For your setup, I would suggest the smallest fan you can find. Turn it on low and blow the air across the tops of the seedlings. Try not to blow the air directly on them at first. It will dry out the potting soil too fast. Something like this should work. You could attach it to your plywood?

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How would you wire up a PC fan for use with plants? Any help appreciated. Thx

I have a bunch of 5", 15 watt, 120 volt fans that I bought at an electronic surplus parts store about 35 years ago. If I connect 2 in series, they turn sufficiently slowly so that the plants do not sway. These are nice fans because I can easily take the motors apart, oil the parts, and put them back together. Incidentally, if I turn the armature around (front to back) then the motor rotates in the opposite direction.

About 60 years ago, electronic surplus junk parts stores were common in Chicago (I would guess, at least, 100 stores). These stores gradually dwindled in number until they became extinct around 1980. I bet that nobody recorded this information in a history book.

Most PC fans run on 12VDC and a wall outlet supplies 120VAC, so you need a power adapter (one of those annoying bricks that come on the end of some power cords and take up too much outlet space). You need to find one with the correct voltage and mA rating. The voltage should be listed on the fan, and is usually 12V. To find the mA rating, you need to take the fan's power rating in watts, divide by the voltage, and multiply by 1000. So if your fan says 5W and 12V, you take 5W/12V*1000=417mA. This is the minimum mA rating you need on your power supply. A 500mA power supply would work well for this example. Radio shack should have power adapters, or maybe you even have one from a home device that's no longer used. Once you have the correct power supply, you just strip the ends of the wires and connect them, preferably with some small wiring caps and electrical tape. The fan will not run when the wires are reversed, so test before you tape them up. If the fan has a third speed monitoring wire, it will usually be yellow and can be clipped off or left alone.

I've done this several times and it's pretty easy, but the power adapters can be more expensive than they should be, so it's nice if you can find an old one somewhere.

@ horseflysgarden, the fan in the picture comes with an AC adapter. It's made by Dayton and costs around $25.

A PC fan isn't powerful enough to imitate the wind. They supply enough air for ventilation. I use PC fans in my terrariums but I use a pedestal fan oscillating on low about 6' from the plants in my grow area.

Maybe not powerful enough to imitate the wind, but definitely powerful enough to propagate seedlings. All the fan is used for at this stage is to circulate the air, bringing fresh air to the plants. A larger fan would simply dry out the medium too fast and lower the humidity around the plants.

Mother nature doesn't baby her seedlings. They'd be better off moving around a bit.

I use 14" floor fans some distance away; they circulate the air in the entire room.

The fans at the ends of the chamber blow out and the fans at the bottom blow upward. The fan pairs are connected in series which makes them turn relatively slowly. Used individually, those fans are 15 watt each but a pair in series should be about one fourth of that, i.e., the total of four fans use about 15 watts of electricity. The bottom fans are on continuously whereas the end fans are on the same timer as the lights. Note the ~3" space at the bottom of the front mylar shroud that lets in air.

the total of four fans use about 15 watts of electricity.

The total of four fans should use about 2*15/4 = 7.5 watts of electricity.

I could still be wrong because my electrical engineering class on motors was my least favorite (like having my teeth pulled) and I didn't pay attention (or attend class much).

I don't think the fan is running in this picture, but this is what I use (top shelf). I rotate it shelf to shelf, even outside it isn't windy everyday. For room air movement, I use a 100 lb. bernese mountain dog running through the house like the small horse that he is. ;-)

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Please feel free to keep other non-constructive criticism of my light set-up to yourself. This is a vast improvement from last year and I don't pretend to be a professional. :-P

even outside it isn't windy everyday

That's not the point. When the winds reach gusts of 30-40MPH are your plants going to stand up to it or fold at the ground?
No one says your plants have to be 2' tall before you support them so if you would rather support them at 8-10" you can.
Nothing wrong with your setup. It's very close to mine.

My point is that you do not need a fan on them 24/7 while still inside.

OK - looks good to me, but what do I know ;) (newbie) I was actually wondering if I needed to use an oscillating fan rather than a stationary one. What do you think?

OK I'm the cheapo. I use a 9 inch 3 speed stationary fan I got on sale at Wally world for under 4 bucks. To much wind and It will dry out the soil. When the plants or Mylar just starts to wiggle then I am happy. I have it on the timer with the lights. BTW I grow all winter in my kitchen starting seedlings every two weeks for greens.

Curt*

Any suggestions on what kind of fan to get (Amazon) for seedlings inside on a table?