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Will 100w Solar Panel Direct-Wired Run an 80w Cooling Fan "OK"?

farmhand

farmhand

Solar Enthusiast
Joined
Aug 26, 2022
Messages
232
Want to mount a 14" 80w radiator fan for a roof-vent in the pole building. Will a simple 100w panel direct-wire run this ok? Seems tight on the numbers but don't want to buy another panel.....

This is just to help vent the pole building when the sun is killing it.

-Thanks
 
JJJJ said:
There are dc vent fans that may be helpful
Click to expand...
Well I had a new dome vent frame from years back, 14.5" hole and had everything but the motor (client needed a motor). So got that installed. Looking towards a DC radiator cooling fan as it's cheap.
 
Rednecktek said:
Should work OK. Probably won't run full tilt most of the time but it'll move air.
Click to expand...
Cool,
I'm still slightly confused on putting a dead short on a panel. I assume the 80w motor would basically be a dead short when the panel isn't 100% sun.... but then the panel is a little higher on the voltage.... hmmm....

Think I'll order it and do a ground test before installing.
 
I mounted a couple of the same fans you mention in my battery room ceiling. When I first got the fans I was playing around with wiring methods. I was using a 65 watt 12 volt solar panel. When I direct wired a single 80 watt rated fan to the 65 watt panel, in full sun, the fan was spinning so fast it seemed like it wouldn't last more than a few minutes before it self destructed. Scary fast. I then connected BOTH fans to the single panel and found they were running plenty fast but not dangerously fast.
I have had the fans mounted now for 8 years and ended up replacing one last year . I love the simplicity of the hard wired setup. The speed self regulates, spinning quite fast when the sun is high in the sky, slows down when clouds float over the sun as well as early and late in the day. Basically the more I need the fan, the faster it spins.
 
farmhand said:
Cool,
I'm still slightly confused on putting a dead short on a panel. I assume the 80w motor would basically be a dead short when the panel isn't 100% sun.... but then the panel is a little higher on the voltage.... hmmm....

Think I'll order it and do a ground test before installing.
Click to expand...
Nope, a short is a connection with 0 resistance letting the power flow as fast and as hard as it can. The motor is the exact opposite of a short by being a load. It's up to the panel to provide enough voltage and current to overcome the resistance of the fan blades and motor windings to actually start turning. You'll be fine.
 
littleharbor2 said:
I mounted a couple of the same fans you mention in my battery room ceiling. When I first got the fans I was playing around with wiring methods. I was using a 65 watt 12 volt solar panel. When I direct wired a single 80 watt rated fan to the 65 watt panel, in full sun, the fan was spinning so fast it seemed like it wouldn't last more than a few minutes before it self destructed. Scary fast. I then connected BOTH fans to the single panel and found they were running plenty fast but not dangerously fast.
I have had the fans mounted now for 8 years and ended up replacing one last year . I love the simplicity of the hard wired setup. The speed self regulates, spinning quite fast when the sun is high in the sky, slows down when clouds float over the sun as well as early and late in the day. Basically the more I need the fan, the faster it spins.
Click to expand...
Having the spare parts, here's what I ended up doing: Mounted the 100w panel, mounted an old breaker panel to house a MPPT, a might-mule 7ah sealed battery, a 10A panel breaker, and estop, and the fan. I have the very cheap controller set to shut off at 11.2v, and auto load-on at 12.6.
-This way I'm not feeding 18v to the fan, and it's properly fused. Not quite finished with the control box but hey, it works for now. That radiator fan puts out a TON of air!
 

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farmhand said:
Having the spare parts, here's what I ended up doing: Mounted the 100w panel, mounted an old breaker panel to house a MPPT, a might-mule 7ah sealed battery, a 10A panel breaker, and estop, and the fan. I have the very cheap controller set to shut off at 11.2v, and auto load-on at 12.6.
-This way I'm not feeding 18v to the fan, and it's properly fused. Not quite finished with the control box but hey, it works for now. That radiator fan puts out a TON of air!
Click to expand...
Thats another way to go. I prefer the ultra simple hardwired straight to the panel method. As I mentioned my fans have been running for about 8 years. Eventually replaced one but only after 7ish years. Apparently, the higher voltage has no ill effect on them.
By the way anything below 12.2 volts on a daily basis is going to ruin your battery in short order
 
True, but the cheap amazon controller only opts for cutoff between 10.2-11.3!!! What the hell?
 
It'll work just fine if the fan motor runs variable speed according to DC voltage, and it doesn't have a controller that gives up with slow power rise.
I checked out a few fans at a surplus store by connecting to variable supply and gradually turning up. Some trembled and shut off, others ramped up and ran.

I used some Papst fans on top of inverter heatsinks for a while, but wet weather got to them. I have a larger 48V fan meant for a rack mounted in gable vent. It is fed by two "12V" panels in series. Works well.
 
I just got a 12V 80W radiator fan and small 100W panel that to play with and it is running great. I plan to use it in my attic this summer, I will get PWM dc the motor speed control next.
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Last edited:
Another way to control fan speed is to put Duct Tape on a small portion of the solar panel. :)
 
SO an update on our fan:
After a month the mighty-mule battery died, leaving the fan quite erratic with the controller giving .5second bursts of load-on. Even though I disagreed with a direct connection, I bypassed the setup leaving only the 10amp inline fuse (kinda pointless with a 5.5a panel). However, for 6weeks now the fan works flawless and a LOT more run time than with the small battery setup. So yes, direct connection seems to be the way to go.
 
You will probably never see more than 80 watts electrical output from a 100 watt rated solar panel anyway.
Solar panel power is rated at 1Kw per square meter solar irradiation in a test laboratory.

Most geographic locations around the world never reach even 80% of that, and some places much less, even in a clear blue sky.

Its a constant theme on the Solar Forums.
People constantly asking why they can never see more than 220 to 240 watts from their brand new 300 watt panel.
 
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