Here is the electronic version of what you are talking about, a
latching relay.

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

The lower float switch goes on and nothing happens. When the top
switch goes on, current flows through the relay which closes a contact
that then bypasses the upper float switch. When the upper float
switch goes off, the relay remains on and the pump keeps running.
When the lower float switch goes back off, the circuit is interrupted,
the relay springs back, and the pump stops.

All this needs to work is a relay rugged enough to handle the current
draw of the pump without heating up or contributing too much voltage
drop. If anyone has specs handy for such a unit, I'd appreciate a
model number because I'll build this thing and report on it.

--

Roger Long

The other cool thing about relays is that they usually have multiple
contacts. If you want a cycle counter, pilot light, bell, or whistle,
it's just a matter of wiring it in. There are usually N.C. contacts
as well so, if there was something you didn't want to run at the same
time as the bilge pump, you could do that easily as well.

I'd wire the latching circuit across more than one set of contacts in
case of corrosion.

--

Roger Long

Change the circuit so that the relay coil is in parallel with the pump, and
the relay coil is in parallel with the upper switch. Any old 12V relay where
the contacts will carry the load of the pump will do.

"Roger Long" wrote in message
...
Here is the electronic version of what you are talking about, a
latching relay.

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

The lower float switch goes on and nothing happens. When the top
switch goes on, current flows through the relay which closes a contact
that then bypasses the upper float switch. When the upper float
switch goes off, the relay remains on and the pump keeps running.
When the lower float switch goes back off, the circuit is interrupted,
the relay springs back, and the pump stops.

All this needs to work is a relay rugged enough to handle the current
draw of the pump without heating up or contributing too much voltage
drop. If anyone has specs handy for such a unit, I'd appreciate a
model number because I'll build this thing and report on it.

--

Roger Long

I must be having an obtuse moment because I'm having trouble see what
you mean. Any chance you could sketch it?

Is this change necessary to use an ordinary 12 V. relay or just an
improvement?

--

Roger Long



"barry lawson" wrote in message
...
Change the circuit so that the relay coil is in parallel with the
pump, and
the relay coil is in parallel with the upper switch. Any old 12V
relay where
the contacts will carry the load of the pump will do.

Oh of course. Like this, right?

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

(I loaded the new sketch into the same URL)

I remember now the big fog lights I had on a car years ago. There was
a relay under the hood so all the juice for the big lights wouldn't be
running through the tiny switch in the panel. The relay was pretty
well sealed and intended to survive under the hood of a car so should
do pretty well if kept above the bilge water. I'll look for a couple
of those tomorrow.

--

Roger Long

On Sun, 15 May 2005 23:57:08 GMT, "Roger Long"
wrote:

Oh of course. Like this, right?

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

(I loaded the new sketch into the same URL)

I remember now the big fog lights I had on a car years ago. There was
a relay under the hood so all the juice for the big lights wouldn't be
running through the tiny switch in the panel. The relay was pretty
well sealed and intended to survive under the hood of a car so should
do pretty well if kept above the bilge water. I'll look for a couple
of those tomorrow.


Now, you're talking.
1) Make that a 12 volt relay with two normally open
20A DC rated switches
2) Dedicate one switch to the pump supply.
3) Add a snubber of 10 ohms in series with 0.01 microfarad (200 volt +
working)
across each of the two inductive pieces, which are
3.1) the relay coil
3.2) The motor inputs

4) Remember that sparking contacts in the vicinity of a gas
tank/engine make loud noises, so a metal clad relay would be better,
in a decent blade socket.

Brian Whatcott Altus, OK

Brian Whatcott Altus OK

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.

--

Roger Long



"Brian Whatcott" wrote in message
...
On Sun, 15 May 2005 23:57:08 GMT, "Roger Long"
wrote:

Oh of course. Like this, right?

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

(I loaded the new sketch into the same URL)

I remember now the big fog lights I had on a car years ago. There
was
a relay under the hood so all the juice for the big lights wouldn't
be
running through the tiny switch in the panel. The relay was pretty
well sealed and intended to survive under the hood of a car so
should
do pretty well if kept above the bilge water. I'll look for a
couple
of those tomorrow.


Now, you're talking.
1) Make that a 12 volt relay with two normally open
20A DC rated switches
2) Dedicate one switch to the pump supply.
3) Add a snubber of 10 ohms in series with 0.01 microfarad (200 volt
+
working)
across each of the two inductive pieces, which are
3.1) the relay coil
3.2) The motor inputs

4) Remember that sparking contacts in the vicinity of a gas
tank/engine make loud noises, so a metal clad relay would be better,
in a decent blade socket.

Brian Whatcott Altus, OK

Brian Whatcott Altus OK

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

That's it. Headlight relay might do, just make sure it is meant to be on all
the time; not short term like a horn relay might be.
"Roger Long" wrote in message
news
Oh of course. Like this, right?

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

(I loaded the new sketch into the same URL)

I remember now the big fog lights I had on a car years ago. There was
a relay under the hood so all the juice for the big lights wouldn't be
running through the tiny switch in the panel. The relay was pretty
well sealed and intended to survive under the hood of a car so should
do pretty well if kept above the bilge water. I'll look for a couple
of those tomorrow.

--

Roger Long