Powering a parallel array of 4x 70x70mm computer fans

Thread Starter

Engineer112

Joined Jun 26, 2020
17
I've formed an array of 4 BLDC 70x70mm computer fans for use in a project, which I believe to each be rated to 1.2A (see image, apologies for poor quality).
When testing the performance of the array I used a variable DC power supply (image attached). As shown, when in stable operation at the output needed the DC supply was running at around 10V and 4.0A.
However I am now looking for a more permanent and portable solution for powering from a UK plug socket.

From brief research I have found Adapters such as this (1) and this (2) from RS which output 9V 4A from a 230V input.
Would this be suitable for the project? I will likely replace the connector provided with my own.

I would also like to incorporate a potentiometer or similar if possible in order to vary the output current, so any advice on this would also be greatly appreciated.
 

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Thread Starter

Engineer112

Joined Jun 26, 2020
17
Hello,

On the fan is stated 12 Volts 1.68 Amp

On a lower voltage the current will be lower.

Bertus

Thank you for the clarification - I assembled this some time ago and was unsure of the details
Could anyone give some advice regarding powering the array?
 

Irving

Joined Jan 30, 2016
815
Why do you want to vary the output current? Fan speed is voltage controlled, fans will take whatever current they need at the voltage you apply, up to their rated voltage & current loading.

That PSU hasn't really got enough output; depending on how it handles overload the fans may or may not run, but if they do, they probably won't be at full speed.
 

Thread Starter

Engineer112

Joined Jun 26, 2020
17
Why do you want to vary the output current? Fan speed is voltage controlled, fans will take whatever current they need at the voltage you apply, up to their rated voltage & current loading.

That PSU hasn't really got enough output; depending on how it handles overload the fans may or may not run, but if they do, they probably won't be at full speed.
Yes I should've said Voltage controlled in order to determine varying current - my apologies I haven't had much experience with electrical systems.

I'm not necessarily worried about the fans not being at full speed, as the speed reached at the operating point shown (at 10V) was appropriate for the intended use. However if a supply was able to provide a varied voltage from 0-12V and able to handle the required current then I imagine this would be beneficial.

Does anyone have any specific recommendations?
 

bertus

Joined Apr 5, 2008
20,571
Hello,

You can not go to low with the voltage on the fan.
When the voltage is to low, the fan will not start.
I have noticed that fans usualy work until about half the voltage.

Bertus
 

Thread Starter

Engineer112

Joined Jun 26, 2020
17
Hello,

You can not go to low with the voltage on the fan.
When the voltage is to low, the fan will not start.
I have noticed that fans usualy work until about half the voltage.

Bertus
Yes, I seem to remember this effect from testing - presumably however if the output voltage was variable across the required range (e.g. up to 12V) then this would not be an issue?
At an estimate I would say that the suitable operating range would likely be around 8-11V, as there would be no need to run the fan at low speeds.
 

Thread Starter

Engineer112

Joined Jun 26, 2020
17
A fixed output 24v 120W supply like this feeding one of these , lightly modified to bring the adjustment externally & fix it to say 7 - 12v will do the job.
The supply seems to be quite large - is there any chance of getting something more compact? The project which this is used for needs to be portable.

Also I am hoping that ideally I will need to make minimal changes (due to lack of experience), so was hoping that some form of commercially available cable might be able to be adapted with the inclusion of a potentiometer and a switch - would this be possible?
 

Irving

Joined Jan 30, 2016
815
You can't control 80W+ of power with just a potentiometer. Your problem is these are pretty heavy duty fans, rated at 20W each, so 80W total, though you were running them at 10v @ 4A = 40W so approx 1/2 input power but that tells us nothing about flow rate/back pressure. I can't find the curves for this fan as its a Dell proprietary server fan but I can tell you it'll be way off its most efficient operating point. What you need to do is work out what flow rate you need and back pressure to overcome and select one or more fans that fit the bill at their rated output where they are running most efficiently. Then you might find a more equitable solution.

What are they being used to cool? Can you give more detail?

edit: found some flow info..
Max. Air Flow - 1.922 M^3/Min. (Min. 1.729) or 67.85 CFM (Min. 61.06)
Max. Air Pressure - 54.10 mmH2O (Min. 43.82) or 2.129 inchH2O (Min. 1.725)

min figures appear to be at 10.8v/1.2A - the lowest operating point for that fan
 
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Thread Starter

Engineer112

Joined Jun 26, 2020
17
Yeah I was slightly concerned that the power of the fans would be an issue - they aren't in fact used to cool anything but act as a wind source in a scale model which I have made. They were purely chosen because it was what was found lying around when I made the project some time ago, and were far more suitable than much smaller basic computer fans with minimal flow rate and yet still quite compact.

The minimum operating point you mention does still seem likely to be at a suitable flow rate for what I might need given what I can remember from past testing, and although evidently less ideal, a lower efficiency is not too much of an issue in my mind (but correct me if I am wrong?).

I would be happy to sacrifice a greater operating range and efficiency in order to scale down the components necessary to run the fans, but am unsure how much difference this may make.

Thank you for all your help and advice so far, much appreciated


Edit - As a side note the fans are currently connected in parallel with wire rated to 6A, so in their current state presumably wouldn't be safe to operate at 12V anyway (although of course this could be changed if needed)
 

Irving

Joined Jan 30, 2016
815
I can match and slightly exceed that minimum flow rate with 3 x 120mm axial fans running directly off 230v ac and rated at 18W each... Is that a better option? No psu required...
 

