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TurnThePage

North ID

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Posted: 08/29/21 04:57pm Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

What is amazing is the levels some will go to, to work on the “efficiency” of a fart fan….
While we’re on that, new camper doesn’t have a FF (which I’ve IE learned in the last4 pages is apparently horrible inefficient junk, lol, despite all the great press it receives here).

Camper has 3 basic fart fans, but the center one in the kitchen I’m considering replacing with something better/variable speed and directional.

Since FFs are ****, what do the experts recommend?
Looks to me like the current options are FF, Maxxair, Vortex, or the venerable computer style fan.

I guess maybe I'd try the Maxxair as my first choice right now. The Vortex is a super simple retrofit for those that aren't comfortable getting on the roof or getting more involved.


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2112

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Posted: 08/29/21 05:28pm Link  |  Quote  |  Print  |  Notify Moderator

FWC wrote:

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
The PWM measurements are deceiving. The fan still draws 3A during the duty cycle period. Your digital current meter is trying to average the ON periods but its sample rate is too slow to be accurate. This is called aliasing. The true average over time will be higher. No fault of your meter. It wasn't designed to accurately measure high speed pulses.

The first measurements using the "heating elements" should be accurate because this will be a steady analog signal. The "heating elements" are there to reduce current. The higher the "heating element" resistance, the lower the current.


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FWC

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Posted: 08/29/21 08:41pm Link  |  Quote  |  Print  |  Notify Moderator

The PWM frequency is something like 20 kHz and the Victron is reporting at 1Hz, but may sampling a little higher than that and averaging in software. The BMV-712 current measurement doesn't jump all over the place, so it safe to assume that there is a fair amount of capacitative integration on the ADC which should provide a decent average measurement. There is also no chance of aliasing when the response rate of the sensor is several orders of magnitude lower than the PWM frequency. For the type of measurements we are talking about here it is certainly good enough.


2112 wrote:

FWC wrote:

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
The PWM measurements are deceiving. The fan still draws 3A during the duty cycle period. Your digital current meter is trying to average the ON periods but its sample rate is too slow to be accurate. This is called aliasing. The true average over time will be higher. No fault of your meter. It wasn't designed to accurately measure high speed pulses.

The first measurements using the "heating elements" should be accurate because this will be a steady analog signal. The "heating elements" are there to reduce current. The higher the "heating element" resistance, the lower the current.


* This post was edited 08/30/21 08:17am by FWC *

landyacht318

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Posted: 08/30/21 02:25pm Link  |  Quote  |  Print  |  Notify Moderator

I've been a bit of a fan and ventilation enthusiast for years now.

Of all the fans I run, only one, is run by a PWM motor speed controller.

That one is powering the brushed motor of my vehicles Hvac system. It is 21 kHZ and is rated for 40 amps. I bypass the stock resistor packs, gain much more wide range of fan speeds, and can turn it on with no key in ignition.

I've used it powering powerful computer fans and it works well, but it draws slightly more current than using a voltage controller to control the computer fan speed.

A lot of computer fans are 4 wire PWM fans, and the 4th wire is to be sent a PWM signal from the computer motherboard in order to control fan rpm.

Noctua has a NA-fc-1 speed controller that makes it relatively easy to control such fans, and I used to use it to control Noctua's IPPC NF-f12 3k rpm 120mm fans and their 140 IPPC version too. I had tremendous failure rates of these fans, and Noctua was excellent about warranty replacements, and sending shipping labels for returning the fans so they could investigate failure mode, but ultimately all these fans have failed.

Before this Noctua speed controller came out, I cobbled together a 555 PWM signal generator, and achieved full function, but it was clunky as I had to feed the signal generator 5v, not 12v.

As an experiment I tried to just use the 3 amp voltage bucker( lm2596 based), to speed control the fan, and it worked quite well. No whining at reduced speeds, and could slow the fan even more than when a PWM signal was fed via the fourth wire. comparing the amp draw at similar fan noise/speed/flow, revealed controlling fan speed via voltage bucker was more slightly efficient than a PWM signal generator.

I then tried the voltage bucker as a LED dimmer. It was way better than the cheapo LED dimmers I had been using. absolutely no flickering and would dim the lights much lower, to tiny pinpricks of light at nearly unmeasurable amp draw.

I found there were similarly sized XL 4005 or xl4015 based voltage buckers which are rated at 5 amps.

when fed 12v, the max output voltage of the lm2596 bucker is ~11.35v
when fed 12v the max output voltage of the xl4005 is 11.69v
when fed 12v the max output voltage of the xl4015 is 11.81v.

So ALL my leds are now dimmed by either the xl 4005 or xl4015 buckers. LEDs can whine on PWM motor speed controllers, and they can flicker.

Mine dim to lower levels and never flicker on the voltage buckers.

These buckers require removing the tiny voltage trimpot and adding wires to a larger potentiometer for simple finger twist voltage/speed control.

some of these voltage buckers have two potentiometers, one for voltage one for current. Both work for controlling fan speed, led brightness, but I found voltage control to work better each time I compared. I also found the buckers with current control pots to not only be slightly more expensive but less reliable.

My strategy with computer fans evolved to finding insanely powerful fans, and using voltage buckers to speed control them. I will use two potentiometers, one ( the tiny trimpot the buckers some with), inline with a finger twist, to keep it from going below a certain voltage where the fan does not spin.

