Relays and Contactors

Hi Steve,

Really, the net has loads of information! I find it a bit strange to hear that you've found problems getting them. Can I assume that you're new to the 'net?

Anyways, I typed "contactor" in Google and got these two. It didn't take me too long though cause these two sites were in the first two pages of the list. I didn't have to go looking through all 1,560,000 sites that Google gave (don't have that much time).

http://www.allaboutcircuits.com/vol_4/chpt_5/2.html

http://en.wikipedia.org/wiki/Contactor

Contactors and relays are not terribly complicated and shouldn't take you more than a day to get the hang of them. Actually, a day's too much at that.

I like your enthusiasm though. I hope you don't lose it. Don't be afraid to ask even if some people give sarcastic or bad answers.

Hi

Thanks for your reply. I have been using the net for a long time and it not that i cant find anything. It that i cant find the kinda thing im looking for.

My boss showed me a little trick using two momentary switchs looping back in to the relay to be used as a start and stop button.

This is the kinda thing that im looking for. Maybe some simple circits that i can try out to try to get more a feel to what can be achived using these.

Steve

Steeve the switch you are talking about is known as latch switch. This gives luxury of controlling large power with small switch. Also in case of power failure you will have to reset your power. So it works like a motor starter.

To learn about a relay or contactor you need to have some basic info about them.

1 what are critical test parameters,

2 Why they are critical

Here are few critical parameters

1 contact resistance

2 contact sizes.

3 contact ratings. Volts and current

4 type of contact (material) Ag, AgNi, AgCdO, Cu, etc.

5 hysterics

6 trip voltage.

7 reset voltage.

8 coil resistance

9 input current of coil.

10 rated coil voltage.

11 insulation resistance

12 Dielectric strength

13 Burn out protection

14 contact time constant

15 contact life in Cycles.

16 EMI

And there can be many more

Now if this helps you pls reply, then I shell give you info why they are important.

Actually, Rakesh, he's looking for sample circuits that he can use. The motor starter was just an example. Right now, he's more interested in applications, not the details of how they work or how to select or how to design.

I can think of a few samples myself, like a speed answering contest where each contestant has a button. When a contestant presses his button, his light goes on and the other contestant's buttons are disabled. The contest host will then know who pressed first.

I think this is the kind of information he's interested in.

Yes thats exactly what im looking for. Simple stuff that i can make and see how it works.

Like the speed answering contest

How would that be done?

Thanks

Steve

Seems our other guest can't deliver.

Here's something I had to dig deep into my old files for. I don't know if you can save and enlarge it from here. CR4 shrunk it when I pasted it.

Anyways, this is a three-contestant speed answering circuit using all relays. If you want to have more contestants, I'd suggest you go digital.

When a contestant pushes his button, his relay disables the other two buttons and lights up his own lamp. The host or contest chairman then pushes "reset" when he's ready to ask another question.