mechanically driven transistor, no spark but good switching

[sucahyo]

Mechanical switch is the best switch to produce most efficient coil collpase current, but the spark create a problem. Transistor do not have spark problem but it efficiency is noticably lower because of slower switching and some voltage/current leak losses. By using mechanical switch to drive transistor we get sharp signal and no spark.

YouTube - Relay driven transistor

200mA at 12V, 1000mA at 22V, relay resistance is about 500ohm. If relay can not made to self oscillate, put capacitor in parallel with relay coil. I weaken the spring to make it work.

Just a reminder.

[BobBrown]

Cool !

So, your saying that a transister is sloppy but last a long time, and a relay is sharp but wears out fast, at these voltages. So we combine the sharpness of the relay with the non sparking ( wearing out ) of the transister and get the best of both worlds? I'm intrigued ! A Relay system that has a much longer life span ! Tell me its true, and I'll incorporate this in my design.... which for some lazy reason I have yet to put on a bread board.


Andrew T
PATHS ~ Mind Energetics

[sucahyo]

Yes. Relay will work longer because there is no spark anymore to worry about, and since relay contact cut current more effectively transistor will work at its fastest speed. The problem is, relay have limited range of duty cycle and frequency. I think we should use other type of mechanical switch to get faster frequency or more duty cycle control.

[boguslaw]

You know , that's why there are special electronics for military and dumb one for us - mortals.

I hate it.

[electricme]

Trick to cut points damage on relays

Hello chaps,
I came across this item when I was working in telecom australia.

If you want to stop the pitting and arking of points, just arrange the make and break actions in a series relay setup, in other words, use multiple leaf contacts in series.

jim

[nvisser]

Something looks wrong on that diagram.
How will you switch a relay from the base of a transistor?

[sucahyo]

Hello chaps,
I came across this item when I was working in telecom australia.

If you want to stop the pitting and arking of points, just arrange the make and break actions in a series relay setup, in other words, use multiple leaf contacts in series.

jim

Thanks, but can you explain more? I don't get it. Are you saying we use two leaf of DPDT in series? Will that work with 1 Amp current?

Something looks wrong on that diagram.
How will you switch a relay from the base of a transistor?

Relay is not being switched by transistor. It is the opposite.

The circuit show the relay condition at no power. In ON condition, the current will go trough from positive of battery to relay coil, to relay contact, to relay lever, to transistor base to negative of battery. With current going trough its base, transistor will turned on. The relay coil will create magnetic field that draw the lever to move away from the contact.

When lever leave the contact the power is shut OFF. No current going to transistor base will shutting off the transistor. No current going to relay coil will shuting off the magnetic field. Without magnetic field the lever will spring back to touch the contact again.

When the lever touch contact the power is turned ON. the cycle continues...

If your relay can not operate this fast, you may need to add capacitor. Relay will turned on longer by adding capacitor in parallel with relay coil. 100uF would be sufficient.