Relay connection Error

[saurabh252]

I have a 5 pin leone relay (coil :6v DC)
The problem is when ever i connect A & B terminal(coil) directly to 9v cell it works as it should..
but when i put it in my circuit it does not work..
my circuit is very simple 555 timer..

i have connected pin 3 of 555 with resistor(220 ohm) ,led only( it works ) and when i replace led with a relay(with protection diode) it does not work..

if i put led instead of relay, led goes on/off perfectly..
out put voltage at that terminal shows 7.5 volts..
so relay is working with 9v cell but not with circuit and led is working with the circuit..


i am not able to figure it out so help me as soon as possible..

 

[andre_luis]

saurabh,


Relay is a device that require a very high instantaneous current that 9v cell is not capable to supply.
To turn around this problem, try to insert a high value eletrolictic capacitor on 9v bus ( let´s say 100uF ), and a ceramic one ( ~100nF ) near to relay coil.


+++

 

[saurabh252]

saurabh,


Relay is a device that require a very high instantaneous current that 9v cell is not capable to supply.
To turn around this problem, try to insert a high value eletrolictic capacitor on 9v bus ( let´s say 100uF ), and a ceramic one ( ~100nF ) near to relay coil.


+++

actually i also tried with SMPS (cpu power supply) but the same problem was there..

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i am not able to get o/p when connect relay instead of led at terminal 3..btw thanks for ur last reply

 

[betwixt]

I'm assuming you remove the resistor when using the relay - the most likely cause of the problem is the relay demands more current than the 555 can supply. It is also possible that your relay has polarized coil connections because it has an internal diode across the coil pins. If that is the case, try reversing the connections to the coil. Other than that, try adding a transistor driver stage between the 555 output and the relay to increase it's current capability.

Brian.

 

[Audioguru]

You provided no details.
What is your supply voltage for the 555?
If it is 6V then its output high voltage is about 4.6V when it feeds only12mA to a 2V red LED in series with 220 ohms.

You forgot to tell us how much current the relay coil uses at 6V. If it is 200mA which is the maximum allowed output current of the 555 then the output high voltage to the relay coil is only about 3.5V to 4V which might not be enough voltage for the relay coil.

 

[saurabh252]

You provided no details.
What is your supply voltage for the 555?
If it is 6V then its output high voltage is about 4.6V when it feeds only12mA to a 2V red LED in series with 220 ohms.

You forgot to tell us how much current the relay coil uses at 6V. If it is 200mA which is the maximum allowed output current of the 555 then the output high voltage to the relay coil is only about 3.5V to 4V which might not be enough voltage for the relay coil.

I used 9v cell to power up 555 which gives me a 7.5 v between pin 3 of 555 and gnd..

see this link for the relay specification

**broken link removed**

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I'm assuming you remove the resistor when using the relay - the most likely cause of the problem is the relay demands more current than the 555 can supply. It is also possible that your relay has polarized coil connections because it has an internal diode across the coil pins. If that is the case, try reversing the connections to the coil. Other than that, try adding a transistor driver stage between the 555 output and the relay to increase it's current capability.

Brian.

when i removed that current limiting resistor it worked..

 

[Audioguru]

Iwhen i removed that current limiting resistor it worked.

Of course it worked.
The resistor was to limit the current to the LED, not to the relay coil.

The relay coil is 100 ohms and needs at least 4.8V to work. The resistor was 220 ohms. The output of the 555 with a brand new 9V battery is 7.5V.
Then the relay coil got only (7.5V/ 100 + 220) x 100= 2.3V with the resistor in series with it.