Diode question for Brian or Larry
 

I got my bilge pump controller put together and it looks pretty neat.
It will fit right under the fuse panel I put in and the relay can be
easily pulled and replace.

I tested it and my portable 12 V battery immediately gave the "Tink"
that means the fuse blew. I checked and there were zero ohms across
the terminals to the relay coil. I put this together very carefully
so it was hard to believe I had a short. When I opened it up to look,
I noticed that the suppression diode across the coil had burned into
the wire slightly. I cut it and the short disappeared. I then cut
the suppression diodes out of both relay sockets.

There was no + or - indication on the relay wiring but one of the coil
wires was red. Did I blow the diode by hooking up with reverse
polarity?

--

Roger Long

Roger Long wrote:
I got my bilge pump controller put together and it looks pretty neat.
It will fit right under the fuse panel I put in and the relay can be
easily pulled and replace.

I tested it and my portable 12 V battery immediately gave the "Tink"
that means the fuse blew. I checked and there were zero ohms across
the terminals to the relay coil. I put this together very carefully
so it was hard to believe I had a short. When I opened it up to look,
I noticed that the suppression diode across the coil had burned into
the wire slightly. I cut it and the short disappeared. I then cut
the suppression diodes out of both relay sockets.

OOPS

There was no + or - indication on the relay wiring but one of the coil
wires was red. Did I blow the diode by hooking up with reverse
polarity?


YES, wrong polarity would put a massive current through the diode.
Overcurrent is the quickest way to destroy a diode I know. Thhe usual
failure mode for a diode is dead short unless you put enough current
through it to physically rupture the package, when the short may change
to an open circuit.

As you have found, this results in total pump failure because the supply
fuse has blown. :-( Removing the diodes is the correct thing to do. As
you have now removed the protection they offered the switches and
contacts, fit a snubber circuit across each relay coil. Snubbers are
not polarity sensitive. It will work without them but for how long?
They are not exactly expensive or difficult to fit.

Can you clarify that the diodes were ONLY in the sockets, not inside the
relays? At the moment I am concerned that if you plug in a replacement
relay *with* a diode if the system is giving trouble, you may instantly
blow the fuse rendering the pump totally dead. Relays with diodes
usually have some polarity marking on the coil terminals. May just be a
red dot, a tiny plus sign or even a circuit diagram showing the coil and
the diode with pin numbers. Occasionally you get one that you have to
read the manufacturer's databook to confirm it has a diode.

--
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.

Yes the diodes were in the sockets. It makes sense then that the
relay had no polarity markings because it itself is not polarity
sensitive. The red wire on the socket should have tipped me off but
that's the problem with staying up late at night working on this
stuff:)

Here's a picture of the finished controller:

http://home.maine.rr.com/rlma/Bilge.htm#Controller

The diodes are way too sensitive a component to have buried inside a
critical system box like this. I have the snubber components and will
build them this morning. There is now nothing inside the box but
wiring. Even if both relays should go bad, I can jumper a wire across
the terminals to get the system pumping. I'll mark the box with the
appropriate jumper location just in case.

Thanks,

(I should have included you in my header.)

--

Roger Long



"Ian Malcolm" wrote in
message ...
Roger Long wrote:
I got my bilge pump controller put together and it looks pretty
neat. It will fit right under the fuse panel I put in and the relay
can be easily pulled and replace.

I tested it and my portable 12 V battery immediately gave the
"Tink" that means the fuse blew. I checked and there were zero
ohms across the terminals to the relay coil. I put this together
very carefully so it was hard to believe I had a short. When I
opened it up to look, I noticed that the suppression diode across
the coil had burned into the wire slightly. I cut it and the short
disappeared. I then cut the suppression diodes out of both relay
sockets.

OOPS

There was no + or - indication on the relay wiring but one of the
coil wires was red. Did I blow the diode by hooking up with
reverse polarity?


YES, wrong polarity would put a massive current through the diode.
Overcurrent is the quickest way to destroy a diode I know. Thhe
usual failure mode for a diode is dead short unless you put enough
current through it to physically rupture the package, when the short
may change to an open circuit.

