Power Meters: Real Power vs. Apparent Power

yefi · Post by **yefi** » Tue Jun 12, 2007 3:43 pm

Hi, I bought this Power Meter from Maplins to measure my power consumption:

However, I have a problem with the readings it is giving me for volt-amps and watts. If I understand this right, the watts, as a measure of real power, should equal the volt-amps being drawn if the power factor is 1. As my PSU is rated an Active PFC of 0.99, the reading from watts and volt-amps should be roughly equivalent, correct?

But the two are wildly different on it. Volt-amps measures 167 and watts a mere 21, and the device give me a power factor of 0.11. I got a similar PF from an ordinary 60W bulb. Is this device nackered, or am I missing something?

Thanks for your help!

frostedflakes · Post by **frostedflakes** » Tue Jun 12, 2007 5:50 pm

I believe you are correct in your assumption that the meter is defective. Try returning it for another and see how the replacement does.

fractal · Post by **fractal** » Tue Jun 12, 2007 6:08 pm

An incandescent light bulb is a purely resistive load which has a power factor of 1. Fluorescent bulbs are a different story. If your meter is reading anything other than va = watts for a pf of 1 on an incandescent bulb, then it is defective.

yefi · Post by **yefi** » Tue Jun 12, 2007 7:15 pm

fractal wrote:An incandescent light bulb is a purely resistive load which has a power factor of 1. Fluorescent bulbs are a different story. If your meter is reading anything other than va = watts for a pf of 1 on an incandescent bulb, then it is defective.

It was only giving me 8W for a 60W incandescent bulb, which is one way to save power I guess. Looks as if an RMA is in order.

yefi · Post by **yefi** » Fri Jun 22, 2007 7:41 pm

Got a replacement for this model today entombed in a sarcophagus of bubblewrap, and it appears to be working correctly now. I would suspect that this item qualifies as "fragile" and should be treated gently!