I am trying to build a circuit that will power a small 1A DC motor for 0.5-15s. I found a diagram in this forum and built it without a problem. It works great when I only test it with an LED.

When I attach a motor, things go haywire. The problem is that the diagram I have includes two separate sources. 1 source for the 555 timer circuit and another separate source for the motor.

Because this is part of a science olympiad competition, I am bound by the rules to have only 4 x 1.5V batteries. Is there a way to split the 4x1.5V source into two isolated circuits? Is there a way to keep the motor noise/back emf from disrupting the 555 timer?

I could power the motor with 2 x 1.5V. Will the 555 run on 3V?

Chris

 

Could you post the schematic of your circuit?
Are the grounds connected together?

 

No, the 555 needs a voltage between 4.5 and 15V to run. Use a diode in parallel with the motor to absorb the back EMF created. The cathode of the diode has to be connected to the positive side of the motor.

 

I have tried the diode in parallel with the motor. It doesn't work. Should I be using a rectifier diode or a schottky diode? Right now, I have a random diode I got from radioshack in there.

I am working on the schematic...

Chris

 

A shottky diode would be better because is faster but a rectifier diode will be fine. Are you sure the diode is working?

 

good point. I will put the diode on the multimeter and check.

 

My electric model airplane has a Cmos 555 driving a Mosfet using PWM for motor speed control. The motor draws a max of 8A from the 8.4V Ni-MH battery and it works perfectly.

The motor has two 0.1uF ceramic capacitors from each terminal to its grounded case. The battery has a 0.1uF ceramic bypass capacitor and a 100uF bypass capacitor.

 

Were you driving the motor directly from 555 ? If so ,555 overloaded, put 22Ω between 555 & motor; motor may still tunn ,with not much power. Hopefully with driver , might add 47 Ω between motor & 555 + input,with 6V to motor & 100μF to 555+ in. and common[-6V].

 

Thanks everyone.
With the addition of the capacitors that audioguru suggested and a diode to avoid having the back emf trigger the 555, I think we have solved the problem. It seems to run pretty well now.

Thanks for the help.

Chris