As you have found, this results in total pump failure because the
supply fuse has blown. :-( Removing the diodes is the correct thing
to do. As you have now removed the protection they offered the
switches and contacts, fit a snubber circuit across each relay coil.
Snubbers are not polarity sensitive. It will work without them but
for how long? They are not exactly expensive or difficult to fit.

Can you clarify that the diodes were ONLY in the sockets, not inside
the relays? At the moment I am concerned that if you plug in a
replacement relay *with* a diode if the system is giving trouble,
you may instantly blow the fuse rendering the pump totally dead.
Relays with diodes usually have some polarity marking on the coil
terminals. May just be a red dot, a tiny plus sign or even a circuit
diagram showing the coil and the diode with pin numbers.
Occasionally you get one that you have to read the manufacturer's
databook to confirm it has a diode.

--
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 in
:

Did I blow the diode by hooking up with reverse
polarity?


Yep. The diode only conducts when the field in the coil of the relay
collapses, when you turn the power to it off. The diode is reverse biased
(+ power to its banded cathode end, - power to its anode) when the relay is
energized. You had it connected up backward, zapping the diode to a short.

Oops....

+12-------coil----------12
| |
--|--
band noband

"Larry W4CSC" wrote in message
...
"Roger Long" wrote in
:

Did I blow the diode by hooking up with reverse
polarity?


Yep. The diode only conducts when the field in the coil of the relay
collapses, when you turn the power to it off. The diode is reverse biased
(+ power to its banded cathode end, - power to its anode) when the relay
is
energized. You had it connected up backward, zapping the diode to a
short.

Oops....

+12-------coil----------12

| |
--|--
band noband

Not clear. Fuse is blown but one would have to check to see if the diode is
blown. Suppression diodes are generally rugged little things. They may well
last long enough to blow the fuse without going out.

There are only a zillion or two diodes launched in this application. I
don't think I would use a solenoid or a relay without one. If worried get a
bigger diode.

Larry W4CSC wrote:
"Roger Long" wrote in
:


Did I blow the diode by hooking up with reverse
polarity?



Yep. The diode only conducts when the field in the coil of the relay
collapses, when you turn the power to it off. The diode is reverse biased
(+ power to its banded cathode end, - power to its anode) when the relay is
energized. You had it connected up backward, zapping the diode to a short.

Oops....

+12-------coil----------12
| |
--|--
band noband


I'm confused. Perhaps this is why I left hardware engineering for
software. I thought the purpose of a diode was to pass current one
way, and block it the other. Did this fail because the passed current
was too high, or because the blocked voltage was too high? Or is
there something else I'm missing? Should a small resistor have been
put in series? Is the coil storing up too much energy? Why can't
everything just be digital?

While I'm on the subject, since I have twin engines, some of my
instruments, such as the fuel gauge are fed by the key switch from one
engine. Is there a way to hook up 2 diodes to allow either feed to
work/ Radio Shack part numbers please ;-)

Nope. It was a dead short. I'm putting in the 10 ohm / .01 mfd
suppressors instead.

--

Roger Long

Comments below:
"Jeff" wrote in message
...
Larry W4CSC wrote:
"Roger Long" wrote in
:


Did I blow the diode by hooking up with reverse
polarity?



Yep. The diode only conducts when the field in the coil of the relay
collapses, when you turn the power to it off. The diode is reverse
biased
(+ power to its banded cathode end, - power to its anode) when the relay
is
energized. You had it connected up backward, zapping the diode to a
short.

Oops....

+12-------coil----------12
| |
--|--
band noband


I'm confused. Perhaps this is why I left hardware engineering for
software. I thought the purpose of a diode was to pass current one
way, and block it the other. Did this fail because the passed current
was too high, or because the blocked voltage was too high? Or is
there something else I'm missing?

