# Trying to figure out the effect of different amperage for a laptop fan.

i had to change the cooling fan on my laptop but being an old one, i had to get a spare part which wasn't exactly the same - it's by the same manufacturer with similar model number and dimension (size, mounting screw positions, etc) except rated at 5V and 0.55A while the original was 5V and 0.35A

obviously this new fan will draw more current from the power supply, but my questions is what effect it will have on the actual running.

it is a "3-wire" fan, ie. V+, GND and "TACH", which is basically a Hall effect sensor telling the PC/laptop what the rotation speed is at.

will the different current rating mean the fan "under-reports" to the motherboard/controller(?) what the speed is - and thus, not being active (yet) when the "hot" temperature is reached ?

would there be some kind of circuit that would convert the 0.55A draw into 0.35A ?

The tach signal is probably a digital signal, which works quite well in your case. If the computer power source provides 5 V but expects to provide only 0.35 A and the fan wants to suck 0.55 A, there might be a voltage drop and a drop in the fan rpm, but the tach probably gives the correct value to your computer.

hang on, "wants to suck" 0.55 A or actually does so ? :-/

i thought the device determines what current does flow, assuming power supply is sufficient.

and that "drop in fan rpm" is my concern, the correct value may be fed back to the PC, but that slow(er) speed means the fan will not be cooling the temperature correctly.

what i am thinking is that, the temperature will be hotter than the PC thinks it is - am i mistaken here ?

The reason for a higher current draw might be that the new fan is capable of a higher RPM than the old one.
I wouldn't worry too much about that slightly higher current rating.
Leo..

Wawa:
The reason for a higher current draw might be that the new fan is capable of a higher RPM than the old one.
I wouldn't worry too much about that slightly higher current rating.
Leo..

i see... well, i'd rather be overcautious - i'm down to my "last usable laptop" (!) and i don't want to reduce it's (already long) iifespan with unnecessarily (over)heating.

it could be just me, but it does seem the laptop runs hotter now with the new fan....

i need to get a proper temperature sensor and put my Arduino to useful work !

Did you clean the 'radiator' of the fan (with a brush and vacuum cleaner).
Blocked radiators (dust) are a common cause when laptops are overheating.
Leo..

Most modern cpu's have a built-in temperature sensor, and drive the fan to hold it below a limit.

If you look in the bios it'll probably tell you the measured temperature.

Allan

Wawa:
Did you clean the 'radiator' of the fan (with a brush and vacuum cleaner).
Blocked radiators (dust) are a common cause when laptops are overheating.
Leo..

yep - wiped totally clean with a cotton bud after removing the housing cover !
(that was for the old one ofc, and it didn't get as hot... seemingly.)

allanhurst:
Most modern cpu's have a built-in temperature sensor, and drive the fan to hold it below a limit.

If you look in the bios it'll probably tell you the measured temperature.

Allan

this might not be "modern", it's at least 10 yrs old !

i guess if the CPU drove the fan when it reached "hot", it wouldn't matter what the fan required in terms of power, - and since it's not a 4-wire fan, there's no variable speed to mess about with, the CPU just says "ON" or "OFF".

am still wondering about the power supply though, if it is indeed limited to only 0.35A (from the computer) - it might not drive the (new) fan at optimal levels to cool things down (fast/er enough).

does that make sense from the perspective of electronic circuits ?

hang on, "wants to suck" 0.55 A or actually does so ? :-/

If it "sucks" 0.55 A, then your power source is able to provide 0.55 A. Or it will burn after a while. If it sucks only 0.35 A, it is because your power source has an inner resistance, which drops the voltage to .35/.55 of 5 V. Roughly explained.

Johan_Ha:
If it sucks only 0.35 A, it is because your power source has an inner resistance, which drops the voltage to .35/.55 of 5 V. Roughly explained.

thanks!

Johan_Ha:
If it "sucks" 0.55 A, then your power source is able to provide 0.55 A. Or it will burn after a while.

sorry to ask a dumb question, but what do you mean "it will burn" ? - sounds ominous...

The power source itself might provide 0.55 A, but if all components like heatsinks etc are meant for only 0.35 A, stuff might get overheated and start to melt, smoke, burn, boil or explode. In theory. 0.55 and 0.35 is not that much of a difference, frankly I don't think anything will happen, but don't take my word for it.

BabyGeezer:
yep - wiped totally clean with a cotton bud after removing the housing cover !

No, not what I mean. You can't clean the inside of a radiator with a cotton bud.

There is a radiator inline with the fan's air stream that gets clogged up inside.
You need to use a vacuum cleaner and small paintbrush, or compressed air to blow the dust out.
Take care with compressed air. You might get the dust into other unwanted places (CD drive).
Leo..

