Bilge Pump Switch

[Vito]

Well, Vito, not everyone's boat is just like yours. Many people have... oil in the bilges ...
While you may have only one battery and can reach it in seconds not everyone can.

Then "many people" should fix their leaks. It should never be necessary
to turn off the pumps in seconds.

Your installation does not apply to all or perhaps even most boaters.

True, and that's my point. Not ALL boats need a manual switch in series
with the automatic switch either.

If someone is aboard then that person may see the oil and do something to
reduce the quantity pumped overboard. It is that simple.

May ... might ... perhaps ... Hogwash. Nothing on my boat leaks oil
because I fix leaks. I also prudently keep rings of absorbers around any
potential leakers to catch any drip before any reach the bilge.

Quite frankly I worry more about my bilge overboard than I do your
caldera. If your caldera blew up it would not have nearly the same
impact on me as a few tablespoons of oil in the water through my bilge pump.

There'd be several years of winter, with no crops anywhere. The UK would
become like Iceland. Fortunately, it happens almost as often as bilges
fill with diesel (c:

When I pump bilges I monitor the discharge and am ready to switch
the pump off at the first indication of a sheen. I also have an oil
content monitor which will detect oil in concentrations greater than
15ppm and shut the pump off but I still watch the overboard when I am
onboard. It is just good practice, it is not paranoia.

I have a far simpler solution: I examine my bilge regularly and if there
were any oil I'd search out the leak and fix it. Then I'd manually pump
into buckets and decant/filter to remove any trace of oil. But that
never happens because I don't even allow salt water to accumulate, but
instead wash my bilges down with fresh water every few months. Of course
when one's leak prevention regimen is shoddy .... (c:

 

[Rick]

I have a far simpler solution: I examine my bilge regularly and if there
were any oil I'd search out the leak and fix it.

Thank you for being such a good citizen and conscientious boater.

Bon Voyage.

Rick

 

[Ian Malcolm]

The back EMF spike on a diode is due to the device's finite turn on
time, so yes, there is a volt spike to be considered....

Brian Whatcott Altus OK

OK, I freely admit that the diode has a finite turn on time, but PIV isn't
relevent here as the diode is about to go into forward conduction to carry
the decaying current through the relay coil. dI/dt might be an issue as
if it has a large junction area, you may get a transient excessive current
density in one part of the junction forming a hot spot leading to junction
failure, but do you really think this will be an issue with most types of
bilge pump? Also I did suggest mounting the relay up high so there should
be a tiny but significant amount of cable capacitance to take the edge off
the spike as well. I suppose if you want to be really obsessive, a RC
snubber could be added accross each diode. This is however rec.boats and
uk.rec.boats.power, not milspec.boats. -)

I am surprised you havent picked up on the issue that the relay is going
to turn off slower as the flux in the core cant decay as fast if the coil
current continues to circulate through a diode. I'd personally prefer to
use the same sort of diode, capacitor, resistor snubber network as is used
in most SMPSUs, but really didn't fancy explaneing it on usenet in a non
electronics group.

I still belive that my revised choice of parts is a good design choice
albeit not ideal if cost is not an issue, and my original choice was
useable. If you have any source that states otherwise, well in this
trade, you never stop learning, so I'd be glad to continue my education
here or via email.
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.
'Stingo' Albacore #1554 - 15' Uffa Fox designed, All varnished hot moulded
wooden racing dinghy circa. 1961

 

[Larry Demers]

Only half of it. The diode will only kill one polarity of the pulses, leaving a
pretty good spark. Best to use large silver contacts on the relay, with a good
cleaning action when opened. This will help clean through any carbon forming.
The real danger is pitting of the contacts from these pulses. But with large
contacts, and a reverse EMF diode as noted, the power of the arc may be
controlled, but not eliminated. A series cap with the diode seems like a better
idea to try.

Larry DeMers

 

[Derek.Moody]

Haven't heard any discussion of the Bilge Buddy switches. They have two
prongs (conductors) which, when the water level rises, completes the circuit
and turns on the pump. They are also supposed to prevent the accidental
pumping of diesel. I suspect because diesel fuel is not as conductive as
water. Has anyone used this type of switch?

I have seen a crude version. The owner claimed it worked OK (saltwater) but
I'd expect poorer response in freshwater or if rainwater were the main
problem.

Cheerio,

--

 

[surfnturf]

I did, but it runs in the family.
surfnturf

How could I forget Alzheimer's?

Steve

 

[del cecchi]

Only half of it. The diode will only kill one polarity of the pulses, leaving a
pretty good spark. Best to use large silver contacts on the relay, with a good
cleaning action when opened. This will help clean through any carbon forming.
The real danger is pitting of the contacts from these pulses. But with large
contacts, and a reverse EMF diode as noted, the power of the arc may be
controlled, but not eliminated. A series cap with the diode seems like a better
idea to try.

Larry DeMers

This is a DC system in the average boat. There is only one polarity of
inductive kick. Diodes work fine. Capacitors in series with the diode
wouldn't work at all.

del cecchi

 

[Vito]

This is a DC system in the average boat. There is only one polarity of
inductive kick. Diodes work fine. Capacitors in series with the diode
wouldn't work at all.

That's odd considering that literally millions of DC automobile ignition
systems used a capacitor in parallel with the "points" to protect them
from the coil's inductive kick. BTW, the "kick" is damped AC.

