Ideas on a self-oscilliating relay circuit

[RayRay1132]

I've recently started working on a self oscillating dc powered transformer circuit. I would just like some ideas on if this kind circuit would work. (Schematic attached)
Thanks in advance -Ray

 

[Beau Schwabe]

Put a cap across the relay. Start with about a 100uF and go up or down from there.

To save the contacts on your relay use TWO smallish 0.1uF CAPs ... one across NC and COM and the other across NO and COM.

 

[Nigel Goodwin]

I've recently started working on a self oscillating dc powered transformer circuit. I would just like some ideas on if this kind circuit would work. (Schematic attached)

It obviously works, as it was a standard component back in the 40's/50's/60's - called a 'vibrator' - every car radio had one, until transistor radios took over.

Vibrator (electronic) - Wikipedia

en.wikipedia.org

 

[Diver300]

The oscillation will depend on how fast the relay operates. Most relays will break the NC contact before the NO one makes, so to get the relay to close the NO contact, you are relying on energy stored in the inductance of the coil and in the inertia of the contacts to complete the operation. The characteristics of the relay will affect the operation a lot, and it will be difficult to tell from the relay specifications what you might expect.

In the Wikipedia vibrator circuit, the system is in in a push-pull arrangement so that the transformer field is reversed and not just run one way. That will probably make the circuit less sensitive to the frequency and the mark-space ratio. Also the moving part of the vibrator seem to have added mass, and work in a symmetrical way, and that could help to make the circuit work better.

With a simple relay I suggest having a freewheel diode with a series resistor, and allow adjusting the resistor to adjust the speed of decay of the coil current.

 

[rjenkinsgb]

As an experiment, I'd be tempted to try connecting the transformer primary with a series capacitor, across either the relay coil or NC contact.

That should allow the relay flyback energy to be used rather than wasted, plus possibly reducing contact arcing and avoiding the need for the NO contact to reliably make?

 

[Nigel Goodwin]

I mentioned the old vibrators, and where I used to work we had a draw full of them - both normal and self rectifying - for repairing car radios. I started in 1971, and they were there before I started - and we never used one all the time I was there However, their existance is why I know about them.

I imagine they went to a friend of mine?, who took everything when the shop closed down. Chances of finding them would be slim, I call and see him occasionally (as I know he's struggling we pass him work to do from us), and you can't move for stuff piled up everywhere - with quite a lot of it in boxes, cabinets and draws with my writing on. However, it's not just our stuff he's got - he's now taken the contents of 4 or 5 closed down service departments, so he's got a huge amount of stuff.

 

[gophert]

I mentioned the old vibrators, and where I used to work we had a draw full of them

Just a question on Language (UK English to US English translation). I'm only asking because the last time this caught my eye from a UK-member's post, I assumed it was a typo. In the US, we call the 5-sided box that can be pulled out of a piece of furniture, a "drawer". Is it really called a "draw" in the UK? Is it the proper name or slang?

 

[Nigel Goodwin]

Just a question on Language (UK English to US English translation). I'm only asking because the last time this caught my eye from a UK-member's post, I assumed it was a typo. In the US, we call the 5-sided box that can be pulled out of a piece of furniture, a "drawer". Is it really called a "draw" in the UK? Is it the proper name or slang?

It's probably just local slang

I could use either, interchangebly, and probably never even notice?.