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Old 06-03-2014, 06:52 AM   #1
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Convert watts 12 volts to watts 110 volts - question

At anchor I leave a netbook running as an anchor alarm. This uses 11 watts from my 110 volt inverter. Since it is the only AC current running during the night I am planning on powering the netbook with a 12 volt adapter thus allowing the inverter to go into sleep mode.

I don't have a DC equivalent of a Kill-O-Watt and am unable to determine the DC draw the netbook will take.

I think I know the answer but would appreciate someone who is confident to advise what the conversion would be so that I can know what the draw will be over 8 hours in DC amps. Yes I live at anchor and power and water usage are major concerns at all times.


Thanks
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Old 06-03-2014, 07:16 AM   #2
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If the inverter only draws 11watts at 110 volts, then it is using 1/10 of an amp. Drawn off of a 12 volt bank through an inverter, the power required to make that 11 watts would be 1 amp at 12 volts. This doesn't take into account the inefficiency of the inverter which may bring it to 1.1 or 1.2 amps. Also, the inverter may consume as much as 2 amps just to power the inverter. 12 volt power supplies vary widely in their efficiencies. As a result, you may find they may actually consume more power than running it through your inverter. Power consumption in amps or watts should be listed on the devise.

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Old 06-03-2014, 07:20 AM   #3
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The wattage will be the same regardless of the voltage, so it will still draw 11W. At 12V that's 0.9A. So over 8hrs it would consume 7-8 Ah.

Keep in mind that all this ignores conversion losses in the AC adapter and the DC adapter that power your netbook. But assuming both are efficient, which they probably are, the numbers should be pretty close.
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Old 06-03-2014, 07:31 AM   #4
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Another option is to power your 110 adapter with a much smaller sine wave inverter. A 300 watt portable unit is 90% efficient and only consumes .3 amps at 12 volts in no load mode. They are around $80.

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Old 06-03-2014, 07:37 AM   #5
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Quote:
Originally Posted by O C Diver View Post
Another option is to power your 110 adapter with a much smaller sine wave inverter. A 300 watt portable unit is 90% efficient and only consumes .3 amps at 12 volts in no load mode. They are around $80.

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Yes, that's what we do to charge our laptops, and I don't know what it draws really...couldn't care less, because it is beggar all..!
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Old 06-03-2014, 10:24 AM   #6
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The basic formula is;

Volts X Amps = Watts, Watts/volts = Amps. Watts/Amps = Volts

1 amp 120 volts AC = 10 Amps 12 volts DC.

So you can due the math to convert. I would allow a -10% conversion factor for loss over energy.
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Old 06-03-2014, 10:51 AM   #7
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Sorry. You're going 12 volts. Never mind.
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Old 06-03-2014, 01:11 PM   #8
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Thanks, this confirmed my suspicion that amp are watts divided by volts.

As far as inefficiency of the 12 volt converter, many thanks. Hadn't thought of that I may buy (great toy not just for this) an inline device to measure direct current use similar to the kill a watt for ac use.
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Old 06-03-2014, 01:49 PM   #9
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Laptops and IPads do have 12VDC charge adapters. I once had a Dell that required 19VDC to power and charge it. I found a 12 to 19VDC converter specific to the Dell laptop on EBay. I still have both and they work better than trying to run a large invertor to power them. As suggested a small 300 watt inverter would be the way to go if you only want to use 110VAC to keep the units running and charging.
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Old 06-03-2014, 03:41 PM   #10
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On Amazon the prices for the car adapters (Search term, plus your brand) have come way down in price. Originally they were $50 to $75. Now, I'd be surprised if you paid more than $25.

The adapters take your twelve volts and boost it to what is required. 19 for my Toshiba. And yes, it charges too via 12-volts.
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Old 06-03-2014, 06:07 PM   #11
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Quote:
Originally Posted by janice142 View Post
On Amazon the prices for the car adapters (Search term, plus your brand) have come way down in price. Originally they were $50 to $75. Now, I'd be surprised if you paid more than $25.

The adapters take your twelve volts and boost it to what is required. 19 for my Toshiba. And yes, it charges too via 12-volts.
For one of our Dells. There are also lots of adapters from 12 VDC to USB to Kindle, android, etc. Not much reason to run an inverter for personal devices or tablets these days.
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Old 06-03-2014, 07:13 PM   #12
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I agree leave the intermitant heavy loads like the coffee maker or the microwave for the inverter. At the same time the inverter/ charger can charge the house bank properly. Small devices are best left to small form voltage converters. Air conditioning and heavy AC uses are best left to the generator. If the inverter is going to be used for heavy loads consider a 24VDC Inverter/ charger and a large house bank otherwise I'd stick with voltage converters and light duty cycle use of the inverter.
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Old 06-03-2014, 09:00 PM   #13
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Twistedtree and OC Diver

They are correct in their calculations. Wattage never changes and is the work required to power the device. Wattage is the electrical definition of work. Amps is the current that is the result of doing the work (wattage) at the voltage supplied. Wattage is constant with only voltage and amperage being variable to the wattage. As stated these calculations are assuming 100% efficiency, which is never the case unless you are in a vacuum or using super conductors.
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Old 06-09-2014, 09:37 PM   #14
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The formulae challenged (like me) might be interested in this neat app

https://itunes.apple.com/us/app/ohms...389305829?mt=8
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Old 06-09-2014, 10:11 PM   #15
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Here's another alternative, use your phone!

https://itunes.apple.com/us/app/drag...489294173?mt=8

https://play.google.com/store/apps/d...=air.DragQueen
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Old 06-09-2014, 10:41 PM   #16
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This is one of the reasons you should use a smartphone as an anchor alarm. Every phone on the planet has a way to keep plugged in with a normal 12v supply. A phone can also be activated at the bow when the anchor is dropped eliminating a good 20-30+ feet of error from the alarm because the alarm gets set by where the GPS is and I doubt you have the netbook out on the bow.

A phone can be placed right next you your bed at night guaranteeing being woken up if it goes off. And the phone will have a GPS built in. You'll need to make sure your 11 watts included the power needed to keep the GPS alive during the night too.
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Old 06-09-2014, 11:34 PM   #17
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+1 to that
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