The SP & fan are well matched. In the cool of morning it doesn't matter much if fan turn on is delayed
turning on for another 2 hours but in evening, sun still up, every minute of run time is precious. Maybe in this post
we can just reverse AM & PM to keep everyone happy.

 

I, too, agree - there's a lack of information for us to form a good solution to the proposed problem. Here's what I'm taking away from the TS's posts: During mid day the fan runs just fine. As the sun is close to setting the fan slows down. A passing cloud could make the fan stop, and when the cloud has passed the fan should start but it doesn't without a push. In post #9 the TS states he's using an LVD to shut the fan off when voltage drops below a set point and reactivates when the voltage comes back high enough. I'm wondering if the LVD is where the issue is. We don't know anything about the circuit being used to detect low voltages. I'm wondering if just simply connecting the fan directly to the PV (Photo Voltaic) solar panel and not using the LVD would work. I don't know if low voltage would represent a problem to the fan - which also, we do not know anything more than it's a BLDC type.

At first I thought we were talking about a ceiling fan and wondered - aren't those AC? Didn't take long to figure out it's not a ceiling fan. However, I still don't know what kind of fan it is. So hopefully the TS can see the need for greater information to help us form a better solution.

I have a PV in my back yard, a 12 V 9 W panel connected directly to a dog bark device that emits a high frequency when dog barking is detected. It's connected to a buck converter to keep the voltage from going above 10 volts since the device operates normally from a 9 volt battery. During the day there's ample power to run it but at night it shuts off, allowing dogs to bark if there's good reason to do so. It took a couple weeks but the dogs finally learned not to bark so darn much. The device has been up for a year and a half and is still working.

Perhaps a buck/boost converter would be a viable option to making your fan work whenever there's sufficient sunlight. If the voltage rises enough the converter should be able to power up and boost the voltage sufficiently to kick start the fan. of course I'm just guessing here, my skill level is slightly above beginner in most areas, with a few areas a little more advanced but in no way competent to compete with the level of knowledge the senior members demonstrate. So maybe a buck/boost converter will do what you want and you can eliminate the LVD circuit.

 

Thankyou everyone for your valuable solutions.

Actually I assembled the circuit given by Bernard (minus the capacitor as I am yet to get the capacitor), It is working. i mean the Voltage Comparator & MOSFET are Switching/Toggling properly, with varying the Potentiometer & there are 2 different reference voltages under the 2 states. Thanks so much. I will soon get the Capacitor & complete the circuit.

Apologies if the information provided was not sufficient. Let me give in more information.

FAN: It is a Ceiling Fan. A Brushless DC(BLDC) Ceiling fan. It is same size as that of a normal AC Ceiling fan & delivers as much airflow as a normal AC fan, thanks to the BLDC Technology. It is very similar to this fan,
https://www.solarfan.in/product/sol...-24-watts-bldc-made-in-india-blade-size-48cm/

Solar Panel: See attached for specifications.

 

Thanks for the specs. Does your fan have the regulator? With the large difference between 12V & 19 V
you might consider adding a DC-DC buck converter ?

 

Brushless DC motors are very tolerant of a range of supply voltages, at least the ones that I am familiar with. And so yje speed will vary as the voltage changes, which is probably OK, since it would run the fasrest when the sun is brightest. But there is no SIMPLE way to have more power when there is less power from the solar panel in the evening. The clear choice is to save power when lots is available during the day, which can be done, but the effort is not simple. And since it is total power that declines, not just voltage, a step up converter will not help. A battery or an additional solar cell could help, but those are neither simple nor cheap.

 

FAN: It is a Ceiling Fan. A Brushless DC(BLDC) Ceiling fan. It is same size as that of a normal AC Ceiling fan & delivers as much airflow as a normal AC fan, thanks to the BLDC Technology. It is very similar to this fan,
Solar Panel: See attached for specifications.

I suspect that is possibly an 'out-runner' motor, similar to the popular RC BLDC motors, external rotor.
Max.

 

I threw this circuit together to solve the low light motor starting problem. It allows a cap. to charge to OC V of panel. C values varied from 5k uF to 22k uF depending on motor.View attachment 171703

A Couple of more queries

1. In the above circuit, C varies from 5000 uF to 22000 uF. If i do not get that high value Capacitors, will it do if we add smaller Capacitors (say 2000 uF) in parallel. since in parallel, the capacitance adds up. Will this work ?

2. I also plan to use a DC-DC Buck converter for Voltage Regulation. Since Output of a Solar Panel varies throughout the day, so to keep it fixed to 12V, i plan to use a Buck converter. When Solar Panel can supply greater power, then Voltage will be regulated at 12V. When Solar panel is giving less power, how does the Buck Convertor behave ? It is Ok for me, if under low power, it simply passes on, the Input from the panel to the load. (i.e. as good as the Buck Converter is not present & Load is directly connected to the Solar Panel). Does it behave this way ?
Is this a good idea for Voltage regulation or is there a better way.

