a few questions about voltage, amps and computer fans.

before i get flamed for not looking for myself: i have! D: and i think i'm down with the splicing wries part and hooking up a pc fan to a charger adapter thing. i'm just in a bit of a pickle.
i've got two of these fans:

http://www.pcworld.co.uk/gbuk/ak-183-l2b-120mm-amber-series-case-fan-00772801-pdt.html

12v dc
0.18 amps, so 180 milliamps, right?

i've scoured the house for old chargers, but none of them produce more than 7v dc output, and they're from about 500 - 900 mA s: will an ampage (if that's a word) that's alot higher than the input on my fan (0.18 A) blow my fan up? or wreck it, or whatever?

i also found this huge brick of an adapter, which i think was used to power one of those electricity-in-an-orb things. its out put is 12v, but 1.5 A...

and another one that's 13v output with a 1.8 A, but that's too powerful and will fry my fan surely?

can someone please help me out or give me any ideas as to what i should do?

they've got adapters in maplins but they're £20! or $30, and i don't know if i'd have to buy two, or buy a 24v one that i could hook both fans to.
so confused!

the old chargers will work fine man, maybe a tiny bit slower because of the 7v

of not use the big adaprter, it will work fine too.

will it matter about the amps if the output ampage on the adapter is nearly ten times the ampage required on the fan?

also, if i had to pick a fan that's going to run faster, should i use it for the exhaust or for the intake? i would've thought the exhaust, as it's keeping the box cool?

blazingwalrus said:

will it matter about the amps if the output ampage on the adapter is nearly ten times the ampage required on the fan?

also, if i had to pick a fan that's going to run faster, should i use it for the exhaust or for the intake? i would've thought the exhaust, as it's keeping the box cool?

Click to expand...

the amperage on the adapter is the maximum current it can produce. the fan will only draw the amps it needs from the adapter.

the fan on the exhaust is the most important and should be the larger of the two.

I just don't get why everyone on this board seems to want to use an intake fan!

As already said your power sources are fine. they will take what amperage they need and you can run multiple fans in parallel (positive to positive negative to negative) as long as the cumulative doesn't surpass the total available from the power source. The 13v would probably work fine but I think that will be up to the individual fan as to if it likes an extra volt.

Using lower voltage will reduce the power of the fan, but also the amount of noise it creates. A DC fan control simply regulates the voltage, so having multiple adapters to try is a good way to dial things in.

Now, for the intake fan...
The exhaust fan will run slower if it is drawing through a filter vs no filter. If your intake fan overdrives your exhaust fan it will attempt to push stinky air out through other slight gaps in your box. If the exhaust fan over powers the intake fan, then the intake fan is making the exhaust fan work harder! The only way for this to work would be to have them near-perfectly tuned.

If you don't care about smell then NBD, go nuts. If you do care about smell then just use an exhaust fan only. Keep a slight amount of negative pressure on the box by regulating the size of your intake holes to make sure all air leaving the cabinet is via your filter and your exhaust fan.

If you aren't getting enough air flow you need to add more intake holes and/or upgrade your fan. In your case, since you have 2 identical fans, you may try stacking the two fans together and sealing them if 1 isn't enough power pulling through your filter. I did that for a bit with mixed results, ymmv.

Jed

10jed said:

I just don't get why everyone on this board seems to want to use an intake fan!

As already said your power sources are fine. they will take what amperage they need and you can run multiple fans in parallel (positive to positive negative to negative) as long as the cumulative doesn't surpass the total available from the power source. The 13v would probably work fine but I think that will be up to the individual fan as to if it likes an extra volt.

Using lower voltage will reduce the power of the fan, but also the amount of noise it creates. A DC fan control simply regulates the voltage, so having multiple adapters to try is a good way to dial things in.

Now, for the intake fan...
The exhaust fan will run slower if it is drawing through a filter vs no filter. If your intake fan overdrives your exhaust fan it will attempt to push stinky air out through other slight gaps in your box. If the exhaust fan over powers the intake fan, then the intake fan is making the exhaust fan work harder! The only way for this to work would be to have them near-perfectly tuned.

If you don't care about smell then NBD, go nuts. If you do care about smell then just use an exhaust fan only. Keep a slight amount of negative pressure on the box by regulating the size of your intake holes to make sure all air leaving the cabinet is via your filter and your exhaust fan.

