Slowing down a FantasticVent

[MtnDon]

A further thought on the wall mounted touch type dimmer... My experience with another DC touch dimmer indicates it has a low draw all the time. The unit I have draws zero after the power is switched off and back on. But as soon as the control is touched it has a continuous draw to remember the last used setting. It is a low draw, but I have never metered it. I do not believe it would be a concern in ordinary use. However, when parked and stored I don't know.

[dales133]

Id agree with you mtndon on tbe chinese componants.
Ive recieved stacks of small electrical and other parts and if your prepared for a verry small percentage of duds you can save alot of money

[vegask]

Just tried two different PWM controllers that were on amazon, both by RioRand. One had a reverse option, the other did not. The one with the reverse option made a ton of high freq/high pitch noise at low speeds. The non-reverse model made a grinding sound in the fan motor at low speeds. So both are on their way back to amazon, I have a 50ohm 25 watt rheostat on order I will try next.

Video of the reversing pwm model I tired.

https://youtu.be/PCuJ_Mj9-lQ

[rbtrary]

Here's a video of 50 ohm 25 watt rheostat for variable speed control on Fantastic Fan. replaces the fixed 3 speed switch. on/off using in/out switch. super slow and quiet, mid speed and full speed.

https://youtu.be/c-1LE5NNfGM

[wannabefree]

These cheapo PWM controllers are running the audio range, then. You need to look for something running at 50kHz or higher. The best answer is probably a buck DC-DC converter, which is much more efficient than using a rheostat that just wastes excess power as heat and puts out filtered DC, not pulses which make your fan unhappy...

Because I also want to slow down my FF, I would be happy to put together a FF slowdown kit if there is interest. I started describing how to do it with parts from the hobby electronics store, but it got too techy too fast. PM me if you want one. If there is enough interest I'll see what I can do. The kit would be a board that you would have to mount in the airflow of the fan and a potentiometer that would replace the speed switch. No soldering.

[tony.latham]

I went this route. It works well.

See the attached.

T

[wannabefree]

Yep, and that is a good, simple way to do it, it will always work, and will not make noise. But I am an engineer, and feel compelled to find a hard way to do simple things. It's what we do. Nobody would need us otherwise.

Oh, and I want to save that 10 watts or so those resistors convert to heat. But if you don't care, by all means this is the best way to go.

[rbtrary]

The rheostat solution works very well. Its just a variable resistor tho.
https://www.dummies.com/programming/ele ... -rheostat/

I would like to try your FF slowdown kit if it can match the flexible speed control and quietness of the rheostat solution.

[tony.latham]

But I am an engineer, and feel compelled to find a hard way to do simple things. It's what we do.

T

[Tom&Shelly]

Yep, and that is a good, simple way to do it, it will always work, and will not make noise. But I am an engineer, and feel compelled to find a hard way to do simple things. It's what we do. Nobody would need us otherwise.

Oh, and I want to save that 10 watts or so those resistors convert to heat. But if you don't care, by all means this is the best way to go.

It has been said that an engineer is a man who can do for ten shillings what any fool can do for a pound. -- Nevil Shute

I'm with you Wannabefree! Our Maxxfan has ten speed settings (who needs that many?!) and the first thing I did was measure the current draw at each setting. Quite a range (and I have the record if anyone is interested). It'll make the difference between running our battery down in a few hours on the high mode (IIRC), to days on the low mode. Evidently, it does something more sophisticated than throwing away the energy into a resistor. (Which would then run the battery down in a few hours even on the lower modes.) I'd love to break into it someday to see exactly how they do that, but have to make the last push and actually finish our teardrop first!

Anyway, if we didn't already have the variable speeds, I'd've gone for your kit idea, or begged the schematics and made one myself. With all the effort folks go through to collect/conserve battery power, throwing it away heating a resistor is a bad idea. (Sorry friends!)

Tom (Fellow EE)

[tony.latham]

Evidently, it does something more sophisticated than throwing away the energy into a resistor. (Which would then run the battery down in a few hours even on the lower modes.)

I was concerned with this and did an amp test on the mod before and after.

1- .86 / 1.25
2- .11 / 1.7
3- 1.3 / 2.5

The 1, 2, 3, are the fan speeds. The first column is after the resistor and the second is without. Don't ask me to explain how it works, because I'm not Nikola Tesla. It's pure f* magic as far as I'm concerned.

Tony

[Tom&Shelly]

Evidently, it does something more sophisticated than throwing away the energy into a resistor. (Which would then run the battery down in a few hours even on the lower modes.)

I was concerned with this and did an amp test on the mod before and after.

1- .86 / 1.25
2- .11 / 1.7
3- 1.3 / 2.5

The 1, 2, 3, are the fan speeds. The first column is after the resistor and the second is without. Don't ask me to explain how it works, because I'm not Nikola Tesla. It's pure f* magic as far as I'm concerned.

Tony

OK, I should be more careful about making broad generalizations, which is always a bad idea! Sorry about that!

So, clearly your results show an improvement. To play Tesla (or at least Edison) for a moment (just to explain why I'm wrong), the technical reason is that the motor is not a linear device with a fixed resistance. So as you divide the voltage between the motor and resistor(s), the motor evidently offers more resistance than it would at 12 vdc, and so draws less current.

But you still lose a lot of energy in the resistor(s). Looks like you're drawing 69% of the original current in speed 1 and 52% in speed 3. So at those speeds, there is still quite a drain on the battery. (Is the number for 2 correct?)

Obviously you know what you need. If someone wants/needs a more efficient fan though, Wannabefree's idea is a good one.

Dug out the numbers on the Maxxfan: Ranges from a high of 2.65 A (yikes!) down to 0.05 A.

Tom

[tony.latham]

So at those speeds, there is still quite a drain on the battery. (Is the number for 2 correct?)

I'm sure the decimal slipped a bit. It should be 1.1

We hardly ever use the fan. (Maybe three times this summer?) And when we do, it's not for more than an hour. Remember, we're up here at 45º, not down by the equator like you two.



So 1 amp or so isn't much.

Tony

[wannabefree]

Yes, as resistance increases the current will go down; it's just Ohm's law: E/R = I where E is the voltage, R is the resistance in ohms, and I is the current in amps. You can see that increasing R will cause I to go down. As mentioned above, though, some of the voltage is dissipated as heat in the added resistance. When using a fan to cool your trailer, the last thing you want is to add more heat, so we always run the fan in exhaust mode.
Also, we must have different fan models. Mine is loud (another reason to slow it down) and draws 3.22A high, 2.47 medium, and 1.53 low. With a 35Ah battery, high speed gives us about 5 hours of fan time (not wanting to suck the battery down too much). We rarely go above low speed, but even that is too fast most of the time.

[tony.latham]

Also, we must have different fan models.

Or a better amp meter? I was using a $20 Bayite.

Tony