Simple Solar Fan System

AK1

Joined Oct 22, 2015
13
I want to wire two fans in parallel with this simple solar scheme. I've filled in some of the blanks, but I'm confused on what to calculate to make sure it will work... I'm making a bicycle camper. I've already got that drawn up and it should weigh around 50lbs. If anyone could suggest a cheap small/light battery that would work good with this setup, that would be appreciated too.

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Lestraveled

Joined May 19, 2014
1,946
How long do you want your fans to run? Will they power anything else??

AK1

Joined Oct 22, 2015
13
How long do you want your fans to run? Will they power anything else??
I live in FL and plan to take the camper on overnight trips, possible 2-3 nights. During the hotter months (so practically all year) the fans are an integral part of my plan. The power controller I'm looking at is on Banggood and I'd probably use it to plug my phone in, too. http://www.banggood.com/10A-12V-24V-LCD-Automatic-USB-Controller-Battery-Charge-Solar-Panel-Auto-Switch-p-1014032.html

The battery will prob have to be a decent one.

I'm also going to wire in 4-6 small LED's for lighting, but I think I'm going to just use a 9v battery for that.

What kind of run times am I looking at/how to calculate?

Lestraveled

Joined May 19, 2014
1,946
OK, pretty easy.
If I read your data right, each fan draws .25 Amps times two for .5 amps total. If you got a 1 amp hour (AH) battery then they would run for two hours. So this is a pretty easy way to determine how big your battery needs to be. (How long do you need them to run between charging the battery. This will set the minimum size of the battery.)

What do you think?

AK1

Joined Oct 22, 2015
13
OK, pretty easy.
If I read your data right, each fan draws .25 Amps times two for .5 amps total. If you got a 1 amp hour (AH) battery then they would run for two hours. So this is a pretty easy way to determine how big your battery needs to be. (How long do you need them to run between charging the battery. This will set the minimum size of the battery.)

What do you think?
Excellent, looks like a 4AH battery is <4lbs. Id happily pedal that to run a fan all night! Thanks, now with such a small solar panel how long will it take to charge that battery?

Lestraveled

Joined May 19, 2014
1,946
OK, again simple (Not really)
Under Ideal conditions, a cloudless sky, no obstructions, panel pointed at the sun always.

4AH divided by .42 amps equals 9.5 hours. Practically speaking it ain't going to happen. You solar panel is way too small.

First, you only get about 7 hours of 100% sunlight a day. A single shadow falls across your panel and the output drops to 10-20%. Triple your panel power and it might work.

Suggestion - do you really need 6 watts of fans. Look for high efficiency fans. If you can drop the power requirement in half, you can cut the battery and the panel size in half.

Alec_t

Joined Sep 17, 2013
10,609
When calculating battery capacity you should allow a generous margin, since running a battery completely flat will kill it quickly.

AK1

Joined Oct 22, 2015
13
OK, again simple (Not really)
Under Ideal conditions, a cloudless sky, no obstructions, panel pointed at the sun always.

4AH divided by .42 amps equals 9.5 hours. Practically speaking it ain't going to happen. You solar panel is way too small.

First, you only get about 7 hours of 100% sunlight a day. A single shadow falls across your panel and the output drops to 10-20%. Triple your panel power and it might work.

Suggestion - do you really need 6 watts of fans. Look for high efficiency fans. If you can drop the power requirement in half, you can cut the battery and the panel size in half.

Lestraveled

Joined May 19, 2014
1,946
@AK1
When you are looking for fans you should keep in mind a few things.

I went on DigiKey and looked up 3Watt, 12 volt fans. They had one. It ran at 13000 rpm and had a noise rating of 57.3 dBa. This is a screamer and will keep you up all night. Plus it only moved 18 CFM of air.

A different search found a 1.7 watt, 12 V fan that ran at 3200 RPM and only produced 33dBa of noise. Plus it moved 41 CFM of air. Over twice as much as the screamer at about half the power. Plus it is a lot quieter.

Look at CFM, noise and power consumption.

AK1

Joined Oct 22, 2015
13
@AK1
When you are looking for fans you should keep in mind a few things.

I went on DigiKey and looked up 3Watt, 12 volt fans. They had one. It ran at 13000 rpm and had a noise rating of 57.3 dBa. This is a screamer and will keep you up all night. Plus it only moved 18 CFM of air.

A different search found a 1.7 watt, 12 V fan that ran at 3200 RPM and only produced 33dBa of noise. Plus it moved 41 CFM of air. Over twice as much as the screamer at about half the power. Plus it is a lot quieter.

Look at CFM, noise and power consumption.
Wow great site and nice search features. I was familiar with the CFM ratings; good added point on the noise level.

Lestraveled

Joined May 19, 2014
1,946
Wow great site and nice search features. I was familiar with the CFM ratings; good added point on the noise level.
DigiKey is a great company but you pay full retail. Shopping on EBay and Amazon will save you bunches.