If you aren't getting enough air flow you need to add more intake holes and/or upgrade your fan. In your case, since you have 2 identical fans, you may try stacking the two fans together and sealing them if 1 isn't enough power pulling through your filter. I did that for a bit with mixed results, ymmv.

Jed

Click to expand...

thanks, that's really clear.

i don't understand the bit about intake holes though. smell is definately an issue, so i need to be really careful. what d'you mean by intake holes? just random holes in the box? surely fragrant but unwanted smells would leak out through them, aswell as light? inless i covered the holes with black tights material, but that still leaves the issue of smell.

blazingwalrus said:

thanks, that's really clear.

i don't understand the bit about intake holes though. smell is definately an issue, so i need to be really careful. what d'you mean by intake holes? just random holes in the box? surely fragrant but unwanted smells would leak out through them, aswell as light? inless i covered the holes with black tights material, but that still leaves the issue of smell.

Click to expand...

***edit*** I went off on my tangent and didn't really address your question! Key to keeping smells from going out your intake holes is negative pressure. Take a plastic soda bottle and poke a small hole in it. now suck on the mouth of the bottle (lets keep it adult here folks!) and the bottle will crumple. Cut a huge hole in the bottle and nothing will happen. The little hole example is negative pressure, and the big hole example is no pressure. Now if you take your little hole bottle and blow into it, it will puff out and that is positive pressure. You want negative pressure because your soda bottle (med cabinet) will ultimately have many tiny holes and you need to make sure you can still crumple the bottle a bit. the key is to keep your intake large enough to where it supplies the air you need to vent the cabinet while still maintaining a tiny bit of negative pressure so that it doesn't reverse on you and turn to positive pressure! Whew... I hope that helps!!! My original comments are below. ***

The two most important things to consider when building a cabinet are ventilation and light proofing. Yes these factors are more important than your lighting!!! If you don't have good airflow your plants will die from too much heat. If you don't prevent ALL light from entering your cabinet during lights off, your plants may very well stress and turn hermaphrodite. most people kill hermies so you can probably call that dead too!

OK... Here is how the ventilation in a cabinet should work:

You have heat at the top because heat rises and that is most often where your source of heat is located (lights). To most efficiently remove that heat you want a fan drawing air from the top to pull all that hot air from the cabinet. The intake holes should be at the bottom. In your room, that the cabinet is sitting in, the cooler air is near the floor and hottest air near the ceiling, so you are drawing the coolest air available and sucking it over your plants. these holes should not be randomly placed because you need to prevent light from coming and going and you want the holes as close to the bottom as possible. For many people they should be out of site also. Usually they are on either the back or the bottom of the cabinet.

As for light proofing, black pantyhose doesn't cut it! You have 3 typical options:

1. PVC pipe. You can use pvc pipe to baffle the light. this is typically done with 2 1/2" pipe and 2 or 3 "elbows". The interior surface of the pvc should be spray painted with FLAT black paint so that light doesn't bounce off the interior surface. this method is popular and works well but then you have a bunch of pvc pipes and elbows littering up your interior.

2. Dark room vents. These are used in a photographic darkroom to allow airflow and stop light from entering. these are available through photographic supply companies like Calumet or B & H Photo. I assume these work fine but have never used them. I did read a thread at one time where the poster was wishing he had bought the more expensive ones, so they may or may not work well, IDK.

3. Light Baffle/ Labrynith/ False floor. This is the way I have done both of my cabinets and I think it is the easiest and best use of interior space. Essentially you are creating a path for air to move through and making it turn a few corners. This is usually done with wood but other materials can be used as well as long as they aren't reflective and the interior, like the pvc, should be painted with flat black paint. In my flower cabinet I have a hole in the center of the bottom of the cabinet. The cabinet is raised off the floor on 3 sides to allow for this. I then cut a 2nd piece of plywood to allow for roughly 1 inch of space around the second/false floor. This false floor then shades the light from the hole. the hole is probably about 15% the size of the entire floor space. On the bottom of the false floor I attached small peices of 2"x2" wood scraps to lift that slightly over the level of the bottom of the cabinet. When my cabinet is all closed up the fan at the top pulls air from the bottom of the cabinet. The air coming from the cabinet comes up on all 4 sides of my false floor and is forced through my plants. Very simple!!!

Jed

and another one that's 13v output with a 1.8 A, but that's too powerful and will fry my fan surely?

