Fans in barn

Nita
Nita Registered Users Posts: 6
I am very new to all of this, so pardon my lack of knowledge. I have never used anything solar besides a motion activated solar light. I am trying to find information on running two box fans on a marine battery in my barn. I want to hook up a solar panel to recharge the marine batteries.
My main question is, if I run the fans on a 300 or 400 watt inverter, can I leave the inverter running 24/7 for days, even months, at a time? Will an inexpensive inverter work, or would I need a marine inverter. It's outdoors, but will be under a roof. Exposed to lots of humidity, but not direct rain.
It's ok if the batteries drain down at night. I don't need the fans so much after dark. But, if the inverter's low voltage alarm goes off, it would just keep running. Will that alarm go off by itself when the batteries charge back up?
Also, I've searched for large 12 volt fans so I won't have to run an inverter. But, I can't seem to find any that are large enough. Any suggestions there would be appreciated.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Fans in barn

    Welcome to the forum.

    The first question is: How much power do the fans draw?
    This can be measured with a Kill-A-Watt meter and should be done. No sense guessing or trying to go by manufacturer's spec's on the fans. There are two numbers you need: the running Watts, and the Watt hours which is the total amount of energy consumed over a period of time (usually 24 hours).

    The second question is: Why do you want to do this?
    Unless there is no utility power available at the barn there is no point in trying to run the fans from solar.

    That said, it is unlikely a marine battery will be suitable for this. Despite claims they really do not work well for repeated deep discharge/recharge over time. Typically one will have about 90 Amp hours capacity, and be able to supply approximately 500 Watt hours run time. With a fan drawing 50 Watts that's 10 hours of use.

    As for the inverter, since they are motors they would 'prefer' to run on pure sine not the MSW waveform of the cheaper inverters. Depending on how much they actually draw (running Watts) they may not require a large, expensive inverter at all.

    You don't want to get into a situation where the low Voltage alarm goes off. That means the batteries have been drawn down too far, and will severely affect their lifespan if this is repeated. Most inverters have a very low LVD - around 10.5 Volts for 12 Volt units - and it is really too low to be safe for the batteries. Once the inverter is shut down it usually has to be restarted manually (depends on the inverter though).

    How were you planning on recharging the batteries? That is a whole 'nother subject - and expense.

    You probably can't find any 12 Volt fans of the size you need because the volume of air you want to move requires significant power, and it simply can't be had in a low Voltage fan.

    I hope this has answered at least some of your questions.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fans in barn

    Kill-a-Watt meter link... There are many brands out there today--You can find them in the local hardware store--And somebody here said their library would check them out too.

    It may make sense if you need the fans to only run when the sun is up--Using a DC fan directly connected to solar panels can be an OK solution.

    As soon as you go with batteries, the entire system power cost can easily be 4x as expensive (and batteries can be "killed" if over discharged, will need replacement every 3-7 years, etc.).

    If this is just general ventilation--adding more vent area will usually work just as well as adding solar powered fans (most solar powered fans are pretty small--In the 25 range vs the 250+ watt range for AC vent fans--and they move about 1/10th the amount of air too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Nita
    Nita Registered Users Posts: 6
    Re: Fans in barn

    I was guessing at 90 watts each for two fans. I want to replace the dollar store box fans I have right now with a couple of metal wall mount agriculture fans from tractor supply.
    I have the fans for my horses. There is no electricity in the barn and I'm currently running about 200 feet of extension cord out there (I know it's bad in so many ways... please don't flame me, folks, lol).
    I was planning on recharging the batteries with solar panels. There is a reasonably priced 18 watt battery charging kit I was looking at. I know I will have to go with a fairly large battery to do what I'm considering.
    Thanks for your help!
  • Nita
    Nita Registered Users Posts: 6
    Re: Fans in barn

    I thought about hooking the fans directly to the solar panel. However, I would like for the fans to run most of the night as they help keep flies and mosquitoes away. They are a major problem here. So, I wouldn't mind if the fans didn't work all night. I would like them for part of the night, if possible.
    I'm expecting it to be somewhat expensive. So, cost isn't a huge factor. I don't want to exceed the cost of having electricity run to my barn, but I know it won't be cheap. Also, I like the solar option because I can still run the fans during weather related power outages (that has happened for days and weeks at a time here.) the barn does have plenty of ventilation. I just need to move the air so the horses aren't standing there sweating, withy the flies bothering them.

    Am I expecting too much? Would I be better off just having electricity run out there??
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Fans in barn

    I have to say that running a permanent 200' AC line is going to be cheaper than rigging up a solar install even for that small power need.

