Troubles powering PWM cooling fan from solar panel - Page 1
Forum section: electronics / projects

author: valley001
author_rank: Frequent Contributor
timestamp: March 22, 2020, 10:06:36 pm
content: Hello all,I have a battery box that I am ventilating with a 12v PWM fan (salvaged form an old PC). I am powering this fan directly with a 10 watt 12v panel, using the fan ground and positive wires and leaving the green and blue wires disconnected. It worked great at first, spinning the fan up to full speed under good sun. The trouble started with clouds obstructed the panel and the fan diminished speed to idle, when the clouds cleared the fan remained at idle. If I disconnect the fan and reconnect, or momentarily obstruct (completely) the solar panel, the fan will resume full speed operation.I presume there is a controller in the fan that is unhappy and causing this. Any way to prevent it from locking up in idle mode? I know I could simply use a non PWM fan but this seems like a decent fan and would rather not spend the money if I can make this setup work.Thanks in advance all.

author: Prehistoricman
author_rank: Regular Contributor
timestamp: March 22, 2020, 11:15:56 pm
content: Dumb idea:Have a microcontroller control the power to the fan. Cut out the power periodically

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 22, 2020, 11:21:01 pm
content: What you need is a control circuit to adjust the fan speed to prevent the voltage dropping too low.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2020, 12:21:10 am
content: I presume something like this could work? Originally I thought the fan speed would track the solar output but I guess I would need a non pwm motor for that.https://www.amazon.com/gp/product/B077SLWWXL/ref=ox_sc_saved_title_1?smid=A243HB0NZWY05K&psc=1

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 23, 2020, 02:33:26 am
content: Probably the easiest would be to use an Arduino to sense the voltage using a voltage divider and then control the fan using PWM. Or do that with some analog circuits if you prefer to go that route.

author: senso
author_rank: Frequent Contributor
timestamp: March 23, 2020, 02:50:11 am
content: Find which is the pwm control wire and connect it to 12V as well, full speed all the time..

author: Whales
author_rank: Super Contributor
timestamp: March 23, 2020, 04:37:57 am
content: Quote from: senso on March 23, 2020, 02:50:11 amDon't do this, not all fans can take it. Spec requires fan to tie PWM control line up to about 5V max (designed for open-collector drive IIRC?), more may lead to problems. As such pulling it up externally (to 5V) should have no effect anyway.If you want a simple plug and play solution: there are combined buck and boost converters on ebay for less than $20 (probably less than $10, long time since I looked). One of these will give you a constant output voltage (of your choice) over a wider variety of operating conditions.Alternatively: those ideas to periodically cut power sound interestingPerhaps a 555 timer to cut power for a few seconds every few minutes, or would that increase wear to dramatic levels?

author: senso
author_rank: Frequent Contributor
timestamp: March 23, 2020, 11:10:35 am
content: I'm a lot more used to laptop fans, but even the ones that run with 12V(lots of DTRs use 12v fans), just connecting the usually blue wire to 12v will make then run at full speed.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2020, 03:12:36 pm
content: I did not know about those small Dc-Dc converters. I picked up a handful and will give them a try. Seems like they could also be good for making phone chargers out of small solar panels.I took some voltage readings under various lighting conditions and noticed the panel voltage drops dramatically if light is obscured even slightly. In the evening I could watch the voltage drop from 18v to below 8v as the fan spooled up, then it would cut to idle when the voltage dropped to 6v. Hopefully with the voltage propped up to 12v the fan will not reset despite the low current.

author: duak
author_rank: Super Contributor
timestamp: March 23, 2020, 05:23:43 pm
content: Valley, does the fan do the same thing if you reduce the voltage while operating if from a variable supply? If it's a four wire fan, there might be some sort of digital logic inside that gets upset if the the voltage dips. If applying other voltages to the control pin doesn't help does pulsing it make a difference? That fan should produce a pulse output for the MB to determine RPM. Does it make a difference if the RPM out goes into the speed input? You might need a transistor to invert the signal.

author: David Hess
author_rank: Super Contributor
timestamp: March 23, 2020, 07:28:53 pm
content: It is not uncommon for a controller like those found inside of a DC brushless fan to fail to start if the supply voltage is raised slowly enough. Startup circuits in linear ICs sometimes have the same problem.The best solution is to use a different fan which does not suffer from this problem. If I could not do that, then I would probably use an astable oscillator to periodically short the input supply voltage if the tachometer output is not pulsing.

author: Prehistoricman
author_rank: Regular Contributor
timestamp: March 23, 2020, 08:51:24 pm
content: Quote from: David Hess on March 23, 2020, 07:28:53 pmThat's actually a really nice improvement of my idea. Characterise the fan speed across voltage and if the fan doesn't spin at the right speed for long enough, reset it.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2020, 09:58:20 pm
content: As usual, this forum delivers. Cheers everyone.The fan seems to have no trouble starting so long as the voltage is there, im hoping these little buck converters will do the trick, the other ideas are slightly above my skill set..oscillators and such. I do have a non PWM fan on standby in case fixing the voltage dropout does not solve things. Maybe ill put my scope on those other two leads and see what they are doing.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2020, 10:00:57 pm
content: Quote from: duak on March 23, 2020, 05:23:43 pmI dont have a low voltage supply to test this, but varying the voltage from the panel by controlling the amount of light seems to accomplish the same idea. If voltage drops to 6v the fan will lock into idle mode.

author: David Hess
author_rank: Super Contributor
timestamp: March 23, 2020, 10:32:06 pm
content: Quote from: Prehistoricman on March 23, 2020, 08:51:24 pmThe practical implementation is to implement a low frequency 2 transistor astable multivibrator which drives another transistor to short the input. Then the tachometer output is wired to reset the multivibrator so it never switches while the fan is operating. Or the multivibrator could be replaced with a relaxation oscillator of some sort. Essentially the idea is to make a watchdog circuit for the fan and actually you could use processor supervisor ASIC to do it.

author: valley001
author_rank: Frequent Contributor
timestamp: March 25, 2020, 02:03:17 am
content: Well...i'm not sure if the buck converter/booster will work or not. In fairness we did not have good sun today until the evening when solar energy would be low anyway. One encouraging result is with poor sun the fan draws voltage down to the point the converter resets, so what I end up with is a fan that cycles on and off every 10 seconds or so. With full sun it should run full out, if obscured by clouds it should drop, reset, and resume at full power with full sun. I guess ill see.Will this cutting in and out potentially harm the electronics?