# Temp sensor and PWM for 12v fan-2 wire or 4 wire?

#### wopachop

Jul 22, 2012
47
Hello everyone my goal is to install a 12v fan onto a travel trailer to pump cool fresh air into it while im away. Would be great if i could buy a low cost temp sensor that could control the fan. Would be even better if the fan speed could change relative to how hot it gets.

Started to search around and saw a guy using Arduino. That is waaaaaay beyond my skill set. I enjoy soldering and tinkering with electronics though.

Hoping people here could introduce me to products that might work. Maybe use a digital timer instead of a temp sensor? Here are some questions i have so far.

1. This 4" blower fan looks good. Its a 2 wire motor and pulls 3amps. Now i have a PWM controller that i use for LED lights. Its rated for 6amps i believe. I tried using that PWM controller on a different 12v radiator fan. But when dimmed that caused a very loud screeching sound. Im not sure why, also not sure if that same PWM controller would work with the blower. Its a cheap product and maybe not suited for DC motors, but works great with LEDs.

Any ideas to make a 2 wire blower fan turn on and off when the trailer gets hot? If the most budget friendly option is a cheap digital timer that ok as well.
http://www.attwoodmarine.com/store/product/store/turbo-4000-ii

2. Im also seeing very efficient computer case fans. Some are 3 wire, some are 4 wire. I think the 4 wire fans are designed to connect to a computer? Wondering if i can use just 2 wires from a 4 wire fan and somehow attach to a temp sensor or timer. Would be great if my PWM controllers worked with the small computer fan. Supposed i could buy one and test.
https://www.silverstonetek.com/product_fan.php?tno=3&area=en

#### wopachop

Jul 22, 2012
47
"Regarding using PWM Motor speed controllers to control fans, one must seek controllers with 21Khz or higher. Many are 13Khz, and will make the motor whine loudly, annoyingly when it is slowed down. I have several 13Khz LED dimmers i used on fans ansd the whining is louder than the fan itself."

#### dave9

Mar 5, 2017
1,181
Don't think you really need a variable speed control, just to have sufficient airflow and have it come on and turn off at set trip points.

There are a few thermostat modules on eBay and elsewhere, around $2 and up depending on how fancy you want them to be. Example: https://www.ebay.com/itm/50-110-C-W...Control-Switch-12V-Sensor-Module/172159965906 Some also have video reviews on Youtube. I'd hook one up to multiple 120mm x 38mm computer fans to move more air Frankly since I am in the US and just happened to see a deal on some heavy duty fans with metal housings recently, I'd use 3 of these which have a built in temperature sensor circuit, and activate them by one of the modules I linked above. Their temperature range seems about right too: http://www.mpja.com/06-04-18.asp?r=00000&s=21 MFG: NMB P/N: 4715ML-012P542-P1 Volts: 12VDC Current: 0.50A CFM: 88 CFM at full Temp. NMB Smartfan Built in Temprature sensor rated at 26-42 deg "C", Fan starts at around 1/3 CFM to full speed at 42 "C" Plastic blades and metal housing, 5" leads. Red wire +, Black wire - SQ: 4-11/16" (120mm) T: 1-1/2" (39mm) WT: .9 #### wopachop Jul 22, 2012 47 Thank you!!! Im here to learn. The fan has a temp sensor of 78F to 110F. How do i incorporate the ebay module? #### dave9 Mar 5, 2017 1,181 The thermostat module operates off 12V, you have 12V going to it, and 12V out going to the fans is switched by the relay on the module, based on the temperature you set.. The fans grounds would be wired together with the power supply ground going to the thermostat module. I don't know how much more explanation you need, for example since it has no fan header pins and the terminal block looks set up for much heavier gauge wires than the fans would use, you'd solder a lower gauge wire to the fan leads so it is mechanically compatible with the terminal block, or put a mating connector on the lower gauge wire. I don't see any spec for the terminal block acceptable wire gauge range but would guess around 16 gauge would work, or just skip that and solder the fan leads to the back of the PCB where that terminal block pin is, or pick a different thermostat module that has whatever connection method that you prefer. Last edited: #### wopachop Jul 22, 2012 47 Ok its early and im not a smart man Jen-nay. Ordered 3 of those thermostats thanks a bunch!!$2 with free shipping rocks. Will be here in a couple weeks.

Im still confused if the fan has a temp sensor built in, why do i need the ebay temp sensor module?

Or maybe you gave me 2 different options. Use the ebay module with regular fans..........or buy the fan with built in temp sensor. But i would be limited to its temp settings.

#### wopachop

Jul 22, 2012
47
Shoot....confusing myself. Think i understand now.

The ebay module controls what temp the fan turns on. While the smartFan itself will self adjust and spin faster as the temp gets higher?

This is a lot of fun. Thanks for helping

#### dave9

Mar 5, 2017
1,181
yes

The lower limit on the fan temperature range doesn't necessarily mean it won't spin until that temperature is reached, rather that it won't start ramping up in speed until it hits that range.

Jul 22, 2012
47

#### dave9

Mar 5, 2017
1,181
^ You can have durable or efficient, but keep in mind that the 0.5A rating for the NMB is probably the stall current, not the average consumption. What you linked is 92mm x 25mm and 38CFM, you will need more of them. Being sleeve bearing they should also be mounted vertically.

