555 Timer PWM Not Changing DC Fans Speed - Page 1
Forum section: electronics / projects

author: ashybuuny
author_rank: Contributor
timestamp: June 20, 2024, 10:00:49 pm
content: 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=1Input voltage is 12V 1.5Amps which is enough to power 4 fans. The voltage is from a DC power source.

author: pqass
author_rank: Super Contributor
timestamp: June 20, 2024, 10:37:08 pm
content: 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.

author: Andy Watson
author_rank: Super Contributor
timestamp: June 20, 2024, 10:45:03 pm
content: The fans are not connected correctly. The -ve should be disconnected from ground (blue) and connected to the drain of the mosfet (red).

author: ashybuuny
author_rank: Contributor
timestamp: June 20, 2024, 11:01:38 pm
content: 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.

author: pqass
author_rank: Super Contributor
timestamp: June 20, 2024, 11:22:54 pm
content: Quote from: ashybuuny on June 20, 2024, 11:01:38 pmWhat 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 20, 2024, 11:40:27 pm
content: 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.

author: pqass
author_rank: Super Contributor
timestamp: June 20, 2024, 11:56:04 pm
content: See attached.CUT the existing trace under the RED RECTANGLE.ADD an insulated wire where indicated by the RED LINE.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 12:03:02 am
content: 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.

author: SanctePieDecime
author_rank: Contributor
timestamp: June 21, 2024, 12:14:21 am
content: 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 05:21:55 pm
content: 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?

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 05:43:48 pm
content: Quote from: ashybuuny on June 21, 2024, 05:21:55 pmThe 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 05:55:45 pm
content: 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.

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 05:59:02 pm
content: Quote from: ashybuuny on June 21, 2024, 05:55:45 pmOkay. 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 06:37:43 pm
content: This is my new chip and that has been soldered on. On The multimeter the Hz% is that frequency counter?

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 06:44:50 pm
content: Quote from: ashybuuny on June 21, 2024, 06:37:43 pmThat looks better.Yes. Hz=frequency %=duty cycle.What's the make and model of multimeter?

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 06:50:58 pm
content: I use the Ideal 61-340 Test-ProMultimeter

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 07:01:03 pm
content: 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 07:25:31 pm
content: 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.

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 07:40:44 pm
content: Quote from: ashybuuny on June 21, 2024, 07:25:31 pmWell, 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 07:46:59 pm
content: 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.

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 08:03:21 pm
content: 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.QuoteThis 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 08:08:27 pm
content: 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?

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 08:17:24 pm
content: Quote from: ashybuuny on June 21, 2024, 08:08:27 pmActually, 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.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 08:30:10 pm
content: 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.

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 08:34:24 pm
content: Quote from: ashybuuny on June 21, 2024, 08:30:10 pmIf 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?

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 08:37:48 pm
content: No the fan keeps spinning no matter what position. I verified it now by moving the pot and stopping the fan with my hand and letting go of it. I left the pot at each position about 5 seconds.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 08:45:29 pm
content: Quote from: pqass on June 21, 2024, 08:34:24 pmI did not measure when the PCB was powered.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 08:51:43 pm
content: Quote from: ashybuuny on June 21, 2024, 08:45:29 pmI measure when powered on and I am not sure if I did it correct but I had a lot of OL at different points. What is MOSFET base mean ? Does it refer to the gate ?

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 08:53:13 pm
content: Quote from: ashybuuny on June 21, 2024, 08:45:29 pm(With PCB un-powered) check resistance between 555 output (pin 3) and MOSFET gate. It should be 1K.If I said "base" I meant gate.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 08:55:22 pm
content: Quote from: pqass on June 21, 2024, 08:53:13 pmI got 500 Ohms which is right since R1 and R2 is parallel.

