Trip when relay triggered...

[Js_Ong]

Hi All,

I am controlling 5 valves operation using 8051 with a 12V/5V power supply, it works well to control all the 5 valves I need. At the same time there is a weighing system will turn ON and OFF 6th valve by it's relay. Problem happened when both system operate together.

When the relay at the weighing system triggered the 6th valve, it makes like a short circuit to my 8051 board and completely my 8051 was not functioning anymore. This happen when I use the same 12V supply to all the valves.

I change and make another separate power supply just for the weighing system the 6th valve, it is better but still sometimes it gives a false signal to my 8051 system, at least my 8051 can still operate with next step operation.

I am wondering why this happened when the relay triggered? I can say they are two separate system that electrically are not connected to each other. How to solve this?

 

[barry]

You are obviously getting some kind of transient from that relay. Are the two systems REALLY not connected to each other? Do they share a ground? Is the relay close to your 8051? Do you have a flyback diode across the relay coil? What kind of filtering do you have on your 8051 system's power supply? Have you looked at signals, supply rails etc., with an oscilloscope while actuating that relay?

 

[KlausST]

Hi,

To give good assistance we need to see PCB layout, schematic and a picture of the complete wiring.

Klaus

 

[Js_Ong]

Hi barry,

They do not share ground, when share ground, the weighing system hang. There is flyback diode at relay. See my sketch, I did not draw the diode but there is. I disconnect the relay and make a manual switch, seems like short circuit, but I do not know why?

Hi KlausST,

See attached image.

 

[barry]

WHAT "seems like a short circuit"?

 

[Js_Ong]

Hi Barry,

The power 12V to the relay, I removed it to see if the coil affect anything, and I changed it like a switch. But unfortunately, when I turn ON the switch, it act like short circuit and make my 8051 system failure.

Look at the two 12V supplies, if I used only one 12V supply, when relay turns ON, 8051 system totally failure and no response. I am now changing to use two separate 12V, (2 transformers), when relay turn ON or OFF, it will give a false signal to 8051 to move to next step, but at least now 8051 is not failure.

I have no idea how this could happen, they are like two separate individuals system, but when put them together they are not co-operate well.

 

[KlausST]

Hi,

Hi KlausST,

See attached image.

Is this: PCB layout, schematic and a picture of the complete wiring?

I don´t think so.

Klaus

 

[betwixt]

Do you have resistors in the base pins of each transistor?

If you have connected them directly as in the picture, the pin 'high' output voltage will be clamped by the B-E junction to around 0.7V and excessive current may flow through the MCU pin and cause it to reset or pull the supply line down.

Brian.

 

[barry]

You are saying that you replace the contacts of the relay with a switch and when you close t he switch it shorts the 12 volts to ground? Either your "schematic" is wrong or you've wired something wrong. And what is V6? I think we (And you) need a better schematic.

 

[andre_luis]

This happen when I use the same 12V supply to all the valves.

Valves, rather than relays, are highly inductive elements, especially those that work with lower supply voltage, because unlike those powered by AC, the 12v in your case will be closer to the microcontroller power bus. Think of valves as the same electromechanical principle of relays, but performing greater physical effort, and therefore dealing with higher electric current and associated transients. If your actual circuit and physical mount is as sloppy as shown in the above draft, it is only fortunately that both systems have not yet burned.