i have two CPU fans, a solar panel, some capacitors and no skill!

I'm trying to run two CPU fans from solar power. Thus far I have ascertained that the fans will run if there's enough sunlight. On a cloudy day, I can charge capacitors directly from the panel then connecting the fans allows them to run for a few seconds.

What I need to do is to automate the switching process (keeping the circuit very simple). No ICs. I'm thinking a few resistors and a transistor.

The output of the panel ranges up to 24v but it's rated output is 12v 5w.

The capacitors are big and capable of 59v plus.

I'd like to fill the capacitors from the solar panel. Maybe put a 12v zener across the panel to limit the voltage.
When the capacitors are full, empty them into the fans.

That's it. The fans are 12v CPU fans.

This is where I'm at so far

 

What switching process are you trying to automate?

 

I have current too low to power the fans unless I disconnect them.

When the fans are disconnected, the capacitors rapidly build enough charge to power the fans.

I connect the fans and the power in the capacitors is sufficient to start and run them for a few seconds.

Rather than switching the fans off and on manually, I'd like to automate the process.

So...

Solar panel fills capacitor
When capacitor is full, capacitor discharges into fans
When capacitor is empty, solar panel refills capacitor

Rinse, repeat

 

I have current too low to power the fans unless I disconnect them.

When the fans are disconnected, the capacitors rapidly build enough charge to power the fans.

I connect the fans and the power in the capacitors is sufficient to start and run them for a few seconds.

Rather than switching the fans off and on manually, I'd like to automate the process.

So...

Solar panel fills capacitor
When capacitor is full, capacitor discharges into fans
When capacitor is empty, solar panel refills capacitor

Rinse, repeat

The thing is... Once the capacitors are charged, the current from the solar panels should bypass them and go straight to the fans. So, theoretically, you don't need to switch anything.

However. I do have two suggestions.
1. Put blocking diode between panel and capacitors. This way the current will always flow from panel to the capacitors, and never from capacitors to the panel.
2. That zeiner diode you were talking about. You probably want to put it between capacitors and fans. That way fans will receive 12 volts and you will not fry them with 59 volts from the caps.

 

@Mary Johanssen

Mary, Welcome to the forum!

That's kind of a cool rig you put together. You know CPU fans can be very inefficient (sometimes). I bet you could find some fans that would run from your solar panel without any fancy switching.

First, what does the other side of the fans say as far as voltage and current? Can your panel run just one of the fans you currently have?

 

The thing is... Once the capacitors are charged, the current from the solar panels should bypass them and go straight to the fans. So, theoretically, you don't need to switch anything.

However. I do have two suggestions.
1. Put blocking diode between panel and capacitors. This way the current will always flow from panel to the capacitors, and never from capacitors to the panel.
2. That zeiner diode you were talking about. You probably want to put it between capacitors and fans. That way fans will receive 12 volts and you will not fry them with 59 volts from the caps.

The panel already has a diode. With the capacitors and fans wired in, nothing happens. The fans take too much power so the capacitors never charge. Had it sitting in the light for hours and never saw the fans spin until I disconnected them.

The problem is they have a higher starting current than the running current. The smaller 40mm fans need even more current to start. These are 90mm fans.

 

@Mary Johanssen

Mary, Welcome to the forum!

That's kind of a cool rig you put together. You know CPU fans can be very inefficient (sometimes). I bet you could find some fans that would run from your solar panel without any fancy switching.

First, what does the other side of the fans say as far as voltage and current? Can your panel run just one of the fans you currently have?

These are mystery fans from China. They're 2 wire 12v fans but run well also off 6v. I tried them off 4 D cells.

I'd like to use what I have because I have it.

 

@Mary Johanssen

Got it. What do they say on the other side?

 

@Mary Johanssen

Got it. What do they say on the other side?

I just looked at one of my 90mm fans. It shows 320 mA on the label.

 

The fans have on,y 12v marked. The other side is blank.

 

I think you need to take a step back and take a look at what you are looking to accomplish (i.e. What are the requirements). For. Example...

How long does the fan need to run?
When do you want the fan to run?
What is the power rating of the solar panel?
What is the power requirements of the fans?

Once you have all of the data, you should do a little math to make sure that what you want is possible with the chosen components.

I'm conerned that the panel is underrated for the design intent.

 

OK, a 12V 5watt panel should put out 416 ma. Two 12V, 14o ma. fans should run just fine from that panel. You can easily get fans that will run from your panel without any other parts. You trying to build an On/Off device is far more troublesome and expensive then finding the right fans.

 

I think you need to take a step back and take a look at what you are looking to accomplish (i.e. What are the requirements). For. Example...

How long does the fan need to run?
When do you want the fan to run?
What is the power rating of the solar panel?
What is the power requirements of the fans?

Once you have all of the data, you should do a little math to make sure that what you want is possible with the chosen components.

I'm conerned that the panel is underrated for the design intent.

The fans are intended as extractor fans on my motor home. Even today, it was 95 inside whereas outside it was 80. I figure if I can extract the hot air near the roof and blow it out of some vents I'll install, I can keep the interior comfortable. Last summer, the internal temperature rose to 140f as opposed to 90 outside.

This fan is to run solely during daylight. If I have to collect power and pulse it to power the fan then so be it. I'm just not prepared to spend much more than I already have.