Motor Load vs HP vs Current

[Mark]

or the Voltage at the motor is too LOW, yes LOW..

Mark

[.p.jm.]

Oh, kee-rist.

It's a little 1/2 HP residential blower motor - sealed bearings.

[The Daring Dufas]

It sounds like you have an electrical supply problem and you're chasing butterflies. You mentioned losing connection to the net, I would assume you're referring to your Internet connection and the power to the whole house is sagging. If that's the case, your problem may be in your main electrical panel. It's not unusual for loose connections in main electrical panels to burn up in hot weather when heavy loads from AC systems stress them to the braking point. I would start at the main electrical panel first and inspect ALL of the connections and circuit breakers related to your AC unit. I've traced many AC problems back to the electrical service.

TDD

[.p.jm.]

baptised at the factory properly.

I guess if the leads are trimmed really close, that means it's Jewish ( been snipped ) ?

[Tony Hwang]

Hi, Was the motor working normal before? If answer is yes, either you have bad cap. or dying motor motor. Over or under rated motor has poor efficiency. RPM is pretty steady at rated independent of Hp.

[Tony Hwang]

Hi, Brand name of the motor? Sounds like El Cheapo. Decent blower motors are actually under rated.

[Stormin Mormon]

Sure, if the voltage is too LOW, the motor won't run EFFICIENTLY. Yes, EFFICIENTLY.

[Stormin Mormon]

I've seen service panel problems. It sounds like good advice, to check the panel box. Look for white corrosion, or dark burnt areas. If you find either, call a licenesed electrician.

[tm]

Since you are seeing a sag in the voltage, maybe the wiring is inadequate for the blower. Low voltage will cause an increase in current. Putting a larger motor in will increase the current.

Have you measured the voltage at the motor?

t

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[Tony Hwang]

Hmmm, Not just HP vs. RPM. Think winding. Doesn' tha motor has any speed taps? If it is running at hi speed tap and bogging down, The motor is too small. Byt other factors are duct size, blower blade pitch/size, mothr efficiency. Not all is created equal. Also why is the voltage sagging? If you turn off the motor, it does not happen? Thin simple.

[Sparks Fergusson]

Now, let's think about that. If a motor speeds up, is it more loaded or less loaded?

That's right. For an induction motor, the heavier the load, the more it slips, and the slower it turns.

When you put your hand over the vacuum hose, you *unload* the motor (no airflow = no work) and, thus, it speeds up. Still don't believe me? Put your ammeter on a vacuum and try it!

[bud--]

How do you know the cap is good? How do you know everything is fine?

Almost 2x rated current for 10 years. I don't really think so.

And you could find that the HP is proportional to the cube of the RPM. Not really likely that the electrical side is OK. Exact replacement motor? Is there a run cap? Did you replace it? That is my bet.

If the duct was totally blocked the fan would spin a hole in the air. As the duct gets blocked, the HP does not go up drastically - this is not a piston pump.

[Grumpy]

Any chance that wire has loop where you are taking current reading?

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[JosephKK]

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Definitely. Way more is wrong than the fan motor (and never buy a cheap motor). Start with checking all filters, dampers, heat exchangers, evaporators, condensing unit, also all of the rest of the electrical work.

[JosephKK]

Which immediately generates the questions of why and how?

[gerry]

Is this a motor problem or a supply problem? A 9A load should not sag your mains such that other equipment (net) fails.

Did you measure RMS current? Peak (common) are misleading.

What was the voltage at the motor and at your mains? Low voltage can cause high currents. In computer electronics, peak voltage is usually more important than RMS.

gerry

[Michael A. Terrell]

Click WHERE? All I see is plain text. If you want a link that works for everyone, you need to prefix the text with http://

Like this:

[Real Pisser]

The link (Paul's), works fine for me. I click it several times a week, as we care for animals too. I am using IE8 as a browser. sometimes with IE8, the http:// prefix causes problems; go figure! easy enough to overcome either way.

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[.p.jm.]

Thanks so much for the internet wisdom. Seeing as it works just fine for everyone else the way it is, I think I'll just leave it like that.

[Steve]

Check to make *sure* that you have not got any air flow restriction issues...... excessively restrictive filter, registers closed, dirty evap coil, insulation that came loose inside the plenum, etc.

BTW... when you did the amp draw and rpm measurements, did you have the cover off the blower compartment??

Gotta love it when an EE plays with stuff. :-)