Good Sam Club Open Roads Forum: Tech Issues: Fan Speed Control
Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > Fan Speed Control

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 5  
Prev  |  Next
2112

Texas

Senior Member

Joined: 07/16/2011

View Profile



Posted: 08/27/21 08:51am Link  |  Quote  |  Print  |  Notify Moderator

Quote:

The one I had did make noise, and I have heard others mention the ringing noise from the pulses, so might not be a bedtime item...
I'll touch on this: All PWM controllers have a fixed operating, or switching frequency. Let's say it's operating frequency is 1000 Hz. At that speed it will turn on and off every millisecond. The time period it is on during that millisecond is called duty cycle. At half speed (50% duty cycle) the fan has current flowing through it (turned on) for.5 milliseconds and no current flowing through it (turned off) for .5 milliseconds. At 3/4 speed (75% duty cycle) the fan has current flowing through it (turned on) for.75 milliseconds and no current flowing through it (turned off) for .25 milliseconds.

The noise you hear often comes from the fan turning on at a too low switching frequency. The human ear can normally hear from about 20hz-15khz. I can't hear anything above 8kHz because I'm old. Some controllers will have a switching frequency from 500Hz to 10kHz. You can hear that. A better controller for a fan or motor will have a switching frequency of 20kHz or higher, above the human hearing range. That's why I said the one you found on EBay SHOULD not be noisy because it operates at 25kHz.

However, we are dealing with a mechanical device, the fan. Its blades may not be balanced, bearings may be loose, may not be aligned, etc...
When you change its speed you may fall into a resonant frequency to where it just starts vibrating to the point of making noise. This is not a result of the controller, it's the fan not operating smoothly at a certain speed. It would be hard to overcome that.

Sorry for carrying on but again, I hope this helps you understand what's under the PWM controllers hood.


2011 Ford F-150 EcoBoost SuperCab Max Tow, 2084# Payload, 11,300# Tow,
Timbrens, PullRite SuperGlide 2700 15K
2013 KZ Durango 2857


ajriding

st clair

Senior Member

Joined: 12/28/2004

View Profile



Posted: 08/27/21 10:24am Link  |  Quote  |  Print  |  Notify Moderator

ok. good points.
I dont think my fan is worn in any way. The noise is a ringing, not a mechanical issue. The controller I showed , as I mentioned, is similar, and I am not able to find anywhere the exact controller online anywhere to be able to look at its specifications... It might operate in the human ear range and be audible.

The FF has coils that act like a heating element to burn off power. However you want to exactly define what a heating element is or not does not matter bc in the end it still is doing the same thing, heating up a wire at the expense of power. I thought I used words to give clues that this is not important nor something that matters or needs further discussion. What I keep try to say politely is that I dont really care if you call it this or that. Nothing changed now that you defined it. It is hard to write on a forum post something that can both be understood and polite, I tried. Now lets stop with the heater analysis....

shastagary

minnesota

Senior Member

Joined: 07/16/2007

View Profile


Offline
Posted: 08/27/21 12:52pm Link  |  Quote  |  Print  |  Notify Moderator

i always buy a speed controller that handles way more amps than the fan draws they will run cooler and last longer. i am using one like this from ebay for 7 years now 40A DC Brush Motor Speed Control PWM

i am running a 12" car radiator fan i mounted in my vent cover that draws up to 8 amps. i also bought a 6 channel remote control relay circuit and have it switch different resistances for the speed controller instead of the variable control on the speed controller.

frankwp

Calgary, AB, Canada

Senior Member

Joined: 09/07/2004

View Profile


Offline
Posted: 08/27/21 02:00pm Link  |  Quote  |  Print  |  Notify Moderator

ajriding wrote:

ok. good points.
I dont think my fan is worn in any way. The noise is a ringing, not a mechanical issue.


The noise is a function of the PWM controller. The high speed on/off switching that is used to effectively lower the voltage produces the high pitched sound. You probably noticed that at full speed the sound goes away or is greatly reduced. Some controllers are noise, some not. BTW, The noise is mostly generated at the motor, not the controller.


