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Watts supplied to modem's ac power supply unit?

foxbrook
Sophomore

Re: Watts supplied to modem's ac power supply unit?

We're supposed to have good weather here for the next week. Next time a storm comes through I'll try to remember to take a measurement.
Timothy Southwa
New Member

Re: Watts supplied to modem's ac power supply unit?

Thanks for using such nice equipment. From what you and curtis- m have said, I suspect I might use normally about 20 to 25 watts if I actually get HughesNet. This amount might be acceptable and doable for me. And I can prepare for it.
Please explain something to me about your readings. Why do volts shown times amps shown not equal watts shown?
Timothy Southwa
New Member

Re: Watts supplied to modem's ac power supply unit?

Please do, BirdDog.
foxbrook
Sophomore

Re: Watts supplied to modem's ac power supply unit?

in AC circuits watts only equals volts*amps if the power factor is 1. The power factor of this power supply is about 0.6 because it doesn't have power factor correction like some computer supplies do. So if you take the volts*amps and multiply by 0.6 you will get the true power in Watts. This is why when sizing a generator you need to take the power factor of the load into account because the generator will need to provide the volts*amps of the load. BTW volts*amps is known as apparent power.

This is also why large utilities will charge large industrial facilities extra if the power factor of their load is less than 1. 
Timothy Southwa
New Member

Re: Watts supplied to modem's ac power supply unit?

Foxbrook, thank you for your explanation. So, if I were to use a pure sine wave inverter with 90% efficiency connected to a 12 volt battery and I used the same amount of power as you did in your test and I had a meter just like yours to measure it, would (10/9 x volts x amps ) represent the actual power depletion from my battery? So that I would be drawing about 36 watts from my battery for downloading? And I would deplete my battery by about 36 watt hours in one hour of downloading?
foxbrook
Sophomore

Re: Watts supplied to modem's ac power supply unit?

The lousy power factor doesn't actually contribute to additional power draw from the battery, at least not much. So for a first order approximation you can take the true power drawn by the modem and power supply during a download, about 19.5W and divide that by the efficiency of you inverter, 90%, and you get 21.7W of draw from the battery.
BirdDog
Assistant Professor

Re: Watts supplied to modem's ac power supply unit?

Timothy, going to jump in as I lived off grid for 12 years. You're being way too precise on figuring your power requirements. Things never draw exactly what you figure on paper for power requirements. You need to get a ball park figure like you've been given already then factor in at least 20% higher for everything. Panels, batteries, chargers, generators, etc.

A 12V system needs to be charged during the day to at least 14.1V then float at 13.4V after that. These values will need to change with any battery temperature changes. Having a good inline meter that you can use to monitor voltage and current draw is essential, it is the gas gauge. I used the TriMetric and it was great and never had a problem with it.

So, during the day when voltage is higher everything is drawing less current, the opposite at night.

Having a large enough battery bank is a key component. One that can store enough of the unused solar power from daytime to use at night and on cloudy days.

Even after you think you have everything figured out down to the watt you'll probably end up having to add batteries and/or a solar panel or two once you start actually using the system. Things on paper don't usually line up with actual use, especially with a totally off grid system. Predicting how much sun you'll actually get to generate enough power for each and every day of the year is next to impossible. That is why systems are oversized significantly.

My experience and what I learned from 12 years living without grid power.

There are lots of solar information and sales sites but I particularly liked this one: http://www.backwoodssolar.com/
Chris11
Alum

Re: Watts supplied to modem's ac power supply unit?

Timothy,

Check the power suppl cord. It is listed there on the tags and stickers. And I think Liz answered this already in your previous thread.

https://community.myhughesnet.com/hughesnet/topics/average-modem-power-consumption-in-watts

- Chris
Chris11
Alum

Re: Watts supplied to modem's ac power supply unit?