Need high CFM fan, one speed

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skizman
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Need high CFM fan, one speed

Post by skizman » Fri Aug 21, 2020 5:56 am

Can someone recommend a pc fan with 250 CFM that runs at ONE speed? I already bought one but it keeps revving up and down. The fan will be used for a homemade air filter system.
Does a 3-wire fan mean it only runs at one speed?
Your info is appreciated!!!! Thanks!

CA_Steve
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Re: Need high CFM fan, one speed

Post by CA_Steve » Fri Aug 21, 2020 7:32 am

Welcome to SPCR.

2-pin fans: Vdc, Ground
3-pin fans: Vdc, Ground, sensor (for rpm)
4-pin fans: Vdc, Ground, sensor, PWM signal

Even a 2-pin fan can ramp up and down if the source that it's plugged in to is ramping the Vdc pin voltage up and down.

skizman
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Re: Need high CFM fan, one speed

Post by skizman » Fri Aug 21, 2020 11:14 am

Thanks for the reply. So....if I am understanding this, I would be safe with a two pin fan that would run at it's highest rpm constantly? I'm using a converter 110v to 12v. I am using another pc fan 125cfm on the same converter and it runs without it revving up and down. Thanks!

CA_Steve
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Re: Need high CFM fan, one speed

Post by CA_Steve » Sat Aug 22, 2020 9:27 am

skizman wrote:
Fri Aug 21, 2020 11:14 am
Thanks for the reply. So....if I am understanding this, I would be safe with a two pin fan that would run at it's highest rpm constantly? I'm using a converter 110v to 12v.
Yes. Make sure the 110V to 12V converter is providing 12Vdc and not 12Vac. :)

If you want to manually control the fan speed, you can always get a Fan Mate. I've used them in the past when motherboard fan controls were non-existent/poorly done.

Another method is to find a fan that runs at a speed you like when driven by 5Vdc. Then, just cut the end off of an old USB phone charger. High efficiency, cheap.

CA_Steve
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Re: Need high CFM fan, one speed

Post by CA_Steve » Sat Aug 22, 2020 9:31 am

Another thing you can do is find a fan that'll run at a speed/cfm you like when driven by 5Vdc. Then, grab an old USB phone charger (pre USB-PD spec = 5V output) to run it.

skizman
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Re: Need high CFM fan, one speed

Post by skizman » Sat Aug 22, 2020 10:16 am

Thanks gents! Great info. I just want the fan to run full speed all the time. I'll shut it on and off with a remote. So again....will a two wire 250cfm fan run at it's highest speed off the 12v converter, without revving up and down?? Will a three wire fan do the same only wiring the black and red wires? I just don't want to spend the money again, because the 250cfm fan I bought had 4 wires, and no matter how I tried wiring it, it still revs up and down.
Thank you!!

CA_Steve
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Re: Need high CFM fan, one speed

Post by CA_Steve » Sat Aug 22, 2020 10:27 am

yes to both.

skizman
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Re: Need high CFM fan, one speed

Post by skizman » Sat Aug 22, 2020 12:19 pm

OK thanks but....if that's the case then why does my 4-wire 250cfm fan rev up and down with only the red and black wires hooked up? I just don't know exactly what type and name of fan that I should order to get around this problem. :(

CA_Steve
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Re: Need high CFM fan, one speed

Post by CA_Steve » Sat Aug 22, 2020 6:13 pm

Yeah, I don't know what's up with your fan, but you might check the supply to see if it's a stable 12Vdc source.

As far as a specific fan goes...250cfm? really? Anything less than a 200mm fan will be spinning like crazy / really loud for that.

Using Noctua fans as an example:
NF-A20-FLX is 200mm, has a max speed of 800rpm, and provides ~245cfm. noticeable noise.
NF-A14FLX is 140mm, has a max speed of 1200rpm and provides 192cfm. probably noisy.
NF-A12x25 FLX is 120mm, has a max speed of 2000rpm and provides 170cfm. probably very loud.

skizman
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Re: Need high CFM fan, one speed

Post by skizman » Sun Aug 23, 2020 4:54 am

I really appreciate you taking the time to explain this to me! Very good info! Good idea about checking the 12Vdc source. I will be ordering one of those Noctua fans. Thanks again!!!!!!! :D

Olle P
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Re: Need high CFM fan, one speed

Post by Olle P » Tue Sep 01, 2020 2:58 am

skizman wrote:
Fri Aug 21, 2020 5:56 am
Can someone recommend a pc fan with 250 CFM that runs at ONE speed? ... The fan will be used for a homemade air filter system.
If it's a dense filter you might be looking more at a fan capable of building pressure rather than moving free air.
skizman wrote:
Sat Aug 22, 2020 12:19 pm
OK thanks but....if that's the case then why does my 4-wire 250cfm fan rev up and down...?
Because there are shifts in the restriction/flow of air?
To keep the fan running at a constant speed you either need a static setup with constant voltage and constant pressure gradient or have some regulator controlling the fan speed to keep it (near) constant.

skizman
Posts: 8
Joined: Fri Aug 21, 2020 5:48 am

Re: Need high CFM fan, one speed

Post by skizman » Tue Sep 01, 2020 4:56 am

Thanks for the reply. I fixed the revving up and down problem. I ordered a 110v to 12vdc converter that puts out 5amps and the fan is blowing like a hurricane now. Just needed more amps. Old converter only had 1 amp.

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