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Discussion Starter #1 (Edited)
I have a 30w, 12v solar panel that feeds into a 12v regulator (just makes sure the fans get 12v) that powers a couple fans that are literally the $20 12v cigarette lighter fans you get at the auto parts store. I want the fans to run only when the sun is out, but not run when dark/rainy/cloudy so no battery in the system.

In the morning and evenings when there isn't enough sunlight the fans don't spin but make a buzzing sound... late morning the fans spin at really low speed, as the sunlight comes they increase in speed until at some point they kick into full gear... then slow down as the sun goes away to the point they buzz and eventually when dark stop buzzing.

Is this going to damage the fans? Thanks
 

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It probably will damage them. You need to change your system up.

You need to add a "Low Battery Cutoff" circuit in beteen charge controller and fan. Really it would help to have a modest size battery in between those two things, wouldn't need much, a stack of 9 NiMH AA cells would suffice. The battery isn't there to really be used, just to add some capacitance so the charge controller and battery cutoff can work as designed.

You're not supposed to hotshot loads straight off the solar panel if they're not made to work on a variety of voltages. Because yeah, solar panels will create a huge variety of voltages under different conditions.
 

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Njuneer
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You will have to get educated on solar. One of the issues you have is trying to run a load directly off the panel, and your panel is only 12V.

What I would do is get another panel with a higher voltage, then a small charge controller in which most have a "load out", then a small SLA battery. The battery will stabilize the load, and you can then program the controller for a low voltage cutout.

Basically 2 of your panels, 60w/24V (in series), then a charge controller that outputs nominal 12V, set it to 13.8V max charge voltage, and cut out at 12.5V. This should stop output to the load as it detects a low battery condition.

If you want to keep trying on a shoe string budget, you can "try" to use an IR diode as a light indicator that would switch a small reed relay to on when the sun is up.

A solar panel is NOT a good setup without electronics between the panel and load because the load will pull the voltage down on the solar panel. Every solar panel has an "optimal operating voltage" called the Vmp or voltage at max power. If you drive the solar panel voltage lower, the power drops like a brick.

Tech today uses MPP (maximum power point) tracking which means it will find the voltage that extracts the max power from the panel. For instance, I have a small setup that I run at 68V from the panels, and that charges batteries at 13.8V.
 

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Discussion Starter #4
Thank you, I have tried to understand solar panels and spent over 30 hours. I'm trying to do this on a shoe string because it's only to power fans of a fun kiln project I don't want to go overboard. I do have a 12v regulator in the system that takes 8-40v and outputs a steady 12v but it sounds like when the voltage drops below 8v it just sends whatever voltage it can to the fans.

Reading both your posts, what I gathered is that because I don't have a low voltage cutoff my 12v regulator is sending less than 12v when the sun drops. I should have a low voltage cutoff, HOWEVER from what I read from Viper the problem I will likely have with adding one is that when I have enough voltage and the fans kick on it's going to drop the voltage and trigger the low voltage to kick off the fans... which will raise the voltage and trigger the thing to turn on the fans, which will lower the voltage and trigger it to turn off the fans, am I correct? So I can't do this without a battery pack. To fulfill my goal of having it run only when the sun is out, a small battery pack would be best because it will quickly deplete when the sun goes down and likely quickly charge when the sun comes up. So, a low voltage cutoff and a battery with low aH? Thanks
 

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Njuneer
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You got it! It would be helpful to know what the voltage is when your panel is powering the fans.
Don't discount my mention of a photoswitch. I think the easiest for you is to grab one for low voltage lighting ! A big box store. You can kind of tune when it works and such by shielding it. Some even have sensitivity adjustment!

Basically you wire it in series between your panel and fans. They have a relay in them. So no sun, no flow. This is NOT the right way to do this, but it is the cheapest/easiest way I can think of and I know it will work.
 

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Discussion Starter #6
Thank you! I didn't originally like the photoswitch idea originally because I didn't think they were adjustible, kicking myself for not thinking of something as simple as shielding it.

I'm going with the photoswitch, I found one that has both Normally Open and Normally closed outputs so I can have it go on when it detects light.
 

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Njuneer
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Just remember that you may not have enough power at sun up//down and may need to shield so it only kicks on when you have reasonably good sun.
 

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You're correct that the low voltage cutoff would tend to "hunt". That's because there's no battery.

