DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (http://www.diychatroom.com/)
-   Electrical (http://www.diychatroom.com/f18/)
-   -   determining wattage usage of electronics (http://www.diychatroom.com/f18/determining-wattage-usage-electronics-60847/)

greenlivn 01-02-2010 06:11 PM

determining wattage usage of electronics
 
I'm familiar with the amps x volts = watts. On many electronics, however, it gives a range for the volts, maybe 100-240 volts and then something like 1 amp for the current. Is this saying that the wattage in, say, Africa is higher than in the US? If it pulls 1 amp no matter, then would it be 120 watts (120 volts x 1 amp) in the US and 240 watts in Africa (240 volts x 1 amp)?

Thansk!

Yoyizit 01-02-2010 06:23 PM

It pulls whatever power it needs and tolerates a wide range of input voltages. The wide range implies that it is a switch-mode power supply, as opposed to a linear supply.

You could infer that the max power draw is 1A(120v) = 120 w and the current draw would probably be a half amp at 240v.

micromind 01-02-2010 08:05 PM

Actual watts of any AC device is Volts X Amps X Power Factor.

Both linear and switching power supplies usually have horrible power factor. Somewhere around 20-50%. Power Factor usually goes lower as voltage increases. Some are corrected, but usually only large ones (over 1 KW).

The only way to know for sure is to use a watt meter, but it's pretty safe to assume the Power Factor to be 50%.

In the above example, it'd be pretty safe to assume that a device marked 100-240 volts and 1 amp would consume less than 60 watts, more like 40.

A better way is to look at its DC output. Say it's 12 volts and 2 amps. That's 24 watts (Power Factor has no effect on DC circuits). Figure about 25% more, and you're pretty close to the input power. In this case, it'd be about 30 watts.

The input amp figures on power supplies are notoriously inaccurate.

Rob


All times are GMT -5. The time now is 11:04 PM.


Copyright 2003-2014 Escalate Media LP. All Rights Reserved