Morris Minor Owners Club

Hi,

I'm trying to wire a security device that would keep a switch A open when ignition is off, keep it open when the ignition is on then close it and keep it closed when a control switch is pushed then released. When the ignition is cut the switch A would open again.

The different states would be as follows:

1. Ignition off: switch A open
2. Ignition on: switch A open
3. Ignition on + control switch C closed: switch A closed
4. Ignition on + control switch C released: switch A closed
5. Ignition off: switch A open

Reportedly it would be possible to do this with a SPNO relay (e.g. Maplin ref N02AW)

http://www.maplin.co.uk/Search.aspx?cri ... ce=15&SD=Y

As anybody tried this or would know how to do it?

Regards,
Pascal

Position 3: Ign on +control switch Closed: Control SW live feed is taken
from the side of the ignition switch which is only live when it is ON. This would operate the relay. The relay would have contacts wired to supply
Live feed to itself thus keeping it operated when the Control SW was released. Provided that this live feed was supplied by the ignition switch only in the ON position the relay would remain operated until the
ignition was turned off. This 'self operatiing ' condition would used one
set of the relay contacts but you would have at least one other pair to
play with.

It can be done with a single pole normally open or a double throw relay.

diagram below shows how.



'supply' is from the switched ignition supply
'ground' and 'output' are obvious

BUT if you draw too much current on the output you may cause the relay to turn off, the switch must be able to handle the current required by the output as for a brief period it will carry that current.

hope that helps

Thanks, this makes sense. The idea would be to control the fuel pump with this so output should be ok. Using a SPDT relay would probably be a cleaner option I think.

Regards,
Pascal

I just ran across this page, http://www.the12volt.com/relays/page2.asp . It has some interesting ideas for "hidden" security.