Also keep in mind the motor's "Locked Rotor Amperage". This is the current it draws when the fan is starting up (going from zero RPM to any speed). LRA is quite a lot larger than running current. Which means, if there isn't a battery present, the fan may not be able to start, even if there was enough solar energy to keep it running if it was already going.

The battery takes care of that.

Since you're regularly going to deplete the battery, I'd recommend you use a low AH battery type that lends itself to that. Lead-acids will quickly be destroyed if they're depleted everyday - that's right, a lead-acid cannot perform the basic function that a battery is expected to do.

NiMH batteries will handle deep discharge pretty well, and a stack of 10 AA will be a voltage that will work with solar charge controllers tuned for lead-acid. I do just that with a 10-stack of NiCd wet cells, and they don't boil off water, which they would if they were being overcharged. Or possibly a stack of four 18650 lithium batterie, or three with a protection circuit.
 

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Njuneer
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You're correct that the low voltage cutoff would tend to "hunt". That's because there's no battery.

Also keep in mind the motor's "Locked Rotor Amperage". This is the current it draws when the fan is starting up (going from zero RPM to any speed). LRA is quite a lot larger than running current. Which means, if there isn't a battery present, the fan may not be able to start, even if there was enough solar energy to keep it running if it was already going.

The battery takes care of that.

Since you're regularly going to deplete the battery, I'd recommend you use a low AH battery type that lends itself to that. Lead-acids will quickly be destroyed if they're depleted everyday - that's right, a lead-acid cannot perform the basic function that a battery is expected to do.

NiMH batteries will handle deep discharge pretty well, and a stack of 10 AA will be a voltage that will work with solar charge controllers tuned for lead-acid. I do just that with a 10-stack of NiCd wet cells, and they don't boil off water, which they would if they were being overcharged. Or possibly a stack of four 18650 lithium batterie, or three with a protection circuit.
What I proposed does not need a battery to operate. As well inrush and LRA of DC brushed motors should not present any significant challenges here. Inrush only becomes a factor when slamming a motor across the line at full voltage.

I proposed an SLA battery because they are 12V nominal, and I certainly mentioned about disconnection before depletion. An 18650 would certainly die the same premature death if taken to the absolutely bottom. an SLA battery will not boil if held at optimal voltage. Damage will occur just the same for any chemistry you mentioned. I am not really a fan of SLA, just that they are cheap and easier for people to understand, even though they are not even 12V...lol

While I do agree that a battery system could help optimize the system, the OP has indicated this is device is a spandex tight budget so I just threw him what it would take to get it to turn on and off with the sun. Having absolutely nothing to go on like specs on the fans, what were are even doing, I won't waste the time to push further.
 

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Discussion Starter #10 (Edited)
Well, I got the photoswitch that has both a normally open and normally closed... and it didn't work for the simple reason it always allows power to the fans even when not plugged in. So, when unplugged, dark or not much sunlight to run the photoswitch its default state lets the low volts through and the fans buzz. When it gets enough voltage to work correctly it will then shut off the fans, but at that point there's enough sunlight for the fans to run. Now, if it worked the other way... and didn't provide power to the fans even when unplugged and only switched on when it had enough power AND the light sensor told it to I'd be in good shape! I then fried it when it got dark so I brought it inside to play/test and connected it to my battery backwards... it was only $7. It seems important that you know my setup, I have an Newpowa 30W solar panel to a 8-40v to 12V dc regulator that runs these 2 fans in my kiln for circulation and this little fan exhausts the hot moisture rich air in my kiln. Know of a photoswitch that works the way I need? Almost all of them I came across only worked at night, I thought this one good because it has NC and NO outputs but as mentioned the issue is that it needed power to open the circuit so when not enough power or dark it was closed allowing power to fans and buzzing, when it got enough power from the solar panels to open the circuit that was when there was enough sunlight to have the fans run. Thanks
 

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Njuneer
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I just cannot understand your logic or thinking. One of the very first requirements is the LOAD! Saying "2 fans" tells me nothing. As well, I cannot not do all your homework here, but I have provided a path that WILL work with the right gear. This is one reason my first mention was a simple diode and reed relay, because those are less than a buck, total, and they would work! It can become a crapshoot figuring out who makes what. I would operate the reed at 3-5V, ensuring there is easily enough voltage from a 12V source. These are things that are harder to do at Home Depot.

Use batteries and a light source to test.
 

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Sounds like you wired up the photocell wrong, and had the fans connected to the NC terminal.
 
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