Need help with power consumption of appliance.

I'm trying to figure out how much it costs to operate some electrical equipment that is on 24/7.

I'm running a cell phone/EVDO amplifier. It operates on 8 to 28vdc and according to the spec, pulls between 100 to 490ma current draw depending on how much its boosting the cell signal.

The amp is powered by a transformer (from a laptop pc) that outputs 16v dc to power the amplifier.

The transformer lists its power specs as:

Input = 100 - 240 v, 50/60hz, 1.5 - 0.9Amp

Output 16vdc 4.5a

I pay about $0.15 per kilowatt hour for electricity where I live.

Will the transformer output a constant 1.5 amps, or will it only output what the device (the amplifier) connected to it draws (490ma.)

Am I right at thinking that the transformer will only draw from the house what it needs to transform 110 to 16v and 490ma to supply what the amplifier needs? Or will the transformer always pull its maximum draw from the house power?

Re: Need help with power consumption of appliance.

The primary side will draw some current with no load on the secondary windings. The current will be low until a load is put on the secondary. Once a load is put on the secondary, the primary coil will demand enough current to keep the secondary voltage in the same ratio as the number of turns between the primary and secondary.

Re: Need help with power consumption of appliance.

To many issues in your question...
If a transformer is rated at 1.5A... that means its maximum capacity before it starts to melt.
The amp is going to draw whatever it wants to draw... If the transformer can support it then it will work. If the transformer can not support it... then it will melt.
You say this transformers (is it a step up, or step down transformer?... it appears to sound like a step down). input is 100-240... Is that AC or DC???? Either way a laptop out of any periphial connection is not going to output 100 volts ac or dc.

To much stuff to answer your question.

Re: Need help with power consumption of appliance.

captJason said:

Is that AC or DC????

To much stuff to answer your question.

Click to expand...

Transformers can't step up or step down a DC input.

The amplifier that he is powering is being powered from a transformer that normally powers a PC..at least that is what I understand. A PC is not powering anything.

If the amp is drawing 495mA @ 16V, the power being supplied is 7.92 Watts. For an 85% efficient transformer, that would be a little over 9 watts. With power cost of $0.15KW, the cost is a little over $0.03/day. The duty factor of the amp will determine how much of the time you are requiring all that power.

Re: Need help with power consumption of appliance.

bruceb58 said:

.... If the amp is drawing 495mA @ 16V, the power being supplied is 7.92 Watts. For an 85% efficient transformer, that would be a little over 9 watts. With power cost of $0.15KW, the cost is a little over $0.03/day. The duty factor of the amp will determine how much of the time you are requiring all that power.

Click to expand...

Thanks Bruce! So the VxA=W still applies to any voltage, right? I wasn't sure how the transformer played into the power consumption. Is 85% a typical effecientcy for small "power supplies/transformers" used by small home appliances?

Also, if the transformer were to be plugged into the 110v, but not plugged into a small appliace (ie no load), does it actually consume any power?

Re: Need help with power consumption of appliance.

If the transformer was completely efficient, watts going in would be equal to watts going out...problem is that nothing is 100% efficient...that is why the transformer gets warm...the inefficiency is what causes the transformer to heat. 85% is a typical number. Depends on how the transformer is made.

When the transformer is plugged in with no load, it will draw some current due to parasitics. Since the output gets converted to DC, the output of the transformer gets rectified and possibly filtered which will also introduce more parasitics and inefficiency.

If you are absolutely interested in that, my suggestion is to just measure the AC input current draw with a meter...being careful that you don't kill yourself in the process

Re: Need help with power consumption of appliance.



If you really want to find out at 25 dollars the KILL A WATT will plug in and upset you with how much power things draw

Tommays

Re: Need help with power consumption of appliance.

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