Relay problem

[planty]

I have a timed circuit which activates a relay and after a timed period it will switch off, but now it wont switch off,

When the relay works it switch's the cars fogs on and after a timed period and then it should switch them off but they stay on, but if you run the circuit with out the fogs (wired up) then the timed period works, i dont know why. the relays are 15amp so enough for the cars front fogs.
Any one got any ideas, they run though a 556 chip, so i can have 2 timed units working.

 

[Boncuk]

You perhaps didn't connect a free wheeling diode across the relay coil.

Please post the schematic for further assistance.

Boncuk

 

[planty]

Thank you for your reply, i think i have fixed it, i changed the 556 chip and it is working as it should be,

Never heard of a diode going across the relay, i know they are built in.

 

[rjvh]

Never heard of a diode going across the relay, i know they are built in.

If you switch a relay with a semi conductor (transistor is one) it's always recomended to put a freewheel diode over the coil of the relay

if the relay fals off the stored energy in the relay coil will than be disapated in the diode and not give the otherwise nasty (and posible higher voltage than your transitor can handle) spike

I never came across relays that had the diode already build in

I do know that sertain car relays do have a resistor parralalel over the coil (just changed one 2 days ago)

which I believe does have the same function but car relays are just swiched by switches and not transistors (at least not the one I replaced for my electric window)

Robert-Jan

 

[planty]

If you switch a relay with a semi conductor (transistor is one) it's always recomended to put a freewheel diode over the coil of the relay

if the relay fals off the stored energy in the relay coil will than be disapated in the diode and not give the otherwise nasty (and posible higher voltage than your transitor can handle) spike

I never came across relays that had the diode already build in

I do know that sertain car relays do have a resistor parralalel over the coil (just changed one 2 days ago)

which I believe does have the same function but car relays are just swiched by switches and not transistors (at least not the one I replaced for my electric window)

Robert-Jan

yep, your right, i am thinking of the coil built in the relay.

But what you have just said means nothing to me sorry, i only know a few basics, i have bought some kits from maplins and modded them to try and suit my needs.

and now i have had made 2 boards for me, I need another kit making up but dont know who to ask.

 

[rjvh]

me, I need another kit making up but dont know who to ask.

If you have the schematic (which I asume it did come with the previous kits) it's in my opinion not that hard to repreduce the same on an other print board

if you need to make something different than first try to find a schematic that suits (can always ask for help on this forum)

with learning the basics I would venture on internet as there are quite a few websites that teach you the basics very well (explanantion of the theory can also be asked on this forum)

sucsess

Robert-Jan

 

[planty]

If you have the schematic (which I asume it did come with the previous kits) it's in my opinion not that hard to repreduce the same on an other print board

if you need to make something different than first try to find a schematic that suits (can always ask for help on this forum)

I have a program called "circuit wizzard" which has been a help, but it doesn't have the 556 chip in it, which is what i want,

with learning the basics I would venture on internet as there are quite a few websites that teach you the basics very well (explanantion of the theory can also be asked on this forum)

So on the timer chips, 555 and 556, could you explan what does control, threshold and discharge?

Robert-Jan

and with the trigger, i know is works with a pulse voltage but how can i get it working with a perm input with out it keep resetting.