Need a simple motor rotation indicator

[Clay LaHatte]

Hi,

I have looked for a long time now, and have not been able to find a device to do the simple task I need done. I want to put a simple device on my attic vent fan that will light an LED when the motor is running.

Does anyone know of such a device? Surely there is an inexpensive option off the shelf?

Thanks.
Clay

 

[alec_t]

A lever-operated microswitch with a light-weight vane attached? Vane deflects/tilts when fan blows air on it and operates switch.

 

[Clay LaHatte]

A lever-operated microswitch with a light-weight vane attached? Vane deflects/tilts when fan blows air on it and operates switch.

Well, that is certainly an interesting option. I might prefer something a little more robust, but I will certainly consider that.

Thanks.
Clay

 

[KeepItSimpleStupid]

They are robust. They make them commercially that way. I had one in a piece of equipment. In another piece, they used a differential pressure sensor. The cost was well over $100 and it had to be replaced. An air velocity meter which uses a thermal sensor got dirty and required cleaning, Cost was well over $500 - $1000. One system had a readout and the other didn't, hence a failure meant you had to clean it or some other problem. With the readout, you could proactivley clean it.

Trust me, the vane and microswitch is more robust. It's just a lightweight piece of metal with a small piece of wire attached to it and the microswitch lever in the exit air stream.

 

[crutschow]

Can't you just wire an indicator light across the power to the fan motor?

 

[jbeng]

Can't you just wire an indicator light across the power to the fan motor?

He could do that, but it would only tell if power was applied to the motor. It wouldn't indicate if the fan was actually moving air.

 

[Clay LaHatte]

They are robust. They make them commercially that way. I had one in a piece of equipment. In another piece, they used a differential pressure sensor. The cost was well over $100 and it had to be replaced. An air velocity meter which uses a thermal sensor got dirty and required cleaning, Cost was well over $500 - $1000. One system had a readout and the other didn't, hence a failure meant you had to clean it or some other problem. With the readout, you could proactivley clean it.

Trust me, the vane and microswitch is more robust. It's just a lightweight piece of metal with a small piece of wire attached to it and the microswitch lever in the exit air stream.

Any thoughts on a microswitch to use? The ones I have require more force to activate than the wind from the fan would generate.

For this option, if I can find a light touch switch, I suppose I could attach a thin piece of sheet metal directly flat to the switch arm, with a small screw,
to catch the air.

 

[alec_t]

It's just a lightweight piece of metal with a small piece of wire attached to it and the microswitch lever in the exit air stream.

Or it could be in the flow entering the fan.

 

[Clay LaHatte]

My original thought was to have something magnetic that I could attach on the shaft. Or, some sort of hall effect sensor. I have seen sensor bearings, but they are far more expensive than what I need for this.

 

[KeepItSimpleStupid]

Something like this: https://www.newark.com/honeywell-s-c/311sm703-t/micro-switch-straight-lever-spdt/dp/78K5282

 

[dr pepper]

You can get such thngs pre made, a piece of equipment I used to maintain had a ultra low force microswitch with a little square of ally fastened to it, airflow pushed on the flap making the switch.
You might not be able to get these anymore, but you can get the switches, just a matter of a little fabrication.

**broken link removed**

 

[Clay LaHatte]

Something like this: https://www.newark.com/honeywell-s-c/311sm703-t/micro-switch-straight-lever-spdt/dp/78K5282

I ordered some of these... https://www.aliexpress.com/snapshot/6194342692.html

 

[KeepItSimpleStupid]

OK, the arm isn't as long and I have no idea where you are.

See, https://www.lowpressure.com/products/103.html they are made.

Anyway, https://www.aliexpress.com/item/One...013-NC-With-Protective-Grille/1666123101.html

Look for "vane airflow switch"

 

[crutschow]

He could do that, but it would only tell if power was applied to the motor. It wouldn't indicate if the fan was actually moving air.

Agreed. But how important is that for an attic fan?

 

[Clay LaHatte]

OK, the arm isn't as long and I have no idea where you are.

See, https://www.lowpressure.com/products/103.html they are made.

Anyway, https://www.aliexpress.com/item/One...013-NC-With-Protective-Grille/1666123101.html

Look for "vane airflow switch"

Nice. That could be perfect. That second link I like. Thanks!

 

[Clay LaHatte]

Agreed. But how important is that for an attic fan?

If the motor fails in the attic, how would you know? That's why I want to know if it's running.

 

[ChrisP58]

I would try a photoelectric approach. An LED on one side of the fan, and a photo transistor on the other. If the fan is running. the optical path is alternately blocked, then not blocked, many times per second.

Wire the transistor output to a missing pulse detector set up to to alarm if no pulses were received within some short period of time.

Of course, the fan won't be running when it's turned off, so you'll need to disable the alarm during that mode of operation.

 

[MrAl]

Hi,

Can you actually see the fan or is the LED going to be remote?
If you can see the fan then a ribbon tied to the exhaust grill will show it running.

Also, monitoring the temperature of the attic would tell you if it was not working anymore. Perhaps inside and outside temperature measurements. As you monitor temperature over time you will see a trend in the temperature where it will be different when the fan is running then when it is not running.

 

[cowboybob]

Overkill, perhaps, but definitive.

We needed to know if our shrimp pond aerators (3 phase) were working.

I monitored four conditions of one leg of the motor's current draw with a current transformer:

1. Zero amps = off, tripped breaker or starter relay failed
2. Normal = motor turning with appropriate load (also, belt intact)
3. < normal = motor free wheeling (belt broken)
4 > normal = aerator component stalled, motor damaged etc..

That said, as Mr Al notes, an indoor/outdoor thermometer. You could extend the wires of the outdoor sensor, to suit your length needs, without seriously altering the readout accuracy.

 

[MikeMl]

When I wanted to know what was happening in the attic, I placed an RF-link remote reading thermometer there. I could tell if the fan was running by the temperature drop within a min of starting the fan...