# Solar Panel Setup to Operate a Box Fan?



## How Do I

Can anyone tell me _what size solar panel_ it would take to operate a box fan? Would you just need an inverter, solar panel and then the box fan itself if you only wanted the box fan to run while the sun was shining? And I'm just thinking your run-of-the-mill box fan, nothing special. Oh, I guess I would need to know what size inverter too if that's what the setup would need. Any ideas on how you would do it personally would be helpful. Thanks.


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## justin_time

Well if I understand your question I think by box fan you mean muffin type fan, then I think I know what you mean as I plan to do something like that for the green house.
You could buy a 12 volt panel, say 120 watts , some maybe less, or find one more.

Then use a 12 to 24 volt DC fan. They dont care if the voltage goes from 12 to 24 vdc or more it will run fine the rpm will change as the voltage fluxtuates but thats no big deal. from memory they use roughly 33 watts so you should be able to run three directly off that 120 watt panel I suggested, with a little head room to spare.
no inverter or other costs. The ones I am thinking of are used in Miller xmt 304 inverter welders, and likely cost around 80 or so bucks from a welder repair place, but you can get them from electronic supply houses, google "New arc" and see what they have in their on line catalog, I bet they are 30 to 40 bucks. you can all so try surplus places as I once found some there for 7 bucks, and bought all I could carry. If you have trouble finding one I can allways get you a part number.

Now I have hooked these up direct to the panel, and used them the way I described, but I have not done so for months on end type of thing, so its possible over time this may be hard on the motor (I dont think so). I am thinking of as the sun is coming up and the panel voltage is just starting to rise, maybe just before the motor starts to get enough voltage to spool up, it could be drawing a little to much current.Just something, to be aware of if any fail soon. The solution to that would likely be adding a regulator (again from new arc) but I really dont think you will need one.


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## How Do I

I was trying to find more info on the watts and came across another thread on HT talking about a similar situation. Theoretically, (as is mentioned in that thread) if I have a fan that does run at 70 watts (which seems to be the range many are near) would I be able to run say a 100 watt panel (and how do you figure that?) and then....what size inverter / or how would you calculate what size inverter you need for a given electrical appliance run in this particular application? Meaning, I don't want someone telling me what the answer is for this application. I want someone to explain how to figure out the answer. The whole 'teach a man to fish' thing and all that. 


ETA - Yes, I should have said like for a green house, but I'd like to use a box fan, or if there is a 12 volt fan which would push the same amount or more air, that would do.

Oh and yeah, I think I see what you're saying about it initially coming on. I could use a timer on the fan to make sure the panel is in full sun before powering up first, right? Or maybe I'm not following you.


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## Jim-mi

I have a 16" box fan 12 vdc . . . . . . .
Those little muffin fans can NOT compare to the amount of air that my box fan can move..\
To run it panel direct it is best to put a LCB (linear currant boaster) between the PV and fan.
Backwoods Solar Still carrys them-- I think. 
A bit pricy (the fan) . . but they work very well . . .Ideal for a green house............


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## blooba

How Do I said:


> Oh and yeah, I think I see what you're saying about it initially coming on. I could use a timer on the fan to make sure the panel is in full sun before powering up first, right? Or maybe I'm not following you.


remember timers require electricity to keep time, you need a battery operated one or something if your not using a battery.


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## Jim-mi

Yes Backwoodsolar.com still carry's the 16" fan . . . . good stuff . . .gets the job done..


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## wy_white_wolf

How Do I said:


> I was trying to find more info on the watts and came across another thread on HT talking about a similar situation. Theoretically, (as is mentioned in that thread) if I have a fan that does run at 70 watts (which seems to be the range many are near) would I be able to run say a 100 watt panel (and how do you figure that?) and then....what size inverter / or how would you calculate what size inverter you need for a given electrical appliance run in this particular application? Meaning, I don't want someone telling me what the answer is for this application. I want someone to explain how to figure out the answer. The whole 'teach a man to fish' thing and all that.
> 
> 
> ETA - Yes, I should have said like for a green house, but I'd like to use a box fan, or if there is a 12 volt fan which would push the same amount or more air, that would do.
> 
> Oh and yeah, I think I see what you're saying about it initially coming on. I could use a timer on the fan to make sure the panel is in full sun before powering up first, right? Or maybe I'm not following you.


To run an 120V AC fan you will need a battery. It will not work trying to run an inverter without a battery to stablize the voltage and convert from a current source to a voltage source.

