Thread Tools Search this Thread Display Modes
Old 02-28-2019, 02:06 PM   #1
City: Qualicum Beach, Vancouver Island
Country: Canada
Vessel Name: Capricorn
Vessel Model: Mariner 29 - Sedan Cruiser 1969
Join Date: Feb 2019
Posts: 1,109
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.

rsn48 is offline   Reply With Quote
Old 02-28-2019, 02:46 PM   #2
DavidM's Avatar
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23
Join Date: Aug 2012
Posts: 5,344
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.


DavidM is online now   Reply With Quote
Old 02-28-2019, 03:55 PM   #3
City: Seaford Va on Poquoson River, VA
Country: United States
Vessel Name: Old Glory
Vessel Model: 1970 Egg Harbor 37 extended salon model
Join Date: Jan 2016
Posts: 2,189
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.
sdowney717 is offline   Reply With Quote
Old 02-28-2019, 08:09 PM   #4
Senior Member
Sabre602's Avatar
City: NW Washington State
Country: United States
Vessel Name: Kingfisher
Vessel Model: 37' converted gillnetter/crabber
Join Date: Oct 2017
Posts: 362
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
Anson & Donna

Be kind whenever possible. It is always possible. ~The Dalai Lama
Sabre602 is offline   Reply With Quote
Old 02-28-2019, 08:37 PM   #5
Veteran Member
Beekeepergreg's Avatar
City: Manasquan NJ
Country: United States
Vessel Name: Mayrose
Vessel Model: Mainship 30 pilot
Join Date: Nov 2017
Posts: 95
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.
Beekeepergreg is offline   Reply With Quote
Old 03-01-2019, 07:56 AM   #6
FF's Avatar
Join Date: Oct 2007
Posts: 20,590
"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.

FF is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 11:07 AM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012