Question How to estimate the power draw of laptop fans ?

[Amr22126]

Hello.

I am trying to profile energy usage of all components in a laptop when running a simulation. I know that fans don't draw that much power but is it possible to estimate how much power fans draw in a laptop? As in are there built in sensors similar to those that estimate gpu and cpu power draw? if not, does anyone know if there's a fan spec sheet or any reliable resource, I can refer to for estimating the power consumption of laptop fans in general (I'm assuming they should be all similar to an extent).

Laptop: Asus ROG Zephyrus G14 GA401IV (2020 version) RTX 2060, Ryzen 9 4900HS
Thank you!

 

[Lutfij]

You could look up listings for replacement fans for your laptop akin to this;
https://www.amazon.com/Replacement-...H-13NR03F0AP0301-DFSCK22115181H/dp/B0B614H1TR
then you get a max power draw of the fan. You could get a replacement fan just as an experiment and lower the value from 1A down to 0.1A and see if the fan moves at the lowest amperage. from there you can calculate power draw as you have values for current and voltage.

 

[helper800]

Hello.

I am trying to profile energy usage of all components in a laptop when running a simulation. I know that fans don't draw that much power but is it possible to estimate how much power fans draw in a laptop? As in are there built in sensors similar to those that estimate gpu and cpu power draw? if not, does anyone know if there's a fan spec sheet or any reliable resource, I can refer to for estimating the power consumption of laptop fans in general (I'm assuming they should be all similar to an extent).

Laptop: G14 GA401 IV (2020 version, RTX 2060, R9 4900HS)
Thank you!

Get a wall meter to check total power when plugged into the wall and subtract all known power usage, assuming you know everything but the fan, you can get the answer by such a deduction. You can also open up the laptop and remove the fan and they usually have the amp and voltage written on it somewhere. If we assume its a 12v fan all you would need to know is the amperage. A multimeter can give you an exact answer but that may be a bit more difficult to pin down if you don't know what you are doing.

 

[PiersPlowman]

You will need to find the fan's specifications, either by Googling it or opening up the laptop.

I have NF-A14 ULN fans in my tower and, for illustration, they draw 0.48 watts each, but in truth, there is no "ball park" figure; the specs vary wildly.

 

[BFG-9000]

Don't estimate, measure with a clamp-on ammeter. DC is a bit tricky at low currents, as you have to zero it and take the measurement without moving anything.

 

[Misgar]

is it possible to estimate how much power fans draw in a laptop?

Google (or Duck DuckGo) is your friend.

Seek and ye shall find.
https://www.amazon.co.uk/Cooling-Zephyrus-GA401IU-GA401IV-Replacement/dp/B0D4MH63XV?th=1

The spec says 12W which I take to mean per fan, so that's 24W max when running both fans flat out. So much easier than opening up the laptop, unplugging a fan, inserting a modified 4-way extension lead (if you can find one) with a DC Ammeter or digital multimeter in series with the 12V supply rail and measuring the current properly. Most of the time the fans will draw less than 12W each.

Size Name: CPU- en GPU-koelventilator

Brand	Annadue
Power connector type	4-Pin
Voltage	12 Volts
Wattage	12 watts
Cooling method	Forced air
Compatible devices	Laptop

 

[PiersPlowman]

@Misgar

I would not trust those numbers - a 12 watt fan in a laptop would sound like a Dyson hair dryer, not to mention it would be a substantial source of heat in its own right.

1.2 Watts, maybe.

 

[Misgar]

1.2 Watts, maybe.

Well, the picture of the fan I posted shows 12V 1A printed on the body of the fan and that's 12W max as far as I'm concerned.

a 12 watt fan in a laptop would sound like a Dyson hair dryer

True, but the G14 (2021 version) was described as "the world's most powerful gaming laptop" so it probably requires more cooling than a standard laptop:-
https://rog.asus.com/laptops/rog-zephyrus/2021-rog-zephyrus-g14-series/helpdesk/

Both Zephyrus fans will only run at full speedn in the G14 when running benchmarks or possibly during very intensive games.

For the rest of the time, fan speeds will be lower, depending on CPU and GPU power. When the laptop is idle, you might not hear the fans running.

In any case, when gaming, you may well be using headphones or big speakers turned up loud, so the "Dyson hair dyer" fan noise might be drowned out.

not to mention it would be a substantial source of heat in its own right.