Thanks.

 

Thanks for the specs. Does your fan have the regulator? With the large difference between 12V & 19 V
you might consider adding a DC-DC buck converter ?

Yes, I plan to use a DC-DC buck Converter Exclusively for voltage Regulation to 12 V. See the post above.
Also. there is a separate Speed Controller regulator, that comes with the fan as an optional addition.

 

You can add more caps. in parallel.
What FET are you using ?
As V input is listed 10 V to 19 V, , does not seem that buck converter adds much unless a steady air flow is desired.

 

So this is a "12V" solar panel ! "..... open circuit 22.05 V .... Max power voltage 19.25 V !!!

TS has been running a 12V fan on about 20V ! God bless the manufacturer for making the product so resilient !!...

From my experience we can expect the fan to stop turning at about 5V . At that voltage the sun is very low in the sky , you can't get blood out of a stone !!

No sun the fan won't turn, no mater what capacitors (within reason) or circuitry you add ... And clearly no need for a regulator ...

Leave everything as it is. The panel is perfectly matched to the fan !

 

Maybe there is a tall palm tree that blocks SP at 4 PM stalling the fan. Not enough power to restart the fan but a slight manual push or an electronic push will restart the fan as the sun reappears giving another hour of operation ?

 

Thanks !!! Yes i plan to use a slightly bigger solar panel 50W (existing one is 40W) for a little more power towards the evening.
So the Buck Convertor will be needed to limit the voltage at 12V during peak noon & also in general to maintain a uniform speed for large part of the day.

FET used is IRF9540

 

I think the best solution is to position the panel so it's aimed at the setting sun ... This way the fan will work well into the evening ...

Of course this will not give rotation in early morning ... but you don't really need a fan in early morning when it's still cool. Ambient temperature usually lags about 2 or 3 hrs behind the sun.

 

I think the best solution is to position the panel so it's aimed at the setting sun ... This way the fan will work well into the evening ...

Of course this will not give rotation in early morning ... but you don't really need a fan in early morning when it's still cool. Ambient temperature usually lags about 2 or 3 hrs behind the sun.

yes True. Fan is required only in Noon & a little past Noon.

 

Thanks !!! Yes i plan to use a slightly bigger solar panel 50W (existing one is 40W) for a little more power towards the evening.
So the Buck Convertor will be needed to limit the voltage at 12V during peak noon & also in general to maintain a uniform speed for large part of the day.

I tried using the DC-DC Buck Convertor for limiting the Max o/p Voltage to 12V, when the Sun is blazing. It works but has the following disadvantage.
1. It's self consume voltage is about 1.5V, so o/p voltage Max is 1.5V less than the i/p voltage. This can be disadvantage in the evening when o/p power of Solar Panel is already low.

Could anyone suggest of a simple Circuit, that clamps the Max voltage to the Motor to 12V.
Requirement is that this circuit must be safe (not getting excessively hot or having unsafe levels of current)
This circuit must not self consume any voltage, preferably.

i have come across some Circuits employing Zener Diodes to do the Upper voltage limiting, but not sure they are safe, because they Short Circuit the Solar panel current, when voltage rises above 12V.

Could anyone help.

 

This circuit must not self consume any voltage, preferably.

Then how will it clamp the voltage at 12V?

 

I made a short V clamp circuit but drawing will not scan.
SP, 3.5W, Vmp = 18 V, I mp = 190 mA, Voc = 20.7 V, I sc = 210 mA
SP shunted with N ch FET, 3055V. Z diode, 6.5 V cathode to + SP & drain, Zd anode to top of 5k pot, bottom to common & SP -, wiper to gate. Pot adjusted to 12 V SP output where it stays as long as there is enough sun. FET just warm. Sorry for confusion.

 

I tried using the DC-DC Buck Convertor for limiting the Max o/p Voltage to 12V, when the Sun is blazing. It works but has the following disadvantage...

I think you must be looking for something to do !! Why limit the voltage to 12V when the manufacturers say the fan can run at 19V !!!

This fan has obviously been designed to run on exactly the panel you have with nothing else ... this is a very common voltage for a panel (20 to 22V open circuit) , and the wattage is perfect too (40W max panel running a 20W fan ).

Start another project.

 

Thanks for the suggestions. I will try out.

 

N ch. FET needs to have power rating = to SP, with a heat sink to match.
What power the motor does not use is dissipated as heat so heat sink can get hot, maybe around 30 W mid day.