12v to 3v

[Maxamillion]

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.

 

[Lord Garth]

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.

How much current does the fan require?
What is its specified operating voltage?

 

[atec77]

How much current does the fan require?
What is its specified operating voltage?

http://icc.skku.ac.kr/~won/electro/psu.html will give direction and get
back to us if you are confused ( low voltage section)

 

[Maxamillion]

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.

 

[Maxamillion]

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.

 

[Franc Zabkar]

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.

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

 

[Maxamillion]

500mA is a little tooooo minimalist for my liking. I would rather spend the
couple of extra dollars and make it more bullet proof and go for 1.0A.
These need to be reliable. Have the space of the 2 x D cells to fit the
electronics in, and the cover for the batteries will place the
potentiometer.
I also need it to be variable 1.5v to 3.0v

 

[Poxy]

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.

You could try this circuit:
http://www.cpemma.co.uk/555pwm.html

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.

 

[Maxamillion]

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.

 

[Maxamillion]

25% efficiency would be worse than using a resistor - yes/no?

Could I use something like a 2N3055 with a few bits and pieces?

 

[atec77]

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.

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 .

 

[Franc Zabkar]

500mA is a little tooooo minimalist for my liking. I would rather spend the
couple of extra dollars and make it more bullet proof and go for 1.0A.
These need to be reliable. Have the space of the 2 x D cells to fit the
electronics in, and the cover for the batteries will place the
potentiometer.
I also need it to be variable 1.5v to 3.0v

As suggested elsewhere, you could add a cheap transistor to the
circuit to handle the extra current.

See the application circuits in the datasheet:
http://www.onsemi.com/pub/Collateral/MC34063A-D.PDF
http://www.onsemi.com/pub/Collateral/AN920-D.PDF

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

 

[atec77]

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 ?

 

[Maxamillion]

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.

 

[Lord Garth]

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.

You get the easiest build by stripping a mobile cell charger as was earlier
suggested.

 

[Terryc]

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.

In that case, look at replacing the fan with a 12 volt version as they
come in all sorts of sizes.

Otherwise, loo at a 7805 regulator circuit, then burn up the excess
voltage in a resistor. Simple calc.