    If you wanted to run 90 Watts for 24 hours that's over 2kW hours. You're looking at 360+ Amp hours @ 12 Volts, and 600+ Watts of array to recharge it.

    That vs. 200' of 12 AWG and conduit to put it in.

    If you try to go to "ag fans" you'll see they draw even more; usually 1/4 HP motor pulling 200 Watts each (depending on exact design and loading). Yes, I've had experience with them. That would need even more power.
  • Nita
    Nita Registered Users Posts: 6
    Re: Fans in barn

    Well, I gotta say, it makes me a little sad to give up on my dreams of a solar barn. :(
    I was looking forward to doing it myself a little at a time. With cash. I hate to pay an electrician to do all of that.
    I might still try putting up panels direct to fans for now.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Fans in barn

    There is no reason not to run the electric line to the barn your self. It's pretty simple stuff, If your loads won't be more than 600watts, you might even just bury a line(use wire designed for direct bury, or conduit) and hard wire it into an existing outlet. You might put a notice of some sort on the outlets in the barn.

    Be sure to run heavy line 10 gauge would be nice and likely would be fine for 15 amps even over that distance, if you wanted to add a breaker (though I'm no electrician)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Fans in barn
    Photowhit wrote: »
    There is no reason not to run the electric line to the barn your self.

    I agree. You just dig an 18 inch trench and bury the cable. Direct burial cable will probably be more expensive than two wires in a conduit, but it's much easier to install. For 300-500W fan you only need #14 wire.

    I have a big fan in 720 sf barn - 1500W. Works really well. I'm not sure 300W would be sufficient. For 1500W fan you would need #8 wire.
  • Nita
    Nita Registered Users Posts: 6
    Re: Fans in barn

    Only problem is, any way I go with it, I'd have to cut across a concrete driveway to bury the lines. And, I think a larger breaker box. Plus, I still won't have any power during power outages.
    I was sooo hoping for another option.
    I could come across the back of the neighbor's place with a new line and a new meter. That would actually be the easiest thing as there is already a line back there. I'm sure I need someone licensed to wire it in that case. Or at least a licensed inspection.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fans in barn

    There are various ways to go under a driveway--How far and what kind of soil?

    This Bullet Mole system looks interesting for a pure mechanical system (rod+sledge hammer) (don't know anything about product or vendor).

    In our area, a second meter would probably be a nightmare of permiting and excessive costs by the utility (cost for the drop). And in some areas, the fixed/billing fees are not cheap anymore.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Nita
    Nita Registered Users Posts: 6
    Re: Fans in barn

    Thanks for the video. Interesting little tool! We are going to install an electric gate opener. I will look for one of those tools for that project. (Smaller part of the driveway, so only going about 8-10 ft. on that one.)
    The driveway is about 25 feet wide. And I'm in southeast Louisiana, so our soil is rock free. There is no more room in the breaker box I have now. I had kinda ruled that out. It just seemed like it was going to be so much more trouble than just putting a stand alone system like solar/batteries in the barn. I will have to mull over the electric option. Right now, during power outages, we run the house on a portable generator anyways. I really need to invest in a whole house generator.
    I wanted to go solar in the house, but there were obstacles there as well. I just thought this little project would be a nice way to get a glimpse at the whole solar thing. I was really looking forward to setting it up.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fans in barn

    For solar to work well... You really need to identify what you need to power for weeks-months or more.

    For example:
    • 1 kWh per day (30 kwH per month)--Enough for lights, laptop computer, shallow well pump/pressurize home plumbing from cistern.
    • 3.3 kWh per day (100 kWH per month)--Add running a full size energy star refrigerator, washing machine, in well pump (near normal electric home if operated very efficiently)
    • 10 kWH per day (300 kWH per month)--A pretty efficient standard home with natural gas for most cooking/hot water
    • 33 kWH per day (1,000 kWH per month)--Full home power for most everything outside of A/C, electric hot water.

    A 3.3 kWH per day home would require (very roughly) a 1,600 watt array and a 650 AH @ 24 volt battery bank and a ~2,400 watt AC inverter...

    This is a lot to "power" a couple of barn fans:
    • 2x 250 watt fans * 24 hours per day = 12,000 WH = 12 kWH per day for too "ag fans" running 24x7

    Power use is a highly personal set of choices--I am trying to give some very rough ideas of what you are looking at and how to justify a system and power usage.

    Very roughly, off grid solar power costs ~10x what utility power costs. So, if you want/need off grid power, look at what you want to power and see if it is "worth" $1-$2+ per kWH to run those guys (yes, some folks here are getting below $1 per kWH for solar power--But this is a good starting point for estimating your needs).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset