What type of battery to run this fan?

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Old 12-08-10, 03:52 PM
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Cool What type of battery to run this fan?

Hello!

I'm working on a project and confused as to how I would figure what size/type of battery would be appropriate. Any help would be appreciated!

The idea is this -

Solar panel used to trickle charge a battery during the day, battery used to power a fan for as long as possible at night. Ideally, I would be able to run the fan for up to 10 hours.

Here's a look at the manufacturer's information-


Thanks for your time!
 
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Old 12-08-10, 04:18 PM
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Battery

Batteries provide DC power and will not operate an AC appliance.
 
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Old 12-08-10, 04:21 PM
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I would be using an inverter, Ive seen these types of home-brew power systems work quite well, just not certain what components would be best. Thanks!
 
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Old 12-08-10, 05:08 PM
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21 watts at 12v is 1.75 amps. Figure an inverter efficiency of 80% at that current. The inverter/fan will draw 2.2 amps from the battery. Over ten hours that's 22 amp hours.

You will need a true deep cycle battery, and since they shouldn't regularly be discharged more than 80%, you'll need a minimum capacity of 27.5 amp hours.

But wait, there's more. A battery's amp hour capacity is typically given at a 20 hour discharge rate, you will be discharging the battery in ten hours, which batteries don't like. So you'll need another ten percent or so.

That means you need a 12 volt true deep cycle battery with a capacity of at least 31 amp hours (20 hour rate).

31 amp hours is quite small for a storage battery. You'll have no trouble finding one big enough. Just be sure it's a true deep cycle battery.
 
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Old 12-08-10, 05:34 PM
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Outstanding! Thanks for your help - have a great holiday season!
 
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Old 12-08-10, 08:26 PM
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The battery isn't the problem, the solar "trickle" charger is the problem. You need to replace the power used used by the fan and there is no way that you will be able to do that with a solar trickle charger. You would likely need a solar panel with an output of at least three times the draw of the fan (likely more) and you would have to have it pretty well aligned for maximum solar gain during the day. Since the sun shines only for part of the 24 day cycle you need to get as much power back into your battery as possible during those sunlight hours.

I had wanted to run my Internet connection, FiOS terminal and router, with solar-generated power but after I ran the numbers I deduced I would have to invest so much money in solar panels and batteries that it would take a minimum of ten years to just break even.
 
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