Resistance in a circuit caused by the wiring

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Discussion Overview

The discussion revolves around the unexpected current draw of a CPU fan in a DIY laptop cooler circuit, specifically examining the potential causes of resistance in the wiring and connections. Participants explore the implications of the fan's rated current versus the measured current, as well as the impact of components like wiring and switches on overall resistance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • The original poster (OP) notes a discrepancy between the expected current draw of 0.37A for the fan and the measured current of 0.28A, raising questions about the source of the additional resistance.
  • Some participants suggest that the fan's rated current may represent a maximum value, implying that a lower current draw could be normal.
  • The OP calculates the resistance of the fan based on its ratings and the measured current, leading to a hypothesis that the difference in resistance could be attributed to the wiring.
  • One participant questions whether the aluminum foil switch used by the OP might be contributing to increased resistance in the circuit.
  • Another participant suggests that poor connections could be responsible for the excess resistance observed in the circuit.

Areas of Agreement / Disagreement

Participants express differing views on the expected current draw of the fan and the potential causes of the resistance. There is no consensus on whether the wiring or the switch is primarily responsible for the observed current discrepancy.

Contextual Notes

The discussion does not resolve the assumptions regarding the fan's rated current, the impact of the aluminum foil switch, or the exact contribution of wiring resistance. The calculations presented are based on the OP's measurements and interpretations, which may not account for all variables in the circuit.

Who May Find This Useful

This discussion may be of interest to individuals involved in DIY electronics projects, particularly those working with fans and power circuits, as well as those exploring the effects of wiring and connections on circuit performance.

fulmenatrum
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Recently, I made a laptop cooler using an old CPU fan (rated 12V, 0.37A) I removed from a desktop. The cooler was comprised of the cooling fan, a base for the laptop to go on, and a DC power adapter (rated 12V, 1A)...nothing too complicated. Now from what I know, the current being drawn by the circuit should be equivalent to what the device, in this case the old CPU fan calls for, or 0.37A. However, when I connect the multimeter in series with the circuit, the rating i get is 0.28A.

The following calculations are all based on what I thought to be correct which may be totally wrong so please correct me by all means. Using V=IR, I found what I thought the resistance of the fan should be using its ratings (so, R=V/I...R=12V/0.37A...R=32.42Ohms). Next, I found the resistance of the fan using the measurements I got from the whole circuit which included the power adapter, cheap wire, and fan (R = 12V/0.28A = 42.85Ohms).

My question is if I could credit the 10.43Ohms (42.85Ohms - 32.42Ohms) to the wiring (and thus, the lower reading of current) since it is in series with the fan or whether it would be totally incorrect to assume this as the fan itself is composed of other electrical components I have no way of including in my calculations.

Any help would be much appreciated. Thank you!
 
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Is the fan running like you expect it to?

The rating given on the fan is probably a maximum value. If so, the fan only drawing 0.28A is probably about right. You can calculate the impedance of your wire, but I would expect it to be less than 1 Ohm.
 
It's running well enough, though I always assumed that it draws as much current as shown on the label. I wonder if the aluminum foil switch I made increased the resistance.
 
fulmenatrum said:
It's running well enough, though I always assumed that it draws as much current as shown on the label. I wonder if the aluminum foil switch I made increased the resistance.

aluminum foil switch ?? how about spending a buck and getting a proper switch
the poor connections are probably what is causing your excess resistance

Dave
 

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