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HX750 Fan Speed trigger - Defect


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I have Three of your Top Rated Corsair HX750 power supplies installed in Three brand new i7 computer setups, also note these rigs sport excellent Corsair Computer Cases too, which by the way I love.


I built these new rigs from the ground up back in December, the goal was to have brand new new low current low heat i7 setups to be Silent or Super Quiet running computer systems, which they are... well so I thought until Spring came here in the northeast and the room temperature rises warmer than the winter, and lo and behold as This Thread and soooo many other threads I've now found in google searches and on this forum, have the same problems with this HX750 Power Supply, that when their heat sensors reach its preset value it turns on the cooling fan, which is perfectly fine! ... but the problem is it turns the fan on way too fast which certainly is very audible - these fans are noisy...what the heck! ...Yes the Corsair case filters and vents are clear, clean, and that's Not the problem! ...the problem is the HX750 cooling circuit has a design flaw.


I feel deceived in my purchases - especially considering I bought these very expensive HX750 for their marketing on how quiet they are, but they clearly have a design flaw.


It's certainly poor design to have the fans come on so fast and then spin down then gradually to off, and then if the temperature warrants, it keep repeating this noisy method at regular intervals; again depending on temperature. It's misguided for an engineer to design a circuit this way, which clearly seems was the case. It should be that when it reaches it's trigger temperature value, that the fan slowly spins to meet the needs, etc...


I would much rather have the fan spinning at 5% all the time which actually is all it would need to keep the values in check.


Anyway, I want to return these Three HX750 power supplies to get my $ back to buy ones that are proper and truly professional, maybe the AX series?

After reading here I see that returning them as RMA is fruitless since they send you new ones having the same issue - is Corsair even aware of this problem - well yes you would think so, but what has been done about it for the last 8 months, or more?


I see in some threads at this forum that some folks have mounted a fan on the back of the power supply to gently draw air though the unit and it works - hey I don't mind modifications and the creativity of those to think of them to fix problems, I love it, but to the owners of Corsair, do you really want me to spend even more money and mount a fan on the back of your beautiful Corsair Computer Towers onto the outlets of their mounted Corsair HX750 units to fix this problem? I don't think so. There's got to be a 10 cent fix of electronics parts installed within it to put these units right


I'm thinking to return these and get the even more expensive AX series hoping they would not have this flaw, but is it true that I see there are threads about the AX series doing the same thing?


Please, which of the Corsair Professional power supply series do not have this fan speed problem?


Thank you,

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  • Corsair Employees
I am sorry but that is how they work. If you are at a low load say 40-50% load the temp internally will hover around the start and stop point about 49 deg C where the fans turn on and they will turn off about 45 deg C so if the system is lightly loaded and the fans turn back off the next time they start up they ramp up to 100% as a self test. The AX series will manage the fans in a similar fashion but not exactly the same as the HX series.
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Hello Ram Guy, you have an impressive amount of posts at over 1000,000, congratulations of that amount of work.


Back to the HX750 though, honestly though, for any builder worth half their salt, we want Quiet running builds, and that's why we gravitate toward and spend the extra money on the beautifully made Corsair Computer cases, designed to be Quiet as well, and the expensive Corsair Power Supplies also designed to be Quiet, then please tell us, better yet have the Engineer who designed this, tell us how does it make any sense to as they tell you to say "the next time they start up they ramp up to 100% as a self test" honestly sir, honestly, whomever came up with this ramp up to 100% does not get it, not only (respectfully said) is it a ridiculous and unnecessary task, it's out of touch with the modern professional computer building reality and even with Corsairs own commitment on quality silent products.


The fan only needs to respond to reality, which in this case is a simple gentle silent low rpm cooling...


It's cloudy and cool outside here right now and my room is 67 degrees, and so my HX750 fan at the moment and all day has been on off, dead quiet, I love that! ...the i7's themselves run so efficient and low current/heat that their fans are barley spinning and are totally silent, my builds were dead silent all winter and spring, but nearing summer now when it gets sunny outside and heats the room 10 degrees or more, the HX750 makes itself known in an most unpleasant and technically distressing way.


There has to be a re-design for this PS, I'm stating it's necessary for the engineers to do this for the good of your power supply division.


I'm willing to do anything to help accomplish that right decision.


If there is no fix, then how do I get all my money back for these 3 new HX750's, or how can I swap them up for one of your Professional Modular products that works appropriately?





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I do agree with you to some extent and I do not have a problem replacing the unit for you but if you have the above listed scenario I am not sure that will change the outcome much but we can sure try and replace it there may be something wrong with the PSU you have, have you requested an RMA?
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Two of my new HX750's do this and so logically it appears this is how they were designed as you have said, and so in that light they are not defective from that original design schematic, however imho & professional experience it is defective...maybe better worded to say 'deficient design' of the 'ramp up to 100% at every 49 deg C trigger' Certainly the Quiet part is misleading marketing, even though at first I'm sure it was unintentional being an unknown until it was out in the world. (My third HSX750 is still in it's retail box waiting for my new Haswell build later this week or next)


You see since my (and the majority of) HS750's on a warm day, plus the heat from normal operation 'inside the PS' before ramp will hover at that temp, and so on warm days we easily can get into that 'constant fan cycling rut' which is frankly ridiculous and engineering-wise should of been foreseen. These units when encountering that temp only need to initiate a quiet slow spin to cool it, of course proportionally to the actual load, not an unnecessary ramp-up test; and so if/when the engineers do that, then Corsair would have a few extra hundred thousand dollars or more in their pocket instead of dealing with what they have now which is also making poor pr, and so my advice is to fix this problem sooner than later and save the $


No I have not initiated an RMA since as we have seen customers are sent new units that have the same problem since the HS750's are as you say built that way - and so why waste that time & $ only to render more dissatisfaction.