Click to expand...

thats the one you want, and it will not fry the fan. motors like a little overvoltage, actually. undervoltage, will fry the armature on the motor quicker than anything else......

Jedi gives a good breakdown, ill try to kee p it simple-

air behaves like water.
if your going to remove air, it must be replaced, or else you will create a vacuum.
if there is no intake, to allow the replacement of exhausted air, then no air will be exhausted!
if the intake is not big enough, and restricts the passage of air, it will create backpressure on the fan
backpressure will cause cavitation, which is a fancy term for a loudass fan that isnt moving air like you want it too
air expands as it heats, it takes up more space than cooler air so
the passive intake total diameter must be larger than the exhaust total diameter....
hope it helps



edit/ps- the reason you do not want an intake fan has to do with cavitation as well... since the exhaust fan is pushing out hot less dense air than the intake fan is pushing in, it creates pressure differentials between the 2 fans, which will decrease the efficiency of the system to remove heat at a rate proportionate to the fan speed.....lol fancy huh.

in other words the intake fan pushes in air faster then the exhaust fan can remove it......... so thats why we go passive on the intake unless your running pressurized sealed ducting

and another edit-
i also use a labyrynth light trap setup... one thing ive learned over the years is that the air closest to the bottom of the floor (and i mean like 1/4-1/2 inch) is much cooler than the air in the rest of the room... so if your passive intake sucks up that cool air.... you get the idea

IAm5toned said:

motors like a little overvoltage, actually. undervoltage, will fry the armature on the motor quicker than anything else......

Click to expand...

I didn't know this! Good info!! Are there some fans that are more susceptible to this like brush-less or ball bearing etc?

IAm5toned said:

Jedi gives a good breakdown, ill try to kee p it simple-

Click to expand...

yeah... sorta stumble with the keep it simple thing!

Are you following all this Walrus? Coo coo ca choo?

Jed

10jed said:

I didn't know this! Good info!! Are there some fans that are more susceptible to this like brush-less or ball bearing etc?


yeah... sorta stumble with the keep it simple thing!

Are you following all this Walrus? Coo coo ca choo?

Jed

Click to expand...

shaded pole/capacitor start motors are the most vulnerable.

squirrel cage/brushless and wound induction motors fair about the same

desertrat said:

the amperage on the adapter is the maximum current it can produce. the fan will only draw the amps it needs from the adapter.

the fan on the exhaust is the most important and should be the larger of the two.

Click to expand...

ah, right. thanks

10jed said:

As for light proofing, black pantyhose doesn't cut it! You have 3 typical options:

1. PVC pipe. You can use pvc pipe to baffle the light. this is typically done with 2 1/2" pipe and 2 or 3 "elbows". The interior surface of the pvc should be spray painted with FLAT black paint so that light doesn't bounce off the interior surface. this method is popular and works well but then you have a bunch of pvc pipes and elbows littering up your interior.

2. Dark room vents. These are used in a photographic darkroom to allow airflow and stop light from entering. these are available through photographic supply companies like Calumet or B & H Photo. I assume these work fine but have never used them. I did read a thread at one time where the poster was wishing he had bought the more expensive ones, so they may or may not work well, IDK.

3. Light Baffle/ Labrynith/ False floor. This is the way I have done both of my cabinets and I think it is the easiest and best use of interior space. Essentially you are creating a path for air to move through and making it turn a few corners. This is usually done with wood but other materials can be used as well as long as they aren't reflective and the interior, like the pvc, should be painted with flat black paint. In my flower cabinet I have a hole in the center of the bottom of the cabinet. The cabinet is raised off the floor on 3 sides to allow for this. I then cut a 2nd piece of plywood to allow for roughly 1 inch of space around the second/false floor. This false floor then shades the light from the hole. the hole is probably about 15% the size of the entire floor space. On the bottom of the false floor I attached small peices of 2"x2" wood scraps to lift that slightly over the level of the bottom of the cabinet. When my cabinet is all closed up the fan at the top pulls air from the bottom of the cabinet. The air coming from the cabinet comes up on all 4 sides of my false floor and is forced through my plants. Very simple!!!

Jed

Click to expand...

awesome i get the negative pressure thing now - nifty. probably saved me alot of time there, and i think i'm going to put my two fans together for extra force, as i need it to draw the air through a small carbon filter on the outside.

dark room vents: such a good idea! i'll see if i can get hold of some cheap ones, but if not the pvc piping sounds good.

cheers for all the advice