The squirrel cage fan. How the air flow works.
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- เผยแพร่เมื่อ 10 ก.ย. 2024
- I check out the blower assembly for furnaces and air handlers. I demonstrate how amp draw is related to air flow. This video is continued on next video.
This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.
Thanks for the educational videos that you give to us without charge. People do not realise how lucky we are to have experts like you in your field do these videos. Really appreciate them. God bless
For the last 9 years after 27 years as a serviceman, I was a teacher. Now I do it for free and love it. Thanks.
GFM
Just looking through youtube on a rainy day and ran across your videos. Great job, ther clear easy to under stand with lots off good tips. you are a very good teacher, Keep up the good work..
The amp draw is related to how much power the blower is using. The power the blower requires is the work it performs at some rate. In this case it is air being moved at some pressure within some time. Knowing that, compare the work being performed, basically how much air is moved, when the blower outlet is not blocked to when the blower outlet is blocked. Way less air is moved when the outlet is blocked. In fact no air is moved through the blower when the outlet is totally blocked. Therefore way less work is being done and less power is required. The amp draw goes down to reflect this and the motor speeds way up, because it is doing less work.
That is the nature of centrifugal fans and pumps. This is always surprising to people not familiar to these machines but who have certainly put their hand over a canister vacuum cleaner hose and heard the motor start a high pitched scream. Maybe they think the motor is struggling, screaming like a living being, but if they thought about it a bit more they should wonder why the motor spins faster instead of being bogged down.
It is important to know in these cases what is being moved, air and water, provides the way heat is rejected from these machines. Running them in this blocked or partially state will be damaging because some power is required but heat cannot be rejected. In the opposite condition where the blower is blowing lots of air, therefore doing a lot of work, the motor and its wiring may not have been selected to reject the waste heat fast enough associated with that condition.
Sorry about the delay. Actually the opposite. I know it seems backwards.
GFM
I just do it for fun now. Thanks
GFM
Yes. If the amp draw is above rated on a 1.0 service factor motor, it will overheat and kick off on overload. If the bearings are bad, that could cause it but I would guess the windings are shorted.
GFM
If start winding is bad, the motor should operate with higher than normal amp draw. Also, are the bearings overly tight? To check start winding, the easiest way is to check amp draw thru the cap.
GFM
So if I want to put one of these in a basement window to suck air out,I should restrict the exhaust port?
If you want to limit the air removed, yes.
GFM
The cupped side of the blade pushes the air, while the curved back-side creates low pressure so more air is drawn in to the center area and then it's drawn toward the outer edge of the wheel, which is where it gets pushed? So the pushing (cupped side) of the blades should always be facing towards the exit channel of the housing?
I wanted to learn how the air flow works; but I seemed to see how the current (amps) works instead.
You certainly did. Of all the ways to measure air flow, amperage draw is the best.
GFM
I have a blower motor that will only start with a manual push from me on its wheel. New capacitor didn't help. There was a black wire from blower motor connected to the fan relay, and a white (yellow? forgot now - is a General Electric motor) wire connected to "C" of dual run cap. Measured 240vac across these two points. Assuming that the wires are good, this is obviously a bad motor (start winding)? It's a multi-spd motor w/2 brn wires (one w/white stripe) to 7.5uF cap. How chk start winding?
Your problem appears to be shorted windings. Normally you can get a PSC motor to run either way if you flip the wheel.
GFM
But isnt that you said only true multimeter is field piece ? Thanks
So I'm currently looking to find a Centrifugal fan to move some air. I would like to mount it on the outside of my project. but it seems that what I'm seeing is all of these blowers have a squared outlet; exhaust port, pulling air from the circular port in the side of the blower. So my question is, is it possible to change this so that it actually uses the square port as an inlet? Do they make blowers that are reversed, Where the circular port of the fan is exhaust instead of intake?
You can't reverse the blower flow. You can use a transition to change the outlet to circular outlet. Some blowers are equipped with a circular outlet, namely gas furnace inducer fans. You could use one of these for your application. These blowers are much smaller than the circulating fans you are probably considering. Hope this helps.
GFM
If the start winding (my other comment) is bad, or hypothetically if the fan's run cap were bad, could it make this squirrel cage wheel run backwards? And if so, would it be normal to give this backwards-running wheel a starting push in the right direction, only to have it stop then reverse direction to the wrong direction?
It sped up because It was trying to catch the airflow being restricted right? I mean motor does not sense electronically anything.
+Guy Hakverdi Only the ECMs do that.
GFM
The motor was just camera shy and became timid on the zoom in, also why the amps dropped.
It is, indeed, pulling higher than normal (data plate) amp draw. Data plate: 1.8 A - it's pulling 2.5 A. Can I assume excessive amp draw would cause motor to overheat? Thx GFM
How can I find out direction of airflow so I install my vent filter properly?
+Instinctive Firearm Reviews I am not sure what a vent filter is but if you mean the furnace filter, the air flow arrow on the filter points towards the furnace. Hope this helps.
GFM
+grayfurnaceman yes that's what I mean. So the arrow should face towards the furnace fan? I currently have it facing up the venting. As I thought it meant direction. Of airflow
+Instinctive Firearm Reviews The reason for the arrow is on some filters, there is a wire screen to prevent the filter from being pulled into the fan. On others (the cheap ones) oil is sprayed on one side of the filter to catch dirt.
GFM
Took me 10 minutes to find but here's the "next video"😊
th-cam.com/video/H0eLgEzKxd4/w-d-xo.html
I made it by myself. I used woodprix woodworking plans for that.
This video had nothing to do with its title.
Wtf was this??!!