Reduce relay coil current

139

02:40:27

This circuit reduces the current consumption of a relay in the active state. The capacitor provides a transient current when switching on.
It takes advantage of the fact the the minimum hold current is lower then the minimum activation current.
It also works for solenoid valves, which is what I use it for.
Note the high power dissipation of the resistor.

published 7 years ago

hurz

7 years ago

yes, but dont try that in a mechanical vibrating environment, cuz the relay might fail to be active. The reduced current does reduce the magnetic field and its force, so for a static environment it might do the trick to save power, but not for a truck 😉

benarmstrong89

7 years ago

Yes, definitely not for vehicles. I use that mainly with solenoid water valves bought in eBay as they have a tendency to overheat. Reduced current and load sharing with the resistor greatly increase the life of the coil.

hurz

7 years ago

i dont expect a longer lifetime for the coil itself. the coil is not stressed by current. but less power consumption

hurz

7 years ago

and a two watt resistor is also not for infinity, must be 5Watt minimum to have an exceptable lifetime.

benarmstrong89

7 years ago

The coil does run a lot cooler, dissipating only about 2W instead of over 5W if operated at full voltage.

hurz

7 years ago

And the coil is made for this. Relay's do get problems at contact side and not at the coil.

hurz

7 years ago

this 5.76Watt is anyway an invention you made, right? The coil resistance with 100 Ohm?

hurz

7 years ago

anyway, if you think the lifetime depends on the coil current and less on contact issues, keep it as is, it does save current definitive.

benarmstrong89

7 years ago

Hi, in my case, it concerns cheap eBay solenoid water valves. They work on 24V, draw 0.24A, which amounts to 24V * 0.24A = 5.76W. They are simply badly designed. If you run then more then half an hour at full current, their temperature rises to 75°C. If you leave them on for long enough, on a hot day, the plastic casing starts warping. So in this case, running then at reduced current does increase their lifetime by a lot.

benarmstrong89

7 years ago

And I have had the same issue with cheap eBay relays.

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