driving a motor from 555

[patroclus]

I just want to drive a motor on from an output of a NE555. I conected it to the base of a NPN transistor (547B), and emitter to ground. It works for LEDS, but when I connect motor's cathode to collector, it just doesn't work...

Any help please?
This means that motor takes up to much power?
May I need a relay?

Thanks..

 

[patroclus]

motor is an electri motor, not stepper, but don't know specs.
I try with more base current, and it works but just a little time, then stops, and transsistor gets TOO hot.
then I tried with an small fan and it works...

But It reduces Ne555 pulses duration by 5-10%..
I don't get it and need to finish a project... any help?

 

[Exo]

a BC547 can only handle 100mA. I don't know about your motor, but it is likely to need much more. Use a bigger transistor, or make a darlinton configuration with your 547 and a 2N3055.

Also add a reversed diode over the motor terminals. To protect your transistor when the motor stops

 

[patroclus]

What about a relay??

 

[Exo]

It depends, how long are these pulses that your 555 outputs? if they are seconds, or longer you could use a relay. But a relay is to slow to handle faster pulses.

what frequencies are we talking about ?

 

[patroclus]

pulses are one minute long

 

[Exo]

Then you could indeed use a relay. Still, don't forget a reversed diode over the relay coil. Since it is a coil, like your motor. It will have a reverse emf when shut off wich might kill something in your circuit

 

[patroclus]

Anyway, a "bigger" transistor would do?

You know any I could use instead of 547B??
I also have 2N3904 and 2N4401.. but I could get others, of course.

Anyway, using a fan instead of motor worked, but pulses got 55 seconds long only.. is this normal?

 

[patroclus]

Yes, I use a diode (1N4148) between ground and emiter (thanks!)

 

[Exo]

The 2N4401 you mention can handle 500mA. You could try it. Measure the current your motor requires (or maybe it is printed on the engine somewhere) and see how much you need, then choose an appropriate transistor

'bout the pulses getting only 55 seconds. I don't know much 'bout the 555 so i don't know this is normal or not. But you should be able to handle this by modifying the 555 circuit... (change the value of the resistor in the RC that sets the time)

 

[patroclus]

Thanks for your help. I'll try relay.
But I never used relays, though I know the theory..

One circuit, two position relay will do?
Do I need to know something else?

 

[Exo]

Yes, a simple relay will do, but just as with the transistors you will have to check if it can handle the current.

 

[patroclus]

Thanks