555 Timer PWM Not Changing DC Fans Speed

[ashybuuny]

Apologies if this isn't the right spot to ask.

I am trying to control 4 PC DC fans for a grow room and want to control their speed via PWM. I followed The Engineering Mindset "Motor speed controller tutorial - PWM how to build" YouTube video and made the changes that added the additional 3 motors. I ordered the PCB and soldered all the components however, the fan speed does not change as I change the potentiometer. I triple-checked the circuit and believe it is correct, using the correct values of the capacitors but since it's not working clearly something is wrong and I need some help.[attach=1


Input voltage is 12V 1.5Amps which is enough to power 4 fans. The voltage is from a DC power source.

[pqass]

D1 is backwards and in-series with the MOSFET drain.
See attached as what is usually expected (substitute motor for relay).

To correct, disconnect J1-J4 ground terminals and attach to MOSFET drain instead.

[Andy Watson]

The fans are not connected correctly. The -ve should be disconnected from ground (blue) and connected to the drain of the mosfet (red).

[ashybuuny]

Thank you for the reply, Is it possible since they are all connected I can cut the line on J4 which leads to ground on the PCB and solder a wire to D1? And If so how could I accomplish this? I don't care for looks as its for my personal use.

[pqass]

Thank you for the reply, Is it possible since they are all connected I can cut the line on J4 which leads to ground on the PCB and solder a wire to D1? And If so how could I accomplish this? I don't care for looks as its for my personal use.

What does the opposite side of the PCB look like? 
Is it one large ground plane? 
If so, it'll be a pain to cut away J1-4 pins 1, 3 (with an exacto knife) from the rest of the ground plane.

[ashybuuny]

I dont have a ground plane, which in hindsight probably is dumb idea for signals clarity but perhaps its good that I have not?

They are connected by just one line to ground by one of J so I was thinking of cutting it and soldering to D1 on the underside.

[pqass]

See attached.
CUT the existing trace under the RED RECTANGLE.
ADD an insulated wire where indicated by the RED LINE.

[ashybuuny]

Thank you so much, I put all my stuff away but tomorrow I will do just that. You saved me quite a headache and time.

[SanctePieDecime]

Not at all to take away from what anyone else is saying since they have probably solved your problem, but I also noticed that the traces from the power supply input appear to be the same thickness as all the rest of the traces (which do not appear particularly thick. I don't know if this has been giving you any trouble or will give you any trouble in the future, but it is something I thought you should be aware of.

[ashybuuny]

I did the fix, verified the line was cut and soldered the new line. However, I measured the fan and it was always 12V despite me turning the potentiometer. Would this be some sort of damage I did while soldering or damaged chip or potentially even bad solder on the 555?

[pqass]

I did the fix, verified the line was cut and soldered the new line. However, I measured the fan and it was always 12V despite me turning the potentiometer. Would this be some sort of damage I did while soldering or damaged chip or potentially even bad solder on the 555?

The 555 does look a bit off-center (see attached). I'd fix that first then check the output.

Do you have an oscilloscope or a frequency counter to confirm the output waveform?
Also, some multi-meters have a frequency counter capabilities.

Is the 555 upside down?  Is that a dimple at top right?

Even if not upside down, pins 7 and 8 look shorted which may have killed the IC; pin 7 being an open collector.

[ashybuuny]

In that orientation, the dimple is bottom left. I will right now desolder and resolder it perhaps its because its not properly aligned. I also don't have that equipment just a Multi meter.

[pqass]

In that orientation, the dimple is bottom left. I will right now desolder and resolder it perhaps its because its not properly aligned. I also don't have that equipment just a Multi meter.

Okay.  Check your multi-meter as it may have frequency counter capabilities.


Alternatively, you could try to slow the frequency down with a 10uF cap across C2 pins (GND toward the PCB edge).
Then you would be able to see a 1Hz blinking LED+1K resistor between 555 output pin 3 and GND.

FYI: no need to remove existing C2; just tack another across its leads to increase the overall value.

[ashybuuny]

This is my new chip and that has been soldered on. On The multimeter the Hz% is that frequency counter?

[pqass]

This is my new chip and that has been soldered on. On The multimeter the Hz% is that frequency counter?

That looks better.

