Building(or buying) a cheap relay that puts out at least 15hz at low voltage

[ben123324]

i want to build a cheap relay that puts out at least 15hz at low voltage. the relay should operate with an input of 9v, and put out 9v but the output should be oscillating at at least 15hz(15 off-on, per second), and please don't tell me to build anything with circuitry or components. thank you.

 

[Averagesupernova]

Your request makes no sense to me. It's like saying: "I want this ordinary light bulb to flash on and off when I plug it in, but I don't want anything else besides the bulb, socket and cord." It quite simply cannot be done.

 

[berkeman]

i want to build a cheap relay that puts out at least 15hz at low voltage. the relay should operate with an input of 9v, and put out 9v but the output should be oscillating at at least 15hz(15 off-on, per second), and please don't tell me to build anything with circuitry or components. thank you.

I'm assuming from your last comment (and your other thread) that you are trying to keep this as simple to build as possible. Can you use 2 relays? (and maybe a couple small components... I'm not sure yet) It might be possible to make an oscillator with a couple of relays.

Also, 15Hz is pretty fast for a relay, even a reed relay. And it will wear out over time from all the mechanical hammering. Can you tell us more about what you want to make? There may be other alternatives.

 

[berkeman]

For example, since you mentioned the "buy" option, you could look at the simple/cheap hobby electronics kits for oscillator kits that put out the waveform you want. Something like this:

http://www.electroniccity.com/shopping/pricelist.asp?prid=512

You said in the other thread that you can solder, so you can assemble your own kit to do what you want. Or the kits are often available pre-assembled, for a few dollars more.

 

[vk6kro]

You can make a buzzer circuit from just a relay.

You arrange it so that the relay coil is fed power through a pair of contacts that opens when the coil is activated.

So, the coil gets power, opens the contacts, loses power, closes the contacts, gets power and so on.

Here is a drawing of it. The bottom contact is being attracted to the coil when it is activated.

[PLAIN]http://dl.dropbox.com/u/4222062/buzzer.PNG

The speed of this will vary with the relay and you can take an output between the point shown as output and the bottom battery connection. Battery polarity doesn't matter.

The output will contain large voltage spikes and you should be careful about what you connect it to. It may need diodes and resistors and capacitors to clean up the output.

 

[ben123324]

Your request makes no sense to me. It's like saying: "I want this ordinary light bulb to flash on and off when I plug it in, but I don't want anything else besides the bulb, socket and cord." It quite simply cannot be done.

by that i mean i don't want a cuircuitboard with components. all i want is a device that you put in series with the load so that the battey sends pulses to the load.

 

[ben123324]

You can make a buzzer circuit from just a relay.

You arrange it so that the relay coil is fed power through a pair of contacts that opens when the coil is activated.

So, the coil gets power, opens the contacts, loses power, closes the contacts, gets power and so on.

Here is a drawing of it. The bottom contact is being attracted to the coil when it is activated.

[PLAIN]http://dl.dropbox.com/u/4222062/buzzer.PNG

The speed of this will vary with the relay and you can take an output between the point shown as output and the bottom battery connection. Battery polarity doesn't matter.
The output will contain large voltage spikes and you should be careful about what you connect it to. It may need diodes and resistors and capacitors to clean up the output.

thanks that was wat i was looking for, but how would i make, or buy 1 that works for me? i really don't need 15hz more like 2,5,10 or something. I am building an induction coil curcuit, and i need a way to send my 15vdc to the coil pulsed at a rate where i see a steady stream of sparks, but if i can't get that from a relay, il setle for 2-5 sparks per second.

could you show me the best one from here, if i want to send pulses of 9-15v using 9-15v to power the relay itself? link:http://www.skycraftsurplus.com/relayssolenoids.aspx

 

[Bob S]

i really don't need 15hz more like 2,5,10 or something. I am building an induction coil curcuit, and i need a way to send my 15vdc to the coil pulsed at a rate where i see a steady stream of sparks, but if i can't get that from a relay, il setle for 2-5 sparks per second.

