How to Control Induction Load using micro ?

driving an inductive solenoid valve

Hello!

I had used micro to control the induction load but the problem is the arc at the contacts of the relay. do any one can suggest or share the experience here.

Binu G

rc circuit of inductive load

I don't know of this will fit your schematic. But you could add a reverse-biased diode in parallel with the inductive load. It should absorb the kickback. Post your schematic (or axcerpts from it) and we'll be able to tell you more.

load life contact relay

Arcing at relay contacts can cause problems by inductively coupling currents back into the microcontroller. A diode across the relay coil only helps for kickback of the relay coil itself.

When switching large currents into an inductive load with a relay, you have to be very, very, very careful with parts placement and routing. If at all possible, do not have the micrcontroller and the inductive load sharing a ground connection. Make sure the large current paths are not flowing under the microcontroller on the PCB or flowing in parallel with any tracing going to the microcontroller. Traces that must remain parallel may have to have inductors installed to suppress the induced currents from flux coupling.
Really large currents can be very troublesome. I know individuals have attempted to control arc welders with microcontrollers and found that it works fine on the bench with simulated loads, but failed when switching the real currents.

controlling a relay with a bjt

Hello....
Well i have attached the schematic here.
the load is totally isolated from the digital circuit
load is AC 230V/10 A inductive load.

what will be the best solution to protect the relay contact life?



Binu G

driving relais from µc

Base on your schematic I have a question, do you directly control the relay coil with µC port? I think you have to use a transistor to drives relay coil, and the µC control the base of transistor.

how to suppress ac solenoids kickback

i have a ULN2003 to drive the Relay.
every thing is fine , iam concern about the contact life

Binu G

I kind of agree with budhy. You are not driving the relay from a BJT or a FET but from the uC itself? What kind of relay that is? On the other hand, a contact is a contact. A reverce bias diode can protect it. I also have a second suggestion, I don't know if it will work in discrete, but you can give it a try: Place dummy FETs around the contact. Control the gate of the FETs with the complementary signal that you use to control the relay. Shortcircuit Drain and Source. This way you create a fairly same enviroment around the relay contact and you give equal path to accumulative carriers to both directions, instead of creating an arc.This, in conjuction with a reverce bias diode places in both ends can save your contact some life.
I haven't tried it but you can check it out.

D.

In the case of DC-driven inductive loads, such as mechanical relays, solenoids, and DC motors, a diode placed across the inductor will reduce the spike ..
In AC circuits the answer is resistor-capacitor “snubber” circuits .. see picture below ..
The snubber prevents arcing and burning of the relay contacts ..
The selection of optimum resistor and capacitor values is often a matter of trial and error, but the values shown in the Table2 are good as a starting point ..

Regards,
IanP

there is only one thing you have to do in the ckt..
connect a freewheeling diode,1n4007 should be fine.anode at the pin2 and cathode at pin1.
dont worry about the relay contact life,if you are using the relay with comes with some standards.because i've not come across any circuit which protect the contact life of the relay.it'll stay long as it is.

Hello Dkace

i dont have any issue with the drive side(microcontroller Circuit). so please forget that.

question is
How to protect the Relay Contact whos load is inductive , 10A 230 V ?

Relay Specification

30A/230 V

Binu G

is there any circuit that protects the contact of the relay??
me to eager to know about that...
what i believed was the contact itself is enough for any kind of switching,and also the relay u specified well meets your specifications.
lets wait for the replies.

Hello IanP

I have a question here....
please correct me if iam wrong.

when we add a resistor and capacitor in a AC cirucit there will be current passage in the circuit. so the circuit will be partly conductive.

means i may experience an electric shock if i touch the output of the swithching terminal.

Binu G

Hi!

I think that IanP solution is better solution, but I have a question, whats happen if you don't know if the contact load is DC or AC (but you know that it is inductive load). Is better to put a R-C circuit or may be is better to put a varistor? A diode is not possible if the load is AC.

Thanks in advance...

Regards,