Thread Starter

Engineer112

Joined Jun 26, 2020
17
They are unfortunately already quite integrated into the project with a 3D printed casing - not really the kind of thing I can easily replace now, although yes admittedly I should have originally looked into my options further before committing to it. However the project was on a limited time scale and these were lying around, and the variable power supply could be used temporarily when needed but now I would like to make it more portable if possible.

Out of interest though do you have a link for some options that I could have used instead? Would just like to see what kind of alternatives there are.

If I am still able to stick with the current assembly would you still recommend these components with relevant adjustments? Or is there perhaps an alternative which is slightly smaller but with a smaller voltage range?
A fixed output 24v 120W supply like this feeding one of these , lightly modified to bring the adjustment externally & fix it to say 7 - 12v will do the job.
I would also have to buy some appropriately rated wire etc. and form a casing presumably.

Thanks again
 

Irving

Joined Jan 30, 2016
815
Sadly yes, as the anecdote goes, if I was going there, I wouldn't start from here...

I'll have a look see if there are some 70mm 230v AC fans that'll fit, or a smaller adjustable solution. Can you confirm these are definitely 70mm as I've seen them listed as 60mm on some sites.
 

Thread Starter

Engineer112

Joined Jun 26, 2020
17
Sadly yes, as the anecdote goes, if I was going there, I wouldn't start from here...
Yes can completely understand your reasoning here

I have checked and realised that I had stupidly misremembered the dimensions of the fan - they are indeed 60mm in size, and 70mm was the diametrical spacing of the fixing holes, as shown in the images.
Apologies for the confusion
 

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RIKRIK

Joined Oct 11, 2019
93

Thread Starter

Engineer112

Joined Jun 26, 2020
17
I would say at 1.6a. Its best to add 20% for safety. Me personally id go 2a per fan. You can pick up 12v 10a wall bricks pretty cheap http://www.ledlightingsave.com/index.php/12v-10a-transformer-120w-ac-to-dc-switching-power-adapter.html

18cm long. You could stick the two fans along the adaptor two more on top. Using it as a stand. Okay you cant control the speed but you could have two switches for the left anf right side .

Anyways god bless the queen and i hope your project turns out
Thanks for the suggestion, it looks promising.
Would I still be able to use this (suggested earlier) or perhaps something similar to vary the output voltage?

Also, I am unsure how I would adapt the potentiometer adjustment such that it could be changed outside a casing, would anyone have any suggestions?
 

Irving

Joined Jan 30, 2016
815
I would say at 1.6a. Its best to add 20% for safety. Me personally id go 2a per fan. You can pick up 12v 10a wall bricks pretty cheap http://www.ledlightingsave.com/index.php/12v-10a-transformer-120w-ac-to-dc-switching-power-adapter.html

18cm long. You could stick the two fans along the adaptor two more on top. Using it as a stand. Okay you cant control the speed but you could have two switches for the left anf right side .

Anyways god bless the queen and i hope your project turns out
That might work but my personal experience of these cheap sealed bricks is their reliability is suspect when run anywhere near their limit. YMMV, but I prefer the open-cased units with decent air-flow and a fan eg this one. Either can be used with the variable converter I suggested earlier. The open-case supply can be adjusted directly, but its a limited range and means possibly opening the box to connect a potentiometer which is why i hesitate to offer that as an option without more research.

Other considerations

Open-case PSU is constant fixed, i.e. regulated, voltage output and suitable for the purpose intended.
Brick PSU is sold as LED driver which actually requires constant-current but its not... however its not being sold as a general purpose PSU. It also has output wiring and a connector rated at 5A on a 10A psu? Your call onthat one.

The seller of the open-case PSU also offers a LED-specific supply in an open case form that is similar in size & spec to the sealed brick, but has an output voltage spec of +5%/-10% because it is a true constant current supply.

The open-case PSU is 200 x 100 x 42mm = 840cc
The brick PSU is 180 x 62 x 40mm = 446cc (the open-case version from the above seller is 188 x 47 x 35mm = 310cc)

All of these are sold by drop-shippers out of China who generally have no expertise and my experience is you're on your own deciding what works/doesn't for purpose.

I'm not associated with either seller, though I've used the Maker's-Hut products before as they supply one of the Maker-spaces I used to frequent.


I also have this lying around, but would it be suitable for this use?

Would be much more user friendly as I have a casing along with it, but appreciate it may not be the right thing at all.
No good, that looks like a 230v AC dimmer. Not suitable at all.
 

Thread Starter

Engineer112

Joined Jun 26, 2020
17
Many thanks for all of your advice here - much appreciated.

I think for now I will order the variable converter, and am currently leaning towards the brick PSU.
I can clearly see the advantages of the various open-case PSUs which I would definitely choose either if this was a fixed tabletop project or if I was still only in the design stage, and hence would have more flexibility.

However:
- The dimensions of the brick PSU are ideal for what little space I have remaining to store it in transport
- There is no need to fabricate a casing (which would also clearly further increase the size)
- As far as I am aware I will not need to run the supply at/close to its limit
- They aren't too expensive anyway so it it isn't suitable I'll take the hit and work out how to incorporate an open-case alternative instead

I also can't seem to find the mention of the 5A output cable rating - or is it the case that the output connector used is only suitable for 5A? Could this be avoided by attaching a different connector?

I also found this LED PSU (12V 10A option) from the same seller which seems to have similar specs but but can't seem to find the other one you mentioned which has smaller dimensions - do you have a link by any chance as this was the only other option I might lean towards.

As an aside, where might you recommend as a source for some suitable cable, presumably rated for 10A?

Thanks again
 
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