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
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