Simple answer, explained elsewhere, repeated here. Roger hooked his new
sump pump system to a test battery to test it, but unfortunately connected
the battery backwards (+ where - should have been). The diodes (two pumps,
two relays, two diodes) normally would have blocked the 12 v. from the
battery and passed only the reverse current from the collapsing relay coil
field when the circuit opened. Instead, because the polarity of the circuit
was reversed, the diode passed the full current available from the battery,
essentially, the diode was a dead short accross the battery, so the diode(s)
burned up and shorted itself (themselves) permanently.

Rodger won't do that again I'll bet.

Should a small resistor have been
put in series? Is the coil storing up too much energy? Why can't
everything just be digital?

While I'm on the subject, since I have twin engines, some of my
instruments, such as the fuel gauge are fed by the key switch from one
engine. Is there a way to hook up 2 diodes to allow either feed to
work/ Radio Shack part numbers please ;-)

Yes, two diodes, arranged in a Y, each diode feeding power from each key
switch coming together, then feeding power to the instruments you want to
continue to operate with only one engine on. The diodes need to be rated at
a high enough wattage (volts x amps = watts) to pass enough current to
operate the instruments. There will be a slight voltage drop across the
diodes so you may experience lower than expected readings on the
instruments.
--
Ken Heaton & Anne Tobin
Cape Breton Island, Canada
kenheaton AT ess wye dee DOT eastlink DOT ca

Jeff wrote in :

I'm confused. Perhaps this is why I left hardware engineering for
software. I thought the purpose of a diode was to pass current one
way, and block it the other. Did this fail because the passed current
was too high, or because the blocked voltage was too high?

When he hooked it up backwards, the diode was forward biased straight
across the battery's terminals. Current went through the roof, welding the
junction to a short which, microseconds later, blew the fuse. Once welded
to a short, unless you can really melt the mounting, it stays a
short....across the coil, not in series with it. It's a short both ways at
that point.

This diode's function is to short the relay's coil when the coil's field
collapses, producing inductive kick which forward biases the diode for a
few milliseconds each time power is removed from the coil. Otherwise, the
inductive kick, which could be several hundred volts for a few microseconds
like the spark from an ignition coil, could destroy the control electronics
or switch contacts which arc each time it is de-energized. With the diode
in place, inductive kick produces .6v pulses, the forward bias voltage of
the diode as it sinks the kick's power current pulse.

Or is
there something else I'm missing? Should a small resistor have been
put in series?

No, as the diode is normally REVERSE biased by the applied power. I
doesn't conduct except for that little kick of the coil at de-energization.

Is the coil storing up too much energy? Why can't
everything just be digital?

It is digital...(c; 1 = relay on.....0 = relay off...but it's not
hexidecimal..making it harder for a software man to comprehend...hee hee.


While I'm on the subject, since I have twin engines, some of my
instruments, such as the fuel gauge are fed by the key switch from one
engine. Is there a way to hook up 2 diodes to allow either feed to
work/ Radio Shack part numbers please ;-)


Any 1 amp, 50V piv or higher rectifier will work.....for this OR
circuit...(c;

Hook the anodes of the diodes, one to each power switch on each engine.
Hook the cathodes (banded end) together to the common power + lead to each
fuel guage. If either engine is turned on, its diode will conduct turning
on both fuel guages. (classic OR gate - DDL logic!)

engine 1----------------||---------\
\
\
engine 2----------------||------------\-----------fuel guage +

Circuit may be too simple for mainframe engineers...(c;

Roger Long wrote:
Yes the diodes were in the sockets. It makes sense then that the
relay had no polarity markings because it itself is not polarity
sensitive. The red wire on the socket should have tipped me off but
that's the problem with staying up late at night working on this
stuff:)
Well I reckon you'll learn to get some sleep before working on
expensive/critical stuff (if possible). :-)

Here's a picture of the finished controller:

http://home.maine.rr.com/rlma/Bilge.htm#Controller

Nice to see the end result.

