I'm a little confused about PWM. I want to control my fans with the FC5 from Lamptron, and I really like the Corsair SP120 High Pressure fans. I realised they were 3 pin and was wondering if I would still be able to control them. If not, are there any 3pin to 4 pin adaptors?
PWM related Question
- Thread starter sushisky
- Start date
jamesriley94
New member
You'll be able to control them fine yes.
4 pin has the same connections as 3 pin, but with an extra feedback for telling the fan what speed to spin if used on a motherboard header.
On a fan controller, the voltage is either reduced, or the fan is rapidly turned on and off, so there won't be a difference between 3pin and PWM.
4 pin has the same connections as 3 pin, but with an extra feedback for telling the fan what speed to spin if used on a motherboard header.
On a fan controller, the voltage is either reduced, or the fan is rapidly turned on and off, so there won't be a difference between 3pin and PWM.
alpenwasser
New member
I've read several times now that the Lamptron controllers actually use PWM internally
to step down the voltages. Haven't verified this though, but I thought I'd mention it.
jamesriley94
New member
PWM is just turning the fans on and off rapidly isn't it? (basically anyway)
I have big issues with fan controllers that do this tbh. Half the fans aren't cut out for it and causes them to produce way more motor noise than it should. When I was more nooby at this, I had an NZXT Sentry (the single bay touch screen one) and it added so much noise to the coolermaster ones, it was actually quieter to run them at 12v.
I now run everything directly from molex at 5v or 7v as I find that so much simpler and overall quieter too.
jamesriley94
New member
3 pin fans have the wires positive, ground, and a tacho signal back to the motherboard to report the fan speed.
4 pin PWM fans have the same 3 wires, in the same places too - positive, ground, the tacho back to the motherboard so you can see the fan speed, but then also the 4 pin is another tacho signal, but this time from the motherboard to the fan. This tells the fan to aim for the RPM you/your motherboard tells it to, and so it internally lowers the speed (generally through rapidly turning itself on and off) to achieve the target speed.
However, PWM is only really beneficial if you're running off a motherboard fan header - which tbh nobody ever should be anyway.
On a fan controller, or resistors, that will limit the power going through it to the actual power input (ie, the 4th pin of a PWM fan won't be used at all).
A 3 pin connector will work fine on a PWM fan, assuming the connector doesn't have a shroud blocking you from plugging it in.
4 pin PWM fans have the same 3 wires, in the same places too - positive, ground, the tacho back to the motherboard so you can see the fan speed, but then also the 4 pin is another tacho signal, but this time from the motherboard to the fan. This tells the fan to aim for the RPM you/your motherboard tells it to, and so it internally lowers the speed (generally through rapidly turning itself on and off) to achieve the target speed.
However, PWM is only really beneficial if you're running off a motherboard fan header - which tbh nobody ever should be anyway.
On a fan controller, or resistors, that will limit the power going through it to the actual power input (ie, the 4th pin of a PWM fan won't be used at all).
A 3 pin connector will work fine on a PWM fan, assuming the connector doesn't have a shroud blocking you from plugging it in.
alpenwasser
New member
Wikipedia has a nice little article on PWM here.
The basic concept is that by switching voltages between a high and a low value
very quickly you deliver on average an effective value somewhere in between
the two to whatever you're powering with it.
Example:
- D: Duty cycle, the amount of time the signal is active (see here). 0<=D<=1
- y_max: maximum pulse value
- y_min: minimum pulse value
The formula from the Wiki article gives us:
Code:
y_average=D*y_max+(1-D)*y_minSo, let's say we have a PWM signal with a minimum of 0 V and a maximum of 12 V, active
for 5/12 (roughly 41.67%) of the time:
Code:
y_average=5/12*12 V+(7/12)*0=5 VSo your fan will effectively run at 5 V in that scenario.
This is pretty much what the fan controller does to control the fan's speed, and
is what jamesriley mean with "switching the fan on and off very quickly" above
(I think). So we're talking about a fan controller with 3 pin connectors in this case.
I haven't really looked into the 4 pin PWM fans and how that's done in detail, so
I'm not entirely sure how that works in the circuit.
Be aware though that since fans also have internal control circuits there can
sometimes arise problems between controllers and fans.
vorticalbox
New member
i have a fan 3 pin fan controller laying around if you want i could plug a 4 pin fan (only one i have is an intel CPU cooler sadly) and see what happens?
you can plug 4 pin into 3 pin fan headers so it should be fine.
you can plug 4 pin into 3 pin fan headers so it should be fine.
alpenwasser
New member
It doesn't happen very often, but one example I've recently come across is this
review. Skip to the "Issues" section.
I've never personally had one, but from everything I've heard and read they seem
to have very good noise/performance ratio. But it's not like they're miles and light
years ahead of everything else. There's no magic silver bullet in physics, and moving
air just has certain consequences with regards to noise etc. that you can't avoid,
no matter how well-stocked your bag of tricks is.
Alternatively, you may be interested in the Noiseblocker eLoops, they're also quite
phenomenal from what I've read. Phobya also make a red/black version of that fan.
paulstung
New member
I'd be careful with PWM fans with a controller, I have Akasa Apache's, and tried them with an NZXT controller, and they made a god awful noise, a very low pitched hum. I was looking for a way to have control over my fans and when searching Google a lot of PWM fans make that noise when connected to a controller. In the end I bought 5v and 7v molex to 3 pin and they work like a charm
jamesriley94
New member
Noctua's are good...
A few years ago, when there wasn't really much choice in the high end fan market - I mean, without spending £20 on Noctuas, the next best option was £5 Xigmatek fans, so that's where they made their name really.
Their fans are very good, move a low of air, have a decent static pressure and are very quiet.
But...
These days you can do just as good really for half the price. Scythe GTs, Silverstone AP121s, Corsair AF/SP can easily compete with them, and don't have the high cost or the 'prosthetic limb beige' colouring.
In my case at the moment, I have 11 Silverstone AP121s on my rads and one as a case fan. If they were Noctua, they'd have set me back over £200, and even second hand they're generally over £10 each.
Edit - in reply to Paul -
That's not the PWM part that's the problem. That's a poor quality motor in the Akasa fan itself, that doesn't like being rapidly turned on and off. A lot of the cheaper fan controllers do this, the Scythe ones I think are the only ones that don't these days, but some fans just won't have it at all.
Just better off sticking with 5v and 7v reducers.
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its not that your fan controller is in danger, it is the PWM fans are in
danger. PWM fans do not like to be voltage controlled. that was why
the PWM function is there.
