DC fan & Panel for small dehydrator project, suggestions.

Peterr

Making a solar dehydrator and will need a 5" fan, thought I go with a DC motor and small panel to run it for a aim and shoot project. Just about the right size project for me to get started with. Small budget, won't need any Fed & State incentives paper work, batteries, inverters, converters, and mother in laws.

Any suggestions on configuration and where to purchase such an item would be helpful. We will actually be in the east bay and Petaluma Ca. area this coming week, and would rather see and purchase the item directly, if possible and visit a candy store, rather than via the internet. Thanks for any help.

BB.

Re: DC fan & Panel for small dehydrator project, suggestions.

After you have visited our host in Flagstaff... NAWS is not far from you and would be a good place to purchase your solar panels--especially if you have reason to be up near Flagstaff (no shipping charges or AZ state sales taxes on solar panels--if I read their info correctly).

There is the Solar Living Institute / Real Goods in Hopland Ca. About 1 hour 10 minutes north of Petaluma.

The hold training classes and can be an interesting place to spend 1/2 a day.

Fan--I would try an old 12 volt or 24 volt DC computer fan (surplus store, old PC's/computers) and a solar panel.

The issue is that solar panels are not really that good as a "battery"... They really output current in relationship to the amount of sun. Most 12 volt solar panels have a Vmaxpower of ~17 volts. You could get a larger 24 volt fan, or a cheap 12 volt fan to run off an appropriate solar panel (roughly the wattage of the fan or a bit larger...

Computer fans are not that efficient at moving air--but they are cheap.

I would probably get a 24 VDC fan (oversized) and a good sized solar panel--guaranteed not to exceed the fan's maximum voltage and will be fairly quiet. Since the fan will be running under voltage, you probably don't even need quite the full rating solar panel (in watts).

If you are going by San Jose, there are probably still some surplus computer goods stores in the area... Weird Stuff (computer fans) is one... And there are probably still others--I have not been in one of them for almost 10 years now (not the same since the dot.com crash).

-Bill

Peterr

Re: DC fan & Panel for small dehydrator project, suggestions.

Hmm.. education continues, thank you, it makes sense

solar panels are not really that good as a "battery"...

The dehydrator will be rather large, as I had available a 4' square dual pane glass panel that will act as the solar collector top. Its 'heat' will be channeled into the actual existing Excalibur, 5 tray, dehydrator without its fan and heating element in the rear. Most likely it will be set in a 'permanent location'. To keep it simple what would be the smallest battery I could use without getting into more equipment, or is that impossible?

cow_rancher

Re: DC fan & Panel for small dehydrator project, suggestions.

Unless you are off the grid, solar fan power is not the way to go.

Having said that, there are the large computer fans that mount in the side of the panel, I think they are either 6 or 9 inch. And you can buy the small 2" size for less than a dollar each in quantities of 10. They are 12vdc and you probably only want to be moving the air when the sun is shining, so no battery would be necessary.

Rancher

mike95490

Re: DC fan & Panel for small dehydrator project, suggestions.

Depending on you air path, you may get enough convection from you air heater box (lots of plans for those online) to circulate air through the dehydrator. But this would only run daylight hours. To get 24/7, you will need some fans, battery, and charge/load controller. There are many 12VDC, low power fans used in the PC cooling industry, large computer stores (Frys.com) often have large, low speed (quiet) case fans in the 4" - 6" range. A wild guess, that you will be using this in the summer only, a 100watt panel should work. It all depends on the fans you use, what the load is.

BB.

Re: DC fan & Panel for small dehydrator project, suggestions.

Do you need to run the fan when the sun is not up? (reason for having a battery)...

Very roughly, adding a storage battery will at least double the cost for your solar power unit (more panel power, battery, charge controller, switch/timer to cycle fan) and add a lot of maintenance requirements (batteries may need watering, don't like being deep discharged as this will quickly kill them, keeping track of battery state of charge, etc.).

If your only need is to run the fan when the sun is up--do it with just a solar panel + fan.

If you need the fan to run 24 hours per day (as example), then you will have to have a larger solar panel + charge controller + battery at a minimum.

For example lets say you want to power this 36 watt 12 volt fan--first just when the sun is up and shining:

36 watt fan / 12 volt = 3 amps

3 amp * 17 volts (typical Vmp for solar panel) = ~51 watt panel

• $10 fan + $280 Kyocera 50 watt panel = $290 + tax and shipping

Now, to run the same fan 24 hours per day... Assuming Summer/Fall operation (4+ hours of sun per day):

36 watt fan *24 hours per day * 1/0.77 sys eff (solar PV + controller) * 1/0.80 battery eff * 1/4 hours of sun = 351 watts of solar panels

A pair of Evergreen Solar ES-A-200 200 Watt "12 volt" Solar Panel for ~$825 each...

You will need a 30+ amp solar charge controller ($115-$600 each).

And, using our standard 3 days of no sun and 50% maximum discharge for a storage battery... You need ~6 times your daily load:

3 amps * 24 hour * 6x load = 432 Amp*Hour Battery bank (at 12 volts)

You can get some Trojan "cheap" flooded cell golf cart batteries like 4x T105 225 Amp*Hour (6 volt) for $140 each + taxes and shipping:

• 2x $825 + $115 + 4x $140 + $10 = $2,335 + wire + fuses + mounts + taxes + shipping

The above is just a guess at your needs and the components needed to support them... Of course, you can change anything you want (fan, how long it is on, size of battery bank, etc.)... But it should give you an idea of how to size the system for your needs.

In reality--I would be suggesting the "less high tech" method of solar drying... Something like this would be better much lower in cost. Basically, you have a tilted solar thermal collector to heat the air at the base of the drying box... Just natural convection of hot air wanting to rise draws air through the collector and up into the drying box+racks.

-Bill

Peterr

Re: DC fan & Panel for small dehydrator project, suggestions.

Unless you are off the grid, solar fan power is not the way to go.

Nope where on the grid.. and starting to understand and salute all that are off..
Its beginning to look like more expense and trouble than its worth. I may get a separate ac motor or rework Excalibur's with a switch so I can have the heating element off. During the day, the heat from the collector may be enough and will not need to have a fan, but at night, need to keep the air moving.

BB your explanation is excellent. Helps break down the need into smaller bits to really understand. I'll be studying it. This is a great forumn. Thanks also for some excellent leads on solar dehydrator, had done what I thought was a good search but did not come up with the Sustainable Village one.

I've constructed mine in a manner that will enable me to make changes to it. (Its screwed together.)

BB.

Re: DC fan & Panel for small dehydrator project, suggestions.

Your are very welcome Peterr...

We where all "there" at one time.

-Bill