This minimum voltage ranges from 3 to 7 volts depending on the fan, and voltage required to get impeller spinning is usually 1 to 1.5v over this minimum rpm voltage.

I also employ some 24vdc fans, and use a voltage buck/boost converter to speed control them.

I like Delta brand computer fans, but beware there are clones and counterfeits out there, some of which still work quite well, but I can tell the build quality is less, and the blade balance is worse.

If one does go the computer fan route, their biggest failure point is the solder joints where the wires enter the hub. I recommend peeling up the sticker on the hub and covering these joints with dielectric grease, or something like Amazing goop.

Some of the fans, the wires are routed a bit differently to the hub, and enter the underside, and one needs to remove the impeller with some c clip pliers to access the circuit board.

Most of the fans at minimum speed are well below 0.1 amp, even through a buck boost converter or just a buck converter, and quiet enough that I sleep with them inches from my head.

I would recommend high rpm 120 or 140mm fans. 38mm thick.
Those with stator blades/ hub support keep the fan's flow a narrow dense column, not important for an exhaust fan, but great for interior circulation.

the CFm ratings of fans is misleading, as the cfm figure is not actually measured by the volume of air moved, the speed of the air is measured and the diameter and some math is performed.
Fans with just 4 hub supports usually have 4 'hotspots' of airflow, and the velocity of these hotspots is not representative of the total aperture.
Static pressure ratings is another way to measure fans flow, and is more important when there is a restriction to flow, such as when it is trying to exhaust a closed bathroom or push air into a finned heatsink.

I have achieved much better balance of some fan impellers using an accellerometer app on my smartphone, and some trial and error. These improved balance fans make less noise and can spin faster for the same voltage applied.

My favorite fans a few years back were made by silverstone, as some models would come with a built in fingertwist speed control. the fm 121 and the 181, and the AP182.
The AP182 hated charging voltages though.


n

afidel

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Posted: 08/30/21 10:21pm Link  |  Quote  |  Print  |  Notify Moderator

I've used this fan controller for a Vortex 2 for 3 years without issue. The heatsink is tiny and even after running the fan all day it never felt hot, just a tiny bit warm. It's good down to 5V so you won't have a problem with voltage dropout.


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LittleBill

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Posted: 08/31/21 07:21am Link  |  Quote  |  Print  |  Notify Moderator

I have used these before, but its a bit larger then some

Click





ajriding

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Posted: 08/31/21 12:33pm Link  |  Quote  |  Print  |  Notify Moderator

This one I got and now installed PWM eBay one
Works the same, even has OFF function, and does not ring.

I looked at the other controllers, but that this is the same case means the holes will line up with the old holes where I had it mounted, and being all enclosed and contained is just what I needed as opposed to having a pot that needs to be mounted somewhere.

2112

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Posted: 08/31/21 01:35pm Link  |  Quote  |  Print  |  Notify Moderator

ajriding wrote:

This one I got and now installed PWM eBay one
Works the same, even has OFF function, and does not ring.
Excellent. After running it in the condition the last one heated up, measure the voltage at Power + and - to see how low it goes. That would be a good data point. It may be getting too low.

ajriding

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Posted: 09/01/21 11:01am Link  |  Quote  |  Print  |  Notify Moderator

0.5 volts to keep it running, barely, and that low you can see the fan blade bouncing between the magnets.
0.8 to move it from a stop.
4 volts is super quiet, no blade noise, and 6 volts is still lower than low speed, but seems fast enough to move enough air to keep heat from building up. At 6 you start to hear the air, there is always some fan bearing noise.
4 volts would be a good sleeping speed since it is very quiet, a huge bonus.

The other one would not run so slow, it would stop before the fan got this slow.
So, this buys me a much bigger safety margin if I leave it on low and the batts get drained down super low. If batt is going to be 0.5 volts at the controller then I have much bigger issues than a $13 pot.

I do not have an amp meter to measure so low, mine measures up to 50 amps, so would not be good for small numbers, it is a needle.

Also, side question.. what is difference in having the switch or controller on the neg side vs the positive side (other than ability to turn off the wire current)?
Is this controller switching the neg side? Maybe just so if it does burn out that the full 12v can still flow through? I know an on/off switch means nothing to the fan, but the control on neg or pos side, is that different?

* This post was edited 09/01/21 11:20am by ajriding *

DrewE

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Posted: 09/01/21 01:18pm Link  |  Quote  |  Print  |  Notify Moderator

ajriding wrote:

Also, side question.. what is difference in having the switch or controller on the neg side vs the positive side (other than ability to turn off the wire current)?
Is this controller switching the neg side? Maybe just so if it does burn out that the full 12v can still flow through? I know an on/off switch means nothing to the fan, but the control on neg or pos side, is that different?


Most cheaper PWM controllers are switching the negative/ground side of the circuit for the speed control--and indeed many not cheaper ones as well. This mainly has to do with the characteristics of available switching transistors; N channel MOSFETs, which are what are used to switch the low side, inherently tend to have better performance than P channel MOSFETs that you'd use to control the positive side. The same generally applies to other types of semiconductor switching devices, too. To get equal performance from the high side switching, you'd need to use more expensive switching transistors...and often slightly more complicated control/transistor drive circuitry as well.

It makes no difference at all to a DC load which side of the circuit is being switched. In fact, there is no way at the load to tell which side is being switched if you don't use some additional voltage or ground reference.





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