Very true. Two Zephyrus G14 laptop fans would add a signifiicant amount of heat (24W total at full speed) but that's perfectly normal and will have been taken into consideration by the thermal design engineers.

If you want an example of a small high power fan, consider the Delta FPR0612XHE. It's only 60mm x 60mm, but can run up to 16,500RPM at 12V 2.3A (27.60W):-
https://www.delta-fan.com/pfr0612xhe.html

This version is rated at 12V 3.3A max (39.6W):-
https://www.amazon.co.uk/PFR0612XHE-High-end-server-violent-strong/dp/B09NBMRNZ2

I have four 80mm x 80mm Delta fans in each of my HP servers and yes they can get exceedingly loud. That's why you wear ear defenders when working long-term in large server halls. Not typical laptop fare, but small powerful fans do exist and perform a very effective cooling job, despite adding to the heat load.

 

[PiersPlowman]

Well, the picture of the fan I posted shows 12V 1A printed on the body of the fan and that's 12W max as far as I'm concerned.


True, but the G14 (2021 version) was described as "the world's most powerful gaming laptop" so it probably requires more cooling than a standard laptop:-
https://rog.asus.com/laptops/rog-zephyrus/2021-rog-zephyrus-g14-series/helpdesk/

Both Zephyrus fans will only run at full speedn in the G14 when running benchmarks or possibly during very intensive games.

For the rest of the time, fan speeds will be lower, depending on CPU and GPU power. When the laptop is idle, you might not hear the fans running.

In any case, when gaming, you may well be using headphones or big speakers turned up loud, so the "Dyson hair dyer" fan noise might be drowned out.


Very true. Two Zephyrus G14 laptop fans would add a signifiicant amount of heat (24W total at full speed) but that's perfectly normal and will have been taken into consideration by the thermal design engineers.

If you want an example of a small high power fan, consider the Delta FPR0612XHE. It's only 60mm x 60mm, but can run up to 16,500RPM at 12V 2.3A (27.60W):-
https://www.delta-fan.com/pfr0612xhe.html

This version is rated at 12V 3.3A max (39.6W):-
https://www.amazon.co.uk/PFR0612XHE-High-end-server-violent-strong/dp/B09NBMRNZ2

I have four 80mm x 80mm Delta fans in each of my HP servers and yes they can get exceedingly loud. That's why you wear ear defenders when working long-term in large server halls. Not typical laptop fare, but small powerful fans do exist and perform a very effective cooling job, despite adding to the heat load.

Well, well. I couldn't imagine laptop fans consuming more than 20x the power of my 14" Noctuas.

Do you have to lash the laptop to the desk to stop it taking off and flying out of the office?

 

[CelicaGT]

Well, the picture of the fan I posted shows 12V 1A printed on the body of the fan and that's 12W max as far as I'm concerned.


True, but the G14 (2021 version) was described as "the world's most powerful gaming laptop" so it probably requires more cooling than a standard laptop:-
https://rog.asus.com/laptops/rog-zephyrus/2021-rog-zephyrus-g14-series/helpdesk/

Both Zephyrus fans will only run at full speedn in the G14 when running benchmarks or possibly during very intensive games.

For the rest of the time, fan speeds will be lower, depending on CPU and GPU power. When the laptop is idle, you might not hear the fans running.

In any case, when gaming, you may well be using headphones or big speakers turned up loud, so the "Dyson hair dyer" fan noise might be drowned out.


Very true. Two Zephyrus G14 laptop fans would add a signifiicant amount of heat (24W total at full speed) but that's perfectly normal and will have been taken into consideration by the thermal design engineers.

If you want an example of a small high power fan, consider the Delta FPR0612XHE. It's only 60mm x 60mm, but can run up to 16,500RPM at 12V 2.3A (27.60W):-
https://www.delta-fan.com/pfr0612xhe.html

This version is rated at 12V 3.3A max (39.6W):-
https://www.amazon.co.uk/PFR0612XHE-High-end-server-violent-strong/dp/B09NBMRNZ2

I have four 80mm x 80mm Delta fans in each of my HP servers and yes they can get exceedingly loud. That's why you wear ear defenders when working long-term in large server halls. Not typical laptop fare, but small powerful fans do exist and perform a very effective cooling job, despite adding to the heat load.

