# How to use 24V relay at 12V operating voltage

1. ## How to use 24V relay at 12V operating voltage

I am building a remote control circuit for operating water pump.It operates only ON and OFF mode.
I use a relay at the end of the controller in order to start/stop.
I have an excellent and precious 24V relay and want to use it in that circuit.But the problem is my circuit operates at 12V.
How to use 24V relay at 12V operating voltage.
All replies greatly appreciated.

•

2. ## Re: How to use 24V relay at 12V operating voltage

Something is wrong here

3. ## Re: How to use 24V relay at 12V operating voltage

Is this 24V AC or DC?
You can use a doubler ( see picture )
But if you want to know more about step-up convertion check my request on the subject:
h**p://www.edaboard.com/viewtopic.php?t=109476&highlight=

•

4. ## Re: How to use 24V relay at 12V operating voltage

If your 12 V supply is from mains, this means that you should have a rectifier, a capacitor and a voltage regulator.
Taking the voltage before the voltage regulator it should be some 17 to 20 V, usually enough to excite a relay.
If instead the supply is froim a 12 V battery I don't see any easy solution.

Mandi

5. ## How to use 24V relay at 12V operating voltage

Use two power supply, 12 volts to drive your circuit and 24volts to drive relay. You can use LM7812 regulator to bring 24volts dc down to 12volts.

•

6. ## Re: How to use 24V relay at 12V operating voltage

1. Companies make the same basic relay with different coils. See if they make a 12 V version.

2. Relays can operate at lower voltages. As you reduce the voltage the closure time increases. There are two ratings. The voltage it takes to close and the voltage it takes to hold. The holding voltage is lower than the closure voltage.

You could use a step up circuit like a capacative voltage doubler to charge a large capacitor to 24 V. This will do the closure operaton. Once the relay is closed, the 12 V may be able to do the holding.

7. ## Re: How to use 24V relay at 12V operating voltage

You don't need additional +24v power supply.
According to the schematic, during standby, when your microcontroler port pin is at low level, T1 and T2 are locked,
and the C1 is charged at +12v through R1 and R2.
When the port pin goes to high level (+5v), T1 is polarized through R4.
The voltage VCE of T2 decrease near to zero and the voltage across C1 is added with the power supply and applied to the relay (almost +24v).
This is enough to energise the relay until the C1 is discharged by R1.
The relay will receive enough power (current which flow through R1) to keep his contacts closed.
The value of R1 is critical and is strong related to the relay resistance.
In order to find the appropiate value for R1 you must check with a variable power supply, the minimum hold voltage for which the relay is still energized.
If this value is bellow +10v then you can use the schematic. Otherwise it's useless.
On the other hand, the value of R1 must be as higher as possible in order to not discharge quickly the C1 when T1 is driven, or not until the relay is energized.

Hope it will work for you.

Regards,
silvio

--[[ ]]--