Pc fans' setuo, amp, voltage, size (80 or 120mm) - gen. Questions (1st grow)

jabolo

jabolo

Active Member


    • Hi,​
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  • Im building a pc grow box, have done the lights and now onto the ventilation.

    I have 2 size 120mm fans, and 5 or 6 size 80mm fans and one 40mm one too i think.
    Im not sure which combo to use for exhaust:

    1) 3 size 80mm fans OR
    2) 1 size 120mm fan?

    Question 1: Are 3 medium fans more efficient than 1 large(r) fan?

    I cant tell the rotation speed but i gather that the Ampage on each fan, is an indication of its max rotation speed, right?
    If so, should i use a 0.27A fan rather than a 0.12A one?

    Question 2: Should i use fans with higher amp?

    Powering the fans:

    I understand that my charger amp rating should be higher than my total amp for all fans connected. E.g. 3 fans at 0.12A = 0.36A total; would need a charger with a rating of at least 0.40A (400mA).

    Q 3: Is the above correct regarding the amp etc?

    Now for the voltage. Fans are at 12V. Charger is at 5 or 7 volts (have a few phone chargers lying around the hse).

    Q 4: What voltage should my charge have?

    Q 5:What is the effect of using a lower voltage than 12V?

    Q 6: As long as my charger's amp rating exceeds my total fan amp rating, does it matter what my charger's voltage is?

    I apologise if my questions seem stupid or if i used the wrong terminology. This is my first grow and i really want to get it reasonably right (i am dying for a decent herb since moving in a country with extremely poor supply of quality cannabis).

    I have seen quite a few comprehensive and helpful threads and therefore joined this forum to first get advice and hopefully give some advice too at some point.

    So thanks in advance for any replies.

    One.

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n0tmycupoftea

n0tmycupoftea

Well-Known Member
I'm no physics major and/or engineer but I believe it's more complex than just choosing the bigger number and simple addition/subtraction. I think you'll want the 12v charger if your fans are 12v even though the amps on your charger are higher than the amps on the fan. From what I 'think' I remember from college is that volts and amps are measured in relation to the resistance in ohms. And I believe that the size, number of blades, general construction, etc. all play parts in how much cfm the fan can move.

To be safe I wouldn't mess around with different volts/amps, if you do you may end up risking the designated cfm's that your fan is actually suppose to be putting out. That is unless an expert comes in here and breaks everything down for us heh.

So... completely taking an educated guess at things...

Q1 - Totally depends (I have 2 80mm fans that pull just as hard as my 120mm fans, but have seen smaller ones pull harder and bigger ones pull harder).
Q2 - Don't know
Q3 - Yes
Q4 - 12v
Q5 - Lower running power on the fans, meaning they won't be able to run at their full potential (CFMs). Say your fan says it can move 120cfm and it's 12v and you're running a 6v. Your fan may be only moving 60cfm now (just an example).
Q6 - I believe it still matters, again I don't know for sure.

For my grow I have 4 80mm fans and 1 120mm fan. I have 2 80mm side by side on the top left corner as exhausts and my 1 120mm on the top right as another exhaust. bottom left and bottom right I have 80mm fans. My 80mm fans move 50cfm and my 120mm moves 60cfm and I have a constant temp range of 77-86 with lights on depending on overall temperature inside the house (mind you, here in New Mexico we've been hitting 100+ days; no a/c).

Hope I helped a little bit.
 
jabolo

jabolo

Active Member
Hi n0t,

Thanks a lot for ur reply. :)

You say that uve got exhaust fan on either sides of ur case at the top. This means you got an exhaust fan on the front of the pc case? How does that work, im thinking it will be blocked by the front panel on the pc case (u know that plastic thing where the dvd drive, power button are...).

Im very keen to know how this works because if i could put fans on the front side of my pc case (at the mo, only planned on putting them at the back of the case), this would greatly improve my ventilation.

Also thanks for ur feedback on ur experience with diff size fans and cfm. Too bad the cfm isnt always written on the fans, which is why its great to know i can sort of rely on the amp on the fan to have an idea of its cfm.

Im super excited about this project. If only this was legal...people would have so much fun with building their grow box. I mean theres the electric part, the wiring, the ventilation, the stealth and finally the biology/horticulture side! This is a great project which i will share with my son or daughter when i hav kids lol;)

Thnks again n0t :)

J.
 
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