Running a 5vDC fan on 9vDC - Electronic Circuits Projects Diagrams Free

moody07747 · 30th April 2007, 04:11 PM

I'm making a mini guitar amp, (AKA the Ruby amp) and want to put a small fan in the case to add a little style.

http://www.runoffgroove.com/ruby.html

Anyways I'm running the circuit at 9VDC and the small 25mm fan I have runs at just 5VDC

Now I know I have to use the ohms law calculation and I'm great at it......When the number of amps is at or over 1...

So I'm just wondering what rating resistor I should use to get this fan running at the correct voltage

Also, would it be safe running it at 9VDC?
The most this amp would be running at one time is around 1 1/2 hours.

Power supply:
9VDC, 800mA

Fan:
5VDC 0.3W

Fan link:
http://www.allelectronics.com/cgi-bi...LING_FAN_.html

ericgibbs · 30th April 2007, 04:19 PM

hi,

As the fan is rated a 5Vdc 0.3W.

I= 0.3/5 = .06A

You want to drop 4Volts so, 4/.06= 66R, nearest preferred value is 68R.

Wattage of 68R, 4V * 0.06 = 0.24W, I would recommend at least a 0.5W.

Dont run the 5V motor from 9Vdc, it will generate about 1W and overheat!

moody07747 · 30th April 2007, 05:10 PM

thanks for the walk though on that calculation.

audioguru · 30th April 2007, 06:41 PM

The fan needs a high current to start running because it is stalled. A simple series resistor limits the current then it might not start.
Add an electrolytic capacior across the resistor so the fan gets its charging current for starting.

ericgibbs · 30th April 2007, 06:50 PM

hi,
If you add the electrolytic cap as suggested by 'agu',
make sure you connect the '+' positive of the cap to the +9v end of the resistor and the '-' to the motor end of the resistor.

Styx · 30th April 2007, 10:53 PM

unless... it can cope running at the higher speed

V ~ speed
I ~ torque

Torque would of increased (cube law and bearings)
speed as more then doubled

moody07747 · 30th April 2007, 11:34 PM

My parts just shipped out today and will be here in three days.

My local radio shack said the MPF102 FET and resistor I needed were in stock at the store but after looking they seemed to be, "missing at the time".....
I'll try another shack tomorrow.
If all else fails I'll just order them online.

Any general stats for that cap?
I have a few in the electronics bin that I can try. Thanks for that info.

ericgibbs · 1st May 2007, 07:41 AM

hi dave,
>> Any general stats for that cap?
I have a few in the electronics bin that I can try.

Try without first, then try 10uF[16Vwkg], then increase the value until you get a consistent motor start at switch ON.

moody07747 · 5th May 2007, 04:53 AM

Ok I have a problem...The power is getting to the circuit but the fan won't turn on.
I have tried with the resistor and the 10uF/50V, 22uF/50V, 33uF/50V caps.

Now my understanding is this cap will give the fan a surge of current to get it spinning but without it I should be able to spin the fan by hand and it should run after that..The caps just for the start up.
however when I powered on and flicked the fan I got nothing at all....no movement or signs that it wanted to.

I have another problem with the power jack shorting right now so I'll be running a meter over the circuit tomorrow and do some tests to see whats really going on.

edit
I got the power jack working and with the meter I read around 10VDC at the motor leads after the 68 ohm resistor and a 10uF 50V capacitor....same reading with that bypassed.

Before I had shorted a (+) lead to ground in the circuit unknowingly with my metal power jack set to outer (+) and the case it was mounted on was ground so I'm not sure if I blew anything up but I cant get any sound out of the amp now.
I've replaced the FET and amp chip as I have a few more but still now sound...everything looks find in the circuit as well.
I will have to trace it out with an audio probe some time today.

CheapSlider · 5th May 2007, 02:29 PM

The motor should be connected only after the capacitor has charged up. If the motor is across the capacitor at switch on then the capacitor won't be able to get charged as the motor is shorting it out.

Have you tried using a low current bulb is series with the motor?
A 60mA indicator bulb like this or this may do the trick. They are available in 6V and 12V versions. It may need some experimenting with different bulbs. Normal torch bulbs will be too high current.
Maybe a 12V 40mA ?

picbits · 5th May 2007, 02:36 PM

It could be that the fan you have has an electronic controller onboard which is rated at 5 volts. By running it through the resistor you are still presenting it with a 9 volt supply. As the electronics control the motor speed (there is normally a small hall effect switch in the motor and a controller) there is a very very low current draw until the controller starts the motor fields.

