12v Timer Relay

[andys]

Thanks. All I can think of is use it to close a 2nd trigger relay as in your original option 2 layout.

 

[mmi]

Thanks. All I can think of is use it to close a 2nd trigger relay as in your original option 2 layout.

Ok, I think we are going to misuse this relay thingy, probably at least using not the way designer intended. But should be still safe.

As in the picture, connecting the switched negative through a resistor seems to do the trick. The timer starts/restarts every time when the line connects to the Batt neg (on the leading edge only). So if switched negative stays “active” the timer will stay on only set time. A “pulse” is needed to restart the timer - if pulse comes before the expiry the timer starts over again .


As we are misusing the circuit, the resistor is needed to limit current into circuit and the chip below the board. Without the resistor the circuit draws more than 30 mA into the chip itself. I’m afraid that would pretty soon fry the chip. It seems that the resistor could be soldered actually to the board - by replacing a one there.

I did some experimenting and at 13V it seemed to work reliably up to 47 kohm. Didn’t yet check if/how undervoltage would change the threshold. So I think anything 5-22 kohm would be fine not frying the chip and giving decent marginal against voltage fluctuations.
I'll try to verify next week if there are any revelations...

EDIT:
Did some tests at lower voltage range to check and verify the operation. Turned out that to ensure reliable operation at lower voltages lower resistor values of 4-10 kohm are preferred option thus leaving some more margin for a reliable triggering. (At 10 V it was still working at 20 kohm but not anymore at 47 kohm).

The gadget works fine down to 10 Volts. Below that the pull of the actual relay noticeably weakens.

Retested the current draw:

60 mA @ 9.0V (lower limit of relay pull)
67 mA @ 10.0 V
80 mA @ 11.0 V
90 mA @ 12.5 V
105 mA @ 15.0 V​

Anyways, tested only on one sample but I don't expect too much variance among those.

 

[andys]

Ok, I think we are going to misuse this relay thingy, probably at least using not the way designer intended. But should be still safe.

As in the picture, connecting the switched negative through a resistor seems to do the trick. The timer starts/restarts every time when the line connects to the Batt neg (on the leading edge only). So if switched negative stays “active” the timer will stay on only set time. A “pulse” is needed to restart the timer - if pulse comes before the expiry the timer starts over again .
View attachment 31754

As we are misusing the circuit, the resistor is needed to limit current into circuit and the chip below the board. Without the resistor the circuit draws more than 30 mA into the chip itself. I’m afraid that would pretty soon fry the chip. It seems that the resistor could be soldered actually to the board - by replacing a one there.

I did some experimenting and at 13V it seemed to work reliably up to 47 kohm. Didn’t yet check if/how undervoltage would change the threshold. So I think anything 5-22 kohm would be fine not frying the chip and giving decent marginal against voltage fluctuations.
I'll try to verify next week if there are any revelations...

Thanks again for looking at this. My back still isn’t up to working bent over anything but I’ll have a try with this circuit in a couple of days hopefully

 

[mmi]

Thanks again for looking at this. My back still isn’t up to working bent over anything but I’ll have a try with this circuit in a couple of days hopefully

Edited some conclusions in my post above. I hope you get back to working soon.

Another possibly useful multipurpose relay/isolator package to play with: 1PCS 4 Channel 12V Relay Module 4 Channel Module High and Low Trigger Red Board-in Relays from Home Improvement on Aliexpress.com | Alibaba Group
Each input can be selected either positive or negative switched using the jumpers (low/high) on the board.

 

[andys]

Well nothing seemed to go to plan with this but I've finally got it resolved. I couldn't get the relay to work with 10k, 22k or 47k ohm resistors, but momentarily grounding the connection did set it off so the circuit seemed as if it should work. I then tested the output from the alarm on a multimeter and got 0.25v constant, whether the alarm was being triggered or not! I don't know whether it was a pwm signal as I don't have an oscilloscope I can take out to the garage but it didn't change which baffled me.

So I tried the red/white wire which is also listed as a 200mA switched ground with exactly the same result. So then I tried what the installer told me not to do and connected the brown wire labelled siren output and got constant +12v when the alarm was triggered and nothing when it wasn't. I don't know if using this is ok but I never questioned why I shouldn't use it when it was installed as he'd pointed out a specific output that I could use, but just in case it doesn't like the current draw I've used it to close an ordinary relay that connects the leisure battery to the auxilliary sounder and strobes and everything works fine. Thanks for the help @mmi , I don't know why the outputs don't work as specified but at least that's one project finished

 

[travelvolts]

You need a relay with a high impedance coil.

 

[andys]

You need a relay with a high impedance coil.

Thanks, I'm assuming the one that's in is then as it works perfectly now