David Jenkins
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| posted on 26/3/03 at 09:35 AM |
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relays
Anyone know if you can get 2-pole auto relays?
I don't mind if they are make-only, rather than change-over.
...although I don't hold out much hope.
All I want to do lock a relay on once I've operated it, using an independent circuit to the one that turned it on (if you follow what I
mean!)
rgds,
David
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Deckman001
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| posted on 26/3/03 at 08:15 PM |
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David, what is it you are trying to do with the relays?
Jason
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David Jenkins
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| posted on 27/3/03 at 08:42 AM |
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What I want to do is what I said in my last paragraph!
I'm using a home-made security circuit that opetates a relay. The contacts then connect the ignition coil live supply. I don't want to
trust the electronics to hold my ignition on, 'cos no matter what you do with the 12v, a microcontroller may 'hiccup' when using the
very noisy car power supply.
So, I wanted to set up the relay to lock itself on using a spare set of contacts - but as this is unlikely I've decided to use a spare relay
I've got to perform the "lock-on" function.
It goes against all my principles to use 2 components where 1 should be sufficient - but at least it will work and won't cost a penny!
regards,
David
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Rob Lane
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| posted on 27/3/03 at 09:29 AM |
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Hi David,
Most of the good auto discount stores sell the relays.
I think you already know you require a double pole relay with one set fed from supply and then through relay coil to self latch when energised.
That will latch the relay when first activated.
Normally then a 'break' pushbutton is placed in supply line which will then kill supply to coil, which in turn de-energises relay.
Alternate but with more components is a seperate energised relay with supply fed through first which is then de-activated momentarily to kill latched
relay.
Interestingly, latching, de-latching relays with inbuilt single pin electronics are available from the likes of Farnell etc BUT at a cost. Somewhere
around £30 each I believe.
Rob Lane
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Rob Lane
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| posted on 27/3/03 at 09:35 AM |
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Sorry David,
just re-read your post. A second relay is not required as you will probably derive supply via ignition switch, which will in turn kill latched relay
when 'off.'
Rob
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David Jenkins
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| posted on 27/3/03 at 09:37 AM |
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Rob,
I've not found double-pole relays in the catalogues from the "usual suspects".
My aim is to get the relay(s) to latch on until the ignition is turned off at the key, at which it/they will drop out.
A secondary aim is to connect the coil live lead to a high-wattage lowish-value resistor when the car hasn't been properly enabled, to interfere
with any attempts to "hot-wire".
I'm not too fussed now - I've worked a circuit out in my head that I'll try out this weekend (or maybe tonight!)
regards,
David
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Rob Lane
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| posted on 27/3/03 at 09:58 AM |
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You're right. Many relays have been dropped from latest catalogues.
I found one that might suit at Farnell.
10A DPCO £4-29 part no. 309-4984
it will take terminal tags but doesn't have a fixing lug.
PICs will have drop outs on output pins when on a noisy car supply. I have been told that it's worth putting a 12v 1.2A burglar alarm battery
in supply line to act as a cheap spike soak and a backup. That's rather than put decoupling caps, chokes etc on supply line.
Rob
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