View Full Version : Power measurement - electromagnetics question

03-06-2011, 09:36 PM
The attached arrangement works rather well for measuring low powers such as the standby power of adapters.

I'm wondering if I can increase the amplifier to x20 or x100? What is the limiting factor?

I'm particularly interested in increasing the turns to 24 which would give me x1, x23, x24 and make 10mV indicate 10W

03-06-2011, 10:07 PM
Hi BBCmicro

Noticed you are trying to measue watts using a digital multimeter on a voltage setting. While such arrangements work Ok for lower values it is not a very accurate way to measure greater wattages.

To answer your question - the limiting factor is Phase Shift - alternating current voltage changes fifty times a second (hz). What you need to measure is the instantaneous voltage x current. Your simple arrangement can't do this. Therefore it becomes less and less accurate with greater wattage draws.

Even if you overcome this problem it is going to cost you more than THIS (http://www.jaycar.co.nz/productView.asp?ID=MS6115&keywords=power+meter&form=KEYWORD).

Hope this helps...