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 08:59:54 pm
content: Quote from: ashybuuny on June 21, 2024, 08:55:22 pmThey aren't really in parallel; they both start from same 555 pin 3 but one goes to the gate the other to GND.But what you said was interesting. It would look like two parallel 1Ks IF the MOSFET is damaged.Again, with the PCB un-powered, check the resistance between MOSFETGATE and SOURCE, and between DRAIN and SOURCE (while you short GATE and SOURCE).

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 09:03:09 pm
content: Quote from: pqass on June 21, 2024, 08:59:54 pmRed on Gate black on source I get 0ohm, Red on drain and black on source I get 230ohm.

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 09:04:29 pm
content: Quote from: ashybuuny on June 21, 2024, 09:03:09 pmSorry, I was to quick to post.Can you retry the DRAIN and SOURCE resistance when GATE is shorted to SOURCE.Yes, BLACK lead on source, RED on DRAIN.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 09:15:42 pm
content: if I did it correctly it's 220Ohms, but I wonder why is C1 and C2 connected when on the schematics it wasn't? Am I just confused because they lead to ground?

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 09:20:51 pm
content: Quote from: ashybuuny on June 21, 2024, 09:15:42 pmNo. That's not what I meant. You can remove that jumper from R1 to C2.What I mean is just to measure the resistance (with your MM) from the DRAIN (RED lead) to the SOURCE (BLACK lead) pins on the MOSFET while, with a flat-blade screwdriver, just touch the GATE and SOURCE pins together.The idea, is make sure the MOSFET is completely off (by shorting GATE and SOURCE) and if there is a low resistance between DRAIN and SOURCE, then the MOSFET is broken.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 09:24:55 pm
content: Quote from: pqass on June 21, 2024, 09:20:51 pmIts still 220 ohms

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 09:25:41 pm
content: Actually, I see what you did there. Yes this does short GATE and SOURCE (GND).As such, you've measured 220ohms, which means the MOSFET is permanently ON when the gate should be off.Replace with a new MOSFET.FYI: MOSFETs can be turned-on just by touching the GATE; they're very sensitive. They can also be damaged by static electric charge.If you don't have a ground strap, before handling any static sensitive components, ground yourself by touching a large metal object like a desk lamp.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 09:38:08 pm
content: Quote from: pqass on June 21, 2024, 09:25:41 pmNew one is replaced and it should work now right?

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 09:39:21 pm
content: Quote from: ashybuuny on June 21, 2024, 09:38:08 pmIt should.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 09:45:19 pm
content: IT WORKS! Although It screeches like a siren. I thought it was the fan blades but when I stopped it with my hand it kept going. It was definitely coming from the PC fan and I am not sure why. The screeching only occurs if about 85% or lower than the pot turns to what I believe is CCW. So if the pot is above what I think is like the 85% turn threshold it runs silently and fast.

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 09:49:04 pm
content: Quote from: ashybuuny on June 21, 2024, 09:45:19 pmGREAT!You probably have to increase the PWM frequency. As it's now only 1.2KHz.Change C2 to 1nF which should boost the frequency to 12Khz. That's easier than changing the pot to 10K.

author: ashybuuny
author_rank: Contributor
timestamp: June 21, 2024, 09:54:29 pm
content: Is that all I have to change to fix that? I don't have it so I will probably order 1 when I am doing my next project. Will this change also make the change of speed smoother.THANK YOU so much!

author: pqass
author_rank: Super Contributor
timestamp: June 21, 2024, 10:04:44 pm
content: Quote from: ashybuuny on June 21, 2024, 09:54:29 pmLow PWM frequencies can cause audible resonances. Boosting it to high or above hearing range makes them go away usually.The "smoother" issue may be related to the fact that you can't dial a motor down to a very low duty cycle without stalling it. To remedy this, we put in a default low resistance on the D2 (cathode) leg of the pot; ie. to not go lower than a minimum speed. You may choose to add another resistor on the D3 (anode) leg of the pot too if you find there isn't a visible speed change on the upper end of the dial. This way, the pot range will be tuned to have the most effect on the fan speed.