I don't see this design problem getting solved in time for me and my desires and needs.


I've spent a lot of cash on these Quiet builds, and I/we deserve better. We were marketed that the Professional HX750 were to be so quiet. Certainly my builds run @ minimum wattage usage - my Cyber Power UPS digital display meter shows 'Everything' that's within my beautiful Corsair Computer Cases are only drawing 25 watts under normal load and only 40 watts under full video load! (...aren't these new i7-3770 combinations remarkably efficient and yet powerful)


I want to exchange these Three HX750's up to the next more professional level, perhaps the AX760.. of course as long as they don't have the exact same ramp-up problem. I'm asking do the AX760 have that same self-test full ramp up in the same way? I know you said they were similar but are they more reasonable, I can live with most anything reasonable, slow spin, but the current HX750 unnecessary ramp-up cooling design is unreasonable!


How to proceed to exchange these for brand new retail boxed AX760's please - that is if they behave better of course. If they don't which Professional ones do?


Thank you,

Kind Regards


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Please request an RMA and post the case number I will call you next week and we can see what we can work out.


That is very nice of you Ram Guy, thank you very Much for your considerations, appreciate it...

...the only problem is now that since a few days went by I was not sure that I was going to get an answer in time, and so yesterday afternoon before you posted I was working on solving my problem, and I believe I have, which there Definitely are some of the newer lots of HX750's that work right, that is, currently on all mine when the PS sensor reaches it's trigger temperature, all mine the fans ramp up to a fast speed and slows down to off, and cycles this way often as it reaches the threshold again, however I have confirmed that a certain group of newer HX750's do Not do that, they operate as they should and that is when they reach the threshold temperature the PS fan 'Gently, Slowly' spins up operating at an 'Appropriate' Slow Gentle speed, and in a minute or so when it cools itself below the threshold then it shuts off, next time it reaches threshold they Gently, Slowly, do the same thing - no fast ramp up stuff, just proper operation as you would expect - this is how they all should operate.


As of yesterday I am in the process of exchanging the other two of all three of my PS's for brand new ones within that same serial range that work correctly, all at no charge or shipping. This is not directly through RMA or directly with Corsair but with one of your retailers, I'll explain later.


In the mean time I just noticed in your first reply to me you said:

"....If you are at a low load say 40-50% load the temp internally will hover around the start and stop point about 49 deg C where the fans turn on and they will turn off about 45 deg C"


Which is correct, but you see all the ones of mine and the hundreds of posts I've read, we, I, Am Saying saying that when they hit that 45 deg C level, the fans kick on FAST, way to FAST, and that is what we are talking about, then they cycle Fast then down to off... reach threshold and ramp up Fast then down to off ..and on and on... ...And That is what is unacceptable and broken.


You continue to say


"....so if the system is lightly loaded and the fans turn back off the next time they start up they ramp up to 100% as a self test."


Yes but when they are lightly loaded is where we get into a cycle every time it hits that temp trigger, as I said the fans kick on FAST, way to FAST, then they cycle Fast down to off, and this cycle repeats itself, but again not on the newer range of serial #'s I am getting - they work properly.


Anyway, I have to go out of town for a week and am leaving shortly, when I get back I'll install the other new ones received and let you know the serial number ranges of what works right and what does not - that is if your interested?


Bottom line it seems my HX750 problems are solved, well, one out of three at the moment and I'll confirm the other two next weekend when I'm back home and install them, if you want to know the results?

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Thank you Ram Guy..


Okay I have all three brand new HX750's installed now and they all work very good. I tested them all under load, and when it reaches the threshold the fan will come on ..and spins up slowly, and pretty quiet.. for a few minutes and then shuts off when it has cooled to meet it's threshold. Now this is the way it should be! (Testing note: ..my setups draws under 100 watts from the HX750)


My next observations although totally accurate for my power supplies, I'm sure the serial ranges are even more specific to whichever vendor and lot #'s, but this is what I've found so far


HX750 in the serial ranges of 12497148000004000000 range (+/- a few hundred thousand or much more I'm sure) ...but in this vicinity these are the ones that have that Fast Fan response when reaching threshold issue. These are from 2012 +/-


HX750 in the serial ranges of 13167180000009000000 range, (again (+/- a few hundred thousand or much more I'm sure) ...but these are the ones that work properly. These are most likely from 2013


fwiw, the ones that Amazon is currently (as of May & June 2013) selling are in the good serial range and work well.


I see NewEgg has these HX750's on an exceptional sale for $99 today but I have no idea what serials ranges they have in stock.

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