On Wednesday, November 9, 2016 at 2:46:10 PM UTC-5, Jon Elson wrote:
wrote:

On Tuesday, November 8, 2016 at 3:42:12 PM UTC-5, Jon Elson wrote:
wrote:

On Tuesday, November 8, 2016 at 7:21:17 AM UTC-5, N_Cook wrote:

Much Snippage

Questions:

a) What is the actual resistance in ohms of the OEM fan and the
replacement fan if measured across the contacts.

Meaningless. These fans have a commutation circuit and some FETs in
them, so you will not read anything that resembles a resistance on them.

Jon

No. The two that work ohm out at ~10 meg. The two that do not ohm out at
~20K. So, yes, you are seeing 'resistance' on them. Clearly "these fans"
are not created equal.
But, clearly, if it was TRULY a 10 Meg resistor, the fans would not produce
any airflow. When you get enough voltage on them, the circuitry turns on
and starts drawing current to spin the rotor.

The 20K ones might have a popped component, or just a different control
circuit.

Jon

You miss the point - no surprise there - what the "protection mode" sees is the initial state of the fan, which is around ~10 megs. Which does not trip it. When it sees 5% of that, it trips. When the fan is running, clearly the protection circuit is OK with what must be a much lower operating (spinning) impedance.

Yes, perhaps a different circuit, no sh*t. Point being, yet again, is that the fans are not created equal. And the point of measuring initial resistance is to be able to separate the ones that might work from the ones that will, clearly, not work without having to test-by-substitution, a not very efficient method.

Peter Wieck
Melrose Park, PA