Start motor

[Whippersnapper]

I have wired up a 12V computer fan that can only run through my small solar panel if I start it with my fingers. Can I use a capacitor to build up a charge and boost it into operation?

 

[audioguru]

Yes, if you charge the capacitor from the solar panel without the motor connected then connect the motor to the charged capacitor and the solar panel in parallel. The capacitor will probably need a high value.

 

[Whippersnapper]

Yes, if you charge the capacitor from the solar panel without the motor connected then connect the motor to the charged capacitor and the solar panel in parallel. The capacitor will probably need a high value.

Thanks, I guess what I need is a circuit that could automatically activate the motor when the sun is out. It is set up on a solar heater I made and I won't be around to connect it to the motor when it's needed. Do you or anyone know what type of circuit that would be called so maybe I can find a schematic to follow? I've got the most basic of knowledge in electronics, but I have a bunch of components. Perhaps I can build a circuit for this task.

 

[Ylli]

What is the open circuit output voltage of your PV? Can it actually supply enough current to run the motor, just having issues with starting? Perhaps something as simple as this:

 

[audioguru]

You need a circuit that charges the capacitor and activates the motor ONLY when the capacitor voltage is high enough AND it is sunny.
The Mosfet circuit shown will simply feed the capacitor charging current into the motor before the voltage is high enough.

 

[Ylli]

The mosfet is off until the voltage across the capacitor is >10 volts, at which point it turns on and allows the capacitor to assist with the current surge require for the fan to start. Once it is started, as long as the PV is generating enough to run the fan, it will keep running. If the PV is not generating enough, it might end up going on and off and on and off.....

 

[Whippersnapper]

What is the open circuit output voltage of your PV? Can it actually supply enough current to run the motor, just having issues with starting? Perhaps something as simple as this:

I don't suppose I could use this mosfet in a different circuit could I? https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d I have 10 of them! But I think it's a different style...I don't know what a QFET is.
There is enough power to run the fan, but I feel it does not run at full speed. The open voltage is generally over 14V. But it is only rated at 1.5W. Similar fans are rated at 1.2 to 1.8W, I don't have my fluke meter at home and my other meter only measures AC current. The fan was scavanged off a notebook cooling platform and does not show it's rating.

 

[Ylli]

The IRFZ44 should work in the circuit I posted, You do need to adjust the two gate resistors so that the MOSFET starts to turn on when the capacitor charge is sufficient to start the motor. Data sheet lists the turn on threshold as between 2 volts and 4 volts.

Edit: Just realized the IRFZ44 is an N-channel device so it would have to be installed in the negative power line instead of the positive supply line.

 

[Whippersnapper]

So does this mean when the capacitor is charged to 2 to 4 V it will send the charge to the fan? Or by changing the resistor values I will be able to up this number? I'm not quite sure.

 

[Pommie]

Not sure about this. Once the gate gets to 2V the MOSFET will start to turn on but with a high resistance. This high resistance will wasre power as heat. So, I think it'll be less efficient.

Mike.

 

[dr pepper]

Just another option if you dont want to go the electronics route, you can get motors designed for use with solar panels, you see them on ebay.
So you could either get or make a fan blade for one of these or butcher an old computer fan and fit a solar motor to it.

Miniature Low Inertia Solar Motor 2V 1540RPM Clockwise for Low Power Application | eBay

Direction: Clockwise. High quality miniature DC Motor. Ideal for Low Power Applications. No load speed rpm: 2200. Max efficiency speed (rpm): 1540. Stall torque g-cm:11. Output watts:0.05. Torque g-cm: 5.5.

www.ebay.co.uk

 

[audioguru]

The mosfet is off until the voltage across the capacitor is >10 volts, at which point it turns on and allows the capacitor to assist with the current surge require for the fan to start. Once it is started, as long as the PV is generating enough to run the fan, it will keep running. If the PV is not generating enough, it might end up going on and off and on and off.....

No, there is nothing to sense the voltage on the capacitor then turn on the Mosfet so the Mosfet slowly turns on too soon, before there is enough charge in the capacitor. You need the Mosfet to turn on suddenly at the correct voltage, not slowly at a voltage that is too low.

 

[Ylli]

No, there is nothing to sense the voltage on the capacitor then turn on the Mosfet so the Mosfet slowly turns on too soon, before there is enough charge in the capacitor. You need the Mosfet to turn on suddenly at the correct voltage, not slowly at a voltage that is too low.

The MOSFETs Vgs(th) and the resistive divider determine at what point the power starts to come on. Probably want to set that so that the MOSFET starts to come on at about 75% of the maximum available voltage. You are absolutely correct that it will start to come on slowly, and waste some power, but I think at start there may be enough energy stored in the capacitor to get the motor going. Then as long as the PV outputs more than the motor uses, the voltage on the cap will continue to increase and MOSFET will end up fully on.

It certainly is not the ideal circuit, and may not even work. Ideally, one would want a 'snap on' voltage detector that would enable the series pass device. But we are already trying to work with an energy source that is limited and adding a voltage reference and comparator just uses more of that needed energy.

 

[audioguru]

A Cmos comparator is needed that is driving the infinite resistance of the Mosfet gate, draws almost no power.

 

[be80be]

I have wired up a 12V computer fan that can only run through my small solar panel if I start it with my fingers

I'm running a 12v computer fan that only take's 1.6 amps to run and it's a common case fan used in old computers
Think the op needs to find a better fan first.

 

[JimB]

Think the op needs to find a better fan first.

Burt may be correct.

What is this recent fascination with trying to power fans from a solar cell?
Look here:

Simple 6th Grade Project - Solar Panel and DC Battery

I got a 2.5W 5V/500mAh solar panel, which reads 5.7V under a full sunlight, and a 3V-12V DC motor, which someone said in a comment that at 3V no-load takes 35-40mA. If I wire the motor directly to AA battery reading 1.23V, it spins fast. But when wired directly to the panel, it won't spin at...

www.electro-tech-online.com

Solar cell too small, fan too big.

JimB

 

[Whippersnapper]

Burt may be correct.

What is this recent fascination with trying to power fans from a solar cell?
Look here:

Simple 6th Grade Project - Solar Panel and DC Battery

I got a 2.5W 5V/500mAh solar panel, which reads 5.7V under a full sunlight, and a 3V-12V DC motor, which someone said in a comment that at 3V no-load takes 35-40mA. If I wire the motor directly to AA battery reading 1.23V, it spins fast. But when wired directly to the panel, it won't spin at...

www.electro-tech-online.com

Solar cell too small, fan too big.

JimB

It is as you say, solar cell too small, fan too big. I would guess most poeple here already know that. The trick is, how to overcome this problem with what I have available. A possible solution has been given and I am currently working on locating the parts needed to try it out. I will let everyone know my results, or troubles in making this circuit.

 

[be80be]

Like I said I have a computer case fan there very common most say 12 volt and never say how much current But this baby uses 1.6 amps that's a lot for a small solar panel I played with some that are maybe foot square that charged a bank of cap's it would't run this fan long
and would never run it while charging

You need about a 40 watt solar panel 20 would do in full sun.

 

[Whippersnapper]

I have tested the fan, it was drawing 1.44W.

 

[Whippersnapper]

I know I am supposed to change the resistor values. I used a 1 mega ohm and a 4 mega ohm. I will try to hook it up to the PV, but it's really cold outside right now, like 15F! I wish I had another small PV to test it on, but if I had that, I wouldn't need the circuit! HA HA!