What I don´t get from that circuit is how after the X seconds delay
the relay- initially open (in my case)- briefly shorts my two pins and then opens again.
The two pins must not remain shorted: I think this is the difficult part to achieve.

 

To relay or wh.y



















Existing circuit To relay or wh.y


thanks
im still working on the thumbnail bit

pic shows switch suggestion

 

sorry adriadri that didnt go too well.

in the motor trade you probably have easy access to 12v relays, so why not stick with those, just add another relay to give you the momentary action , not too pretty but if it does the job
first one timed at 3 seconds, second one momentary

 

thanks,
I think you shouldn´t use doc files for your attachments. Try to convert it to jpeg and will work. Anyway I saw your schematic.

 

If at first

new pic

 

you did say a simple circuit?

both relays timed, second for half a second? you will need to find resistance of relay coils- ohmeter, or trial and error,
include a 1 amp? fuse at battery

 

just spotted a possible snag re kens relay circuit, does it need a pb switch in order to work.to enable the cap to discharge.

 

It´s very simple indeed! I think I´ll easily do the task using the ideas you brought and reading this site I´ve just found, it looks interesting
http://www.simprojects.nl/toggle_to_momentary.htm

 

just spotted a possible snag re kens relay circuit, does it need a pb switch in order to work.to enable the cap to discharge.

If you are referring to this: http://forum.allaboutcircuits.com/attachment.php?attachmentid=12524&d=1254870511 The 1k resistor and the diode discharge the cap when the switch, to the +12V, is opened. Without the diode, the circuit will output a pulse then the switch is closed...and when the switch is opened.

It´s very simple indeed! I think I´ll easily do the task using the ideas you brought and reading this site I´ve just found, it looks interesting
http://www.simprojects.nl/toggle_to_momentary.htm

These will just give you a momentary pulse when the switch is switched....with no delay. That's what mine did.

ken

 

thanks ken
im wondering if there might be a bit of jitter as the relay coils rise and fall past the coil operating voltge
i might put one together if i get chance later on,

 

thanks for your interest Ken and Tibbles,
So it would be necessary to:
-correct me if I´m wrong - Use a timer first , that triggers a relay
which in turn powers Ken´s circuit .
And including a diode not to allow the pulse in the other direction.

 

hi
ive just thrown a relay circuit together, even with a 470 ohm cap and a 10 k resister there is hardly any delay, were looking at a large capacitor
which might create its own problems.
be ok for the second relay i suppose,

 

hi
ive just thrown a relay circuit together, even with a 470 ohm cap and a 10 k resister there is hardly any delay, were looking at a large capacitor
which might create its own problems.
be ok for the second relay i suppose,

Which circuit?

ken

 

hi ken
help!
i was just trying out the relay circuit as per your earlier post (relay monostable)am i doing something wrong?

 

hoping to do it with relays alone as http://forum.allaboutcircuits.com/attachment.php?attachmentid=12538&d=1254922237

but im having trouble getting a long enough delay on the first relay,
so we might be back to 555 timers

 

The extra set of contacts on your power switch (that turns on box A), are they SPST (single pole-single throw) with two contacts, or SPDT (single pole-double throw) with three contacts?

And do you know what the resistance of you is, or have a link to a spec sheet.

Ken

 

it is a dpdt the top half replaces the original switch for isolation

did you mean relay resistance, auto relays are around 90 ohms i think but i will check
i am using a small 2 amp relay to test delay at the moment,

im just redrawing using 555s in case we cant get the relays to work

it will look something like this

 

ken
the switch would work like this
http://forum.allaboutcircuits.com/attachment.php?attachmentid=12536&d=1254919625

 

I updated the pic a bit.

 

KEN
IVE ADDED black box roughly see pic

time for bed