# AH and what do i need?

Registered Users Posts: 19 ✭✭
Ive tried to read other posts and figure this out,but still need some help.I f i have a swamp cooler(small portable kind)65 watts.so eight hours would be?65 times eight=520 ahs?so to keep this above 50 %=1100ahs sounds right?golf cart batterys,225ah=5 batterys ?and how much panel to power this? Also what if i used the cooler only two hours a day,just to cool the room off,130ahs?this is for a place in the desert with lots of sun.i have a genny to power up a washing machine and provide power for a charger to help give the batterys a charge a few hours a week.mabe this well help other confused people also.

Re: AH and what do i need?

Ron,

Your confusion is between Watts and Amps, and Watt*Hours and Amp*Hours:

The basic electrical equations:

V=Volts
I=Amps current
R=Resistance
P=Power in Watts (a Rate, like gallons per hour)
Watt*Hour=Total Work in Watt*Hour (an amount, like gallons)

P=Power in Watts (an amount, like gallons)
Watt*Hour=Total Work in Watt*Hour (a Rate, like gallons per hour)

V= I*R
P= I*V = V^2 / R = I^2 * R

65 Watts * 8 hours = 520 Watt*Hours

520 Watt*Hours / 12 volt battery bank = 43.3 Amp*Hours (at 12 volts)

43.3 Amp*Hours * 1/0.50 max battery discharge = 86.6 Amp*Hour

Normally, a good rule of thumb is to size the battery for 3 days of no sun and 50% maximum discharge--or 6x daily load.

43.3 map*Hours * 3 days * 1/0.50 max discharge = 260 Amp*Hour 12 volt battery for 8 hours of operation per day

Lets say you are near Dagget California and average ~7+ Hours of day seven months of the year. Assume your panels+charge controller are 77% efficient and the battery is 80% efficient (flooded cell golf-cart type battery)... Then to run your system would take:

65 watts * 8 hours * 1/7 hours sun * 1/0.77 eff * 1/0.80 batt eff = 120 Watts of solar panels

If you only want to run the system 2 hours per day:

65 watts * 2 hours * 1/7 hours sun * 1/0.77 eff * 1/0.80 batt eff = 30 Watts of solar panels

Now--if you only want to run the swamp cooler when the sun is up--you can skip the batteries, and just connect the solar panel directly to the swamp cooler (probably around 100 watt panel) plus a linear current booster:
Used to control and power a DC motor from a solar panel. The unit prevents stalling of the motor under less than full sun condition. The power of the sun is transformed to the motor running conditions so as the sun goes down the motor slows down instead of stalling. Conversely, or as the sun comes up the motor starts running much earlier instead of staying stalled for hours when it could be running. This translates into more running time of the motor where it spends a lot of time working instead of stalled doing no work.
If you are purchasing a DC powered swamp cooler--they can probably recommend a solar panel+linear boost controller that works best for your installation (depends on internal DC motor setup).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: AH and what do i need?

hey bill, where you have "(a Rate, like gallons per hour)" and "(an amount, like gallons)" i believe you need to reverse them. we don't want him more confused than he is.;)

P=Power in Watts (a Rate, like gallons per hour) >that isn't a rate, but watt/hours are.

Watt*Hour=Total Work in Watt*Hour (an amount, like gallons) >gallons would apply to the watts that you have listed as a rate.
Re: AH and what do i need?

Niel,

You are confusing me...

Gallons per Hour is a Rate... Like Watts (or Miles per Hour, etc.)

Watt*Hours is an amount of work done (equivalent to Gallons or Miles--to use the first 1/2 of the example).

Watts * Hours = Watt*Hours

Gallons per Hour * Hours = Gallons
Miles per Hour * Hours = Miles

???? (is this where the analogies are causing more confusion than just the original statement) ????

-Bill Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: AH and what do i need?

you aren't seeing it so i'll bold it in the original post of yours and show the corrected version too.
Re: AH and what do i need?

Niel,

I still believe you have it backwards and I am correct.

The common mistake is to call it Watts per Hour, trying to copy Miles per Hour or Gallons per Hour... Watt is a rate all by itself.
The watt (symbol: W) is a derived unit of power in the International System of Units (SI). It measures rate of energy conversion. One watt is equivalent to 1 joule (J) of energy per second.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 264 ✭✭✭✭✭✭
Re: AH and what do i need?

Bill is right. Watts are Joules per second, rate of energy flow.
The watt (symbol: W) is a derived unit of power in the International System of Units (SI). It measures rate of energy conversion. One watt is equivalent to 1 joule (J) of energy per second.

In terms of mechanical energy, one watt is the rate at which work is done when an object is moved at a speed of one meter per second against a force of one newton.
1W = 1Js-1 = 1kgm2s-3 = 1Nms-1
GP
Well ! Bill seems to have a quick hand to add this same definition.
• Re: AH and what do i need?

