DC battery / PV

[Grelinette]

Hello,

A small question to low-voltage DC specialists:

The goal: Forced ventilation of a fruit and vegetable dryer (creation of a draft) by starting a small computer fan connected to a small solar panel. When the sun is hot and the dryer is full, the fan starts and forces the dryer to air.

Materials used:
- A small PV panel recovered in a trash
- a small motor (probably in 6 V) from a child's toy, or a PC fan (voltage to be determined, probably 6 Volts DC)

The problem encountered:

- I test the PV current with a controller that gives me up to 9,5 V in the sun
- I plug the small engine on the PV ... and it does not start all alone, while if I start the movement by hand (forced rotation of the rotor), the engine starts to run at full speed.
- I plug the small engine on a single battery 1,5V it starts alone normally, but runs slower than with the PV panel (PV: 9,3 Volts battery: 1,5 V).

Questions:
a) Why the PV panel that discharges 9,5 V (in direct sunlight) does not allow to start the rotation of the rotor of the motor, whereas once started manually it turns quickly and well, while with the 1,5v battery the engine start alone?

b) Is there a simple component to add to the assembly so that the electric motor starts rotating itself as soon as the voltage delivered by the small PV is sufficient?

DC Test (1) .JPG (37.83 KIO) Accessed 4648 times

Battery Voltage Test: 1,5 Volt

DC Test (2) .JPG (30.22 KIO) Accessed 4648 times

Test the engine with the battery: the engine starts and turns slowly

DC Test (3) .JPG (48.83 KIO) Accessed 4648 times

PV voltage test: 9,3Volts under the sun

DC Test (4) .JPG (85.36 KIO) Accessed 4648 times

Test the engine with the PV: it does not start all alone, but once primed by hand, the rotor turns very fast! ...

[Gaston]

It is likely that the panel can not provide the power needed to start the engine.
To verify this, it would be necessary to measure the output voltage of the panel when the motor is connected but does not turn.

A computer fan is usually powered by 12V (but it can run at low speed with a lower voltage), and its power varies from 0,5 to about ten watts depending on the model.
As you can see, the solar panel you use does not produce 1W.

[Forhorse]

+1
Power of the solar cell much too weak to allow the takeoff of the engine. (when starting a motor behaves almost like a short circuit)

[izentrop]

In addition the round PV is an error because the smaller cells limit the maximum current that can be delivered.

It would take a small buffer battery like 8.4 V NIMH. A schottky diode between PV and battery for charging.
A schmitt trigger to connect the fan to the battery when the sun is enough. set to 8.5 V for example.
I made a little drawing.

trigger.jpg (27.72 Kio) Viewed 4626 times

[chatelot16]

[b] Questions:
a) Why the PV panel that discharges 9,5 V (in direct sunlight) does not allow to start the rotation of the rotor of the motor, whereas once started manually it turns quickly and well, while with the 1,5v battery the engine start alone?

you have to understand the electricity and the mechanics

a panel that debuts 9,5V is absurd! 9,5V is the voltage not the flow ... in electricity the word is rather current than flow, but debit is the same notion as current

the tension makes the speed ... the current is the strength or the couple

a low voltage battery can be able to make a big current, to do all the current that the engine wants to consume to start ... the photovoltaic can be very strong voltage it is completely limited in current and it does not start

do not look for a miracle component: the photovoltaic makes a limited available current, to start a motor it takes a battery ... or it takes a number of oversized photovoltaic panel to make the demarage and useless then

[Forhorse]

Or you need an impedance adaptation: an electronic circuit capable of transforming this "high" voltage but this low current produced by the cell, into "high" current but low voltage that the motor requires to start (for only the power, product of current and voltage, sufficient of course)
This is typically the role of a MPPT regulator (but which does not only do this impedance matching, it adapts the power that flows the system according to the maximum power that can produce the panels ... it is a little an impedance adapter with automatic variable geometry)

[izentrop]

There is no impedance in direct current.
On the other hand, we speak of internal resistance. That of the receiver is 10 times larger at startup and that of the generator is determined by the size of 18 PV cells in series. The smaller ones increase this resistance even more. A battery or battery has a very small internal resistance, hence this solution for starting. http://www.mongosukulu.com/index.php/en ... ?showall=1

A small 9V / 170 mA battery like 6LR61, LR22, LF22, 6LF22,9V, 9V battery, 9V battery, 9V battery, HR9V, NH9,6LR61 is enough.
There is no need for a charging circuit since the maximum charging voltage 9.8 V will not be reached.
The schottky diode prevents battery voltage from circulating in the panel (out of the sun).
On the panel side (PV), the potentiometer (10 kohm) is used to adjust the voltage that will put the motor into operation.
Do not go below 7 V, which is the discharged battery voltage.

If the voltage delivered by the PV exceeds the set threshold, the zener diode drives and saturates the transistor. The fan is connected directly to the battery and starts up.
With the engine running, the panel should power the engine and charge the battery at the same time. To be monitored in case the panel lacks power.
Finally, a cloudy passage will disconnect the engine from the battery.

Alternatively, buy a PV 12 V from 5 W;)

[dirk pitt]

what I see here is not a computer fan but a small brushed DC motor.
the starting current is too much.
take a real computer fan that are in fact small brushless with a minimal integrated electronics and there, it will start direct.
no need to break your head anymore.

[Grelinette]

Thank you for your answers (especially to Izentrop for the sketch); these answers correspond to what I thought: the tension the small PV panel is high (9,5 V, compared with the 1,5 V battery) but its "power" or "current" is too weak to start the small engine.

That said ... I tested several small fans recovered on PCs (actually all in 12 Volts) and curiously for the same voltage and amperage announced (12 V and 0,18 A), some start very well once connected to the small PV panel, others do not, and the smallest fans are not necessarily the most sensitive !!! ...
Probably for a mechanical reason of friction of the propeller bearing freer on some fans than on others.

ventilo pc.jpg (11.45 KIO) Accessed 4592 times

It is all the more curious that the most "sensitive" fans start to turn even when the PV only supplies 5 or 6 volts, when for example a cloud passes in front of the sun!

A question in passing: there are 3 wires on the fans, 1 red, 1 yellow, 1 black, and depending on the connection to the PV with 2 wires, the speed of rotation is not the same. What is the use of these 3 wires on the fans?

It is therefore sufficient to choose a fan more "sensitive" to low current, and the problem will be solved: the fan will start well at the first ray of the sun a little strong, and will turn all the better and all the faster as the sun shines ... and the ventilation of the dryer will be more active. CQFD

So problem a priori settled!

I take this opportunity to make a small sketch of the dryer (made by a friend), and tell you that the fruits and vegetables that are dried in are excellent! If you have the opportunity to make one, put fruits and vegetables (apples, bananas, tomatoes) cut in thin slices and leave them for 1 day or 2 according to the sun to have good dried fruit.

One last little question: where would you ask the small fan to have optimal air circulation in the dryer?
- air inlet before "solar radiator"
- between the "solar heater" and the drying box
- at the outlet of the drying box

[izentrop]

Hello,
Indeed it is obvious that this is a series engine on the first picture. ... it made me a review

The yellow wire must give the information "speed" to the computer to regulate the cooling of its circuits according to a temperature sensor. So connect between black and red.

A PC fan starts at 3 - 4 Volt, actually higher in voltage if the bearings are worn or dirty.

For the air to brew the whole volume, I would close the air outlets and make a hole on the top of the box to fix the fan. This is the natural sense of natural convection.