You might ask the company if they have UV stabilizer added, otherwise the nylon or PBT frame may degrade from UV exposure (sunlight). Something intended for an indoor computer application may not. For that matter the blades on the NMB are also plastic, but possibly PAG, glass reinforced.

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#### wopachop

Jul 22, 2012
47
Ok screw that choice. Im about 3 days in when it comes to learning about computer fans. Sleeve bearing is out.

Im looking to cool a 30 foot toyhauler, and also maybe cool my truck. The temp controlled fan would be sweet for the truck. I didnt know they existed until you linked that 120mm for me. I looked around that site for a smaller one. To use in my truck. I think it was a 90mm and goes full blast at 100F. Half throttle before that. So the fan you linked was much better with specs. But to cool a truck it might be too much.

Another issue is loss of pressure. I have a 2002 f250 and i looked inside the vents with a flashlight. They aint sealing very well. Also how will i make the fan seal to the vent in a good enough way.

#### dave9

Mar 5, 2017
1,181
I'm not clear on exactly what you're trying to do. Your factory air ductwork can be sealed with (get ready for it) duct tape. However these axial fans are not capable of much static pressure. The thicker they are, the more the static pressure rises but still, if you intend to use the existing ductwork then that is why the factory fan on it is a squirrel cage type and you should pick a squirrel cage add-on for such an application.

You might even measure what the factory fan draws spinning very slowly, possibly you can just wire a thermostat circuit up to it and need no addt'l fan, but being larger still, it will have lower airflow to current than any fans mentioned so far.

Does the truck have a sliding rear window? I would be inclined to make a panel out of polycarbonate that sits in the window track and has a fan hole cut into it.

I am doubting you will end up with any fan that is too much. The NMB 120mm fan is 88CFM at full speed, meaning that if it is doing its job effectively, it is lower than 88CFM. If you find that is still too strong, throw a couple of diodes in series on the fan lead so it drops around 1.4V, resulting in the fan spinning slower. You can continue to add more diodes in series until you reach a threshold where the fan is spinning too slow to overcome the magnet and starts spinning in a notchy, uneven fashion. This is more true for fans thicker than 25mm because they tend to have higher torque motors and a stronger magnet.

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#### dave9

Mar 5, 2017
1,181
There are other temperature controlled fans, but the prices are significantly higher. That one I linked, at retail it probably sold for \$35 (due to the metal frame). You can see some others at electronic supply houses like Digikey:

https://www.digikey.com/products/en...ity=0&ColumnSort=0&page=1&stock=1&pageSize=25

I forgot to mention something. Weaker fans like the Gelid you linked, they are not very dangerous, but thicker fans like that NMB, there is a chance it could cut a finger off or at least do serious damage to one. You definitely want fan grills on them if there is any exposure to people or pets. Really even the cheap thin ones can be dangerous because they may have sharper edges on the thinner blades... but if you stick your finger in a typical 120mm x 38mm fan, the finger may give before the blades do.

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#### wopachop

Jul 22, 2012
47
dang its at 6 bucks!!!!

#### wopachop

Jul 22, 2012
47
I was looking at its younger brother too. I searched that site and saw 2 temp controlled fans.

#### wopachop

Jul 22, 2012
47
Hi again i bought some of the temp switches. Cant seem to get them to work. I have it programmed and the LED light stays lit when its on. I can hear the relay click.

I have no voltage on the output. I have tested 2 of them and both act the same. Using a 2amp fan and also a 2amp LED light. Both are 12 volt and my input is 12v.

What the heck am i doing wrong?

#### dave9

Mar 5, 2017
1,181
^ You mean the switches I linked previously? Measure for 12V on the relay output pin when it has clicked on. Check for continuity between that pin and the output connector terminal you have the fan hooked up to. I assume your power supply is capable of 2A?

#### wopachop

Jul 22, 2012
47
Thanks so much. I have 13.5v coming into the input.
When i put the meter on the pins shown in the pic its at 12.11v.

Is the middle pin the one that gets hot? I get zero volts between the middle pin to any ground.
But there is continutity between that middle pin and what i assume to be the + output connector.

I bought 4 of them cause so cheap. I guess at this point i have 2 with broken relays? I do hear the sucker click.

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#### dave9

Mar 5, 2017
1,181
The two relay pins you have your probes pointing at are the coil positive and ground. Because the relay model # ends in "AL", the A means it is a normally open type relay (meaning it only has 4 pins, does not have a normally closed pin). The middle pin should always have power, as should output K1.

Output K0 should get power when the relay is activated. Here is the datasheet for it:
https://datasheet.lcsc.com/szlcsc/Ningbo-Songle-Relay-SRA-12VDC-AL_C86414.pdf

You are stating that you bought 4 and two of them seem to work correctly but the other two do not? If that is the case then yes it appears that half of them are bad.

In that case you might contact the seller, many sellers selling these types of cheap products will issue a partial refund for product that is non-working or damaged in shipping, without your having to mail it back to them. Sometimes they want a picture.

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#### wopachop

Jul 22, 2012
47
I have not tested the other 2 switches yet. I bought a total of 4.

The middle pin, K0 and K1 dont ever seem to have power on 2 of the switches i tried so far.

Thank you for all the info im learning a bunch.

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