Roger Long wrote:
Why would the pump motor need snubbing in this design more than in the
usual set up? Or, is snubbing one of those things that is always a
good idea but seldom done?
Snubbing provides a path for the current flowing in a coil to decay into
rather than sparking accross the opening switch contacts. The bigger
the coil the more it needs snubbing. Worst case, the arc can actuallly
weld the contacts so they dont switch no more. Lack of snubbing on
motor loads is probably a major factor in the notorious poor reliability
of float switches.



Good idea on the potting.

I've been constantly updating the jpg behind the original link which
is:

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

Hmm, if EITHER switch fails open, you loose the pump. If you move the
pump +ve to the JUNCTION of the two switches (dont change anything
else), then only the top switch is critical. Also you could then
manually override the switches to run the pump by pulling the relay and
stuffing a (pre prepared?) jumper wire down the appropriate contacts of
the socket. Otherwise it WILL work the way its ment to, the discussion
is now just "Can we 'gold plate' it at no/little extra cost?".

The socket I'm getting for the relay has a "coil suppression diode".
I assume that is intended to do the same sort of thing by preventing
current from flowing in reverse when the field collapses through the
coil.
Yes and No. it does the same thing by letting the existing current in
the relay coil flow round and round chasing its own tail until it
dwindles to nothing. If you ever want an electric 'palm tingler' try a
9v battery, and a fairly chunky relay connected so as to open its own
coil currrent circuit (no snubbers/diodes). Typically it will develop a
couple of hundred volts accross the contacts. Oddly enough, this is the
first thing about relays an average to bright 10 year old will discover
.. . . :-)

I'm off sailing for a couple of days, back Friday. Probably get to spend
this afternoon upsidown is someon else's bilge & lockers looking at
'lectrickery. . .
--
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.