Wawa:
No, not what I mean. You can't clean the inside of a radiator with a cotton bud.

this is a very small fan, only 5 cm; and it's the "side-blowing" type so there's no "radiator section" - here's a picture of what it looks like with the cover plate taken off, the cotton bud was for wiping each individual blade.

Johan_Ha:
The power source itself might provide 0.55 A, but if all components like heatsinks etc are meant for only 0.35 A, stuff might get overheated and start to melt, smoke, burn, boil or explode. In theory. 0.55 and 0.35 is not that much of a difference, frankly I don't think anything will happen, but don't take my word for it.

those other parts should be my main concern then, but so far no over-heating detected, so i guess no explosion to worry about - although i'm thinking there will be a higher rate of "normal wear & tear" - 0.2 A might not "be much of a difference" but it is a 57% increase !

BabyGeezer:
this is a very small fan, only 5 cm; and it's the "side-blowing" type so there's no "radiator section"

If that fan is inside the laptop, then the fan MUST blow (or suck) it's air through a radiator (aluminium grill).

If that's blocked (common), than the fan must work harder, and will fail.
Leo..

BabyGeezer:
i had to change the cooling fan on my laptop but being an old one, i had to get a spare part which wasn't exactly the same - it's by the same manufacturer with similar model number and dimension (size, mounting screw positions, etc) except rated at 5V and 0.55A while the original was 5V and 0.35A

The laptop's power supply should be able to handle it. The old fan required maybe 1.75 watt ... the new one requires 2.75 watt. So it will be just up to the laptop's power supply. At a guess ..... shouldn't be a problem.

On the other hand, it's beneficial to get replacement parts that match the original part in terms of ratings..... unless confident that the rest of the system can easily handle a part that has different specifications.

Wawa:
If that fan is inside the laptop, then the fan MUST blow (or suck) it's air through a radiator (aluminium grill).

If that's blocked (common), than the fan must work harder, and will fail.
Leo..

oh that - yes, that's part of the chassis - i've given it a general dusting when i first cracked it open, but i'll give it an extra look and wipe it (the aluminium grill.)

but whatever the condition it was in, it was also valid for the older fan.
(i'm replacing it because it makes a rattling noise, the housing is like in the pic above, no screw so i don't know how to force it open to (perhaps?) add lubrication to the inside).

Southpark:
The laptop's power supply should be able to handle it. The old fan required maybe 1.75 watt ... the new one requires 2.75 watt. So it will be just up to the laptop's power supply. At a guess ..... shouldn't be a problem.

yeah - "should" - that still worries me, i will be scientific about it and try to compare the performances thermally - ie. that temperature measuring exercise, just to be sure.

Southpark:
On the other hand, it's beneficial to get replacement parts that match the original part in terms of ratings..... unless confident that the rest of the system can easily handle a part that has different specifications.

it's a really old laptop, so i can't be too choosy - i haven't tried sourcing it (the exact model) from the manufacturer (searching online) - don't know how much i'd have to fork out if it came to that.

BabyGeezer:
yeah - "should" - that still worries me, i will be scientific about it and try to compare the performances thermally - ie. that temperature measuring exercise, just to be sure.

heheheh..... don't worry at all. Consider a desktop power supply....eg 600W supply. It's sort of like ...... a system is using 300W, and then you add a small extra load on it... so it becomes 301W. No problem for the supply. It is meant to handle it. The wire(s) will be able to handle it as well. No problem.

Wawa:
Did you clean the 'radiator' of the fan (with a brush and vacuum cleaner).
Blocked radiators (dust) are a common cause when laptops are overheating.
Leo..

I'd recommend not doing this with the fan installed - suction or blowing can overspeed the fan,
maybe damage its bearings or generate high voltages in the windings and damage the electronics
of the laptop.

Southpark:
heheheh..... don't worry at all. Consider a desktop power supply....eg 600W supply. It's sort of like ...... a system is using 300W, and then you add a small extra load on it... so it becomes 301W. No problem for the supply. It is meant to handle it. The wire(s) will be able to handle it as well. No problem.

well, the power adaptor is rated at 20V and 2.0 A so i suppose the power supply is fine.

i just hope the surrounding components don't get over-strained with the extra current draw.

MarkT:
I'd recommend not doing this with the fan installed - suction or blowing can overspeed the fan,
maybe damage its bearings or generate high voltages in the windings and damage the electronics
of the laptop.

yes, i make it a point to never connect power when the computer is "nekkid".

i make it a point to never connect power when the computer is "nekkid".

No you misunderstood, even without power connected a fan spinning fast can act as a generator and force current through the dormant circuits. This is not a good thing to do with electronics.