Some DC motors can be ran solar direct. Look for one that uses PM magnetics

WWW


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## justin_time

Forgot about this, but instead of a timer as such just a snap disk on/off for a preset temp so As the sun warms up the temp reaches your set point and spools up the fans .
You can also get adjustable mechanical temperature swithes, what ever works, I will be going with a few fans of the type as I described, as I trust nothing to last forever,and if you depend on a single fan it will fail when you need it most, and there goes your crop.


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## Jim-mi

The type box fan I am thinking about--- 12 / 24vdc--- is far and away higher quality than a dollar store piece of junk..
It would have a long dependable service life......


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## justin_time

Well my memory must be going the way of my hair as I have been using two of these for stove (fireplace) blower motors for years. I could have just looked over and gave you the part number with my first post.
It is TYP 6424 /2h and when I googled it up came stock at supluscenter for the price of 16.99 and they are 26 watts, I remembered the wattage wrong. So off that same 120 watt panel I used as a example you could run four of these no problem at all, wired in parallel Now in my case if I did that, as my green house is 12x8x8 or 800cuft Each fan at rated output moves 282 cuft of air. So if I put two for air input down low, and two up high to help move air out, I expect (using 200cuft est for each of the fans, just being conservative) I expect to be able to do a complete change of air every 2 minutes or so, as 400 cuft of air should be being pushed through. I think this will be enough.... somebody who knows should check my estimate just in case I have goofed.
So 68.00 dollars in fans, and the cost of a panel should do it for a greenhouse the size of mine. You havent said how big yours is?


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## Jim-mi

Are those 26 watt fans AC . . .??

Your last post makes me think you are confused about AD and DC


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## wy_white_wolf

justin_time said:


> Well ...It is TYP 6424 /2h and when I googled it up came stock at supluscenter for the price of 16.99 and they are 26 watts, I remembered the wattage wrong. So off that same 120 watt panel I used as a example you could run four of these no problem at all,...


No. Running solar direct you need to pay more attention to the IMP, VOC and VMP. 



> ...Papst 12-28 VDC axial fan, p/n TYP 6424/2H. Ball bearings, metal housing w/plastic impellor. Specs: flow 282 CFM max, # Voltage (rated) 24 VDC, useable on 12-28 VDC, amperage 1.1 Amps, power 26 Watts, noise 63 dB. Mount 4 thru-holes, blade dia. 5-5/8", number of blades: 7, overall size 6-3/4" x 5-7/8" ...


Voltage range of 12-28VDC - You want a solar panel with as close to a VOC of 28V as possilble *without going over* and a Vmp of at least the midpoint of the range. (12+28)/2=20VMP. You do need to check and see if the given numbers are nomial or working. If they are nominal you need to get the working numbers.

You need the panel to supply at least 25% more IMP than the load or get a LCB (linear Current Booster). 1.1Amps * 1.25 = 1.37Amps per fan.

WWW


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## Gray Wolf

If you are running direct and live in an area with snow, solar panels can go over their rating as they work best in colder temps and the reflection off the snow. We get about 10 amps over rating with snow and below freezing. Don't know if you would need a charge controller of some sort?


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## justin_time

wy_white_wolf said:


> No. Running solar direct you need to pay more attention to the IMP, VOC and VMP.
> 
> 
> 
> Voltage range of 12-28VDC - You want a solar panel with as close to a VOC of 28V as possilble *without going over* and a Vmp of at least the midpoint of the range. (12+28)/2=20VMP. You do need to check and see if the given numbers are nomial or working. If they are nominal you need to get the working numbers.
> 
> You need the panel to supply at least 25% more IMP than the load or get a LCB (linear Current Booster). 1.1Amps * 1.25 = 1.37Amps per fan.
> 
> WWW


Being able to do the math is one thing, being able to understand it is another. I am fully conversant on IMP, VOC, and VMP. I can select a sharp, BP, siemens,Canadian solar, Sunbee, or many others to do this with.
I stand by what I suggested. I will double down at this point and say what I suggest will work perfect.... no ifs ands or buts, I dont know if you were just in a hurry, or maybe you dont understand the nature of how this will work, and by your definition of Needed IMP of greater than 25%, hell I have 100% or nearly so, Dont rush think about it.... A linear current booster is not needed, but no harm in adding one if you wish, as I said in another post only thing I would add is a thermal snap switch to make sure the sun is out and warming things up. You have used accurate data but made some faulty assumptions...Or so I think, ultimatly if we still dissagree I can just go ahead and hook them up to prove myself correct...or you.
I admit I have not driven four of these fans with a 120 watt panel but have two and know they will do two more...
I think you were in a hurry, ironically so am I its after midnight, and I am typing fast as I have to get to bed

Ps, I am not stating were I think your error is in this post as I suspect you would like the chance to find it yourself, as I would.


