potentiometer efficiency

retched

Joined Dec 5, 2009
5,207
ok. The sarge has seen thousands of new electronics hobbyists and whatnot come through these here forums.

It is just most people that start buying before understanding, fail at there first project and then never get over it. They trash the hobby.

Ok what you need is a 100 Kilo Ohm Potentiometer.

http://ca.mouser.com/Passive-Compon...s/Potentiometers/_/N-5g9h?Keyword=POT&FS=True

There are Linear and Logarithmic.

Linear is an even change throughout and Logarithmic is used for audio where the resistance follows human hearing.
 

Bychon

Joined Mar 12, 2010
469
To answer the first question, if a pot is reducing the 24 volts so that the fan gets 12 volts and the fan is still using .1 amps, the power in the pot is 1.2 watts. Meanwhile, the pot will be putting 120 ohms in series with the fan. 2 fans will cost 2.4 watts under those conditions.
 

Thread Starter

admin

Joined May 5, 2010
17
ok. The sarge has seen thousands of new electronics hobbyists and whatnot come through these here forums.

It is just most people that start buying before understanding, fail at there first project and then never get over it. They trash the hobby.

Ok what you need is a 100 Kilo Ohm Potentiometer.

http://ca.mouser.com/Passive-Compon...s/Potentiometers/_/N-5g9h?Keyword=POT&FS=True

There are Linear and Logarithmic.

Linear is an even change throughout and Logarithmic is used for audio where the resistance follows human hearing.
thanks, could you take a look at the other parts and see if I selected the right ones?
 

Jaguarjoe

Joined Apr 7, 2010
767
Don't forget to get something to reduce your 24 volts to something suitable for the 555 like 12 or 15 volts.

Also, don't forget a back emf diode to put across your motor.

It's not a bad idea to buy extra 555's just in case you accidentally smoke the first one. They're only $0.50 each.
 
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Wendy

Joined Mar 24, 2008
23,415
Joe, if you looked at Wookie's schematics you would have seen what the LM317 was used for.

You will find Radio Shack has most of them, at around a 300% or more markup. I don't know what pot you used, but you could be lucky it didn't burn up.

Mouser Electronics or Digikey both can be found via Google, but I see you found one of them.

Why the 5 month delay in posts?
 

Thread Starter

admin

Joined May 5, 2010
17
took up basket weaving and gave my project a break , waiting for other parts, decided to give them pwm another chance
 

retched

Joined Dec 5, 2009
5,207
I took up basket weaving also, about 20 years ago.

It is NOT easy.. Not at all.

Dont believe me? Try it!

You think a soldering iron burn hurts? Try getting a reed splinter out from under your fingernail.. just to have it break off.

For the next month or so, you cant even reach in your pants pocket to get your keys without some agony!
 

SgtWookie

Joined Jul 17, 2007
22,230
admin,
I apologize for my rude comment. I must've been having an off day; I'm usually pretty patient and understanding. It is all too easy to forget that when I started in electronics, I didn't know one thing about it, and spent a good deal of time floundering around.

Please accept my apology.

Would you please tell us more about this/these fans you wish to control? Are they brushless DC fans, or are they brushed-type? If they are brushless, the PWM idea may not work.
 

SgtWookie

Joined Jul 17, 2007
22,230
Coincidentally, I also have some FFB series fans, but mine are the FFB0912VHE's; 12v, 0.5A, 85 CFM - quite a bit more power than the ones you have.

I'm going to have to look at this later on; I have to leave for the evening.
 

SgtWookie

Joined Jul 17, 2007
22,230
I have a couple of Papst TYP 814 L fans, which are 24V DC 0.8W, with a range of 12v-30v. Yours are .96W, but other than that the specs of the fans I have aren't that far off from yours.

Seeing as it's almost midnight here, it's a bit late to make any progress today. However, I have some ideas that I'm kicking around; trying to keep it simple yet pretty efficient.
 

Wendy

Joined Mar 24, 2008
23,415
If you buffered it maybe. The problems of current remain, if you try to drive high current through any pot there is a good chance it will smoke. Standard practice is you use the pot as a control, then use a high current device (such as a simple transistor circuit) as the buffer.

This circuit, found in my LEDs, 555s, Flashers, and Light Chasers article in Chapter 5, could easily drive a fan if the fan weren't too big.



R4 and R6 should be brought down to 9.1KΩ to guarantee full on and full turn off, and don't forget to put a swamping diode across the motor to protect the transistor. Something like this...



This is another simple PWM scheme. It doesn't complete turn off or on however, but very close.

I've also written an article for the AAC book to explain why PWM works so well.

Chapter 11: DC MOTOR DRIVES

Pulse Width Modulation

Linear controls tend to dissipate heat, PWM doesn't.
 
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