 

[Vito]

The climate of Iceland is not much different from the UK one, maritime
temperate with mild winters and cool summers.
You were probably thinking about Greenland?

Thank you for correcting my misconception. I hope I can visit someday.
But what makes your fishermen eagerly attack, beach and kill 660#
sharks?

 

[Vito]

.... Guess what -- the pump draws 5 times that, so the switches
fail predictably after a couple hundred days of use. This is a long
time for the typical rec boat, but a nuisance for the live-aboard.

My bilge pump switch is powered up 24/7 whether I'm aboard or not, so
why would it die faster if I lived aboard?

 

[Del Cecchi]

That has a different reason. Damping a coil with a diode does the job, since
the induction voltage is ALWAYS the opposite as the originating voltage.
But, using a diode keeps the current flowing while the magnetic field
collapses. This causes a slow collapse of the field. In a coil in the car
(is it called bobbin?) has to produce a high voltage and therefore the field
has to collapse as fast as possible. Therefore a capacitor is used with
certain value to get the best trade-off between generated high voltage and
RF interference surpression.

Meindert

The capacitor across the points has its voltage reset to zero when the
points close. The capacitor acts to supress arcing by slowing the rise time
of the current decrease when the points open. The resulting oscillation in
the series tuned circuit is damped by the secondary driving the spark
through the plug.

In the case of the relay coil, there is no secondary. If there were no
diode, the tuned circuit would oscillate for a long time. With the diode,
the inductive kick will be stored on the capacitor and, being unable to
discharge through the reverse biased diode, will stay there for a long time.
During that time the diode will never turn on, due to the voltage on the
capacitor.

del cecchi

 

[Glenn Ashmore]

The climate of Iceland is not much different from the UK one, maritime
temperate with mild winters and cool summers. You were probably
thinking about Greenland?

I figured it must not be terribly bad in Iceland. Otherwise they would
not be able to grow all those gorgeous women.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Paul E. Bennett]

If you checked back the 1N4001 was for across the relay coil. As Ian
stated "If you are getting 100V spikes on your 12V bus, you've got
other problems than premature failure of bilge pump switches. -)"
The purpose of the diode is to clamp the reverse EMF to the supply
rail (which should be a low impedance path). The resistor and capacitor
network I mentioned reduces EMI (which will keep RCA and/or FCC happy).

I also indicated that a much heavier diode would be required across the
pump. Most motors require of the order of 2.5 times the maximum running
current to start. Stall currents can be higher than this.

Such protective components need to be rated with enough margin to ensure
that they are unlikely to fail. A minimum factor of three is good. Better
would be a factor of ten.

--
********************************************************************
Paul E. Bennett ....................<email://[email protected]>
Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************

 

[Vito]

the induction voltage is ALWAYS the opposite as the originating voltage.

At first. But electrons have inertia so they keep flowing until they've
recharged the coil in the opposite polarity, albiet not as fully. Then
they go the other way, etc., creating a damped AC current.

 

[Vito]

The small oscillation you get has nothing to do with mass of electrons and
their inertia. It is caused by the fact that every coil has a bit of
parasitic capacitance, forming a resonant loop with the inductance of the
coil, ...

Yes but Meindert old bean, if electrons didn't have inertia resonant
circuits wouldn't resonate.

 

[Del Cecchi]

Yes but Meindert old bean, if electrons didn't have inertia resonant
circuits wouldn't resonate.

Is this a feeble attempt at humor, or are you an idiot? Sometimes hard to
tell on the net.

del cecchi

 

[Paul E. Bennett]

///


What is it about UK contributors? Slow scopes?
While I was there, I saw plenty of Tektronix scopes capable of showing
at least some of the transient excursions to which autos are subject.

By other problems we do not imply that we cannot see or measure the
transients. It is just that if these do exist to an extent where
they are significant there are likely to be Radio Frequency
Interference issues that need to be dealt with to comply with the
EMC directive.

--
********************************************************************
Paul E. Bennett ....................<email://[email protected]>
Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************

 

[Vito]

Is this a feeble attempt at humor, or are you an idiot?

Neither one. Do you doubt that electrons have mass and therefore
inertia? If they did not, then current would stop at once when the coil
unsaturated. But it does not. The little buggers keep going til they've
charged the capacitor (parasitic in this case but still real). Then
(Bugle sounds retreat) they head the other way re energizing the coil
..... etc. .... creating a damped AC wave.

Sometimes hard to tell on the net.

Yes indeed.

 

[Vito]

A little OT, isn't it true that the reason that virtually all auto and
boat DC systems are negative ground is that going that way was the
automakers' consensus of the better place to have the erosion in the
points -- the positive ground cars (including Rolls Royce into the
fifties) thought the other side was better?

Most Brit autos used positive ground (Earth) but I think it was more a
toss of the coin for standardization than any technical reason. Britian
held onto positive earth electrics and Whitworth fastners until the
export market made them rethink their decisions. Same reason we (US) are
drifting toward the meteric system.

 

[Rick]

And if you still believe in electron inertia, I advise you to go and read a
book about basic electric laws.

But Meindert, I weld from time to time and as you probably know welding
requires large current flows. This means huge numbers of electrons are
racing along the wire to the welding rod.

I have noticed that when I pull the rod away from the work it always has
a big blob on the end. Are you saying this isn't because all those
electrons kept rushing into the hot metal and caused it to bulge out
when they had no place to go?

Rick