2010 Cruiser CF30QB
2003 GM 2500HD, crew cab, SB, 8.1, Allison

Gdetrailer

PA

Senior Member

Joined: 01/05/2007

View Profile



Posted: 08/27/21 02:34pm Link  |  Quote  |  Print  |  Notify Moderator

ajriding wrote:

ok. good points.
I dont think my fan is worn in any way. The noise is a ringing, not a mechanical issue. The controller I showed , as I mentioned, is similar, and I am not able to find anywhere the exact controller online anywhere to be able to look at its specifications... It might operate in the human ear range and be audible.

The FF has coils that act like a heating element to burn off power. However you want to exactly define what a heating element is or not does not matter bc in the end it still is doing the same thing, heating up a wire at the expense of power. I thought I used words to give clues that this is not important nor something that matters or needs further discussion. What I keep try to say politely is that I dont really care if you call it this or that. Nothing changed now that you defined it. It is hard to write on a forum post something that can both be understood and polite, I tried. Now lets stop with the heater analysis....


Your chasing a lot of rabbits down the rabbit hole.

Yes, a resistor will waste some energy as heat, but it isn't as much as you think.

Your fan motor will draw max current (max wattage) when full voltage and load are present.

Insert a resistor and the motor now sees less voltage and that in turn slows the fan blades lessening the load the fan sees which reduces the current drawn through the fan motor and resistor.

We are talking on the order of a couple of Watts worth of power being shed as wasted heat.

PWM controllers while they can reduce SOME of the wasted energy over a resistor can in fact use more energy than one realizes. PWM controllers do get hot, that heat is wasted energy from the controller's output transistors.

Typically the most energy you are going to save may be on the order of 1W or less on small low power applications such as a small fan motor..

Not to mention, you have now added a bunch of complicated circuitry with the potential to break down easier and to create a lot of RF noise in the process..

ajriding

st clair

Senior Member

Joined: 12/28/2004

View Profile



Posted: 08/27/21 03:17pm Link  |  Quote  |  Print  |  Notify Moderator

No, just two issues that really matter.
1. Wasting electricity on the heating element-looking thing (wasting time talking about whether it is a heating element or a resistor), and
2. what controller is most efficient.

Heating up a coil might be a small amount of power in your mind, but do that all night long using a battery that is powering other things might just be enough to run the battery too low after a few cloudy days in a row. Run the battery too low and you got bigger problems than unrelated post.
It's all about the battery. Not everyone understands this. I know some people hop campground hook-up to campground hook-up, but others require everything from a battery set-up.

Instead of guessing, one day I might wire in an amp meter and actually measure the difference between High speed (no resistor), Medium and Low speed.
Eventually someone on forum will have already done this. I appreciate the guess on how much power the settings might use.

Gdetrailer

PA

Senior Member

Joined: 01/05/2007

View Profile



Posted: 08/27/21 07:01pm Link  |  Quote  |  Print  |  Notify Moderator

ajriding wrote:

No, just two issues that really matter.
1. Wasting electricity on the heating element-looking thing (wasting time talking about whether it is a heating element or a resistor), and
2. what controller is most efficient.

Heating up a coil might be a small amount of power in your mind, but do that all night long using a battery that is powering other things might just be enough to run the battery too low after a few cloudy days in a row. Run the battery too low and you got bigger problems than unrelated post.
It's all about the battery. Not everyone understands this. I know some people hop campground hook-up to campground hook-up, but others require everything from a battery set-up.

Instead of guessing, one day I might wire in an amp meter and actually measure the difference between High speed (no resistor), Medium and Low speed.
Eventually someone on forum will have already done this. I appreciate the guess on how much power the settings might use.


Your not going to "save" enough energy wasted by changing to PWM to noticeably increase the time between battery charges or shortening the time it takes to charge the battery.. We are talking maybe minutes at best per day.

PWM controller will eat up a lot of your "savings" in wasted power depending on the "speed" you want the fan to run.