At the best it will work, at the worst you will have fried your controller.

A much better solution is to use a L7805 regulator - anything from 0.1 to 1amp at 5 volt will do.

audioguru · 5th May 2007, 02:40 PM

You measure 10VDC across a 5V fan (that doesn't run) that is in series with 68 ohms resistor.
Then the motor is burnt out.

The amp is also burnt out maybe because the polarity of the 10V is backwards.

picbits · 5th May 2007, 03:02 PM

Quote:

Originally Posted by audioguru

You measure 10VDC across a 5V fan (that doesn't run) that is in series with 68 ohms resistor.
Then the motor is burnt out.

The amp is also burnt out maybe because the polarity of the 10V is backwards.

Not necessarily

If you have a fan with onboard controller it may only take 0.5ma when its powered up - until it decides to turn on the fan motor windings (some of them have onboard speed controllers) then you're not going to be taking much/any current hence no voltage drop across the resistor.

If the controller sees 9-10 volts instead of the expected 5 then it might refuse to do anything and keep itself turned off (or burn itself out - try applying 10 volts to a Pic Microcontroller

)

moody07747 · 5th May 2007, 10:53 PM

As of now the fan is just there for looks and I could really care less about it.
I'm more into getting the amp circuit running now...........however this fan would be nice to get working....

Thers only POTs, resistors, caps, a FET, and a LM386 chip in this circuit.
replacing the FET and LM386 leaves just a few caps or resistors to be burned and they don't seem to be at all.

Last time I turned the amp on I unhooked the fan.

Quote:

Originally Posted by picbits

Not necessarily

If you have a fan with onboard controller it may only take 0.5ma when its powered up - until it decides to turn on the fan motor windings (some of them have onboard speed controllers) then you're not going to be taking much/any current hence no voltage drop across the resistor.

If the controller sees 9-10 volts instead of the expected 5 then it might refuse to do anything and keep itself turned off (or burn itself out - try applying 10 volts to a Pic Microcontroller

)

Yea I figured the fan was just shutting down due to the high voltage.

It looks like ill need a regulator like the L7805

moody07747 · 6th May 2007, 05:35 AM

OK so i looked at the L7805 regulator sheet and found this wiring diagram:

I think it will do the job nicely.

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30th April 2007, 04:11 PM	(permalink)
moody07747	Running a 5vDC fan on 9vDC I'm making a mini guitar amp, (AKA the Ruby amp) and want to put a small fan in the case to add a little style. http://www.runoffgroove.com/ruby.html Anyways I'm running the circuit at 9VDC and the small 25mm fan I have runs at just 5VDC Now I know I have to use the ohms law calculation and I'm great at it......When the number of amps is at or over 1... So I'm just wondering what rating resistor I should use to get this fan running at the correct voltage Also, would it be safe running it at 9VDC? The most this amp would be running at one time is around 1 1/2 hours. Power supply: 9VDC, 800mA Fan: 5VDC 0.3W Fan link: http://www.allelectronics.com/cgi-bi...LING_FAN_.html __________________ Dave www.myspace.com/sonicorbstudios Welcome to "Sonic Orb Studios"

30th April 2007, 04:19 PM	(permalink)
ericgibbs	hi, As the fan is rated a 5Vdc 0.3W. I= 0.3/5 = .06A You want to drop 4Volts so, 4/.06= 66R, nearest preferred value is 68R. Wattage of 68R, 4V * 0.06 = 0.24W, I would recommend at least a 0.5W. Dont run the 5V motor from 9Vdc, it will generate about 1W and overheat! __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 30th April 2007 at 04:22 PM.