The diodes are way too sensitive a component to have buried inside a
critical system box like this.
Its not that they are very sensitive, its their rather unpleasant
failure mode. :-( This was why I and others were encouraging you to use
snubbers instead. One can design them in safely but that can get way
too technical for all except denisons of sci.electronics.design or
similar 'wire headed' hangouts. :-)

I have the snubber components and will
build them this morning. There is now nothing inside the box but
wiring. Even if both relays should go bad, I can jumper a wire across
the terminals to get the system pumping. I'll mark the box with the
appropriate jumper location just in case.
Couple of spare relay going in your spares kit I hope. Might as well
make up the jumper wire with appropriate ends and keep it taped to the box.

Thanks,

(I should have included you in my header.)
No worries. B.T.W., I am off sailing for a while so wont be able to
offer any more feedback.




--
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.

Larry W4CSC wrote:
Jeff wrote in :


I'm confused. Perhaps this is why I left hardware engineering for
software. I thought the purpose of a diode was to pass current one
way, and block it the other. Did this fail because the passed current
was too high, or because the blocked voltage was too high?


When he hooked it up backwards, the diode was forward biased straight
across the battery's terminals. Current went through the roof, welding the
junction to a short which, microseconds later, blew the fuse. Once welded
to a short, unless you can really melt the mounting, it stays a
short....across the coil, not in series with it. It's a short both ways at
that point.

Thanks. The aspect that eluded me was that the dead short to ground
would pass "infinite" current until something popped, like the
breakers. Most circuits with diodes, such as rectifiers, have some
resistance implied elsewhere.




This diode's function is to short the relay's coil when the coil's field
collapses, producing inductive kick which forward biases the diode for a
few milliseconds each time power is removed from the coil. Otherwise, the
inductive kick, which could be several hundred volts for a few microseconds
like the spark from an ignition coil, could destroy the control electronics
or switch contacts which arc each time it is de-energized. With the diode
in place, inductive kick produces .6v pulses, the forward bias voltage of
the diode as it sinks the kick's power current pulse.

Yup. Subtle things like that I tend to remember. Its only the
obvious that I forget.

....
Why can't everything just be digital?


It is digital...(c; 1 = relay on.....0 = relay off...but it's not
hexidecimal..making it harder for a software man to comprehend...hee hee.

I beg your pardon. I'm software from the "old school," as in front
panel lights and flipping switches to install bootstraps and debug. I
still have the front panel from the first computer I owned - a Data
General Nova 1200.
http://ed-thelen.org/comp-hist/dg-nova.html

And since I came from the "mini" world, I learned Octal long before Hex.



While I'm on the subject, since I have twin engines, some of my
instruments, such as the fuel gauge are fed by the key switch from one
engine. Is there a way to hook up 2 diodes to allow either feed to
work/ Radio Shack part numbers please ;-)



Any 1 amp, 50V piv or higher rectifier will work.....for this OR
circuit...(c;

Hook the anodes of the diodes, one to each power switch on each engine.
Hook the cathodes (banded end) together to the common power + lead to each
fuel guage. If either engine is turned on, its diode will conduct turning
on both fuel guages. (classic OR gate - DDL logic!)

engine 1----------------||---------\
\
\
engine 2----------------||------------\-----------fuel guage +

Circuit may be too simple for mainframe engineers...(c;

Thanks. It looks too obvious for me.

Ken mentioned that the voltage drop could affect the gauges. I can
see how the cheap fuel gauge might have a problem but it made me
wonder if the water temp gauges would be affected. Not that I would
need the diodes for them, but the alternator output can vary from 12
something (turned off) to 14.5, depending on what's going on in the
regulator's little mind. I have to believe that such fluctuations
don't make much of a difference in the temp readout, but I couldn't
find a spec on the Teleflex site that indicated they were stable over
a reasonable voltage range. Any thoughts?

Roger,
You can do that if you want to, but diodes work better. You may still
get a spike on the line with the RC setup, but that won't matter to
anything but the electronics. The RC set does what it does by thying to
limit the rate of rise when the switch opens, but the diode makes the
power from the widing stay in the winding.

