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Mystery blower motor

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tomizett

Active Member
Likely a daft question, but it does no harm to ask....

I have a large centrifugal blower, salvaged from old equipment, which I would like to use. My problem is that I don't know how it should be wired - unfortunately I know next to nothing about electric motors.

The blower is manufactured by "Shenzhen Fengbaisheng Fan Manufacturing Co Ltd" and has the part number "DW8-53No1.5C" - it is rated, according to the plate, for 35W at 220V.

It has three wires, Red, Blue and Yellow. The person who originally salvaged it (who is no longer available to ask) labeled the red wire "L" and the blue wire "N".
If I apply about 200V AC between Red and Blue, the motor will draw about 0.5A and rotate slowly if given a spin to start it. It will run in either direction.
Curiously, the motor draws no significant current between Red and Blue until a potential of about 210V RMS is reached - it then continues to draw current until the voltage drops to around 180V or so.

The connections measure as follows when measured with a DMM/LCR meter:
Yellow-Blue: open (several Megohms and no significant capacitance)
Red-Blue: open (several Megohms and no significant capacitance)
Yellow-Red: About 340 Ohm DC and significantly inductive (1.5H or so)

I suspect there should be a run capacitor wired in here somewhere, but I don't know where. I also wonder if there is something more complicated going on inside this motor, due to the strange behavior when powered up on the Variac.
Just to throw in another unknown, of course we can't rule out the possibility that the blower is faulty as I don't know why the equipment is came from was scrapped!

If anyone can make any suggestions then I'd be grateful...
 

MaxHeadRoom78

Well-Known Member
Sounds like a PSC motor which requires a cap, if the L & N are Red & Blue then the cap would be connected between Yellow and the Red wire.
Around a 4μfd AC motor run style cap. should be in the ball park.
Max.
 

tomizett

Active Member
Thanks Max - that was the sort of thing I was expecting/hoping for. I'll give it a go.
 

tomizett

Active Member
She lives! Did as you suggested and it appears to work.

The cap I had to hand was a 6.3uF - is there a way to calculate the optimal value, or is it really not that critical?

The current draw is close to 1A (which is obviously way in excess of what the rating plate would suggest) but I presume that's just an effect of its inductive power factor? I don't have a power meter to hand, but I'll try to dig one out.

Whichever way, thanks for your help.
 

MaxHeadRoom78

Well-Known Member
Many things can affect the current, how the fan is situated, load etc, as well as cap value, 1a is not that high a value for this application.
The manufacturer usually size the cap in order to obtain the closest to 90° phase shift between run winding and cap phase shift winding.
Cap is not super critical, the simplest is to try a few different values and see which way the current moves.
Max.
 

tomizett

Active Member
That makes sense. If I get set up correctly I should be able to have a look at the voltages on the windings and see what the phase shift is.

the simplest is to try a few different values and see which way the current moves.
Do you mean that the optimum value would minimise the current, or have some other effect?

Whichever way, it's probably good enough as it stands, but I might as well take a bit of time to make sure it's done properly as we'd like to use this in a test fixture and I don't want to design something around this blower only to have it burn out after a couple of weeks!

Thanks Max.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Max: Your right on the $ on this thread. I had a paper at one point, that the windings on ceiling fan are slightly different in resistance because, I think, the cap adds to one side. It's probably the ESR.
 
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