120v AC to 12v DC fan wiring

[Byrd]

Hi all,

I'm at the end of my brew controller build and looking to include a fan. I'm having issues actually driving the fan, and I think it's due to a lack of watts. The 80mm 120v AC fans are just far too big for my box so I went with a 50mm 12v DC fan but it's causing issues.

Here is my setup.

This LED driver is inverting from 120v AC to 12v DC

120v AC to 12v DC ~1watt inverter

My fan which is a 50mm 12v DC 1watt fan

https://www.amazon.com/gp/product/B00006B8CM/?tag=skimlinks_replacement-20


It's just BARELY spinning. Not enough to be useful. When I put a multimeter to the 12v or 6v battery test mode and put the black/red pins on their respective wires, it runs perfectly. Any ideas as to what could be the issue?

The fan draws 90mA consumption 1.08W which is around the output of the inverter. Should I get an inverter with more output watts?

Here's a video of what I'm talking about. Thanks in advance!

https://youtu.be/dsWakD0uDYo

 

[lschiavo]

Maybe this?

https://youtu.be/AVovy7UWDQ0

 

[JayEff]

I'm not sure what you mean by putting a multimeter on the wires making the fan run.

Try the following: while the fan is connected, check the output voltage of the driver. I think it might be possible that the slightly too high load drops the output voltage.

Another possibility that I could imagine, is that since the driver is likely a buck converter, it outputs high frequency noise. The fan probably has some control circuitry, if only because it's a brushless motor, but likely because the control wire of the fan allows the PC to control its speed. This circuitry probably expects the smooth, noiseless power output of the PC PSU. You can try to smooth the power by soldering a small capacitor (around 100nf is plenty) parallel to the fan's input wires. But I'm really not sure if this is a possible cause.

 

[Byrd]

Maybe this?

https://youtu.be/AVovy7UWDQ0

This fan doesn't have a thermistor

I'm not sure what you mean by putting a multimeter on the wires making the fan run.

Try the following: while the fan is connected, check the output voltage of the driver. I think it might be possible that the slightly too high load drops the output voltage.

Another possibility that I could imagine, is that since the driver is likely a buck converter, it outputs high frequency noise. The fan probably has some control circuitry, if only because it's a brushless motor, but likely because the control wire of the fan allows the PC to control its speed. This circuitry probably expects the smooth, noiseless power output of the PC PSU. You can try to smooth the power by soldering a small capacitor (around 100nf is plenty) parallel to the fan's input wires. But I'm really not sure if this is a possible cause.

The red and black wires from the fan are soldered to the LED driver. I just touched the black multi-meter probe to the black wire and the red multi-meter probe to the red wire. When it's on 12v battery test it makes the fan run perfectly. In the video, the fan going turning on full speed is when I touched the probes to the wires. I didn't know the multi-meter was supplying any power which was weird.

The fan is a ball-bearing fan, does that change things? I think you're right with the slightly too high load dropping the output voltage. I'm looking at a 24w 120v AC to 12v DC 2amp inverter. This inverter can supply the required volts to power the fan.

https://www.amazon.com/dp/B016FG9KWQ/?tag=skimlinks_replacement-20

 

[JayEff]

The multimeter doesn't supply power in voltage measuring mode as far as I know, no. What voltage does it show when you put it across the leads?

The only thing I can think of is the multimeter smoothing the voltage coming from the driver somehow... That's really weird! Do you have a capacitor on hand maybe? A non-electrolytic one (i.e. one that doesn't have a polarity), around 100 nf, to see if that has the same effect as the multimeter.

This guide here recommends a current-limiting driver: http://www.instructables.com/id/Power-PC-Fan-using-LED-Driver/ rather than a fixed voltage type. I'm not sure why he recommends this, though, and I reckon this could kill the fan, as that kinda driver would output as much voltage as needed to make the current limit kick in, which, if the fan wants less current than the driver wants to deliver, will ramp the voltage up past the safe levels. For all intents and purposes, yours should work, unless the voltage drops too much. But if the voltage drops too much, touching the multimeter probes to the wires shouldn't do anything! I'm rather confused myself now.

 

[SanPancho]

simple solution? stop by your local thrift store. go the electronics section. they usually have a big ass bin full of old power plugs for random electrical appliances, laptops, clocks, etc.

find the appropriate 12VDC transformer with the correct amperage.

wire it up.

 

[lschiavo]

The driver is 300mA. At 12V that's 3.6W. it doesn't seem the driver should be a problem for supplying enough power. The third lead probably needs to be grounded or tied to the positive supply. Not sure which and it may be possible to fry something if you choose wrong. I got one going once but can't remember what I did.

 

[BrunDog]

Why does the game adapter say 3-14V on it? Is there an adjustment screw?

 

[ClaudiusB]

Hi all,

I'm having issues actually driving the fan, and I think it's due to a lack of watts.
Here is my setup.

This LED driver is inverting from 120v AC to 12v DC

120v AC to 12v DC ~1watt inverter

My fan which is a 50mm 12v DC 1watt fan


It's just BARELY spinning. Not enough to be useful. Any ideas as to what could be the issue?

The fan draws 90mA consumption 1.08W which is around the output of the inverter. Should I get an inverter with more output watts?

There are two main types of external LED drivers, constant current and constant voltage.

Constant-current drivers power LEDs that require a fixed output current and a range of output voltages.
There will be only one output current specified along with a range of voltages that will vary depending on the load (wattage) of the LEDs.

Yours is a constant current with an output voltage range from 3 V to 14 V not a fixed voltage.
To get close to the 14 V you need to increase the load current close to the current listed on the device. Get a constant voltage LED driver or buy a regular power supply on ebay.

 

[BrunDog]

Great point ClaudiusB. Hence the 300mA +/- a narrow tolerance.

 

[Byrd]

... But if the voltage drops too much, touching the multimeter probes to the wires shouldn't do anything! I'm rather confused myself now.

You know, i think it's the multimeter drawing power from the driver for it's readings which makes the fan go? Outside of that.... aliens.

There are two main types of external LED drivers, constant current and constant voltage.

Constant-current drivers power LEDs that require a fixed output current and a range of output voltages.
There will be only one output current specified along with a range of voltages that will vary depending on the load (wattage) of the LEDs.

Yours is a constant current with an output voltage range from 3 V to 14 V not a fixed voltage.
To get close to the 14 V you need to increase the load current close to the current listed on the device. Get a constant voltage LED driver or buy a regular power supply on ebay.

Thanks ClaudiusB, I learned something new today and paid $7 in tuition for it. I purchased a fixed voltage 12V DC inverter. Thanks again!