That is why little DIN (automotive default these days) relays are marked
87 for signal and 31 for ground.

Newer cars have a lot of this stuff going on.

Matt Colie

Roger Long wrote:
Nope. It was a dead short. I'm putting in the 10 ohm / .01 mfd
suppressors instead.

Interesting point. I can wire the diodes on the outside of my
controller just as easily as the snubber. If I do see any evidence of
spikes, I'll do that.

For future reference, do you know which diodes to use? I foolishly
tossed the ones I cut out of the sockets.

It's unlikely I'll see a problem though. The water will probably only
get to the high switch in our boat if the stuffing box hose splits.
If the boat is unattended, the minimal electronics we have will be
off. Mostly, this system will be operated by picking up one of the
float switches when checking the bilge. The most used feature of it
will be not having to hang down there holding the switch until the
bilge empties. Just being able to flip it up and forget it will be
worth all the effort I put into it. Operating in that mode, the relay
never engages.

--

Roger Long



"Matt Colie" wrote in message
...
Roger,
You can do that if you want to, but diodes work better. You may
still get a spike on the line with the RC setup, but that won't
matter to anything but the electronics. The RC set does what it
does by thying to limit the rate of rise when the switch opens, but
the diode makes the power from the widing stay in the winding.

That is why little DIN (automotive default these days) relays are
marked 87 for signal and 31 for ground.

Newer cars have a lot of this stuff going on.

Matt Colie

Roger Long wrote:
Nope. It was a dead short. I'm putting in the 10 ohm / .01 mfd
suppressors instead.

Comment below:
"Jeff" wrote in message
...
Larry W4CSC wrote:
Jeff wrote in :

chunks of stuff snipped for brevity

Ken mentioned that the voltage drop could affect the gauges. I can
see how the cheap fuel gauge might have a problem but it made me
wonder if the water temp gauges would be affected. Not that I would
need the diodes for them, but the alternator output can vary from 12
something (turned off) to 14.5, depending on what's going on in the
regulator's little mind. I have to believe that such fluctuations
don't make much of a difference in the temp readout, but I couldn't
find a spec on the Teleflex site that indicated they were stable over
a reasonable voltage range. Any thoughts?

I haven't seen a schematic for boat instrument systems but will make a
comment on how automotive instrument systems used to work. (They may still
work this way, but I haven't been around this stuff for years) Automotive
instrument systems (used to) receive their 12 V. + feed from a simple
voltage regulator mounted in the dashboard wiring system. This prevented
the varying voltage coming from the alternator from causing erratic readings
on the instruments. Automotive gauges at the time were thermal in operation
(because they were much cheaper to build that way), and so were sensitive to
voltage variation. You could tell good instruments (usually aftermarket)
from these thermal types when you turned the ignition switch on. Good ones
would snap to the indicated reading, the thermal ones would take a few
seconds to rise up to the correct indication. Gas gauges would often not
give a true reading of tank level until you started the motor and the
alternator kicked in. Again, I'm not sure if boat gauges are wired this
way.
--
Ken Heaton, Cape Breton Island, Canada
kenheaton AT ess wye dee DOT eastlink DOT ca

"Ken Heaton" wrote in
news:J3Mle.13142$HI.6104@edtnps84:

Gas gauges would often not
give a true reading of tank level until you started the motor and the
alternator kicked in. Again, I'm not sure if boat gauges are wired this
way.


Of course, we all know how DEAD ACCURATE those wonderful BOAT gas guages
monitor the fuel supply that can strand you miles from nowhere.

When my Sea Ray read 1/2 full, it meant you used 6.5 of the 25 gallon tank.
When it read empty, you had used 9.5 gallons of the 25 gallon tank. When
it read below empty, you simply opened the "trunk" and leaned down into the
bilge so you could see the fuel level in the stern end of the cheap
polyethelene tank supported by two little plastic brackets digging into the
milk jug material 25 gallons of fuel were waiting in to blow you all to
hell if it leaked. It's nice-looking Sea Ray gas guage was damned near
useless....

The tach seemed to work....