Evaluating laptop fan health

[pingaroon]

Hi everyone,
I have a big box of laptop fans and have been testing them one by one with a bench power supply.

All are 5v, but have different power ratings in Amps (from .19 up to .6)

Presumably this Amperage rating is the maximum it can theoretically supply, so here is my question.

Given 3 identical fans with the bench voltage set to 5v and the amps set to auto (no cap), you would expect the amps to be the same on all 3. If it draws more amps (closer to the rating limit), does that indicate the fan is in poorer health (as it is having to work harder) ? Conversely, if the amps are low (nowhere near the limit), could that indicate a fault or is it just using as much as it needs and so is in good health?

I noticed for example testing 5A fans, some of them draw .45A, whilst others draw .25A etc.

What can I deduce from the power supply readings in order to test the health of these fans.

THANK YOU

[stj]

Re: Evaluating laptop fan health

the current rating is an indication of power it will draw.
that could mean more flow, or more static pressure, or it could just be bigger

the real test its does the shaft/blades wobble or have any play.
that would indicate the bearing is worn.

[momaka]

Re: Evaluating laptop fan health

What can I deduce from the power supply readings in order to test the health of these fans.

Not much, honestly.

The maximum power and/or current rating stated on the fan is probably what the fan will draw under "worst" conditions, whatever those may be (blocked fan intake or output or locked rotor due to an object.) It's a bit ambiguous, IME, and the -running- current typically tends to be much lower than the stated current, though not always.

You should also consider the fact that the windings on fans are inductive devices... and as such, the typical tolerance for those can be +/-20%... so I imagine the current/power draw may also vary as much even between two identical fans.

Therefore, I don't think you can say anything about a fan's health based solely on the current it draws. Like stj noted, just spin the fan and watch it come to a full stop, then note how much it "wobbles" back and forth as it does that. This will tend to be a lot more pronounced with ball bearing fans, as BBs usually have lower resistance/friction than sleeve bearing fans. Of course, it will also depend on magnet strength and design too - weaker/slower fans with weaker magnets will tend not to wobble as much as stronger fans.

In any case, the easiest way to tell IMO, is to just spin the fan and watch it slow down to a stop - if it stops too fast, the bearing is definitely in need of service (well, if it's a sleeve bearing anyways - ball bearings you can't service and only can replace them.) And also try the fan at full speed and at lower speeds while listening for any grinding or clacking noises (the latter typically only seen in work/broken BB fans.)