Do the math for me...

[eric1514]

...and then tell me how you did it.

I have an appliance that is rated 130 watts at 110 volts (house current). How many amps per hour will this appliance draw from a 12 volt battery?

TIA
Eric

[_40Fan]

It is always 220 volts around here. Half that would be more than I'd like to find out.

[red31]

the OP got that and gave thanks.

[beemerphile1]

Almot wrote:

beemerphile1 wrote:
Lots of different formulas people are posting making a simple calculation confusing.

Watts stays the same regardless of voltage.

130 watts divided by 120 volts equals 1.08 at 120vac

130 watts divided by 12 volts equals 10.8 at 12vdc

Just different ways to get the needed result.

AC amps multiplied by 10 is a good empirical formula for use without calculator - if you already know AC amps.

To get AC amps, you may divide 130 watts by 120 or 110, doesn't matter because real AC voltage is often in between.

But beware the jumping decimal point - it's been known to confuse even the brightest minds.

True, but the OP asked a simple question because they don't know electrical theory. They deserve a simple answer.

A bunch of engineers or wannabes discussing load factors and whatnot just confuses.

[MEXICOWANDERER]

Also tricky is calculating an inductive AC load to DC amps. Use a Wattmeter or VA meter on an inductive appliance. Then run out to your rig, fire up the inverter, mentally multiply empirical wattage times 120% for count for inverter efficiency then stare at your DC ammeter indicative of battery drain. "De nombas, mon, dey doan add up".

[Almot]

beemerphile1 wrote:
Lots of different formulas people are posting making a simple calculation confusing.

Watts stays the same regardless of voltage.

130 watts divided by 120 volts equals 1.08 at 120vac

130 watts divided by 12 volts equals 10.8 at 12vdc

Just different ways to get the needed result.

AC amps multiplied by 10 is a good empirical formula for use without calculator - if you already know AC amps.

To get AC amps, you may divide 130 watts by 120 or 110, doesn't matter because real AC voltage is often in between.

But beware the jumping decimal point - it's been known to confuse even the brightest minds.

[MEXICOWANDERER]

SCHOOL

IS

IN

SESSION...

https://www.brultech.com/files/Difference%20Between%20Power%20and%20VA.pdf

[time2roll]

If it is a heating coil we also may need the temperature coefficient of resistance as I believe the resistance will be a bit less at very low wattage.

So my guess had figured that in with a corrected .1 to .2 amps.

[DrewE]

smkettner wrote:

DrewE wrote:

smkettner wrote:
130w 110v resistive load might still draw 1 or 2 amps from a 12v battery.

A 130W 110V purely resistive load would be 93 ohms, and hence a current of 0.13A at 12V, about 1.5W. If this is an immersion heater, it will be a loooong time before the tea water is hot.

Yes that pesky decimal jumped on me.

Those decimals can be very sneaky that way, I've found. Turn your attention away for even a moment and they might jump all out of line. They're crafty little buggers.

[jarata1]

Glad all on same page

[beemerphile1]

Lots of different formulas people are posting making a simple calculation confusing.

Watts stays the same regardless of voltage.

130 watts divided by 120 volts equals 1.08 at 120vac

130 watts divided by 12 volts equals 10.8 at 12vdc

[time2roll]

DrewE wrote:

smkettner wrote:
130w 110v resistive load might still draw 1 or 2 amps from a 12v battery.

A 130W 110V purely resistive load would be 93 ohms, and hence a current of 0.13A at 12V, about 1.5W. If this is an immersion heater, it will be a loooong time before the tea water is hot.

Yes that pesky decimal jumped on me.

[westend]

I think you'll find common AC ratings use 120V, not 110V.

Dividing the wattage by the source voltage and when using an inverter, using "10" as the devisor will return fairly accurate results for amperage. That will also give the AH draw for one hour.

[DrewE]

smkettner wrote:
130w 110v resistive load might still draw 1 or 2 amps from a 12v battery.

A 130W 110V purely resistive load would be 93 ohms, and hence a current of 0.13A at 12V, about 1.5W. If this is an immersion heater, it will be a loooong time before the tea water is hot.

[MEXICOWANDERER]

If it's a vacuum cleaner split phase motor like a fan then y'all best take a deep breath and sharpen your pencils. Split phase and modified sine wave are like scotch with a vermouth chaser.