A Discrete Puller Fan On Light

davids2toys · #1 (**permalink**) 12-22-2022, 08:45 AM

Same to you

spdbrake · #2 (**permalink**) 12-24-2022, 06:00 PM

You can use a DC current sensing switch, anywhere on the Fan feed power wire. Once the switch trips (meaning the fan is actually working) it will complete the circuit to the LED indicator (grd or pwr) whichever you prefer.

There are a few thousand types and sizes of these. A bit harder to find a DC 12/24vdc one though.
This is one: https://www.amazon.com/Current-Sensi...09YN9Q9YP?th=1

patrickt · #3 (**permalink**) 12-24-2022, 07:49 PM

Quote:

Originally Posted by spdbrake

You can use a DC current sensing switch, anywhere on the Fan feed power wire.

alright. But did you think what happens when the airflow spins an otherwise still fan motor? It will generate a small amount of current through the wire....

spdbrake · #4 (**permalink**) 12-24-2022, 08:54 PM

A motor needs field excitation become a generator. But A: Even if the Motor could generate electricity, it has no current since it goes nowhere.
B: Shunt field is directional and won't measure reverse flow.

patrickt · #5 (**permalink**) 12-25-2022, 07:27 AM

Quote:

Originally Posted by spdbrake

A motor needs field excitation become a generator. But A: Even if...

I have an inductive ammeter and used it in this thread back in 2010: 300 amp X 12 volt Circuit breaker but I'm trying to think of why I would use that switch instead of just tapping directly into the feed. I suppose if the two voltages were different, or if the feed wire was really current sensitive and you didn't want to change it by firing off the next circuit, but I just don't see that on the Cobra.

spdbrake · #6 (**permalink**) 12-25-2022, 08:42 AM

I think I understand the question (or maybe not).
The Current sensing switch is an normally off(open) switch. As current flows thru (used by the fan motor) it closes at a preset amperage. The one I posted is adjustable. The Current switch has a X1 post, where you can hook a local -neg or +Pos to and also an X2 post that will continue the +power or -gnd to the LED indicator once the switch closes. Basically giving you a remote indication that the motor is using electricity.

Tapping into the feed and sending it to the the LED only tells you the power is available but not if the Fan motor is working.

patrickt · #7 (**permalink**) 12-25-2022, 09:18 AM

Quote:

Originally Posted by spdbrake

Tapping into the feed and sending it to the the LED only tells you the power is available but not if the Fan motor is working.

You're absolutely right, I hadn't thought of that. Kind of like the ignitor/valve switch on a gas stove. If it's not seeing six amps or more being pulled, by being red hot, it won't open the gas valve.