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.