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## Jim-mi

There is quite a big difference between a 'box' fan as mentioned in the OP and your 'muffin' fans which are intended to cool electronics......
Using muffin fans for a green house, you will lose a crop, because a muffin fan is incapable of moving enough air..............

Show me a picture of a real green house using those pip-squeak muffin fans for circulation . ?!?! .


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## justin_time

Ok, First I dont know where you are getting your numbers for panels as they dont make since, and wanting my voltage ocv at 28 volts would mean I had a defective panel for charging 24volt batteries, or horribly inefficient for 12 volt charging. In other words they dont make them, Lets use real numbers from panels that are actually made.
Here is what you will find being produced for the 12 volt 120 watt panel I suggested, the ocv will be 21.5 the amperage 7.10 at a voltage of 16.9 You will find these voltages absolutly typical on all 12 volt panels (maybe I should say, all I have seen)
The amperage can be different depending on the wattage of the panel. so using these numbers....There is no way at all, not possible at all, for the fan to draw its rated wattage or current as these are speced at 24vdc and the panel cant even put that out! 
The wattage/ amperage is roughly linier with the applied voltage. The panel is far from ideal as perfect power supply, as load regulation is poor but its voltage wont(i think) begin collapsing until my amperage draw exceeds its rating of 7.1 now my fans can draw at max voltage according to the data sheet 1.1 amps So if I hit them with 24 volts (which I cant) the max draw would be 4.4 amps! I am barely over half the amperage the panel can put out, this tells me right there I wont be droping below 16.9 for a voltage to the fans. So my applied voltage to the fans will be from 16.9 to 21.5. I am going to quess 19 volts ( maybe 19.5 or so) will be where my four fans settle in for a running voltage. What will they draw for amps? well its a linier relationship so simple math tells us 19x1.1/24= .87 amps each, so four fans at .87 =3.48 amps. Less than half what the panel is capable of puting out . I have 100% more amperage available than I am using, thats why I say no booster needed. 4 fans one panel as described, and no problems...


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## 12vman

Kyocera KC120 120 Watt Solar Panel...


Electrical Characteristics..

Maximum Power: 120 watts
Maximum Power Voltage: 16.9 volts
Maximum Power Current: 7.10 amps
Open Circuit Voltage: 21.5 Voc
Short-circuit Current: 7.45 amps


This panel will never produce enough voltage to operate a 24 volt fan at full potential. _*Any*_ load added to this panel will quickly decrease the open circuit voltage towards the maximum power voltage level until the current level of the load reaches 7.10 amps. (During perfect conditions) Every panel has a maximum power voltage and it needs to be considered..

The current rating of the fan(s) is for 24 volts. Any voltage level below this is going to cause more resistance. (Load) *If a fan needs 1 amp to operate at its full potential at 24 volts, it will use 2 amps at 12 volts with much less output.* Increase the voltage to 16.9 volts, its going to use more current then it would normally at 24 volts with reduced output..


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## justin_time

12vman said:


