carbon filter/fan to suit my grow

[blacksaint]

I've been reading up on carbon filters/fans, as I intend buying in the next few weeks or so when the bucks will be available.

I understand it's generally agreed that centrifugal fans are needed, and it's important to match the fan and filter.

OK, my grow cupboard volume is 0.81m3 (0.9m x 0.5m x 1.8m). I currently have a grow going in this cupboard (3 plants) with a 400w HPS, 200mm bathroom exhaust (yeah I know they suck and do pose risks), a passive 300mm intake, and a small desk fan inside the cupboard. This gives me temps of about 26-28 degrees (lights on) and around 24-25 (lights off). Plants are looking good and are about a week or two from turning to 12/12.

 

My problem is finding the right fan/filter combination. (My other problem is I research too much and get bogged down in the detail). An example may explain my thinking.

 

Say I buy a 150mm x 300 Phat filter (150L/s) and an Allvent fan 260 150mm centrifugal (160L/s). Now with this combination I have to move about 810L of air to empty my cupboard. In theory, this will happen about every 6 seconds. In reality, with the drop in pressure due to the filter and the 300mm passive intake, it'll likely still empty in well under 1 minute. Isn't this too much, and won't it also cause a substantial drop in temperature?

 

Also to consider is the noise, which is why I wouldn't want to go any smaller than 150mm. Plus, being my first grow, i'll likely double the cupboard size in a few grows if all goes well.

I better stop now..starting to crap on.....

 

If anyone can offer some help it would be very greatly appreciated. With the luck I'm havin lately, I'm keen to get this sorted, in my head at least, as soon as possible.

[Dr Rockster]

Hey there Blacksaint,

 

I don't drobe grow but have mates that do and they all use fan speed controllers.

You need'nt worry about over venting and chilling your grow as you can fine tune it to a fraction of a degree centigrade.

Edited November 4, 2006 by Dr Rockster

[blacksaint]

thanks Dr Rockster....I'll have a look into the speed controllers... from what I've seen they're not cheap. i also thought about adding 1 or 2 150mm intakes on the bottom to lower the pressure....wdyt? a good option for the moment?

[Dr Rockster]

Hi Blacksaint,

I think they cost about £30-40 UK but they can be very easily made from normal household dimmer switches and they are safe too,if you are worried about modded electrics.

 

Your current set up without the carbon filter is in the zone as regards your temps and you'll just need to uprate fanwise to overcome the additional resistance a fliter will give you.

 

I don't unfortunately have a wiring diagram but surely someone else,another member who has done this mod will read this and reply.

 

 

All the best with your grow squire.

[blacksaint]

thanks alot Dr Rockster...it's those like yourself with sound advice that have gotten me this far....I'll check out some DIY ideas on the forums

[Luke Skywalker]

Do NOT use a dimmer switch for a fan speed control. You will likely damage the fan. You can get fan speed controllers for under a hundred bucks and they won't harm the fan at all.

 

btw, it's hard to overventilate. A 150x300 filter and appropriate fan would work fine. Factor in about a 20% drop for the filter, and then maybe 10 -20% for ducting and corners, (depending on how long the duct and how many corners of course) and you come to roughly the right figure for airflow. But there are other restrictions. Like plants.

 

But yeah, that size filter and fan would be fine, fan speed control or no. Keep in mind that you'll only ever get the temperature down to the ambient air around it, and even then it's unlikely you'll manage that with the best fan and best air-cooled light.

[Luke Skywalker]

You can also use acoustic ducting to great effect for silencing fans, get something like a 150mm length of about 2-3 meters and break it up to have the majority on the outflow end of the fan. Then you can also wrap the fan itself in a small section of 350mm or so acoustic ducting, or perhaps an old doonah or blanket to provide additional sound reduction. Tape it all up, add the filter, (either on the roof of the room with the filter inside or on the outside but in as straight a line from fan to filter as you can get it) and off ya go.

 

The fan speed controller would also help with the sound, as this reduces the airflow, but I don't think you'd be anything like overpowered in airflow for a cupboard. I have the exact same filter and I run quite comfortably in a similar situation.

[Dr Rockster]

I'm sorry my friend but I strongly beg to differ as a dimmer control uses the same components as a shelf bought unit.

 

 

All it is is a variable resistor and varying the output voltage can have absolutely no effect on the integrity of a fan's internal components.I'm a member of a UK grow site and we have dozens of folks who use diy voltage controllers with absolutely no reported problems.

 

These fans are very hardy and the biggest stress they undergo is at start up with FULL current.

[Shithappens]

If that is the case then you have been rorted in the purchase of a fan speed controller

 

Light Dimmers do use a basic resistive load to reduce voltage at the load be that light and or fan that is true.

 

Proper Fan controllers use a more efficient style of PWM (Pulse Width Modulation) to limit the size of the AC that gets to the actual Load thus decreasing the timeframe for the push slowing the motor or dimming the light.

 

The Resistive load style has some major flaws as follows

the unused power is burnt off and wasted

The voltage and power provided can drop below the starting requirements of the fan creating a stopped powered fan ready to sit and burn windings

 

Whilst PWM does the following

Just blocks the unwanted power from getting through

Provides the full wave form with just a narrowed profile so the fan still reaches the required turning values and if that is not enough of a duration then the actual power provided is within a shorter time frame providing less of a burnout factor

 

I have not opened or looked within many light dimmers but have seen damaged ones due to inductive loads gone wrong, yes this is rare but I would hate to have my fingers near them when they go

[Luke Skywalker]

Thanks for explaining shithappens.