Buzzing of relays

[kwame]

Dear friends
i have bought a 12VDC relay for project work.The line voltage is 220VAC so i bought a 12VDC transformer to convert the 22ov into 12VDC for smooth operation of the relay but i keep hearing this BUZZING sound anytime the relay is working.
Folks i am a bit confused.What is causing this strange anytime the relay works?If appears the current needs some filtering .What is the simplest process i can use to filter the voltage?

 

[Ian Rogers]

Are you sure its 12DC? is there a rectifier with the transformer? As 12AC would cause this

 

[kwame]

I do not think so.What type of rectifier should i use and how should i go about it please help me out.What type of rectifier do i need to buy and how should the wiring should be done.It is really bothering me ,i cannot eat because of this.

 

[crutschow]

Measure the voltage across the relay (both AC and DC) and see what it is.

If it's DC then you may just need to add a capacitor to smooth the ripple voltage from the supply. Try adding a few hundred microfarad to start.

 

[Ian Rogers]

A small bridge rectifier and a cap (suggested by Carl will help)

34 English pence...

 

[ben7]

Filter capacitor needed

Most DC-out wall-warts have noisy voltage, some only using a bridge rectifier to make the DC, so a 470uf capacitor would be good to use. Make sure you are careful when connecting the capactor or else it will spit out smoke or explode. + of capacitor goes to the +wire on the wall-wart. -of capacitor goes to the negative of the wall wart respectively. Also make sure the voltage rating of the capacitor is at least twice the wall warts' DC output.

-Ben

 

[kwame]

Bravo

Hi folks
thanks for helping me out.At midnight i powered the relay with a 9VDC and the buzzing stopped.I have bought the capacitor and the diodes this afternoon and the shop technician has explained things to me .I USE AN analogue multimeter.How do i distinguish between the transformer's + wire from the - wire with the analogue multimeter.
I have heard it is almost impossible to use this meter .Does anyone have any idea about to detect the polarity with a analogue multi meter?

 

[carbonzit]

The problem with using an analog meter (physical meter with a needle) to check polarity is that if you get it backwards, it'll pin the needle against the zero stop, which doesn't do the meter any good. This is one instance (among many) where it's better to use a digital multimeter (DMM), as it'll simply put a minus sign in front of the voltage.

 

[crutschow]

To avoid damaging the meter with reverse polarity, initially use the highest range. That will allow you to see which way the meter moves without damage. Then you connect the meter with the correct polarity and increase the sensitivity to get as close to full-scale reading as possible for best accuracy.

 

[carbonzit]

Good advice as usual from our resident curmudgeon ...

 

[kwame]

Hi

I have found my way out the polarity problem.
Thanks