> No....wrong... the beauty of dc motors is the relative ease of control, that is why they were used for decades when you wanted variable speed by voltage with out loss of torque. Only in the last 15 years or so have variable frequency drives aloud the same, and now greater control of AC motors.
> Guys I dont understand where you are getting this stuff? stuff like that motor will draw 2 amps at 12 vdc....no it wont. You actually said the motor is going to use more current at 16.9 volts than at 24 vdc? No it wont. I can plop any, any Dc motor, permanent magnet, or fieldwound motor on a bench, I have them them from fractional HP, 1/2 hp, 1 hp, 2hp, up to multi hp traction motors.To prove this.
> 
> I dont know where you are getting your theory, or if its mixed up with ac motor theory but I do know you have not done this, and measured the parameters of Current vs voltage, with a pm dc motor
> 
> Here is what will happen, lets say that dc motor is running at 24 volts dc. Now you can start backing the voltage down, at 14 volts the current will be way less than it was at 24 vdc, and the rpms will have changed. Thats what the motor is designed to do.
> If you have a treadmill you can confirm this for yourself, hook your meter up to measure the dc voltage to the motor, and another to measure the current, spoll the unit up to max and look at the values, drop the power down to where its just turning over, and look at the values....
> 
> I have doubled down once, and will again, what I have said is acurate, what I recommend will work, clearly I dont know why, but there is way different "theory", and practical experience than I have out there... In the intrest of acurate info being provided I wont post on the thread until someone with some initials after their name vets the electrical theory I gave, as if you dont buy what Im saying we are just cross talking for no purpose, and we can do that in the political threads:huh: I have better things to do.
> Any Electrical engineers on the board? chime in please....
> 
> just adding, the fan motors I suggested, used as described, will function electricaly as I stated. Im just scratching my head as to how we have such opposite idea's as to how this works. Maybe you have some kind of idea that the load is increasing while the rpms are being lowered by oltage control, but that is not the case.


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## justin_time

12voltman, You must be applying ac motor theory to your thinking on this, If we were talking ac motors and all parameters equal with the voltage being lowered from its name plate spec....current will rise... I could agree with you,in fact thats often why they burn up, lower terminal voltage will cause higher current, failure in brown out situations, motors run on long supply cords fail for this very reason, but we are taking DC.....


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## 12vman

"No....wrong... the beauty of dc motors is the relative ease of control, that is why they were used for decades when you wanted variable speed by voltage with out loss of torque."

Not true. A PWM driver controls current by length of pulse. Full voltage and current is always available via the PWM driver and the length of time the driver applies the power to the motor, which controls speed according to the amount of torque required. (Full voltage/current in pulses) Loss in voltage, loss in torque..


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## justin_time

12vman said:


> "No....wrong... the beauty of dc motors is the relative ease of control, that is why they were used for decades when you wanted variable speed by voltage with out loss of torque."
> 
> Not true. A PWM driver controls current by length of pulse. Full voltage and current is always available via the PWM driver and the length of time the driver applies the power to the motor, which controls speed according to the amount of torque required. (Full voltage/current in pulses) Loss in voltage, loss in torque..


 
Now why do you bring that in?, Though I can at least agree with you that PWM is another form of DC motor control, Newer to the game, and commonly used, but it has nothing at all to do with anything we have been discussing, doesnt change how I have described the caracteristics of a dc pm motor, and how it will function!!
Come on, there has to be a engineer on this board who can clarify this, one way or another....
I am more than happy to eat my words if I have missrepresented the functioning of a DC motor....
one thing I am wondering about by the way you and White wolf have expressed your thinking is that I am under the impression you both think that because the motor is rated at 26 watt, your thinking it must try and run at that power level? Its not so, that is only its maximum level, I can run it at any level I wish by applying whatever voltage I want, eg...12 volts dc would draw roughly .6 amps and the motor dissipating 7 watts. It will be runing fine. At 19 volts and with a draw of .87 amps, the wattage is 16.5. The motor does not care what voltage I feed it (has to be great enough to overcome rotor inertia though, and not greater than wire gauge can handle).


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## 12vman

I agree that you can operate a PM motor with any voltage below its designed voltage but how efficient will it be? Efficiency drops dramatically as the voltage drops..

How could you calculate air movement if the air flow is unknown? Fans are designed at a specific voltage with a known amount of air movement. Personally, I'll believe an engineer that designs these things before playing midnight baseball..

You're best bet is to supply the fans with a regulated voltage that the fans are designed for. Only then you can figure how much air movement you will have..


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## justin_time

12vman said:


> I agree that you can operate a PM motor with any voltage below its designed voltage but how efficient will it be? Efficiency drops dramatically as the voltage drops..
> 
> How could you calculate air movement if the air flow is unknown? Fans are designed at a specific voltage with a known amount of air movement. Personally, I'll believe an engineer that designs these things before playing midnight baseball..
> 
> You're best bet is to supply the fans with a regulated voltage that the fans are designed for. Only then you can figure how much air movement you will have..


 :shocked::grit::bdh::bdh::bored::walk:


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## Jim-mi

What an intelligent response............................NOT

This engineer can shoot many holes in all your incorrect posts.

But I will not because your mind was made up before you even posted.................

Your blinders are preventing you from seeing that there is more than a couple guys on here who are quite aware of whats going on...................


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