Fan volume

[Allyn]

I'm hooking up some computer fans on my indoor plant tower to blow across the seed and plant trays.

(Don't laugh at the binder twine. It's only temporary until I get to the store to buy what I need to install a proper mount system.)

The fans I'm using are low volume-- like 20 or 25 cfm. It is a very gentle breeze. I'm wondering if I need fans with a little higher cfm. Yeah? No? Maybe? Along with wanting to provide adequate curculation, I read somewhere and I can't find it now, that a constant breeze keeps whiteflies from moving in. The breeze prevents them from landing on the leaves and if they can't land, they can't establish a life cycle. Is 20 - 25 cfm enough?

[webmaster]

Wow, that's really cool! How are you powering that?

[Allyn]

Wow, that's really cool! How are you powering that?

Easy peasy. I'm using a power supply from an old router. Cut the connector off the fan and off the power supply. Solder the red wires together and the black wires together and voilà! Plug it in and you have a fan.

You can use the PS from an old router or modem or an old charger for a cellphone -- pretty much any of those 'power' or 'charger' cords with the little transformer you plug into the wall socket.

Couple things to keep in mind --

1) There is a volt rating on the PS and on the fan. In my case, PS and fans are 12V. You can use a fan with a rating higher than the PS (eg: fan is 12V but PS is 5V) but don't use a PS with a rating higher than the fan (eg: fan is 5V and PS is 12V). If the fan is higher than the PS, the fan will just run at a lower rpm than it would at its rated voltage. If the PS is higher, you'll fry the fan.

2) You can run more than one fan on a PS if the Amp rating allows. Check the Amp rating on the PS. Add the Amp ratings on all the fans together. The total amps for the fans can't exceed the amp rating of the PS.

I have a bunch of these cobbled fans around the house. Some of them have pretty high cfm and really help with circulation. The computer fans are really cheap -- some for just a couple of dollars and I strip old computer towers so I have plenty around the house. Even if you have to buy the power unit, you can pick up cellphone chargers or router power supplies easily for less than $10 and probably less than $5.

[applestar]

This is great! I always wondered if there was a way to make use of the computer fans. Thanks @allyn!


I don't know the answer to your question but I'm wondering if it would be necessary to rotate the tray periodically if the fan is blowing constantly from one direction -- kind of like a strong light source from one direction? I guess if you have plenty, then you might have a second one blowing from a different direction (not necessarily directly opposite -- like diagonally opposite, maybe? ...no basis at all for this idea that just popped into my head)

[Allyn]

...I'm wondering if it would be necessary to rotate the tray periodically if the fan is blowing constantly from one direction -- kind of like a strong light source from one direction? I guess if you have plenty, then you might have a second one blowing from a different direction (not necessarily directly opposite -- like diagonally opposite, maybe? ...no basis at all for this idea that just popped into my head)

With the fans blowing as gently as they are now, I don't think that's a problem. If I need to up the airflow, however, I don't want the little seedlings to have a permanent lean. I used an airflow conversion table and it says each fan is producing roughly a 3 mph breeze. Do you think that's enough circulation?

[Allyn]

I decided I want more airflow. The seedlings right in front of the fans seemed to be doing okay, but the seedlings at the far end of the tray weren't getting any breeze at all. I swapped out the fans for ones about 40 cfm which converts to about a 5 mph breeze. Let's see how these do.