Slowing down a FantasticVent

Anything electric, AC or DC

Postby eamarquardt » Sat Feb 04, 2012 12:36 am

Both Kayakncamper and Madjack are right (to a degree).

Installing a resistor will reduce the current and since power = current X voltage (and the voltage remains the same) the power/current withdrawn from the battery will be less depending upon the resistance of the resistor.

However,

The voltage drop across the resistor does nothing except generate heat, no motion of the fan. Generating heat takes power. This power is wasted.

A pulse width modulation (PWM) speed control shuts the power to the fan on and off at a rate that drives the fan to the desired speed as determined by the position of the control knob. As no current is flowing through a resistor, no heat is being generated and power wasted as heat.

Now, in reality the PWM does generate a bit of heat and some power is "wasted" but the amount of heat generated by the PWM unit is far less than a simple resistor.

More "World according to Gus".

Hope this helps.

Cheers,

Gus
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Postby Shadow Catcher » Sat Feb 04, 2012 8:41 am

After following this thread or one similar to it I opted to not have a fantastic fan installed in Compass Rose but to have the wring. The two three speed computer case fans draw a LOT less power and make a great deal less noise and conservation of power was one of my big concerns.
When I used the bilge blower for the AC it was noisy and more than needed and remembering this thread first bought a couple of large resistors (Radio Shack) and mounted them between a couple of aluminum plates as heat sink, they worked but got hot, I mean really hot. I knew this was temporary as I had already ordered a PMW which works beautifully. My one regret is that I did not get one that also does frequency control, this is not a big concern with the bilge blower as it is entirely outside the trailer. The PMW does cause the fan motor to buzz a bit.
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Re: Slowing down a FantasticVent

Postby bdosborn » Sun Sep 09, 2012 9:44 pm

I tried an eBay cheapo PWM controller on my endless breeze (fantastic fan in a box) tonight. The up side is that I could control the fan at any speed from nothing to full blast. The down side is it squealed like a banshee, there's no way I'm using it. Has anyone used a PWM controller on a fantastic fan that doesn't squeal? Here's the one I used:

eBay Linky

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Re: Slowing down a FantasticVent

Postby eamarquardt » Sun Sep 09, 2012 10:18 pm

There are two types of PWM controllers. Both types switch the full voltage on and off very rapidly. The width of the pulse determines how fast your fan runs. On the first type the frequency of the pulses (how often the electricity is turned on and off) is fixed but you vary the length of the pulse to vary the speed of the fan. There is apparently a relationship between your PWM and your fan, creating a resonance (vibration) that is causing your fan to squeal. The second type of PWM module allows you to vary both the frequency of the pulse and the length of the pulse. By changing the frequency of the pulse you can break the resonance between the PWM module and the fan and there is a very good chance that you can find a setting that will eliminate the resonance and the squeal.

The PWM that Shadowcatcher recommended is one that allows you to vary the frequency.

http://www.electronickits.com/kit/compl ... KMX067.htm

I'd spring for the few extra bucks and get the better module.

Hope this helps.

Cheers,

Gus
The opinions in this post are my own. My comments are directed to those that might like an alternative approach to those already espoused.There is the right way,the wrong way,the USMC way, your way, my way, and the highway.
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Re: Slowing down a FantasticVent

Postby bdosborn » Sun Sep 09, 2012 10:32 pm

I don't think Shadowcatchers PWM will help as the highest frequency is 3 kHZ and the lowest is 400 hz, all of which are well within the audible range for humans. I have a true RMS meter and measured the frequency of the output of the one I have at 2.6 kHz, I don't think I want to slow the PWM frequency, just the opposite, I think I want one that is much higher than 3 khz. This one has a frequency of 15 kHz.

15kHz PWM Controller] eBay Linky

I can't hear 15 kHz (too much rock music) so I might take one for the team and see if this one works better.
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Re: Slowing down a FantasticVent

Postby eamarquardt » Sun Sep 09, 2012 10:45 pm

I'd tend to think that the problem is resonance between the fan and the frequency of your controller. I agree that the frequency of the PWMs are in the audible range but all of them are and many applications seem to work fine, at the lower frequency switching rates, without noise on some fans

As I recall (but don't hold me to it) others on the forum have had similar problems and a a variable frequency module solved the problem.

Buuuuuuut, the module you can get from EBay is very cost effective and ships for free.

Go for it.

