Increasing release voltage

[jj4091]

I have a 12v dc STDP relay which is being held on after the supply is removed from the coil because of stray voltages in the wiring being higher than the release voltage of the coil. Is it possible to add any components in series with or across the coil that will increase the release voltage & thus prevent it sticking on. The stray voltages are not decaying but finding the source is proving difficult. Coil release volts = 1.6v & stray volts =4.5v. Thanks

 

[JohnW2]

I have a 12v dc STDP relay which is being held on after the supply is removed from the coil because of stray voltages in the wiring being higher than the release voltage of the coil. Is it possible to add any components in series with or across the coil that will increase the release voltage & thus prevent it sticking on. The stray voltages are not decaying but finding the source is proving difficult. Coil release volts = 1.6v & stray volts =4.5v. Thanks

You obviously really ought to discover the source of these 'stray voltages'.

However, pragmatically, a few silicon diodes in series, in series with the coil (in diodes' forward-conducting direction), ought to cure the problem (about 0.6V drop per diode), the only requirement being that the current rating of the diodes was adequate for the current drawn by the coil (at 12V).

An alternative would be a single zener diode, but that would presumably have to have a zener voltage of around 3V, which is a little low, and might not be so easy to find.

Kind Regards, John

 

[bernardgreen]

First
With a 1 megOhm resistor in place select the capacitor value such that the coil pulls in for about 1/10 of a second before dropping out.
The resistor at this stage is only there to discharge the capacitor between tests.

Second
Select resistor value such that the coil does not hold in on the stray voltage, then add 10%to the value.

As John has said finding the source ( or reason ) for the stray voltage and removing it is the best option.

 

[Jackrae]

Interesting circuit but it only works for a pulse input. The capacitor will block steady DC and hence the relay will fail to hold in (the resistor value being too high to supply enough hold-in current)

 

[bernardgreen]

the relay will fail to hold in (the resistor value being too high to supply enough hold-in

The resistor value is chosen to be such that the current is more than enough to hold the relay in when the 12 volts is present.. As mentioned the high value resistor is only used while testing to ensure that the capacitor is discharged between tests.