Slowing down a FantasticVent

Anything electric, AC or DC

Postby planovet » Tue Feb 24, 2009 10:35 am

Hate to revive an old thread but I just got my new Fantastic Vent in and I noticed that it is a little noisy in the slow speed. It's something I could probably get used to but I was wondering:

Of those of you that did this modification, how do you like the results? It's been a while so there has been some time to try it out. Is it worth the trouble to break out the scalpel and operate on my new fan? I figured it would be easier to do it now BEFORE I do the final install.

Thanks
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Postby aggie79 » Wed Feb 25, 2009 6:18 pm

planovet wrote:Of those of you that did this modification, how do you like the results?


Arne said he had good results with adding the resistor. Haven't done mine yet, but what I will probably do is use a single pole-double throw switch so that I can change back and forth between the circuit with the resistor and one with line voltage. I figure that the when I first pull up to a campsite in the summer, I may need the full capacity of the vent fan to cool off the teardrop initially.
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Postby John Boeckstiegel » Sun Mar 01, 2009 11:46 pm

I used a PWM on my fan and it is great. Because it pulses 12v to the fan it does not run hot. I tried it for several hours and felt the fan. The motor was still cool to the touch with the air flowing over it. It will slow down plenty more than I think I will ever want. I did some elaborate wiring on mine with a revesing switch for the opening and another one for the fan direction. It works great now. :D
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The center knob is of coarse the Pulse Width Modulator.
Hope this helps
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Postby aggie79 » Mon Mar 02, 2009 4:32 pm

John Boeckstiegel wrote:I used a PWM on my fan and it is great.


John, did you purchase or build your PWM? Please provide links.
Thanks, Tom
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Postby John Boeckstiegel » Mon Mar 02, 2009 6:37 pm

I bought it on Ebay. I got the 30 amp one even though it is way bigger than you need. Radio Shack sells the knobs and any other connectors you may need. This is not the one I bought but it is close. I dont think mine is listed any longer. If you look there are many kinds and styles. This is the style fit my needs and space. :)

http://cgi.ebay.com/PWM-Hydrogen-Generator-DC-Motor-Control-30Amp_W0QQitemZ320344857078QQihZ011QQcategoryZ294QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Let me know if this helps.

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Resister reduces the overall power used.

Postby KayakNKamper » Sat Mar 07, 2009 7:50 pm

Some have been posting that by adding a resistor to slow the fan down, it wastes battery power. That's not correct, it actually saves battery power. I'm no electronics whiz by any means, but some simple math will show what I'm saying.

To keep it simple, let's say the resistance of the fan is 6 ohms.
E=IR
12V=I x 6 ohms
I = 2 amps (about what the fans use).

P=IE
P=2 amps x 12 volts
P = 24 watts

Now lets add a 6 ohm resistor in series (6 is just to keep the numbers simple)
Rtotal = 6 ohms + 6 ohms = 12 ohms
E=IR
12V = I x 12 ohms
I = 1 amp

P=IE
P= 1amp x 12Volts
Ptotal = 12 watts

So by adding the 6 ohm resistor the total power used is half that of the fan without the resistor. Six watts would be used by the fan, and 6 watts would be used by the resistor.

:thumbsup:

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Postby madjack » Sun Mar 08, 2009 12:08 am

...thus proving that 6watts were wasted by the resistor...the point being made was, you will not SAVE any wattage by slowing down the fan with a resistor...in other words, any power being soaked up by the resistor is being wasted since it does nothing but heat the resistor............
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Postby KayakNKamper » Sun Mar 08, 2009 2:44 am

Yes, 6 watts is wasted by the resistor, but the motor then only uses 6 watts instead of 24 watts for a total of 12 watts used.

The battery will have to supply 24 watts in the first scenario and 12 watts in the second. I see that as a savings of 12 watts regardless of the fact that 6 watts is wasted heating a resistor.

Your battery will last twice as long in the second scenario than it will without the resistor.
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Postby madjack » Sun Mar 08, 2009 3:36 am

Dale, that truly makes no sense..to me...you INCREASE resistance and get a lower amp draw :? ...You have changed the 2amp draw arbitrarily(it seems to me) in your second equation to read 1amp, when it should still be 2amps...you then drop 6v and 2a over the resistor and 6v and 2a over the fan, slowing the fan by 50% BUT still using the same amount of electricity(wasted as heat by the resistor)...it may very well be me, but something in your math does not add up..........

