Cabinet Fan Question

[jim4065]

I'm finally getting some work done on the casting cabinet. It will have 2 or 3 small (computer type) fans to exhaust smoke from fluxing. These fans are 110 volt and 12 watts each. Been thinking of some type of visual signal telling when or if one of the fans quits working. Can I just wire in an LED on the common lead coming off each fan - or something like that? I need more than one fan because the door opening is really big (about 16" high by 36" wide). Already have the fans, so don't want to get a range hood, etc. In fact - I have 6 of the fans, and want to use some. The 2 or 3 fans will be pushing exhaust air thru a 4" duct and then out the wall. If one fan goes out, the others will push some of the air back into the cabinet. It will be very hard to see the fans, which is why I'd like a light for each fan telling me that it is running, not just that the power is turned on (I can tell that by the switch).

If anyone can tell me a part number from radio shack and how (or where) to wire it in, I'd appreciate it.

[lurch]

I'm not sure of the best quick & dirty way to detect an AC fan failure. I do know that putting an LED in one of the leads will only work for about 8 milliseconds maximum - the time it takes for the line voltage to reverse and turn the LED back into sand (won't really do that but the LED will definitely cease to function).

One possibility would be an airflow sensor (an RTD or thermistor with a current through it that wants to heat it up) mounted in the fan blast. The airflow would cool the device and keep the resistance and hence voltage across it withing a certain range. If the airflow stopped the device would heat up, change resistance and hence voltage. That could be detected easily enough and used to turn on an LED.

Small DC fans are a lot easier to work with in this area and there are relatively easy canned (sort of...) solutions there.

I'll do some looking if you want but it's probably going to take a little tinkering. If you're not at least a hobbyist in the electronics area it'll be a challenge, but not outside the realm of doable.

Perhaps the easiest (and probably cheapest) solution would be to wire each fan to an individual switch. Turn them on individually and you should be able to hear each one spin up. Fans don't tend to fail all of a sudden and if it worked when you turned it on, it will in all likelihood work for the duration of a casting session. You should get plenty of warning of impending failure from bearing noise.

[jim4065]

OK - I'll see if I can hear 'em come on. If not, the thought just occurred that I could always simply stick a mirror into the cabinet to see upwards into the fan enclosure. Thanks for responding - it keeps me from going down a dead end.

[Bill*]

Do those 110v illuminated switches go out when they stop passing power? If so, could it be wired into the return side? If power is passing through the fan, does that guarantee (sp?) the fan is actually moving? Just a few thoughts.

[lurch]

If the bearings seize up, the reluctance motors will usually be what is known as "impedance protected". They will pass current just fine even though the fan is locked up and not spinning. The impedance of the winding is high enough that it will not pass enough current to cause serious thermal issues and therefore will not "open up " and stop the current flow.

As to the lighted switches, I think that they only indicate that the switch is in the ON position, not that there is current flowing through the switch to some external load.

[Uncle Grinch]

You might consider placing a micro switch with a flapper to sense the air movement. Or even use a fan proving sensor.

www.grainger.com part #'s 3XG46 or 3ZM96

[moptop]

a micro switch with a flapper

...or "sail switch" as it's commonly known as is what I was going to suggest as well. One for each fan if want to monitor them individually.

[3rptr]

Is there a reason why you don't use a couple strips of plastic strip that would blow in the breeze from each fan ?

Otherwise, a 5w candelabra bulb wired in series should work if an AC fan fries ?


Best


.

[jim4065]

Is there a reason why you don't use a couple strips of plastic strip that would blow in the breeze from each fan ?

Otherwise, a 5w candelabra bulb wired in series should work if an AC fan fries ?


Best


.

Can't see into the space (plenum?) where the fans are blowing. The entire cabinet is made from scrap wood except for a glass window. I like the 5 watt bulb in series idea, if it will stop burning when the fan stops turning, but it seems like the bulbs would burn out much more frequently than the fans. Maybe I should connect a fan outside of the enclosure and put it in series with the bulb. Then just stop the fan from turning and see if the bulb stops burning?

[mdi]

Cut an "observation hole" in the cabinet so you can see the fans work...

Are the fans mounted side by side and blowing into one vent? (4" seems small). Are the fans stacked "in series"?

[jim4065]

I put 'em in parallel. You can hear them very easily - and one makes a bit of a high pitched noise. (I imagine it will be the first to go.) For now - I'm going to just use the noise as an indicator.

The fans move a lot more air than I thought they would. The "plenum" is kinda big and has a 5" duct opening which goes thru a couple of adjustable bends, necks down to 4" and then shoots thru the wall. Took pictures with my cell phone which wants to send "secure downloads" to my email but when I put 'em on the desktop they won't upload to here. Anyway, I'll load a couple of pics from the camera when I'm thru with it all - but before I build the mold storage racks on both sides of the cabinet. Finally finished wiring the damn thing - including a new dedicated line on a 20 amp circuit just for the pots.

Everything seems to work - and it's a triumph of scrap utilization (which dictated most of the measurements). The package from Auber Instruments was delivered today - got to work on it tomorrow.

[Catshooter]

jim,

A small light bulb in series with your fan motor will be lit only if the power to the fan is not flowing. So if the fan stops and the power is still flowing, it won't light up.

Something of a sail switch is the most likey answer.


Cat

[squid1230]

If you could see the exhaust side of the fans, a simple piece of streamer ribbon tied to the fan case would be an indicator of it's functioning. If the streamer isn't sticking straight out - your fan isn't working.