Cheers,

Gus
The opinions in this post are my own. My comments are directed to those that might like an alternative approach to those already espoused.There is the right way,the wrong way,the USMC way, your way, my way, and the highway.
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Re: Slowing down a FantasticVent

Postby sara.azain » Wed Sep 12, 2012 3:38 pm

We power our computer vent fans with 18V electric drill batteries and slow them down with diodes to 12V and we can go slower by adding more diodes. You can slow down any fan by putting diodes in series. Radio Shack 25 diodes for $3. Charge the batteries with small inverter behind car seat. We have 96K on our 2007 Yoder Toter and counting. Got tired of carrying heavy batteries.
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Re: Slowing down a FantasticVent

Postby sara.azain » Wed Sep 12, 2012 3:40 pm

We power our computer vent fans with 18V electric drill batteries and slow them down with diodes to 12V and we can go slower by adding more diodes. You can slow down any fan by putting diodes in series. Radio Shack 25 diodes for $3. Charge the batteries with small inverter behind car seat. We have 96K on our 2007 Yoder Toter and counting. Got tired of carrying heavy batteries.
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Re: Slowing down a FantasticVent

Postby PonyExpress » Fri Sep 14, 2012 12:28 pm

Sounds good sara.azain. Can you post a picture or your computer fan/drill battery set up?
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Re: Slowing down a FantasticVent

Postby bdosborn » Sat Sep 15, 2012 11:05 am

eamarquardt wrote:Buuuuuuut, the module you can get from EBay is very cost effective and ships for free.

Go for it.

Cheers,

Gus


Just bought one, I'll let you know how it works when it gets here from China...

Bruce

P.S. So the two PWM controllers I've bought so far are the same price as the one SC posted a link to. Sigh, I just love how well I save money...
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Re: Slowing down a FantasticVent

Postby droid_ca » Sat Sep 15, 2012 7:26 pm

ok I'm looking at a fantastic fan for my trailer but I'm looking at one of the top models now if I were to slow it down would that also effect the thermostat or the automatic opening mechanism and why would I want to slow it down any ways is it so that it uses less juice or is it quieter???
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Re: Slowing down a FantasticVent

Postby woodi » Mon Jun 03, 2013 3:16 pm

bdosborn wrote:I tried an eBay cheapo PWM controller on my endless breeze (fantastic fan in a box) tonight. The up side is that I could control the fan at any speed from nothing to full blast. The down side is it squealed like a banshee, there's no way I'm using it. Has anyone used a PWM controller on a fantastic fan that doesn't squeal? Here's the one I used:

eBay Linky

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Bruce


I just had these same results with my vent fan and a cheap ebay LED dimmer I had laying around. Did anyone have any success finding a PWM module that didn't make your vent fan squeal? I love the option of having it be adjustable. I have a 3 knob ebay PWM module for my LED lights and it seems to work great in that application with very minimal humming.
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Re: Slowing down a FantasticVent

Postby rbtrary » Tue Jun 04, 2013 2:06 pm

I experimented with various electronic dc motor controllers on my fantastic fan. Although they would slow it way down, the fan always made irritating noises at the lower speeds. The manufacturer publishes an app note recommending high watt resistors to slow it down so I tried the 50 ohm 25 watt Ohmite industrial rheostat in the pictures (~$12 on eBay). With this, I can slow the fan to a crawl and it stays whisper quiet through all lower speeds. I can get a very pleasant mild draft at the slowest settings with one window cracked open. The rheostat small size is pretty much a direct swap for the original 3 position switch and adds infinite speed control settings. No rewiring or adding components and, unlike the solid state controllers, works in both directions. I use the middle position of the In/Out switch to turn the fan completely off. The rheostat windings do not heat up as much the resistor wires did on the original 3 position switch either and, I don't notice much difference in battery use from before when it had the orig 3 position. Hope this helps.

[img]file:///C:/Temp/rheostat.JPG[/img]
[img]file:///C:/Temp/rheostat_2.JPG[/img]
[img]file:///C:/Temp/rheostat_3.JPG[/img]
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Re: Slowing down a FantasticVent

Postby rbtrary » Tue Jun 04, 2013 2:16 pm

try uploading images again...
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Re: Slowing down a FantasticVent

Postby woodi » Wed Jun 05, 2013 9:57 am

Awesome. Just did a search on ebay and see there are still some for sale. Might just have to go that direction. Have you found the 50 Ohm one to be a bit overkill? Does the fan cut out before you've dialed the knob all the way down or just make it down to a real slow tick? I just worry about the knob getting turned down too far (if it can be) and thinking it's off when it's actually just getting fed voltage bellow what it needs to run.
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