# Tent fan [help]

Discussion in 'The Projects Forum' started by Yousuf Al Falasi, Jul 12, 2015.

1. ### Yousuf Al Falasi Thread Starter New Member

Jul 11, 2015
2
0
Hello everyone, I have 2 Yuasa 7AH sealed lead acid batteries and an old 0.2 ampere car fan. I hooked up the batteries in parallel and installed a potentiometer to control the fan, but it burned out. I'd like to make the fan run longer by putting a motor speed controller, but i am worried that the circuit will burn out easily. Could someone help me out in choosing the right connections (parallel/series) that will increase the run of the fan. Also if possible how to calculate the resistors/capacitors needed to provide the correct current for the setup. I am currently a beginner in electronics so please bare with me

One more thing, what is the formula to calculate the current for the Ampere hours like know how much current will be flowing to the circuit

Best regards,

Yousuf

Apr 5, 2008
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3. ### AnalogKid AAC Fanatic!

Aug 1, 2013
5,647
1,595
A resistor in series with the fan is one way to control the speed, but it is very inefficient and the resistor must be able to dissipate a lot of heat. For your fan you would need a 50 or 100 ohm potentiometer rated at 5 to 10 watts.

If the batteries add up to 14 A-h and the fan is 0.2 A, then the max. theoretical run time is 14 / 0.2 = 70 hours. Many things affect this number in the real world, but it gives you a starting point. The most efficient way to control the energy to a DC motor is by switching the power source on and off very rapidly. This is called pulse-width modulation (PWM), a term you can look up and read about. Not all motors respond well to this technique, but again it is a good starting point. It is reasonably easy and low cost try, and it won't hurt anything if it doesn't work. There are many past threads on this forum about this idea, and many of those use the 555 timer chip, another popular starting point for the hobbyist/beginner. Also, PWM controllers are available on ebay.

ak

Yousuf Al Falasi likes this.
4. ### GopherT AAC Fanatic!

Nov 23, 2012
7,244
5,956
Here is a \$2 solution. You may have to wait several weeks for the mail from China.

http://www.ebay.com/itm/1pc-New-PWM...973?pt=LH_DefaultDomain_0&hash=item20f31072fd

AnalogKid likes this.
5. ### Yousuf Al Falasi Thread Starter New Member

Jul 11, 2015
2
0
I'd like to thank you so much for helping me out with this issue. Moreover, the way you explained it made it much easier for me to understand what's going on. I hope this forum always has smart people like you!

Best regards,

Yousuf

Aug 1, 2013
5,647
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7. ### Brownout Well-Known Member

Jan 10, 2012
2,374
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I don't think I'll bare with your, but good luck with your project