Hi all, I've made a 1 hour timer circuit for the car cigar socket so it stays on for 1 hour after the ignition goes off.

It worked OK for a week (although the times it stayed on for varied but that didn't matter) . But now the TS555 chip seems to have failed and output pin 3 is staying low. This keeps the sinking relay on continuously. The relay takes 45ma, is this too much for the chip? It doesn't get warm.
Thanks, Rich

 

Hi all, I've made a 1 hour timer circuit for the car cigar socket so it stays on for 1 hour after the ignition goes off.

It worked OK for a week (although the times it stayed on for varied but that didn't matter) . But now the TS555 chip seems to have failed and output pin 3 is staying low. This keeps the sinking relay on continuously. The relay takes 45ma, is this too much for the chip? It doesn't get warm.
Thanks, Rich

Can you provide a schematic? Do you have a snubber network across the relay coil?

 

Yes got a diode across it

 

Can you provide a schematic? Do you have a snubber network across the relay coil?

Also, that may be close to the maximum dissipation of the chip, so you might need a transistor to help out.

 

hi Rich,
The 555 12V is not 'clean' requires transient forward and reverse protection, ref this PDF.
E

 

I've got some TIP32 transistors, would I put the relay in the collector or emitter?

I swapped the original NE555 to the TS555 to save standby power. NE555 takes 3-4ma and the TS555 takes 0ma.
Would a transistor in circuit put the standby power consumption back up?

 

hi Rich,
The TS555 has a very low source and sink output ability compared to the standard 555 .
E

 

hi Rich,
The TS555 has a very low source and sink output ability compared to the standard 555 .
E

What is it's maximum output ability?
Looks like the easiest option is switch to the NE555

 

hi,
This is a clip from the d/s of the TS555
Have you considered a MOSFET as a relay driver.?

E

 

hi,
This is a clip from the d/s of the TS555
Have you considered a MOSFET as a relay driver.?

E
View attachment 174384

No, how would I connect that?

 

I've got a MOSFET it's an IRF540N

 

hi,
Looking at your original circuit it shows when the relay is de-energised the +OUT is connected to the Battery> Cigar socket.

So, the 1 Hr timing state after the IGN is turned OFF, the relay remains de-energised, until the Trig pins 2/6 go Low, then it is energised

It appears your monostable timing delay is due to the leakage current thru the 10uF.?

Can you confirm this is how you designed it.?

E

 

hi,
Looking at your original circuit it shows when the relay is de-energised the +OUT is connected to the Battery> Cigar socket.

So, the 1 Hr timing state after the IGN is turned OFF, the relay remains de-energised, until the Trig pins 2/6 go Low, then it is energised

It appears your monostable timing delay is due to the leakage current thru the 10uF.?

Can you confirm this is how you designed it.?

E

No I must have drawn the relay contacts wrong then. I drew them in the energised state.

 

Would this work?

 

hi Rich,
'No I must have drawn the relay contacts wrong then. I drew them in the energised state.'

I guess you can see why I was querying the design, it seemed 'backwards'.

E

EDIT:
I would have these resistor values, a TS555 pin 3, may not pull up to 12V, [look at the TS clip I posted] so the 10K should be added.
Don't forget to add the protection diodes in the 12V line.

 

It appears your monostable timing delay is due to the leakage current thru the 10uF.

I didn't design the circuit at all really, I got the (monostable?) configuration off the Internet and faffed about changing the components until it did more or less what I wanted. The timing delay is very erratic, 54 minutes to about 3 hours, but I'm not bothered about that bit.

 

hi,
Looking at your original circuit it shows when the relay is de-energised the +OUT is connected to the Battery> Cigar socket.
So, the 1 Hr timing state after the IGN is turned OFF, the relay remains de-energised, until the Trig pins 2/6 go Low, then it is energised
It appears your monostable timing delay is due to the leakage current thru the 10uF.?

Don't think so. When the ignition switch is closed, the cap voltage is high (above the threshold level), the output is low and the relay is on. When ignition is turned off, the cap holds the trigger input high for an hour. When the trigger input wanders low, the output goes high and the relay turns off.

Yes, the 555 threshold and trigger input impedances in parallel are the discharge path for the timing cap.

Overall, a cute trick - but with a very unstable timing value.

ak

 

hi Ak,
I am was not referring to the threshold voltages, but the possibility of when the TS555 pin3 is supposed to be High, ensuring that the TIP32 is not partially ON, thats the purpose of the 10k.

E

 

hi Rich,
Is there any other info you need for the project.?
E

 

Would this work on my project? It says a low gate switches it on.
Thanks, everyone.