Thread: Blower motor amperage has dropped

Damaged impeller?

Originally Posted by Stanger

For the past little while I've been trying to pinpoint why my dust extractor has lost about 3" WC with a blocked inlet. I initially thought it was a leak somewhere, but after investigating all possible leak points I have discovered that it is an issue with the motor.

The motor used to draw 9.1 A (3hp single phase motor) and now only draws about 7.0 A (inlet pipe fully open). I wondered whether the filter bag on the outlet may be more resistant than when it was new due to dust build up, so removed the bag completely - same reading.

Any ideas why the motor is drawing 2 amps less than when I installed it last year and how I can fix it? The shaft still spins freely...not sure what the issue could be.

Mike

Have you cleaned the filter bags at all?

a) You are supposed to shake the filter bags evert hour of use or so, so the fine dust falls into the collection bags.
OR
b) Better still, although a major PITA, take the filters off and shake them out.

b) is better than a) because whirling sawdust in the collection bag will fluff the fine dust back up so that it again settles on the insides of the filter bags.

A proper cyclone really helps avoid this problem.

I removed the dust bags completely and still had low amperage so it is not a filter bag problem. There is no noticeable impeller damage either.

Could it be bearings or dust in windings or...?

Weird!

What sort of ammeter is it?

Is the impeller on tight?

With the bags off check if there is a difference in the current between when the inlet is blocked or open.

Don't know about dust collectors but assume amps would drop with less load on the motor. Maybe removing all restrictions like dust bag has caused amps to drop.

Peter

Originally Posted by Pete57

Don't know about dust collectors but assume amps would drop with less load on the motor. Maybe removing all restrictions like dust bag has caused amps to drop.

Peter

Hi Peter, it's a bit counter intuitive with blower motors but amps will increase with reduced restriction as this increases the volume of air moved and therefore increases load on the motor. When the inlet is completely blocked the motor is doing the least amount of work and amp draw is at a minimum.

Therefore, in this case a reduction in amps indicates that the impeller is moving less air. This could be due to an increase in resistance to flow at the inlet or outlet side (doesn't appear to be so in this case), or a reduction in impeller rpm ( or a damaged / slipping impeller).

Something else I thought of was try opening up and cleaning out the switch of dust.

Check for an open circuit capacitor.

John

Originally Posted by Yanis

Check for an open circuit capacitor.

John

I was going to suggest that
BUT
If its the start cap, the motor wont start.
If is a run cap I would have though the motor would draw more current rather than less?

Originally Posted by BobL

I was going to suggest that
BUT
If its the start cap, the motor wont start.
If is a run cap I would have though the motor would draw more current rather than less?

But what about the change in power factor?

Actually if the run cap was OC then there would be less current since there would be no power through one of the windings. As I understand it the purpose of the run cap is to sit in series with one of the windings to change the phase of the incoming AC. In this instance if the cap was OC then there would be no current drawn by that winding.

John

I pulled the motor apart - only has 1 capacitor which has 60uf printed on it and measured 58uf so that looks ok. I can't see any centrigugal switch or anything else to check. The windings are not shorted. Any other ideas whiile i have it apart?

The blower side bearing might have a small amount of play so i could replace that, but otherwise i am out of ideas...

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Mike

Teel me about your ammeter. have you been using the same one all the time?

Yes, same ammeter and i can tell the extractor isn't working as well as I'm getting 3" less wc than previously measured with my inclined manometer.

Long shots now.
Dirty switch?