measuring blower motor current

leeelsonSeptember 10, 2013

I've noticed that my electricity consumption has increased recently and for various reasons I suspect an HVAC squirrel cage blower motor. Although it doesn't seem excessively hot, I want to find out if it's drawing more than the rated current. It has a shielded AC cable running to it. What is the best way to measure current? Can I use a clamp meter to do this or would it make more sense to do something like measure impedance with the power off? I don't want to do any dis-assembly and I do have some knowledge of electricity.

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A clamp meter will be extremely easy if you know how to use it.

I will say, a motor like this, even going bad, will not raise consumption that much that you'd notice it on your bill.

    Bookmark   September 10, 2013 at 8:59PM
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Ron Natalie

Note, that you have to isolate a single current carrying leg to use a clamp on meter. If you use it around both legs, you'll just read zero (unless you've got a ground fault).

I agree with Petey, if the motor is spinning and not getting hot, it's unlikely it's pulling noticable additional. Usually, they're current limited somehow (either internally or by the breaker they are on) that they'd stop before they get too much of a draw.

I'd be more suspect of the AC compressor itself or perhaps something else.

    Bookmark   September 11, 2013 at 12:52PM
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Ron Natalie

Besides if the bill is skyrocketing, you probably have a noticable draw. Shut off the fan. Go look at how fast the dial is spinning on your meter. Turn on the fan, repeat.

    Bookmark   September 11, 2013 at 12:53PM
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Thanks for the suggestions. A little more background: there is no A/C use. Several fans manage internal and external air. The one I suspect typically runs 8 hours/day and *should* use about 6-7 KWH/day. I'm seeing about a 5-10% increase over my normal 18-19 KWH/day (total for the house- not exactly "skyrocketing"). The motor housing is not too hot to touch when the fan is running but its in the airstream. When the fan turns off, the housing gets pretty hot for awhile as it dissipates heat.

I could measure the daily consumption with and without using the fan but there are downsides to this (inaccurate, uncomfortable).

    Bookmark   September 11, 2013 at 6:56PM
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