The above is for a series setup, which is wrong...you should use a parallel setup to keep the voltage at it's proper level(to avoid burning up the fan motor)...which would then give you 12v and 1a drop over both the fan and the resistor...and this still uses 24w of electricity, with half of it wasted as heat in the resistor...at least that is what they taught us in electronics school...o'course that was nearly 40yrs ago!!!!!!
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Postby KayakNKamper » Sun Mar 08, 2009 6:39 pm

The battery has only so much pressure (12 volts). If you increase the amount of resistance through the wire, less current will be able to flow through it.

E=IR
Volts = Amps x Resistance.
Volts = 12
If the resistance goes up, the amps must go down.

Think of it this way. You're washing your teardrop and someone picks up the hose and kinks it (puts a resistor in line). They drop both the pressure to the end of your nozzle, and the amount of water flowing through the hose.

Wouldn't you say that a fan set on low uses less battery power than one set on high? I would. Below is a circuit I found on the web that is kind of related to what we're talking about, and shows the diagram of how the High, Med, Low switch works. It basically adds more resistors in series as the switch is turned to low.

Image

-------
I don't know if what you say about the motor having to be at 12 volts to not burn up is true or not. If the resistors are put in parallel then the whole circuit would be as you stated. I think that's the problem, you're talking parallel, and I'm talking series. The switch in the above picture is series though and I was talking about just adding another resistor in series.
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Automotive Headlight Switch

Postby down under tech » Wed Feb 10, 2010 11:05 pm

Hi Guys: Did anyone think of using a dimmer switch from a car headlight switch? You turn the switch CW to make the dash lights brighter and CCW to dim them. I would think this would work. You can run your power 12V positive to a flip toggle switch, then to the headlight switch dash light rheostat. From there onto the fan assembly. You could add another toggle switch from the 12v hot wire of the first switch to power the second switch. The second switch would be full voltage when this switch is turned on (no dimming, wired as if you ran it straight from fuse block to fan). You would have your choice of either toggle switch number 1, power slowed to fan with the dimmer switch or run full power from switch number 2 to the fan. For dimmer control of fan, switch 1 is on switch 2 is off. Full power to fan, switch 1 is off & switch 2 is on. Both switches off no power to fan. These circuits would be run in parallel. I am not sure if the dimmer switch would be able to handle the amps required by the fan to be pulled. Dash lights don't need that many amps, and there is a heat sink on the dimmer part of the headlight switch. The fan might overheat the rheostat in the headlight switch, though. You would only use the dimmer in the low setting on the Fantastic Fan (This would limit the amps drawn from the fan) and run it with full power in the two higher speed settings. This is just a thought I came up with. I am an auto technician, but never tried this before. You electricians out there let me know if this would work or not or I am blowing "smoke".
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Postby Two Showers » Sun Feb 14, 2010 2:44 am

Just thought I'd throw my two penneth in as we say.
I tow with a Trike and as such we are very limited to weight and size. We don't have the luxury of being able to make a tear 19" wide or 63" long

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Hence my 'Sleeper'. which is fibreglass and weighs in at just over the 100Kg mark. Yes it's just a bed, no galley kitchen, no stove, no telly, and no jacuzzi.

Anyway, I ramble.

12V Computer Cooling Fan. Ultra little - ultra leightweight, and ultra quiet.
That's what I use to draw moist air out of the Sleeper.
MY mates CNC'd me a stainless Steel fan housing, so it looks the dogs doodaa's and it works perfectly on all three pre-set speeds.
A dead cheap, dead quiet 12V PC Cooling fan.
No messing about with resistors and such like. They're so small, lightweight, and cheap (Really Cheap) that I fit two. One on suck and one on blow. When it is really warm in the UK (I Know it does happen occassionaly, the sun comes out), I put one on suck, to suck cool air in, and the other on blow to blow warm air out. It gives a circulation of air. No noise. damn cheap, and no physics degree needed. 12V and no resistors.

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Postby rhow » Sun Feb 14, 2010 10:22 pm

I istalled it and it works fine for me. :)
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Postby emmen » Mon Mar 08, 2010 1:44 am

Not sure if this will be helpful on this long thread, but when we picked up our Camp-Inn, they told us that the Fantastic Fans they use are specially made to run slower. Perhaps this is on option that is available if asked for...?

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Postby Martiangod » Sat Feb 04, 2012 12:09 am

I'm not sure what the price is for it but Fantasic offers a upgrade kit
Which give you remote control, variable speed, rain senso, t stat ...all the bells nad whistles for you standard fan, without screwing up your warranty

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http://www.fantasticvent.com/products/model_6600_kit/model_6600_kit.html
If it ain't broke, fix it till it is

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