DC Motor 10V - Creates noise in power line - Page 1
Forum section: electronics / beginners

author: 2X
author_rank: Frequent Contributor
timestamp: May 15, 2018, 07:52:04 pm
content: Hello,I have the below timer swich with NE555 timer on my breadboard and when I connect the DC motor at the tranzistor (BD139) the output stays high only for 1sec instead of 24seconds. If I connect a capacitor "C4" 220nF or 1uF parallel with the motor the output stays ON approximately 19sec which again is not right. I connect the oscilloscope at the power line and I saw spikes even with tha parallel capacitor with the motor. Does anyone know how can I solve this problem (I don't want to use mosfet or optocoupler)?

author: rstofer
author_rank: Super Contributor
timestamp: May 15, 2018, 08:07:16 pm
content: You can try putting a 0.1 ufd capacitor right at the motor terminals. DC brushed motors are always noisy.

author: Paul Price
author_rank: Super Contributor
timestamp: May 15, 2018, 09:36:18 pm
content: Put a 100uF paralleled with a .1uF directly from the + motor terminal to ground.How do you checked for 24-Sec timing with the motor disconnected?

author: 2X
author_rank: Frequent Contributor
timestamp: May 15, 2018, 10:01:04 pm
content: Quote from: Paul Price on May 15, 2018, 09:36:18 pmI connected at the output (pin 3) of the 555 a LEDwith a resistor 330ohm.

author: Benta
author_rank: Super Contributor
timestamp: May 16, 2018, 11:55:28 am
content: As rstofer says, DC motors are noisy.A good way of silencing them is 100 nF across the motor terminals and 2 x 22 nF from each motor terminal to motor case.All three caps should sit directly on the motor.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 21, 2018, 02:50:45 am
content: Does your 555 timer work as expected without the motor?It could be that your problem is because of a wiring fault, and not because of the motor.Try to replace the motor with a led (+resistor) for indication.You can also further isolate the 555 from the motor by putting a big cap parallel to the 555 (100uF or so) and a small inductor in the power supply to the 555.

author: 2X
author_rank: Frequent Contributor
timestamp: May 26, 2018, 03:14:55 pm
content: Hello,I put the caps that you say but the I could only eliminate in some degree the voice "Pictures 2,4,5,6,7" is with a 100nf parallel to the motor's terminals and with an LC filter (L=1uH & C=220uF) "Picture 1" with cutoff frequency at 10KHz. It is very crazy, I have made many tries with different caps and inductors but I couldn't eliminate the motor's noise, so the 555's output turn off exactly at the same time like with no motor at the output. Any idea?Picture 1:Picture 2:Picture 3:Picture 4:Picture 5:Picture 6:Picture 7:Picture 8 - with no motor.. only with a LED in 555s output:

author: jmelson
author_rank: Super Contributor
timestamp: May 26, 2018, 03:37:39 pm
content: R4 is 220 Ohms, giving about 42 mA of base current to the transistor. That sounds like a lot. Trying to get tens of seconds out of a 555 is usually a painful project, as the charging slope of the cap is REALLY slow. Any noise will upset the timing accuracy.Jon

author: Kalvin
author_rank: Super Contributor
timestamp: May 26, 2018, 03:45:58 pm
content: Use a 7805 or similar +5V regulator to feed the 555.

author: 2X
author_rank: Frequent Contributor
timestamp: May 26, 2018, 04:01:16 pm
content: Quote from: jmelson on May 26, 2018, 03:37:39 pmJon thanks for the reply. I have changed the R4 from 220ohm to 1Kohm when I insert the LC filter.

author: james_s
author_rank: Super Contributor
timestamp: May 26, 2018, 05:58:11 pm
content: What does your circuit layout look like? The motor will draw a significant current, layout is important, especially grounding.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 26, 2018, 06:09:55 pm
content: I was also thinking about the layout.If the capacitor on pin 5 is referenced to a noisy ground line, noise will actually COUPLE TO the internal divider.Erratic timing is the result.This is not speculation. I have personally seen it happen.

author: 2X
author_rank: Frequent Contributor
timestamp: May 26, 2018, 06:33:49 pm
content: Quote from: schmitt trigger on May 26, 2018, 06:09:55 pmI have this on the breadboard. Will I try to disconnect the capacitor from the pin 5 and leave it on the fly?

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 28, 2018, 01:41:45 am
content: I would ensure that the motor's return current follows an independent path back to the voltage source's negative from that of the 555 and all its associated components.In other words, single point grounding techniques

author: 2X
author_rank: Frequent Contributor
timestamp: May 29, 2018, 09:31:25 pm
content: Quote from: schmitt trigger on May 28, 2018, 01:41:45 amSingle point grounding as I know it needs components which offer isolation like a transformer or an optocoupler or there is an another way (I would like to find a way to eliminate this motor without using an optocoupler)?Thanks a lot for the reply.

author: james_s
author_rank: Super Contributor
timestamp: May 30, 2018, 12:18:18 am
content: Single point grounding means all of the places where you have a ground symbol get physically tied to the same point so all ground points are the same potential. It has nothing to do with needing isolation.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 30, 2018, 04:35:12 am
content: Put ferrite beads or inductors in series with the motor terminals. Both terminals. Ground the case. Preferably, put small ceramic caps (10nF or so) across the motor leads, to the motor case, just outside the inductors/ferrite beads, to form an L-C filter.Also put a current limiting resistor in series with pin 7, at least 100 ohms.Note also the +10V needs to be well bypassed, both for 555 operation alone, and for the motor's changing load, and for the clamp diode to do its job. Typical would be 0.1uF at the 555; and >= 100uF (low ESR) at Q? and D1, all three located very close together.Tim