[NattyFido2]

Does anyone know if there are any extractor fans with a similar specification to normal extrators, but with DC motors?

The reason I ask is that I would like to have a go at designing a speed controller (which for DC is relatively easy), but without the hassle of buzzing, spikes etc. associated with controlling AC motors.

e2a
I am currently using six 92mm PC fans for extraction (the growbox is quite small and I'm using a cooker-hood filter), and have a low-power speed controller (18V 10%-100% PWM duty cycle, max. 2A).

This post has been edited by NattyFido2: 15 August 2010 - 11:54 PM

[JesusC]

I,m sure Maplin sell a bit of kit tha will let you run ac on dc, i,m pretty positive I got something there before to modify a door release from ad to dc

Sorry i can`t be more specific

JC

[NattyFido2]

JesusC, on Aug 16 2010, 08:14 AM, said:

I,m sure Maplin sell a bit of kit tha will let you run ac on dc, i,m pretty positive I got something there before to modify a door release from ad to dc

Sorry i can`t be more specific

JC

That isn't really the problem. What you are talking about is called an inverter, they can be used in caravans to power mains electrical equipment from car batteries.

What I'm looking for is an extractor fan with a DC motor.

[scraglor]

haven't ever come across one myself. dc motors a way expensive to build compared to ac, and are only really built for special applications that require very high starting torque's, so not centrifugal pump generally. i think you'll be very hard pressed to find one. if you want to build a speed controller that doesn't buzz, the best option at the moment is a variac, or stepped transformer. the ac fans are designed with an external squirrel cage so that the extra heat caused by slip can be easily dissipated allowing the motor speed to be controlled by simple voltage adjustment same as a dc motor

[NattyFido2]

How much can you slow a fan down ie. 75%, 50%, 20%?

The main reason I want a slow fan is because, according to the growroom calculator, my space (0.33m3) needs 15m3/hr (minimum).
Every AC extrator I've seen is at least four times more powerful than I need.

I do remember seeing a DC squirrel cage fan, it came out of an old, valve PA, but that was about 25 years ago!

[L'Emmerdeur]

Vetus VENT17812 / 17824 extraction ventilator

Maybe?

Not cheap though.

E2a - The growroom extraction calculator on here seems overly conservative to me, and I've seen other comments saying the same. By the time you've got a few metres of ducting and a CF on the fan will be shifting maybe 50% of its maximum rated flow. I'd not worry about having too much air being extracted, as long as the intakes are up to the job, I don't think you can have too much air exchange bud.

This post has been edited by Gpierre: 31 August 2010 - 11:03 AM

[lebowski_dude]

The calculations about exchanging the air in your grow room every 3 minutes are to ensure that you provide enough airflow for the health of the plants. It's quite possible that you will actually require more extraction than this to regulate temps effectively.

Get a normal Ruck and hook it up with an expelair wac1 controller - it's designed for ceiling fans but works fine for these, and it's a proper voltage stepping controller ie no buzzing. Much cheaper than the 'grow specific' fan controllers.

[scraglor]

NattyFido2, on Aug 31 2010, 12:16 PM, said:

How much can you slow a fan down ie. 75%, 50%, 20%?

The main reason I want a slow fan is because, according to the growroom calculator, my space (0.33m3) needs 15m3/hr (minimum).
Every AC extrator I've seen is at least four times more powerful than I need.

I do remember seeing a DC squirrel cage fan, it came out of an old, valve PA, but that was about 25 years ago!

oh right, TOTALLY ignore the growroom calculator, the ventilation rates it puts up are for replacement co2 for the plants to breath. and doesn't in anyway count for the rate of extraction you'll need when you take into account the heat for your lights, also humidity and air circulation in general.

as a general rule of thumb, 4" inline fan will do a 250w HID, 5" high powered inline fan for a 400w and a 6" fan for a 600w, all these sizes are more than enough to cope with the assigned lights, and so give a bit of headroom to slow the fan down, which helps with noise issues and/or temps.

personally i use a high powered 5" fan with a 600w, ensuring i only have the lights on at night, and have a very short ducting run etc, and it just about copes all year round.


also, you can slow an inline fan down to virtually nothing

[NattyFido2]

Thanks for the replies folks, looks I'll have to start saving for that fan