Solar Fan doesnt work

[chico]

I have a fan which i hooked up to a solar panel. The will start up at 4V and 0.03A on a power supply. My cells are providing ~ 6.5V and 0.2A under my light source but my fan wont start up.
Why? that seems crazy to me.

schematic of my simple design is below.

[URL="**broken link removed**

 

[RadioRon]

How, exactly, did you measure the cell output? What is the cell output with the fan attached?

 

[MikeMl]

If you have a power supply set to 4V, and you use a clip lead to connect the stopped motor to the power supply, the supply will happily deliver the initial inrush current required to start the motor. As the motor comes up to speed, the current will reduce to your measured 30mA, but during the inrush the current is likely to be 10 times that for ~1/4sec. The solar panel wont deliver the inrush current.

Connect a 1000uF capacitor across the panel (observe polarity). Put it in sunlight, and then connect the motor after the capacitor has charged. The capacitor will deliver the starting surge, and then the panel will keep the motor running.

 

[chico]

is there a way to autostart the fan? like a fet on the output of the cap?

 

[Diver300]

You would need a MOSFET to turn on the fan. You would also need a voltage sensing amplifier to make sure that the fan turned on quickly, even though the voltage on the capacitor would rise slowly.

It could be worth tying the capacitor that Mike suggested, but with everything connected. That might allow the fan to start and you wouldn't need to bother with the MOSFET and circuitry.

 

[4pyros]

chico; Yes your problum is inrush current. It takes a lot more power to start a motor than to run it. Use more solar cells or get a smaller motor. Take a look at "Solar Bots" or "Solar Engines" you may find some usefull info thare. Andy

 

[RMMM]

The cap across the terminals of the motor should iron out this problem.

Using the CAP will allow the energy to DUMP to get the motor going.

This same thing happens with standard mains power also.

Start capacitors are used for motors for this very reason.

If you have ever come across a grinder or fan that you had to manually spin to get going, the start cap was bad...or missing.

 

[ben7]

The cap across the terminals of the motor should iron out this problem.

Using the CAP will allow the energy to DUMP to get the motor going.

This same thing happens with standard mains power also.

Start capacitors are used for motors for this very reason.

If you have ever come across a grinder or fan that you had to manually spin to get going, the start cap was bad...or missing.

Just note that if you use a High capacity super capacitor it will take a few seconds to a few minutes to charge up.

-Ben

 

[4pyros]

The cap across the terminals of the motor should iron out this problem.

Using the CAP will allow the energy to DUMP to get the motor going.

This same thing happens with standard mains power also.

Start capacitors are used for motors for this very reason.

If you have ever come across a grinder or fan that you had to manually spin to get going, the start cap was bad...or missing.

This will not work so good without a "DUMP" circuit. Most motors have a start winding or switch. Andy

 

[ben7]

I have a fan which i hooked up to a solar panel. The will start up at 4V and 0.03A on a power supply. My cells are providing ~ 6.5V and 0.2A under my light source but my fan wont start up.
Why? that seems crazy to me.

schematic of my simple design is below.

[URL="**broken link removed**

The .2A current rating might be a short-circuit current rating too!?

When you connect the fan the voltage probably drops to say, 3volts as the fan tries to draw current.

-Ben

 

[RMMM]

This will not work so good without a "DUMP" circuit. Most motors have a start winding or switch. Andy

Quite true. This is where finding the optimal cap size can come into play.

Preferably, you would charge the cap, then trigger a MOSFET to "DUMP" the juice into the motor.

Would a Zener do the trick?.

It would not conduct until the cap reached the Zener voltage then dump the cap into the fan?

If it were that easy, that would be great.

 

[ericgibbs]

is there a way to autostart the fan? like a fet on the output of the cap?

Use a 1000uF as suggested in post #3
For a autorun circuit use a 4.7V zener to trigger the gate of a 1Amp SCR, choose an SCR that has a low hold on current and a sensitive gate.

EDIT:
This is one option

 

[MikeMl]

I think you need a much bigger capacitor, and the capacitor must have a low Effective Series Resistance. For the capacitor to hold the voltage up for ~2sec while the motor comes up to speed, it will have to be ~0.1Farad (100,000uF). Looking at the cost and available specs on Super-Capacitors on Digikey, I'm thinking you will do better to use a rechargeable Battery. In that case, the voltage rise sensor will have to be very precise.

Here is a sim of Eric's suggestion with a 0.1F capacitor.

 

[chico]

I ended up using EricGibbs design with a **broken link removed** diode.
And the fan does start but only in certain orientations, you can see it trying to start up but it cant make it sometimes.
Is that more of a current limiting issue or a voltage issue? I limited the voltage to 3.6V because the fan starts up at 3.2V with a PSU


If its current limiting would this be more because of ESR or too low capacitance? I just have a typical ceramic 1000uF cap right now.

I was trying to keep the turn on voltage low so it would start up in advaerse weather conditions but it seems to have backfired, rechargable batteries come in 1.2V charges so I could just use 3 in series if i need more current.

 

[chico]

Could the issue be that as the cap voltage drops as it discharges that the voltage goes below 3.2 V and then no longer has any affect on the fan?

 

[chico]

I am still having issues with this, I thought that replacing the cap with a battery would solve the problem but it appears that it isn't the case. In fact with the battery in operation it doesnt seem to do anything without me giving it a push.

 

[ronv]

You loose almost a volt across the scr, so your 3.6 is only 2.6 at the fan. Maybe a 4.7 volt zener?

 

[chico]

really, I didnt see that value in the data sheet so I assumed it was low. I suppose that was silly

To get around that voltage drop could I use the same setup but have the SCR attached to the gate of a N-channel Schottky Mosfet? Schottky so its low V-drop, MOSFET so its voltage controlled and I can make little current lost here, and N-channel so i can attach the fan upstream of the FET

 

[ronv]

I think a comparator and a transistor might work best because of the low voltage, but first what is the current to the fan if you run it at 4 volts from your PSU but don't let it turn?

 

[chico]

In the highest current orientation 130mA.
I have a 4.7 V zener on it and it still doesnt work.
I read ~3.4 V across the cap and ~2.4V across the fan which doesnt make any sense.