[SOLVED] I need help regarding the amount of fans that a 2 amp header can drive!!

Dec 11, 2021
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So I recently got an ASRock FATAL1TY B450 itx board which has one pump header and three fan headers, the issue resides where I have the need to run 24 Noctua NF-A4x20(40mm)fans, now I have done some calculating and each fan draws about 0.05A so in theory I should be able to power 24 of such fans that pull a total of 1.2A since as I mentioned above the Fan header allows for up to 2A!
Though I might be wrong!! :V
Anyway thank you for your time, your opinion really matters for this subject. :)
 
Solution
Perhaps you will need to experiment.
When a fan starts up, it will require more power than it needs while running.
The reason to use a motherboard header is to allow motherboard speed control.
If you wire the fans directly to the psu you can likely run all you want.
If you need speed control, the easy way is to get a manual speed controller.

punkncat

Polypheme
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There was a discussion in another tread concerning this.

I think the first thing to do would be to check your motherboard documentation and see if they state a number of fans to each header. If not in there, perhaps shoot an email off, or see if they have a chat and ask.

Arctic fans with the pwm suggest in their literature not to use more than three in a chain. The issue as was discussed in the other thread is not so much a problem with the header, but with the gauge of wire having to support such a draw.

Personally would utilize the header(s) to hubs such that no single fan wire is running that high a load. I would suggest that the heat might melt the insulation or outright burn the wire. I have no evidence to support it would happen aside from years of experience in the low voltage field and load calculations I have done in reference to items like fire systems.
 
While I agree with punkncat, the "melting risk" is a function of wire gauge AND length. Depending on whether you're daisy-chaining 3-way splitters out until you have enough to plug the fans into, it's really the first splitter coming off the mobo that's going to handle the total load. And if that's a 3-way, you'll have 0.4A coming in on EACH wire (they splice at the connector to the mobo). Inasmuch, the more splits you have off the mobo header, the less the load will be on each wire of that splitter when you've got all the other fans daisy-chained off of it.

I'd still recommend going with less larger fans. Assuming this is a desk PC case? Turn the fan orientation to intake from the bottom instead of the side. No more fan size restrictions! A single 120mm or 140mm fan would be the equivalent of 10+ of these little screamers.
 
Dec 11, 2021
81
2
45
Yeah, the math works out. 40 fans = 2A

24 EA 40mm fans....yikes! Would love to hear the reason that's necessary.
Psst
While I agree with punkncat, the "melting risk" is a function of wire gauge AND length. Depending on whether you're daisy-chaining 3-way splitters out until you have enough to plug the fans into, it's really the first splitter coming off the mobo that's going to handle the total load. And if that's a 3-way, you'll have 0.4A coming in on EACH wire (they splice at the connector to the mobo). Inasmuch, the more splits you have off the mobo header, the less the load will be on each wire of that splitter when you've got all the other fans daisy-chained off of it.

I'd still recommend going with less larger fans. Assuming this is a desk PC case? Turn the fan orientation to intake from the bottom instead of the side. No more fan size restrictions! A single 120mm or 140mm fan would be the equivalent of 10+ of these little screamers.
I' mentioned above I was going to use 40mm x40mm x20mm noctua server fans where each draws about 0.05A but I was not going to use splitters but instead solder them in paralel to the adequate gauge!
Too many splitters are going to cause a <<Removed by Moderator>> inside my 1U case.
When it comes to soldering I'm pretty good at it!
 
Last edited by a moderator:
Dec 11, 2021
81
2
45
Yeah, the math works out. 40 fans = 2A

24 EA 40mm fans....yikes! Would love to hear the reason that's necessary.
This is a "secret project" I have been working on, it's a laptop on a 1U(40mm) form factor!
I was inspired by this guy on youtube that left his project die but since I'am the "good " guy am trying to resurrect it.
This video will provide you with further explanation where the only difference to mine being, mine is going to be 63cm x44cm which is just enaugh to accomodate a 24" screen :V........give it a sneak peek :)
View: https://youtu.be/3ZE_2zsuvmA
 
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Dec 11, 2021
81
2
45
While I agree with punkncat, the "melting risk" is a function of wire gauge AND length. Depending on whether you're daisy-chaining 3-way splitters out until you have enough to plug the fans into, it's really the first splitter coming off the mobo that's going to handle the total load. And if that's a 3-way, you'll have 0.4A coming in on EACH wire (they splice at the connector to the mobo). Inasmuch, the more splits you have off the mobo header, the less the load will be on each wire of that splitter when you've got all the other fans daisy-chained off of it.

I'd still recommend going with less larger fans. Assuming this is a desk PC case? Turn the fan orientation to intake from the bottom instead of the side. No more fan size restrictions! A single 120mm or 140mm fan would be the equivalent of 10+ of these little screamers.
Looks like you missunderstood!!
I was going to use 40mm by 40mm quiet Noctua fans where each fan draws "0.05Amps"
The math lets me wire 40 of them for a total draw of 2Amps but my requirement is 24 which is well within spec :)
 
Perhaps you will need to experiment.
When a fan starts up, it will require more power than it needs while running.
The reason to use a motherboard header is to allow motherboard speed control.
If you wire the fans directly to the psu you can likely run all you want.
If you need speed control, the easy way is to get a manual speed controller.
 
Solution