Posted by on May 5, 2009, 12:01 pm

*> Everybody knows you dont run heavy loads (Iron, AC etc) on batteries but *

*> why?*

*> A normal one ton Air Conditionar (AC) requires 1500 Watts so the current *

*> (amps) required if the mains voltage is 220 should be 1500/220 = 6.8 Amp*

*> A 100 Amp hour battery can provide 100 amperes for 1 hour right?*

*> That means it should be able to run about 14 AC's (100/6.8) for one *

*> hour??????????*

*> I know its nonsense but what am I missing here?*

Wrong calculation.

What was not addressed so far is that 6.8 amps at 220 V is "equivalent" to

125 A at 12 V. Iow, A = P / V.

So, you would need an even *bigger* battery than your already very very

large 100 A-hr battery.

And, a pretty expensive inverter. Altho an inverter providing 6.8 A at 220

may not seem like a big deal, the ability to handle much larger in-rush

currents upon start up *is* a big deal.

And these are paper calculations, as well. Everything gets worse off paper,

such as the voltage drop of batteries with discharge, IR drop, etc.

Now, if this were a car A/C, you proly would need *far less* than a ton of

A/C, AND you probably wouldn't need it to be on for a solid hour, so you

could make do with a smaller (separate) battery. But still a

battery-demanding proposition, which is why the battery should be separate

from the rest of the system, lest you become stranded.

If for an apt/ house, you'd proly need a pile of batteries -- but then,

you'd proly have the room for this.

Fortunately, the newer inverter technology for A/C (mini-splits or ductless)

seems to be pretty power-miserly, altho it is still a motor, but a much less

gluttonous motor.

EERs for minisplits can push 20+, so you get much more bang for your A/C

buck -- but a lot of bucks: these high-end A/Cs (fujitsu, mitsubishi) are

perty pricey.

Inverter mini-splits can have net *triple* the EER of an old clunker, in

particular old sleeve (thru the wall) units, which have notoriously low

EER's -- they claim 8, but proly pushing 6.

If you were actually considering trying this, I'd get the smallest units

possible in multiples, and "stage" them, to be kind to the batteries.

Inverter technology in newer A/Cs already has a kind of built-in staging,

but I'd still go with multiples of the smallest units -- which I think might

be 9,000 btu (3/4 ton), but poss. less.

Oh yeah, and *lots* of batteries. :)

--

Mr. PV'd

Mae West (yer fav Congressman) to the Gangster (yer fav Lobbyist):

Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just

glad to see me??

Posted by *Yukio YANO* on May 5, 2009, 7:57 pm

Alubukhara wrote:

*> Everybody knows you dont run heavy loads (Iron, AC etc) on batteries but *

*> why?*

*> *

*> A normal one ton Air Conditionar (AC) requires 1500 Watts so the current *

*> (amps) required if the mains voltage is 220 should be 1500/220 = 6.8 Amp*

*> *

*> A 100 Amp hour battery can provide 100 amperes for 1 hour right?*

*> *

*> That means it should be able to run about 14 AC's (100/6.8) for one *

*> hour??????????*

*> *

*> I know its nonsense but what am I missing here?*

Amphours = Amps x Hours

Watts = Amps x Volts

Watthours = Amps x Volts x Hours

You left out "VOLTS" in your calculations

what is referred to in power consumption as "Watts" is actually

"Watthours".

Yukio YANO

Posted by *Joesepi* on May 5, 2009, 11:20 pm

One hour may be almost enough to lower the humidity 1% in a room or two.

*> Everybody knows you dont run heavy loads (Iron, AC etc) on batteries but *

*> why?*

*> A normal one ton Air Conditionar (AC) requires 1500 Watts so the current *

*> (amps) required if the mains voltage is 220 should be 1500/220 = 6.8 Amp*

*> A 100 Amp hour battery can provide 100 amperes for 1 hour right?*

*> That means it should be able to run about 14 AC's (100/6.8) for one *

*> hour??????????*

*> I know its nonsense but what am I missing here? *

Posted by *news* on May 6, 2009, 1:18 am

wrote:

*>Everybody knows you dont run heavy loads (Iron, AC etc) on batteries but *

*>why?*

*>A normal one ton Air Conditionar (AC) requires 1500 Watts so the current *

*>(amps) required if the mains voltage is 220 should be 1500/220 = 6.8 Amp*

*>A 100 Amp hour battery can provide 100 amperes for 1 hour right?*

*>That means it should be able to run about 14 AC's (100/6.8) for one *

*>hour??????????*

*>I know its nonsense but what am I missing here? *

A 100 amp/hr battery isoften a 20 hour rating - i.e., 5 amps for 20

hours. That means that the battery can produce 60 watts (12volts x

5amps) for 20 hours. If an inverter is 80% efficient, the output

would be 48 watts at 220 volts.

For 1500 watts, you need 1500/48 = 31.25 times as much power input.

31.25 * 60 watts = 1875 watts into the inverter. 1875 watts at 12

volts is 1875/12 = 156.25 amps. This current level requires big

cables and very good connections - better to use a higher battery

voltage to reduce the current. At 24 volts the current would be 78

amps; at 48 volts the current would be 39 amps (this current level is

likely within the wiring abilities of most DIYers). Four 100 Amp/Hr

batteries wired in series for 48 volts might power that AC for half an

hour.

Serious battery power (as in solar and wind powered houses) uses

multiple large (200 Amp/hr or bigger) batteries to store power.

However, they are more likely to use DC powered devices than to waste

power generating AC via an inverter. (A 6 volt 200 Amp/hr battery can

be moved by two people, anything bigger usually requires a hoist or

forklift. Four of these in series make a 24 volt 200Amp/hr battery

bank.)

There are DC versions of almost every appliance - many designed to

work on a 32 volt marine power system.

I worked with a guy who got fed up with the continuous price hikes and

poor service from his local electric company (north Mississippi). He

set up a couple of Winchargers in the back yard and a battery bank

(surplus from the local telephone company) under the carport. As far

as I know, he used it for years until he moved back to South Carolina

to be near family. He was way ahead of the current green movement, as

he started doing this in the mid to late 70's.

John

> Everybody knows you dont run heavy loads (Iron, AC etc) on batteries but> why?> A normal one ton Air Conditionar (AC) requires 1500 Watts so the current> (amps) required if the mains voltage is 220 should be 1500/220 = 6.8 Amp> A 100 Amp hour battery can provide 100 amperes for 1 hour right?> That means it should be able to run about 14 AC's (100/6.8) for one> hour??????????> I know its nonsense but what am I missing here?