At "full on" your PWM controller will be ADDING it's conversion losses to the wasted energy of the fan motor causing you to actually use more battery than if no PWM was connected.

The fan motor you are using is highly inefficient to start with, it will be a brush type "can" motor with a simple sleeve bearing. Basically late 1890's DC motor design, there is nothing efficient with that motor..

PWMs also have another narly side effect, NOISE. Most cheaply designed PWMs do not filter the output, this results in your motor windings giving off a vibration which depending on frequency may be in your hearing range and may sound like a whistle. Unfiltered PWMs will also have considerable switching harmonics, those harmonics are not "usable" energy and result in your motor burning up as wasted energy rather than constructive usable energy.

The brush motor also can cause considerable issues with backfeeding the PWM controller with brush noise and inductive spikes full of harmonics out of phase with the PWM.. PWM controller may not like that and I suspect that is why yours burned up on you..

If you really want to reduce your battery useage, you would need to hop up to basically a brushless motor like what is used in computers. Those are far more efficient energy wise than a brush type can motor.

Don't get me wrong, PWM under the right use and correctly done can save a couple of watts of lost power, but in the case of small motors, not much savings to be had to make this endeavor worth it.

Try a computer fan, bet it will move as much air or more at half the wattage than the motor you have now.

FWC

The Wilderness

Senior Member

Joined: 09/12/2020

View Profile



Posted: 08/28/21 08:51am Link  |  Quote  |  Print  |  Notify Moderator

For reference the 'classic' Fantastic Fan model 4000R draws ~ 3A on high, 2.3A on medium and 1.9A on low. Using a PWM controller, dialed in for what appears/sounds to be about the same speeds medium and low I am seeing 1.6 and 0.9A, so a saving of about 0.7A on medium and 1A on low. I use about 30 - 50Ah a day, so if I were to run the fan overnight on low using my PWM controller, the reduction of ~10Ah would be a noticeable saving.

With a PWM frequency around 20KHz or so there is nor ringing or noticeable increase in noise. There is no output filtering on any of these PWM controllers (the inductance and inertia of the motor takes care of that) and on full on there are no 'conversion losses' when the controller is at full speed. Many of us have been using PWM fan drivers for years, so clearly they and withstand the current spikes from field collapse, maybe they have a fly-back diode across the output.

ajriding

st clair

Senior Member

Joined: 12/28/2004

View Profile



Posted: 08/28/21 09:34am Link  |  Quote  |  Print  |  Notify Moderator

Interesting. Two conflicting reports, but good topics.

FWC, how did you get the Amp numbers?
Yes, 10AH seems to be significant. In reality, not 10 hours, but from about 4pm to 10 am is 16 hours for us solar users who might be stuck in camper in bad weather. 16aH, or on a cloudy day it could be 24 aH and very little solar charging happening... Thus, the reasons for my interest to eek out every last wave of electrons...

For the daytime, when I am gone and just want vent to run, I would run it on absolute lowest possible speed, so less than half the speed of what the Low setting is, so yes, a computer fan would work too, but easier to put in the controller than wire in another fan and deal with it.

Keep in mind I have a DC fridge and the batts are already about 7 years old, so already running a clip fan all night is noticeable difference in voltage when I wake up. I want to avoid any deep discharge of the battery so I never go too low and I want batts to live as long as possible, yet I want to have the fan run when I want it.

I didnt know the FF has brushes, that's good to know if it ever stops.

FWC

The Wilderness

Senior Member

Joined: 09/12/2020

View Profile



Posted: 08/28/21 09:45am Link  |  Quote  |  Print  |  Notify Moderator

From my Victron BMV-712.

The FF does have brushes, but not user serviceable. Quite frankly the Fantastic Fans, like most RV appliances, are total junk designed in the 1980s.

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 5  
Prev  |  Next

Open Roads Forum  >  Tech Issues

 > Fan Speed Control
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2021 CWI, Inc. © 2021 Good Sam Enterprises, LLC. All Rights Reserved.