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Old 02-28-2019, 01:06 PM   #1
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For newbies, useful AC to DC

I always like the lazy method and using this calculator was a tool I have found useful - how much power through the inverter. So I am looking at adding a Master Chef 1380 watts convection oven to my boat so what is my power usage.

The one negative of the calculator is it only deals in amps. So if you divide watts by 120 (north america) with the above scenario you get 11.5 amps, input that into the calculator and the answer I get is roughly 120 (actually slightly more but to0 lazy to get the exact answer), So I know with this convection oven through the inverters I'm using up 20 amps every ten minutes.

I am also looking at a cheap crappy toaster, you know those ones you can buy for $14. I like these cheapies because they are the lowest watts user. One that I will be purchasing is 750 watts, so again divide 750 by 120 = 6.5

Now using the calculator input 120 in the VAC box, then 6.5 in the "Amps AC" box, tab on 12 volts at the bottom of the box and you get an answer of = roughly 72 amps. So if I use this toaster for roughly 15 minutes in the moring, I will be consuming (12 amps per every ten minutes) 18 amps.

https://www.batterystuff.com/kb/tool...-inverter.html
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Old 02-28-2019, 01:46 PM   #2
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First terminology: you are using the term amps for both current and amp hours. They are obviously different.


Simply either divide the wattage of the appliance by 12 or multiply the AC current by ten to get approximate amps into the inverter. Then multiply by whatever fraction of an hour that you plan to use the appliance to get amp hours.


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Old 02-28-2019, 02:55 PM   #3
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Will take 65 amps, it is about 10 times as much DC amps as AC amps to run something off the 12vdc inverter.

Watts == volts times amps, and inverter is not 100% efficient.
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Old 02-28-2019, 07:09 PM   #4
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It may be helpful to think of these terms using a plumbing analogy.

Volts are like the water pressure in your pipe. Note that water doesn't have to flow for you to measure pressure. Voltage in a battery has nothing to do with how much work it can do, it's only measuring electron "pressure." A tiny 12-volt battery and a massive one both will have the same "pressure" of electrons, but obviously the big one can do more work. We're measuring potential here, not work.

Amps are like the volume of water that flows through the pipe, the current. No flow? No amps. Using the water analogy, this is the amount of water flowing through the pipe; a big pipe will flow a lot more water than a small one, given the same pressure. We're measuring current here, not work.

Watts are like the work that the water could do...the power. Watts = amps x volts. If you're turning a water wheel and doing work with it (creating electricity, grinding grain, etc), you can get more work done by turning up the water pressure (voltage), or by putting in a bigger pipe (amperage), or both. Wattage isn't about pressure (voltage) or volume (amperage), but about actual work being done by the multiplication of pressure and volume.

A meter that measures voltage only tells us about electron "pressure," not how many electrons are left in the "tank."

A meter than measures amperage only tells us how much current (electrons) is flowing through the wire, not the pressure of that flow.

A meter that measures amp-hours is a smart meter that has been programmed to understand both the size of the tank (battery bank) and how full the tank is.

A meter that measures watt-hours only tells us how much work was done, like the meter on the side of your house.

We can take that simple equation above and change it around however we like:

Watts = amps x volts
Amps = watts / volts
Volts = watts / amps
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Old 02-28-2019, 07:37 PM   #5
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Buy a Kill A Watt meter.
Measures watts, kwatt hours, power factor, amps volts...great and cheap tool.
Power Factor comes in play on inductive loads.
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Old 03-01-2019, 06:56 AM   #6
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"I like these cheapies because they are the lowest watts user."


Lowest watts may ease battery life by lower peak draw down , but TIME enters the equation so the cheapie may not cost least amps per use to make toast.
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