If you are using the relay contacts in series with a coil (like automobile ignition coil primary), you will be developing very high voltages across the relay contacts whenever they open. The contacts will be carrying a large current when they are closed. The V=L dI/dt voltage will arc and pit the relay contacts, and needs to be controlled by a small capacitor in parallel with the relay contacts. See my simulation at post #3 in the thread

https://www.physicsforums.com/showthread.php?t=330883&highlight=automobile+ignition+coil+simulation


Bob S

 

[vk6kro]

Induction coils have their own contacts that open and close to switch the supply on and off.
A Google hunt brought up some great pictures of induction coils.
They are notoriously unreliable as the contacts quickly become dirty and pitted.

You should be able to achieve something with a circuit like this:

[PLAIN]http://dl.dropbox.com/u/4222062/spark%20generator.PNG

This would require a second set of contacts on the relay.

Ignition coils from cars are available at wrecking yards and are cheap if you don't care what car they came off. Try to get the capacitor that was used with the coil. I have shown 0.022 uF because it was on Bob S's simulation, but it must be a capacitor off an ignition system.

You would have to ask for the "old type" of ignition coils as modern cars use different arrangements.

 

[Bob S]

Induction coils have their own contacts that open and close to switch the supply on and off...They are notoriously unreliable as the contacts quickly become dirty and pitted.

I went through 3 cars with "old type" ignitions: 1941 Buick, 1949 Ford, and 1956 Olds. At about 10,000 ignition firings per mile, I put many million cycles on the "points". My main problem was the points gap needing adjustment every ~5000 miles, replacement ~15,000 miles. The contacts remained reliable.

An alternate choice is: If you can find a CD ignition circuit on an old car, it can be run directly off a NE555 chip with an open collector NPN transistor output. I still have my old "Mark Ten B" CD ignition circuit I built from a kit ~1970.

Bob S

 

[vk6kro]

I went through 3 cars with "old type" ignitions: 1941 Buick, 1949 Ford, and 1956 Olds. At about 10,000 ignition firings per mile, I put many million cycles on the "points". My main problem was the points gap needing adjustment every ~5000 miles, replacement ~15,000 miles. The contacts remained reliable.

An alternate choice is: If you can find a CD ignition circuit on an old car, it can be run directly off a NE555 chip with an open collector NPN transistor output. I still have my old "Mark Ten B" CD ignition circuit I built from a kit ~1970.

Bob S

Hi Bob,

An induction coil is one of these:

They had a primative rattling switching contact mechanism to provide the varying flux.
These contacts were unreliable, but the coils themselves were beautifully made and lasted for ever.
They are mainly seen in schools and are still available. An easy way to produce scary sparks.

 

[Bob S]

I have 3 old Model T Ford (buzz) coils with the vibrator (relay) contact mechanism on one end. The coils (primary and secondary) were wound like a solenoid around a stranded iron wire core. I suspect you won't find any of these in junk yards anymore.

Search for photos at eBay "ford model t coil"

Bob S

 

[vk6kro]

Ahh! Model T. Now, that was a car. :) Pretty strange to drive, though, I believe.

Did they synchronise the spark with the engine or did they just keep firing the plugs regardless?

The induction coil in the picture above has a piece of soft iron being attracted to the core of the transformer when DC passes through it. This switches the DC supply to the coil off and the cycle repeats.
For some reason this seems to be added as an afterthought and it is usually noisy and erratic.

Ideal machine for instilling a sense of shock and awe into students, though.

 

[ben123324]

I have shown 0.022 uF because it was on Bob S's simulation, but it must be a capacitor off an ignition system.

i don't think i can get that, but should i substitute with the lowest uF cap i have at the required voltage?

 

[vk6kro]

You can probably still get a new one at an auto parts store. They were not expensive.

This is probably better than getting something from an electronics store.
The series resistance of these capacitors would be important and you get good, low, series resistance with an ignition system capacitor.