Inductive load vs resistive load. That 1A will only be drawn at startup (assuming they label the motor the way they are supposed to), likely lowers to the low mA level once running. Also, because a fan is doing actual work (moving air) only a portion of the energy used is converted to heat and transferred into the device.

 

[Misgar]

Inductive load vs resistive load. That 1A will only be drawn at startup (assuming they label the motor the way they are supposed to), likely lowers to the low mA level once running.

I'm not sure this is entirely true.

If you check out this web site, it describes in some detail the difference between the Nominal Rated Current, the Inrush Current and the Startup Current, citing a fan with 3A Rated Current.

https://coolingfans.blog/current-specifications-of-dc-cooling-fans-you-need-to-know/

The Inrush Current spikes at 6.5A but for less than 20us.

The Startup Current peaks at 9.25A for 500ms (remember this is for a 3A fan).

"In conclusion, the published nominal current rating of the fan is based on operating at full speed and measured under open-air test bench conditions.

The inrush current occurs when power is applied to the fan to charge up all the components and is a very short spike.

The start-up current for all DC fans must be considered to ensure your power supply is rated high enough to handle the current."

I believe this means a fan with a published Rated Current of 3A will draw 3A when running at full speed (in open air) and not as suggested "likely lowers to the low mA level once running".

Obviously many/most computer fans do not run at full speed all the time and hence will not draw full Rated Current. A fan rated at 2000RPM max. will draw a much lower current when ticking over at 200RPM.

But, when fans are running at full speed, they draw considerably more current, because they're working much harder. As they'd say in Latin, perspicuum est.

 

[helper800]

I'm not sure this is entirely true.

If you check out this web site, it describes in some detail the difference between the Nominal Rated Current, the Inrush Current and the Startup Current, citing a fan with 3A Rated Current.

https://coolingfans.blog/current-specifications-of-dc-cooling-fans-you-need-to-know/

The Inrush Current spikes at 6.5A but for less than 20us.

The Startup Current peaks at 9.25A for 500ms (remember this is for a 3A fan).

"In conclusion, the published nominal current rating of the fan is based on operating at full speed and measured under open-air test bench conditions.

The inrush current occurs when power is applied to the fan to charge up all the components and is a very short spike.

The start-up current for all DC fans must be considered to ensure your power supply is rated high enough to handle the current."

I believe this means a fan with a published Rated Current of 3A will draw 3A when running at full speed (in open air) and not as suggested "likely lowers to the low mA level once running".

Obviously many/most computer fans do not run at full speed all the time and hence will not draw full Rated Current. A fan rated at 2000RPM max. will draw a much lower current when ticking over at 200RPM.

But, when fans are running at full speed, they draw considerably more current, because they're working much harder. As they'd say in Latin, perspicuum est.

Like I said in the beginning, the only way to know for a fact about their particular fan is by testing with a meter. Looking at specifications will only ever give a tolerance range for any given fan with that model number.

 

[Misgar]

Looking at specifications will only ever give a tolerance range for any given fan with that model number.

In all the years I worked as an electronics design engineer on Milspec and Aerospace projects, I accepted reputable manufacturers' data sheets contained valid data. If a data sheet stated a nominal current of 3A at full speed, it was usually correct.

Of course we measured power consumption of various boards and modules plus complete units under a wide range of operating scenarios, but I don't remember measuring individul fan currents very often. We worked on the principle of maximum current draw when designing power systems, to ensure adequate power under full load, plus a good margin of overhead.

As for tolerance, I usually express that in terms of percent around a nominal value, e.g. a1kΩ resistor could have a tolerance of ±5% (gold band), i.e. 950Ω to 1050Ω.

On a fan, as this article explains, fan manufacturers might not mention tolerances.
https://www.newark.com/pdfs/techarticles/mro/DCBrushlessCoolingFanBehavior.pdf

In terms of maximum speed the article states:
"The data sheets from fan manufacturers may not clearly state this value has a tolerance associated with it. Tolerances vary from manufacturer to manufacturer, but a tolerance of + 10% is typical."

In terms of maximum current consumption, I'd expect a similar tolerance of ±10%, e.g. for a 3A fan, maximum steady state current could be anywhere between 2.7A and 3.3A at full speed. This does not include the initial startup current, e.g. 9.25A for 500ms in previous example.

When maximum cooling performance is not required, the system may reduce fan speed and hence current drawn. This is typical of most laptops and desktop PCs where fans speed up or down as required.