Electronic Q: Wire a relay for self oscillation?

Didn't put this in flashlight electronics as it's not really for a flashlight..

Trying to do an experiment here with mechanical means instead of solid state this time. I tried wiring a SPDT relay to where it would self oscillate, but it will only latch on, and stay on?!? I'm confused. The sucker should be clicking like a tap dancer who's been up drinking coffee all night...

I wired it like this:
85 Ground
30 Hot +
87a is wired to 86.

So when power is applied to 30, it should engergize the coil as power will go to 87a which is normaly connected and is wired to the other side of the coil. When this happens the point will move away from 87a, thus removing power to the coil, and the process will repeat.

Instead it latches to 87 and stays there..?!?!?!???

Re: Electronic Q: Wire a relay for self oscillatio

You should wire the relay to the NC contacts, so that when there is no power the connection will energize the coil, and when the coil is energized it will open the circuit again, alowing the coil to de-energize, which allows teh contacts to close and start the cycle all over again.

Buzzers work on this principle.

Daniel

Re: Electronic Q: Wire a relay for self oscillatio

That's exactly how I have it wired! So I'm puzzeled!!

Re: Wire a relay for self oscillation

Here's how I did mine, great for shocking 4 year olds.
(J/K) /ubbthreads/images/graemlins/grin.gif



T1 can be an ignition coil or step-up transformer

When the relay coil is energized it causes the contacts to close. That shorts out the relay coil which then lets go of the contacts. When it lets go, the relay coil energizes again and the contacts close. This happens very fast.

The relay "output" gets pulsed and is used to drive T1 to make a high voltage source.

Re: Wire a relay for self oscillation

Thanks! I was thinking about doing it that way but couldn't picture in my head if it would be any better.

Do you have any clue why the other way I was trying was keeping the coil latched on???

I'm going to use a motor cycle ignition coil. I'm going to see if I can get better sparks than with my 555 circuit. If it's impressive than I'll forget about other complicated designs for dumping a cap via SCR into the coil, or additional components like a tv cascde. Most I could tune my 555 to was about 1cm spark, or 1 mm hot arc. And some wires got ripped off and I don't feel like going back over the circuit!!!

I'm not sure if I'll like the clicking noise of a relay over the varible high-frequency noise of solid state though.. /ubbthreads/images/graemlins/smile.gif

Any idea how long the relay will last with this kind of abuse? If I use a 12v 30amp bosch style relay? I mean it's not much current going through the relay, but it's getting a lot of mechanical wear. Do I need a diode to protect the relay from CEMF?

The 555 circuit seemed to work best with 2 old can style car ICoils in reverse parallel. But the motor cycle coils seemed to have run off of a CD style system as it had a high voltage cap and 4 heatsinked SCRs or some power transistors, and did poorly when paired up. Probably dumped 200v into them.

I'll eventually run it off of 16.8volts likely (2 NiMH 9v). The higher on demand current capacity and volts should help.

Re: Wire a relay for self oscillation

Wait though, looking at your diagram, it seems as though the IGN Coil will always have voltage goign through it. When the relay coil gets power to move, power is going through the IGN Coil, and then it gets full power, relay drops, and repeats.

The IGN COIL never sees 0 volts... It may spark, but I don't think it's going to be as powerfull as if it were full ON/OFF operation. The IGN coil isn't in sense a true transformer, and does best with pulsed power. It only has 3 total wires after all...

Re: Wire a relay for self oscillation

My poor recollection for Ignition coils as they are constructed as autotransformers with one side of the primary in common with one side of the secondary. They "output" when the current in the primary is cut off (points open). The energy stored in the magnetic field has nowhere to go but out the secondary, resulting in the spark.

Way back you could get what I think they called a Ford tractor coil. It had an integral interupter/vibrator built in. It was very unpleasant to experience the output! /ubbthreads/images/graemlins/evilgrin07.gif /ubbthreads/images/graemlins/grin.gif

Linkie.

Larry

Re: Wire a relay for self oscillation

The really old car radios that used tubes also used a vibrator in the power supply. This was a self-oscillating relay as you've described, and it was wired to act as a chopper to generate HV for the place circuits of the tubes.

The vibrator was in a sealed aluminum can and looked like a large electrolytic capacitor. It ran on 6v.

Re: Wire a relay for self oscillation

Larry, an ignition coil is more like a pulsed inductor than a xfmr.

Intersesting links guys. Upon reading it seems as though I probably will get better output with a 555 setup. Perhaps if I wind a feedback wire around the coil, it will be enough to pick up and set it up using 1 transistor for self-oscillating setup. That way when I adjust the spark gap I won't have to adjust the frequency. Perhaps with 16.8v NiMH I'll have big enough sparks. Or I could find some HV diodes and Caps and pot me a small voltage doubler.

I'll still try to get the relay to oscillate. Since it's a lot less work and I want to at least see what it'll do...