Can somebody please give me assistance with a circuit to power from 12v a variable 1.5 to 3v circuit. Presently the small fan is powered by 2 x D cells and runs for around 6 hours. I would like to have a potentiometer that goes from 1.5 to 3.0v. The fan will be finally powered from a 12v SLA battery charged from a solar panel.
Thanking you in anticipation for assistance.
solar
How much current does the fan require? What is its specified operating voltage?
I don't know how much current the fan takes. I wonder what the capacity of D size batteries is? Googling at the Ah capacity of D size carbon zinc batteries, and the period the batteries currently last, I would assume the fan takes 1/2 amp, but lets work on 1.0A for safety. The specified operating voltage is 3.0v and normally powers from 2 x D cells. As this will be powered from a sealed lead acid battery with a small solar panel, the voltage supply will reach 14.3v.
Yes, I am confused as the one that looked like it could apply the link was dead.
What I would like is a list of a few components and send me on my way to Jaycar and then to solder it together.
On Sun, 01 Jul 2007 21:47:38 GMT, "Maxamillion" put finger to keyboard and composed:
If the fan current is less than 500mA, then you should be able to modify just about any mobile phone car adapter/charger. In fact I've done something like this for a fan inside a DVD player. Many of these adapters use a Motorola PWM IC, MC34063, which can regulate down to
1.25V. You'll just need to modify one resistor.- Franc Zabkar
-- Please remove one 'i' from my address when replying by email.
You could try this circuit:
It's a basic PWM speed controller. As shown, the output will vary from 5% to
95% of the 12v supply. You want 10% to 25% - read the circuit explanation where it talks about the potentiometer - by working out the ratios, you can reduce the size of the the potentiometer and add a fixed resistor to each side of the pot to limit its operating range.Poxy looking for something a little simpler. Something like using one of those three pin voltage regulator chips with a few extra components. I am familiar with PWM and is really over kill for this situation.
use PWM, it's easier and will give the same effect.
OTOH, 12V fans are easily available, some even have speed control built in. I've got one from an old PC powersupply with a temperature sensor attached, I could replace that with a variable resistor to have a speed control.
Bye. Jasen
Normal three-terminal regulators will be very inefficient in dropping a nominal
12V supply to 1.5-3V, and givne that the 12V battery is solar-charged I'd expect you cant afford the 25% efficiency.You really DO need to go switchmode for any sort of decent efficiency, or PWM.
My personal choice would be an MC34063 and an external transistor if required for the load current.
Could I use something like a 2N3055 with a few bits and pieces?
A potentiometer by itself won't be much good, but if you tie it up with an LM 317 regulator circuit it will be fine.
Or there are more sophisticated motor speed circuits that use pulse width modulation -- check DSE or Jaycar for kits.
It is what's needed , if you scrub off 9 vots dc at one amp thats a lot of wasted energy the solar unit has to make , a simple switch unit save most of the wasted energy and so less light/energy will keep things running .Use the circuit or somthing like it .
On Mon, 02 Jul 2007 06:45:55 GMT, "Maxamillion" put finger to keyboard and composed:
As suggested elsewhere, you could add a cheap transistor to the circuit to handle the extra current.
See the application circuits in the datasheet:
A pot in place of, or in addition to, a resistor can give you the 1.5V to 3.0V range. Having said that, if your fan is a brushless type, then it may not run reliably at reduced voltages, nor will it tolerate direct PWM control as suggested elsewhere in this thread.
- Franc Zabkar
-- Please remove one 'i' from my address when replying by email.
25% efficiency IS what you get with a linear reg or a resistor, or any other non-switching method of losing the excess volts. They all do the same.
YOU get to decide if 25% is something you can afford, THEN the decison as to switching-vs-linear can be made very simply.
Max sounds like a lost cause - for every good bit of advice he's been given, he's come back and either rejected it, called it mickey mouse, or passed over it.
Argusy
Troll ?
Max is far from a lost cause, and most appreciative for the replies. You see a little knowledge is dangerous, and was under the impression that if you used a 3 pin regulator or transistor you did not get the amount of wasted power like you do using a resistor.
I did investigate the options in kits at Jaycar and DSE this morning, but nothing really suitable.
I am going to get one of the units this afternoon and see if we can adapt a
12v 80mm Jaycar fan to fit in place of the 3v fan.Sincerely thanks all who replied.
a
You get the easiest build by stripping a mobile cell charger as was earlier suggested.
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