Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

5V relay contact problem.

Status
Not open for further replies.

ahgan84

New Member
Hi guys,
I have attached my relay application schematic below. I have also attached the relay picture that I used.
Now I face the problem that the relay can't be turn off (open contact) after turning it on. My load is 240VAC TV or monitor.
I have tested a few times and it can't be turn off 10 times out of 100 times. How could that be? If my relay is spoilt, it straightaway can't be on or off right?
And my relay got a diode for protection.
 

Attachments

  • relay.png
    relay.png
    6 KB · Views: 945
  • HK3FF-DC5V-SHG-5-Pin-Power-Relay-Black-(5-Piece)1_10-more-5.jpg
    HK3FF-DC5V-SHG-5-Pin-Power-Relay-Black-(5-Piece)1_10-more-5.jpg
    31.7 KB · Views: 351
Have you looked at the voltage at the base of the transistor? Does it go down?

Have you tried different relays out of these 5 pieces?
 
Have you looked at the voltage at the base of the transistor? Does it go down?

Have you tried different relays out of these 5 pieces?
I have not checked the voltage of the base of the transistor. Like I've said, it's quite hard to simulate the problem again (10 time out of 100 times will happen). I will check it when it happen again.

But a weird thing I notice is that:
The normal workable relay wil gv a clear click sound every time on and off right? Mine too. If it is spoilt, u would expect that it won't click when it can't off bcos the contact are weld together. But for my case, u can still hear a very faint click sound when you try to off it. Jz that the relay can't off. How come like that? Now is it the transistor problem or the relay problem?
 
My load is 240VAC TV or monitor.
CRT or LCD monitor?
Do you no/off/on fast OR do you wait 1 minute?
When the relay stops opening, is it all wise stuck closed or does it work next time.
I need to determine if the relay is welded close or if the transistor is not working right.
 
CRT or LCD monitor?
Do you no/off/on fast OR do you wait 1 minute?
When the relay stops opening, is it all wise stuck closed or does it work next time.
I need to determine if the relay is welded close or if the transistor is not working right.

For TV or monitor, it is all LCD.
After I on the relay, I wait quite a long time to try to off it, probably more than 1 minute.
Like I have said, this situation only happen sometimes. Like 10 times out of 100 times when I off it. You can still hear a faint click sound when I off the relay, just that it didn't off the TV. Maybe the contact had be welded together already? Or maybe the charge in the relay had not been discharged fully?
 
I think the "inrush current" is very high on the LCD monitor. The monitor is like a capacitor. If the relay is closed near the zero voltage point the current is low. If the relay is closed near the peak the current is very high. (probably a little above the rated current) You can not time the relay to all wise close near the zero point of the 60hz power line.
 
I think the "inrush current" is very high on the LCD monitor. The monitor is like a capacitor. If the relay is closed near the zero voltage point the current is low. If the relay is closed near the peak the current is very high. (probably a little above the rated current) You can not time the relay to all wise close near the zero point of the 60hz power line.
The what can I do to prevent the inrush current?
Can I do a RC network?
 
But for my case, u can still hear a very faint click sound when you try to off it. Jz that the relay can't off.

I think the relay might be broken. The best way to find out is to try a different relay of the same type and see if it works.
 
So far, I have tried two same relays. Both have the same problem.

I would still suspect the relays. Can you just try get a 5V voltage source, connect one relay terminal to 0V and try to swith the other terminal. Connect it to 5V - see the relay go on, then to 0V - see the relay go off. Do they relaibly work this way?
 
It's hard to tell, but on the surface it's looks OK. It could be a PCB routing issue, a bad batch of relays. Hopefully the diode isn;t a 1n4148 or even a Zener diode accidently?
A bad port. A bad transistor.

The base to ground when on and off and C to Base voltages when on and off would help. Adding a high value resistor 100K+ from the base to ground will help the turn-off time.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top