I think this is fun! I do hope that the OP finds some answers.:roll:

Recalling high school physics, work is a measure of mass moved through a distance. Moving a mass through a distance requires force. It makes no difference how quickly or slowly that mass is moved through that distance, the same amount of work is done (or required.) For purists, I think we are dealing with scalar quantities. Until alternating currents are present.

When time is a factor, the concept of rate is introduced. This is called power and is measured, most commonly by Horse Power or Watts. More on this later.

Energy is required to do work.

Electrically, the amount of energy available to do work is measured in volts. Often called potential. Or the lines over your head in the city "tension." Lots of potential power. BUT, not until that charge begins to move through the distance, i.e., a length of wire (or other load,) can the power delivered/use be known.

I'm no Faraday, Maxwell, Edison or Westinghouse. But there is a way to do this.

I am an amateur. Take nothing to the bank.

I invite the EE's. Correct me.
Re: AH and what do i need?
Kamala wrote: »
Recalling high school physics, work is a measure of mass moved through a distance. Moving a mass through a distance requires force. It makes no difference how quickly or slowly that mass is moved through that distance, the same amount of work is done (or required.) For purists, I think we are dealing with scalar quantities. Until alternating currents are present.
...
I invite the EE's. Correct me.

It is Force across a Distance.

Pushing a ball faster and faster is and example of adding energy to a ball.

Or pushing a block of wood across a carpet is using energy.

The ball (mass) rolling across a glass table at a constant speed does not add or subtract energy.

For extra credit--How "far" does an electron move in an electrical wire with A/C current (a few amps in a standard size wire)?

-Bill Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Re: AH and what do i need?

Extra credit...

Uhhh... Zero?

Buhler?
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: AH and what do i need?

the apparent movement is nil due to the fact it averages the same distance in opposing directions. i was told work is the ability to do the job in 6th grade. i always had a problem with that definition as having an ability isn't the same as doing it or having done it. it certainly would've made me get lots of money without having done the job. watts would be work and watt/hours would be the quantified work in relation to 1 hr.
• Registered Users Posts: 19 ✭✭
Re: AH and what do i need?

Re: AH and what do i need?

Actually, I intended in 1/120 of a second--or even 1 second for DC...

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: AH and what do i need?
BB. wrote: »
Y...For extra credit--How "far" does an electron move in an electrical wire with A/C current (a few amps in a standard size wire)?
The speed of electric current
Since nothing visibly moves when the charge-sea flows, we cannot measure the speed of its flow by eye. Instead we do it by making some assumptions and doing a calculation. Let's say we have an electric current in normal lamp cord connected to bright light bulb. The electric current works out to be a flow of approximatly 3 inches per hour. Very slow!

Here's how I worked out that value. I know:
Value for electric current: I = 1 ampere
Wire diameter: D = 2/10 cm, radius R=.1cm
Mobile electrons per cc (for copper, if 1 per atom): Q = 8.5*10^+22
Charge per electron: e = 1.6*10^-19
The equation:

cm/sec = ________I_______ = .0023 cm/sec = 8.4 cm/hour
Q * e * R^2 * pi

This is for DC. Chris R. points out that for a particular value of frequency of AC, the "skin effect" can cause the flow of charges in the center of a wire to be reduced while the current on the surface becomes stronger. There are fewer charges flowing, and hence they must flow faster. ("Skin Effect" is stronger at high frequencies and with thick wires. The effect can USUALLY be ignored in thin wires at 60Hz power-line frequencies.)

The size of the wiggle
And about AC... how far do the electrons move as they vibrate back and forth? Well, we know that a one-amp current in 1mm wire is moving at 8.4cm per hour, so in one second it moves:
8.4cm / 3600sec = .00233 cm per second
And in 1/60 of a second it will travel back and forth by
.00233cm/sec * (1/60) = .0000389cm, or around .00002"

This simple calculation is for a square wave. For a sine wave we'd integrate the velocity to determine the width of electron travel.

So for a typical AC current in a typical lamp cord, the electrons don't actually "flow," instead they vibrate back and forth by about a hundred-thousandth of an inch. GP
Re: AH and what do i need?

GP,

And another 2 points!

I still remember in high school chemistry (or it may have been physics) doing the calculation and being surprised that the electrons hardly move at all.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 5,400 ✭✭✭✭
Re: AH and what do i need?

You guys are making this boy's head ache! Some of us were too busy in high school doing other things ( fill in your own blank here______) to be absorbing much physics, or math or whatever! Chemistry was another subject,,,so to speak!

As has been said, if you remember the '60's you weren't there!

Tony
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: AH and what do i need?
BB. wrote: »
GP,

And another 2 points!

I still remember in high school chemistry (or it may have been physics) doing the calculation and being surprised that the electrons hardly move at all.

-Bill

as gp pointed out, it is still a movement even though so small and that still makes me correct as that apparent movement is nullified by going in opposing directions making the average of it essentially staying there in the original point. he just went further in depth and stated the opposing distances traveled which does answer your question.

tony,
take what you took in the 60s and you won't remember you had a headache.:roll::p