LED That Indicates 'Powered Fan'
LED That Indicates 'Powered Fan'
(OP)
Hi all,
I have a simple problem to fix, but I can not find a solution equally trivial
There is a small fan powered at 12VDC operated by a thermostat.
When the thermostat closes, the fan starts rotating and a small lamp (placed in parallel) switches on to remotely indicate the activity.
It might happen that the fan starts to rotate freely under the action of the wind while not being directly fed, and this is indicated by a weak illumination of the lamp.
Now, wanting to replace the lamp with a simple LED, how do I prevent that the LED switches ON when the fan is NOT powered on but it rotates spontaneously?
Obviously the best idea is that easiest!
I have a simple problem to fix, but I can not find a solution equally trivial

There is a small fan powered at 12VDC operated by a thermostat.
When the thermostat closes, the fan starts rotating and a small lamp (placed in parallel) switches on to remotely indicate the activity.
It might happen that the fan starts to rotate freely under the action of the wind while not being directly fed, and this is indicated by a weak illumination of the lamp.
Now, wanting to replace the lamp with a simple LED, how do I prevent that the LED switches ON when the fan is NOT powered on but it rotates spontaneously?
Obviously the best idea is that easiest!





RE: LED That Indicates 'Powered Fan'
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RE: LED That Indicates 'Powered Fan'
interesting the idea of inserting a current sense resistor... But it would need additional circuitry to drive the LED.
Do you have in mind a particular model to suggest?
RE: LED That Indicates 'Powered Fan'
How to efficiently protect the small led by extra currents due to the coil?
RE: LED That Indicates 'Powered Fan'
Alternatively, if you have a spare switched terminal on the thermostat that you're laughing:
* if you have CO contacts, connect the common to the lamp and then one of the switched terminals to 12V and one to a loop of wire that shorts the fan out.
* if you have double pole contacts, switch the fan and the LED as separate circuits.
RE: LED That Indicates 'Powered Fan'
Place a diode(s) in series with the LED so the forward voltage is, say, 10V. The wind would have to blow extremely hard to get the LED to turn on then...
Dan - Owner
http://www.Hi-TecDesigns.com
RE: LED That Indicates 'Powered Fan'
There are a zillion possible solutions. Above is probably the simplest.
Another option is to use a PC type cooling fan with built in electronics to drive the motor. These are very common. They don't work as generators due to the complicated circuitry inside the fan.
RE: LED That Indicates 'Powered Fan'
Yes, it looks the simplest way to go, since the lamp have to be replaced by the led.
RE: LED That Indicates 'Powered Fan'
RE: LED That Indicates 'Powered Fan'
There are a lot of solutions to be considered
RE: LED That Indicates 'Powered Fan'
That said, it looks like a simple diode solution has to be revised because of the current, and I guess it need a strong job to be cooled properly.
What about a simple resistor like 1K in parallel to the fan and in series to the diode? It could prevent the fan working as generator for the diode when is not supplied...
RE: LED That Indicates 'Powered Fan'
"Small" fan doesn't normally correlate with "30-40 Amps or so."
If it's a large fan, then the most-practical ordering of the options changes.
RE: LED That Indicates 'Powered Fan'
I am sorry for the missed info.
RE: LED That Indicates 'Powered Fan'
Good luck.
RE: LED That Indicates 'Powered Fan'
Dan - Owner
http://www.Hi-TecDesigns.com
RE: LED That Indicates 'Powered Fan'
RE: LED That Indicates 'Powered Fan'
Dan - Owner
http://www.Hi-TecDesigns.com