' it at no/little extra cost?".

The socket I'm getting for the relay has a "coil suppression diode".
I assume that is intended to do the same sort of thing by preventing
current from flowing in reverse when the field collapses through the
coil.
Yes and No. it does the same thing by letting the existing current in
the relay coil flow round and round chasing its own tail until it
dwindles to nothing. If you ever want an electric 'palm tingler' try a
9v battery, and a fairly chunky relay connected so as to open its own
coil currrent circuit (no snubbers/diodes). Typically it will develop a
couple of hundred volts accross the contacts. Oddly enough, this is the
first thing about relays an average to bright 10 year old will discover
.. . . :-)

I'm off sailing for a couple of days, back Friday. Probably get to spend
this afternoon upsidown is someon else's bilge & lockers looking at
'lectrickery. . .
--
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.