Playing around with an ammeter... (1 Viewer)

[Mike Lenthol]

I just tried measuring different stuff around the house with a Fluke AC ammeter, and most devices were right on the spot. Microwave at 2Kw, incandescent light bulbs were showing within 1w of their rating. Even the 12v outside lighting system showed perfect reading. Pretty accurate throughout the range of the meter in other words.

The 2 devices that showed strange results were an 19" LCD display and several fluorescent energy saving lights.

The monitor is rated at 49w average consumptions, while the meter showed a consistent 240w! The fluorescent bulb rated 15w(60w incandescent light output equivalent) pulled 55w!

Are these type of devices trick the meter by their nature of operation or were they falsely advertised?

 

[Holadem]

You need to provide more details on your device. You said ammeter, but you're citing power and voltage. I will assume it's a multimeter. How do you get your measurements?

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H

 

[Mike Lenthol]

It's a clamp on system. The clamp goes around just one of the AC wires and it displays the A(amps draw) value. I just take that and multiply by the line voltage, correct? Say a regular 100w incandescent bulb would show 0.8amps x 124v on the line = 99watts.

The interesting thing is both device types showing incorrect readings are fluorescent. (LCD backlight)

 

[Dheiner]

I think it has to do with the phase difference between the current and the voltage. It's called the power factor. Check here: Pf

 

[Mike Lenthol]

Yup that explains it. Found a good explanation about it in laments terms on google Btw, what power factor on average would a decent computer PSU have?

 

[Cary_H]

Power factor isn't a big issue with single phase, household stuff. Efficiency of the device itself, or rather, how much power it wastes doing what it does, can count.
I can tell you that I've seen 8 PCs and their CRT monitors, along with an assortment of incandescent and fluorescent lighting, all on one 120V circuit drawing 11ish amps.
How are you taking these "out of whack" readings?

 

[Randall Duncan]

The fluorescent bulb rated 15w(60w incandescent light output equivalent) pulled 55w!

I think I can kinda' explain this...

Ok, all fluorescent lamps use a linear ballast, electronic ballast, or electronic inverter unit to power them.

Most of the ratings displayed on the packaging are the the amount of current the lamp (bulb) itself draws from the ballast/inverter (whichever it may be) and usually aren't how much current the ballast/inverter draws from the power source (120 Volts A.C., 60 Hertz, single-phase).

This means the lamp itself may be drawing 15 Watts from the ballast/inverter, while the ballast/inverter actually draws around 30, 50, or more Watts.


That sound right?

 

[Justin Lane]

The monitor is rated at 49w average consumptions, while the meter showed a consistent 240w!

I would guess that if you read the monitors manual, the average rating was probably based on a certain number of hours used per day. When not in use, the monitor goes into standby, using less power, and hence an overall low average power consumption.

J