30th April 2007, 05:10 PM	(permalink)
moody07747	thanks for the walk though on that calculation. __________________ Dave www.myspace.com/sonicorbstudios Welcome to "Sonic Orb Studios"

30th April 2007, 06:41 PM	(permalink)
audioguru	The fan needs a high current to start running because it is stalled. A simple series resistor limits the current then it might not start. Add an electrolytic capacior across the resistor so the fan gets its charging current for starting. __________________ Uncle $crooge

30th April 2007, 06:50 PM	(permalink)
ericgibbs	hi, If you add the electrolytic cap as suggested by 'agu', make sure you connect the '+' positive of the cap to the +9v end of the resistor and the '-' to the motor end of the resistor. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

30th April 2007, 10:53 PM	(permalink)
Styx	unless... it can cope running at the higher speed V ~ speed I ~ torque Torque would of increased (cube law and bearings) speed as more then doubled __________________ Nothing is impossible. Once a problem is realised, the rest is just details

30th April 2007, 11:34 PM	(permalink)
moody07747	My parts just shipped out today and will be here in three days. My local radio shack said the MPF102 FET and resistor I needed were in stock at the store but after looking they seemed to be, "missing at the time"..... I'll try another shack tomorrow. If all else fails I'll just order them online. Any general stats for that cap? I have a few in the electronics bin that I can try. Thanks for that info. __________________ Dave www.myspace.com/sonicorbstudios Welcome to "Sonic Orb Studios" Last edited by moody07747; 30th April 2007 at 11:37 PM.

1st May 2007, 07:41 AM	(permalink)
ericgibbs	hi dave, >> Any general stats for that cap? I have a few in the electronics bin that I can try. Try without first, then try 10uF[16Vwkg], then increase the value until you get a consistent motor start at switch ON. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

5th May 2007, 04:53 AM	(permalink)
moody07747	Ok I have a problem...The power is getting to the circuit but the fan won't turn on. I have tried with the resistor and the 10uF/50V, 22uF/50V, 33uF/50V caps. Now my understanding is this cap will give the fan a surge of current to get it spinning but without it I should be able to spin the fan by hand and it should run after that..The caps just for the start up. however when I powered on and flicked the fan I got nothing at all....no movement or signs that it wanted to. I have another problem with the power jack shorting right now so I'll be running a meter over the circuit tomorrow and do some tests to see whats really going on. edit I got the power jack working and with the meter I read around 10VDC at the motor leads after the 68 ohm resistor and a 10uF 50V capacitor....same reading with that bypassed. Before I had shorted a (+) lead to ground in the circuit unknowingly with my metal power jack set to outer (+) and the case it was mounted on was ground so I'm not sure if I blew anything up but I cant get any sound out of the amp now. I've replaced the FET and amp chip as I have a few more but still now sound...everything looks find in the circuit as well. I will have to trace it out with an audio probe some time today. __________________ Dave www.myspace.com/sonicorbstudios Welcome to "Sonic Orb Studios" Last edited by moody07747; 5th May 2007 at 12:43 PM.

5th May 2007, 02:29 PM	(permalink)
CheapSlider	The motor should be connected only after the capacitor has charged up. If the motor is across the capacitor at switch on then the capacitor won't be able to get charged as the motor is shorting it out. Have you tried using a low current bulb is series with the motor? A 60mA indicator bulb like this or this may do the trick. They are available in 6V and 12V versions. It may need some experimenting with different bulbs. Normal torch bulbs will be too high current. Maybe a 12V 40mA ? Last edited by CheapSlider; 5th May 2007 at 02:31 PM.

5th May 2007, 02:36 PM	(permalink)
picbits	It could be that the fan you have has an electronic controller onboard which is rated at 5 volts. By running it through the resistor you are still presenting it with a 9 volt supply. As the electronics control the motor speed (there is normally a small hall effect switch in the motor and a controller) there is a very very low current draw until the controller starts the motor fields. At the best it will work, at the worst you will have fried your controller. A much better solution is to use a L7805 regulator - anything from 0.1 to 1amp at 5 volt will do.

5th May 2007, 02:40 PM	(permalink)
audioguru	You measure 10VDC across a 5V fan (that doesn't run) that is in series with 68 ohms resistor. Then the motor is burnt out. The amp is also burnt out maybe because the polarity of the 10V is backwards. __________________ Uncle $crooge

6th May 2007, 05:35 AM	(permalink)
moody07747	OK so i looked at the L7805 regulator sheet and found this wiring diagram: I think it will do the job nicely. __________________ Dave www.myspace.com/sonicorbstudios Welcome to "Sonic Orb Studios"