Yes. Hz=frequency %=duty cycle.

What's the make and model of multimeter?

[ashybuuny]

I use the Ideal 61-340 Test-ProMultimeter

[pqass]

See attached (from here) on how to select the dial function.
Turn on power to the device. Place black lead on GND, RED lead on the 555 output (pin 3).  It should read about 1Khz or so.
Toggle the Hz/Duty button and change to duty cycle display then turn the potentiometer to read PWM percentage.

[ashybuuny]

I connected in the following, I received the expected 1KHz when there is a load or not connected however, when there isn't a load it will only go to 2.7KHz and with a load 1.4KHz. When using the Hz/Duty button nothing changes and does not show me a percent.

[pqass]

I connected in the following, I received the expected 1KHz when there is a load or not connected however, when there isn't a load it will only go to 2.7KHz and with a load 1.4KHz. When using the Hz/Duty button nothing changes and does not show me a percent.

Well, at least it's oscillating. 

By "load", you mean a fan attached?   If yes, is this a standard 3-pin 12V PC fan? 

Does the frequency change when you change the potentiometer?
Any change in the fan speed?

I can't explain why the MM didn't show you a % display. 
Keep toggling the button until "Hz" goes way and "%" shows up on the LCD maybe.

[ashybuuny]

Yes, the load is referring to the fan.

This regular 3-pin 12V PC fan wasn't being used, so I thought to repurpose it.

Frequency does change between 1k-1.4k or 1k-2.7k when fan is attached only when I change the potentiometer(after my shaking hand stops to get a measurement).

The fan doesn't change speed, making me worried that this project is a bust.

I also checked the voltage and despite changing the potentiometer, the voltage stayed at 11V where the fan connects.

[pqass]

555 circuits sometimes change frequency when adjusting PWM so that's not really odd.
What could be happening is that the PWM isn't going low enough for you to notice a change in fan speed.
The circuit should work as far as I can tell (simulation here) but without a way to visualize the duty cycle, it's hard to debug.

The MM averages the pulsating PWM. So if you were to put the MM in VDC with RED lead on 555 output (pin 3) and BLACK on GND, changing the pot should reveal a voltage going up/down.

I also checked the voltage and despite changing the potentiometer, the voltage stayed at 11V where the fan connects.

This may be misleading.  The difference between checking between pins 1,2 on a fan connector and pin 3 and GND on the 555 is that the latter actually forces the output to fluctuate between positive and ground.  Whereas, the former is just disconnecting the connection.  Technically: difference between push/pull and open-drain.  This can fool the meter to report always +11V and not a fraction of the duty cycle.

[ashybuuny]

I checked and it is indeed as you said. Moving the pot changes the voltage 0-12V. How would I make the PWM go low enough to see the difference of my fan speed?

[pqass]

I checked and it is indeed as you said. Moving the pot changes the voltage 0-12V. How would I make the PWM go low enough to see the difference of my fan speed?

Actually, this is good news since it goes to 0V. 
That means we need to see if the MOSFET is working properly.

The only odd thing I see is that R1 is 1K.
Usually, 100ohms is used for a gate resistor.

Also,
on some loads, a PWM duty cycle of, say, 70% to 100% doesn't translate into a visible effect (ie. looks like it's fully-on).
A visible change only occurs when between 0% and say 50%.  The way to lop-side the control is to add a resistor (100K) between D3 anode and the potentiometer pin 3. The frequency will be about 600Hz buts that's okay.  You'll have finer control with the pot.

[ashybuuny]

The resistor value is taken from the video that's the only reason its 1k. I have tested the MOSFET red on drain black on the source I got a reading. Moving the red lead to the gate I get OL.

[pqass]

The resistor value is taken from the video that's the only reason its 1k. I have tested the MOSFET red on drain black on the source I got a reading. Moving the red lead to the gate I get OL.

If the pot is close to the zero duty cycle position, then the 555 output is forcing the gate to 0V most of the time.
EDIT: correction, you said OL, which probably means open circuit in this case.  You had the PCB powered?  If so, then check if you have connectivity from 555 output (pin 3) to the MOSFET base. It should be 1K via R1.

Is the fan stopped when the pot is fully to one side?  (ie. fully CW or fully CCW) Which position reports zero fan movement?