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Old 05-31-2007, 10:41 AM   #1
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Measuring Power Draw from Devices (and solar panels, etc)

This is a fairly simple, yet accurate method to measure power draw (or production) from various DC items. You will be able to measure the following:
*Supply voltage
*Current draw (amps)
*Power draw (watts)
*Total current draw (Ah) over a period of time, or if you use the $99 system, total Wh can be captured as well!!!!
*Measure power produced from a solar panel (see later post)

BASIC TOOLS:

A. Watt’s Up meter ($58.95) from
http://www.powerwerx.com/category.asp?CtgID=3587


or if you want to datalog to a computer and measure up to two temps as well, the Power Analyzer Pro ($99.95) to which you’ll have to add your own PowerPole connectors. I prefer this one, as I can get Wh as well as Ah, and program what the display shows from a computer. See:

http://www.medusaproducts.com/Power-Ana ... 60100R.htm



B. Cigarette Socket with power poles ($14.55) and cigarette plug with power poles ($14.95) from

http://www.powerwerx.com/category.asp?CtgID=1389

I made my own setup, so it looks a little different, but it’s basically the same:



Now you can insert this as a ‘jumper’ in between any cig socket and your 12V device or inverter and directly measure what's actually being sucked out of your batteries.

As a later post when I get motivated, I’ll show how to jack into your fusebox so that you can measure actual power draw of items such as your fridge and your marine diesel heater…

Questions? Start a different post in the General Section.
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Old 05-31-2007, 10:48 AM   #2
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MEASURING SOLAR PANEL POWER OUTPUT

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MEASURING SOLAR PANEL POWER OUTPUT
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Using either the Watt's Up Meter or Power Analyzer Pro listed in the post above, add the following item ($9.95):

http://www.powerwerx.com/product.asp?Pr ... CtgID=1389



Now you can jack your meter in between your solar panels (assuming you're not REALLY putting out over 45A) and measure both instantaneous power production AND get a running total of how much energy you've produced since the meter was plugged in. Cool. Note: The Power Analyzer Pro is a better option for total energy measurement as it'll give you Wh in addition to Ah.

Note: there will be a conversion efficiency loss between your panels and your battery, so you're not really getting all this energy. However, it will give you accurate energy production and is an EXCELLENT "real-time" tool to allow you to position your panels for optimal output if you have a tilting mechanism installed.
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Old 05-31-2007, 11:01 AM   #3
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LAPTOP MEASUREMENTS

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LAPTOP POWER MEASUREMENTS
---------------------------------------



Using the above setup, I measured the draw of my laptop both with and without an inverter.

Laptop: IBM/Lenovo T60. Input: 20V. Rated at 90W on the back of the laptop.

Power Supply: AC/DC Combo Adapter P/N: 40Y7656; supplies 20V power to the laptop from either AC or 10.5-18V DC sources. Sweet.

Usage conditions: Screen brightest, volume up all the way, Wifi on, bluetooth off, DVD in playing movie.

Inverter: small 150W (peak) cig socket inverter from Radio Shack.

-----------
RESULTS:
-----------

Inverter alone (nothing plugged in): 3.6-4W (avg ~3.8W)

Computer plugged into inverter using AC: 38-40W

No inverter, computer plugged directly into DC: 30-31W

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COMMENTARY:
------------------
A. Nice low power draws regardless. I love the Thinkpads. Your mileage may vary, laptop dependant. Especially with a Sony Powerhog.

B. Inverter alone doesn't draw TOO much power. My guess is larger inverters would draw MORE standby power due to larger fans and electronics. However, they may be more efficient at converting larger loads to AC.

C. Assuming a constant inverter overhead of ~4W, then the extra conversion inefficiencies between the inverter and laptop power supply are ~5W over a baseline of 30W. This may be slightly flawed thinking though.

D. Overall inefficiency of moving from DC to AC is a almost a 30% overhead in extra energy cost.

E. Summary: GET A DC POWER SUPPLY FOR YOUR LAPTOP ALREADY!
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Old 05-31-2007, 11:07 AM   #4
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CELL PHONE POWER MEASUREMENT

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CELL PHONE POWER MEASUREMENT
------------------------------------------

Cell Phone: HTC TyTn
12v charger plugged in, but no phone: <0.1W
Phone being charged from cig socket: 5.6W

----------------------
COMMENTARY:
----------------------

Some cell phones charge faster than others, your power draw may vary. Either way, this is sure proof that using an inverter and an AC adapter will at least double the amount of power you're drawing to charge your phone.
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Old 08-22-2009, 02:31 PM   #5
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Re: Measuring Power Draw from Devices (and solar panels, etc)

Really nice measuring equipment!!!

Might NEED to get a Doc Watson meter. $58 not bad. I do have a Kill-a-Watt meter for 110v's and it is handy.

My 1000w Tripp Lite inverter has an idle draw of about 18 watts/hr. I had to estimate this value by battery voltage drop over a 24 hr period and work the numbers backwards from my battery capacity. I Doc Watson meter would be LOTS faster, easier and more accurate.

Thanks again for the power meter lead.
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