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View Full Version : Pulsing a relay (Simi O/T)



radkins
05-16-2010, 09:54 AM
I need to pulse a 12 VDC relay (10 AMP capacity) at a rate of about once every two seconds and I was wondering if there is an easily obtained electronic device to buy or build for doing this?

A similar thread about blinking LEDs and one of the replies in particular hits dead onto this project but rather than highjack that thread I decided to start a new one.

winchman
05-16-2010, 10:07 AM
If you have an extra set of contacts on the relay, you might be able to use them in conjunction with a capacitor to hold the relay open or closed for a set delay. I've done that with a DPDT 12-volt relay in the brake control circuit for my winches. You can see how the capacitor is hooked up to the coil and contacts of relay #1 in this diagram:

http://img.photobucket.com/albums/1003/winchman/Clutch%20Winch%203/000_10092.jpg

IIRC it takes about 47mfd per second of delay for the relays I use. Seems like the coil is 80 ohms or so. It's been a while since I got it working, so I just use the components in the box.

The other option is a timer (555?) of some sort. The electronics gurus will chime in on that approach, I'm sure.

dp
05-16-2010, 10:12 AM
There are simple timers that use the ubiquitous 555 device that will work. What is required is the the timer circuit and a driver device for the relay. http://www.eleccircuit.com/555-ic-timer-control-relay-switch/

fasto
05-16-2010, 11:06 AM
You do know that mechanical relays are usually only good for 100,000 to 10,000,000 operations, less at higher currents?
If you run this 24/7 it'll only last about 23 weeks.
You might consider a solid state relay, if your application calls for continuous pulsing.

macona
05-16-2010, 04:31 PM
555 with a nice big power transistor.

becksmachine
05-16-2010, 04:36 PM
Time delay relays in this configuration and timing range are readily available from a number of sources, is there some reason they won't work for you?

Dave

lunkenheimer
05-16-2010, 05:09 PM
buy an electronic car turn signal flasher, open it up, and figure out which component value to change to get the flash rate you want.

I think a Napa flasher for a 1996 chevy may work if modified, about $20

Some of them use a 555 circuit like the ones above.

radkins
05-16-2010, 05:56 PM
Time delay relays in this configuration and timing range are readily available from a number of sources, is there some reason they won't work for you?

Dave



I went to E-bay following the suggestion to use a solid state relay and found that pulse relays with adjustable rates are quite common, I didn't even know something like that was so easy to find! I found a number of them that look like just what I need, this is going to make the job much simpler.



This is to operate a small solenoid type hammer that will be used to lightly hammer on a small grain hopper to prevent clogging, not my idea I am just trying to build it for someone else but it looks as if it should work just fine. Semi-O/T because I am machining the parts for the guy.

Thanks everyone.

MaxHeadRoom
05-16-2010, 06:22 PM
Is the hammer designed from scratch or is it off the shelf?
If from scratch I would use a DC operated hammer, with that duty cycle, an AC version may get hot pretty quickly?
Max.

becksmachine
05-16-2010, 06:33 PM
Don't know about a battery powered version but hopper vibrators are available to do just that.

Dave

radkins
05-16-2010, 07:41 PM
Is the hammer designed from scratch or is it off the shelf?
If from scratch I would use a DC operated hammer, with that duty cycle, an AC version may get hot pretty quickly?
Max.


Not sure where he came up with the solenoid but it is DC and the relay that was used to operate it was rated 10 AMPs. This thing will be powered from his tractor's electrical system and with it mounted and operated with a momentary switch (just for test purposes) it seems to work quite well. The solenoid is used to pull a spring loaded lever that has the hammer attached and it is more a heavy tap than actually "hammering" on it.


Dave, this is a very small home built hopper and nothing suitable was available locally.

AlleyCat
05-16-2010, 08:50 PM
I use PIC and AVR processors to do this. The output drives a mosfet that switches the relay. Almost any timing cycle can be programmed with this arrangement. It's less work than using 555's and more reliable. If you look around you should be able to find a module off the shelf that will do the job. If you can't find anything send me a PM and I'll try to help you. Tom

arcs_n_sparks
05-16-2010, 09:55 PM
Almost any timing cycle can be programmed with this arrangement.

For many, programming is a problem (no IDE or programming hardware). At least with 555s and discretes, one can spin a design with a soldering iron.

OKChipmaker
05-16-2010, 11:35 PM
To complicated,the way us hillbilles do this is to mount a motor to the hopper-feedbin or whatever.then put a pully on the motor with a chunk cut off one side to through it off balance. When you need it to viberate turn it on or plug it up.

macona
05-17-2010, 12:35 AM
Why just not put a vibrator motor on the hopper like they do on trucks?

Richard-TX
05-17-2010, 01:28 AM
The Teco PLR (Programmable Logic Relay) will do just what you want and with much more accuracy than you could get with a 555 timer or other scheme. It costs a bit more though.

http://www.factorymation.com/s.nl/sc.2/category.11443/.f