Amps v Amp hours v Amps/Hr

[Stu Jackson]

Ach, I been away for three days and this is the same old tired stuff, Stu (the OTHER Stu!!! trying to prove something, I still haven't figured out what (or watt).

Geez,give it a break.

Amp hours or watt hours in or out (and IN being harder to define 'cuz of battery acceptance, compared to USAGE of amps X time for an energy budget ) is all we need to know, in the real world or recreational boating.

Amps X time = amp hours.

"F" the coulombs.

Keep it Simple.

What time is it? I'll tell ya how to build a watch. Who needs it?

[valhalla360]

Originally Posted by exMaggieDrum

The inefficiencies were my point exactly. They can be very significant in the real world on a boat. And, if people are trying to make sure those AGMs are 100.0% charged, it is hard to measure. The tenth is meant to imply the precision that many try to achieve with all this.

This happens whether you use the correct units or not.

[Wotname]

Originally Posted by StuM

......
Methinks Wottie is stirring again

No, not really - this time...
I was responding to Maine Sails post that Amp/hr was incorrect as a unit. Perhaps his post was tongue in cheek - not sure; but as you and Valhalla360 say, it a valid measurement though not very useful to the cruising sailor.

[colemj]

Originally Posted by StuM

Dunning-Kruger.

If that mattered, there would be no Cruiser's Forum at all…

Mark

[Wotname]

Originally Posted by StuM

Copied from the Dozens Poll thread for those who missed it:

Wottie,

"What we have here is a failure to communicate".

I just realised that the problem is we are using "quantity" in two different ways.

To quote Wikipedia (which I dislike doing)

Two basic divisions of quantity, magnitude and multitude, imply the principal distinction between continuity (continuum) and discontinuity

When I said that dozen is a dimensionless term and just the same as 12, 42, a mole or Reynolds Number, I was talking about it in terms of multitude. (How many there are). In that context I was correct in my comparison.

When you say that dozen is the same as pound or foot, you are talking about it in terms of magnitude. (how much of something there is).
In that context, you are correct in your comparison.

It's like me saying an orange is not like a basketball because you can't eat a basketball and you saying that an orange is like a basketball because they are the same colour. We are both right!

In dimensional terms, (multitude) a dozen is more like "12" than a foot.
In "non-dimensional" (magnitude) terms it is more like a foot than "12".

Hmm… this post seems to have disappeared from the Dozen thread and what you say appears to have some (a lot?) of merit. Bit late to take in to-night but will re-read tomorrow - thanks

[Maine Sail]

Originally Posted by Wotname

No, not really - this time...
I was responding to Maine Sails post that Amp/hr was incorrect as a unit. Perhaps his post was tongue in cheek - not sure; but as you and Valhalla360 say, it a valid measurement though not very useful to the cruising sailor.

I did not say anything about it as a "unit". Just that folks often use the terminology incorrectly.

"I have a 125 amps/hr battery."

Or typed another way:

"I have a 125 amps÷hour battery."

Can you use that 125 ampere hours in 1 hour???? That 125 Ah rating is most likely at a 20 hour rate of discharge not one hour or 3600 seconds.

As has been said, even by yourself, amps÷hour or amps/hour is not a very useful terminology in the context many try to apply it.....

[transmitterdan]

Coulombs per day would be a valid unit of measure.

[Lars_L]

StuM mention the energy unit watt second (Ws). It is the same as Joule (J).
Weight is measured in kilogram (kg).
The force to lift 1 kg is approximately 10 Newton (N). It differs a little where on earth you are. If you have a clump of concert with a weight of 20 kg, in the air you need a force of 200 N to lift it. If you have it in water, the weight is still 20 kg but the force to lift is only 120 N.
By the way, a weighing instrument do not shows the weight, it shows the force.

If you have laid out an anchor and chain with a total weight of 20 kg, you need a force of 200 N to lift it. You have a windlass that lifts with a speed of 13 meter per minute (m/min). That’s equal with 0.217 meter per second (m/s). The power to lift the anchor is the force multiplied with the speed, 200 N * 0.217 m/s = 43.3 Nm/s.

As I already said, Joule (J) is the same as watt second (Ws), but it is also the same as Newton meter (Nm). By this we get Nm/s = J/s = Ws/s = W. In this example, the power is 43.3 W.

There is an old thread http://www.cruisersforum.com/forums/...em-136055.html

[Lars_L]

To say A/day is like saying gph/day. There are situation where it make sense but it is seldom used, for example you can say: When we come closer to the equator the water consumption increased with 0.1 gph/day.

[LakeSuperior]

Originally Posted by Lars_L

Weight is measured in kilogram (kg).

Weight is measured in Newtons (MKS) or pounds (English). Weight is a measure of force.


The force to lift 1 kg is approximately 10 Newton (N). It differs a little where on earth you are. If you have a clump of concert with a weight of 20 kg, in the air you need a force of 200 N to lift it.

If you have it in water, the weight is still 20 kg but the force to lift is only 120 N.

...the mass is still 20 kg...


By the way, a weighing instrument do not shows the weight, it shows the force.

weight is force

For this thread you need to be more precise in the language.

[leftbrainstuff]

Originally Posted by StuM

Many people get confused when discussing Amps, Watts, Amp hours and Watt hours. Frequently the confusion is the result of incorrect use of these terms by some forum posters. Hopefully the following will clarify rather than further fog the issue.

First - A bit of background

SI UNITS
When we talk about a quantity or a measurement, we talk about a number of units. To avoid confusion between people, it is essential that everyone is "talking the same language". There is an internationally recognised set of Units called The International System of Units or SI which enables this.

In the SI System, there are two fundamental types of measuring units: Basic and Derived
Basic Units are simple things like length,mass and time.(the specific units for these are the meter, kilogram and second). There are several other such base units including the Ampere (for electric current) and the Kelvin (for temperature)
Derived Units are more complex measurements which are formed by multiplying or dividing two or more different Base Units such as meters per second.

For convenience, we often describe quantities in terms of non SI units such as horse power, gallons, nautical miles, knots or gallons per hour. Any of these units can be converted to their equivalent SI representation by multiplying or dividing them by an appropriate number.
(Example: You can convert nautical miles to the SI unit "meter" by multiplying by 1852 and you can convert knots (nautical miles per hour) to meters per second by multiplying by 0.514444.
10 nautical miles = 18,520 meters and 4 knots = 2.05776 meters per second
The Kelvin is a special case, it is exactly the same size as a degree Celsius, but with a different start point, so you can convert Kelvin to degrees Celsius just by adding a number and when calculating temperature changes, you can use the two interchangeably)

DIMENSIONS
The number of basic units used in a measurement is called the "dimensions" of that unit. So a meter or a nautical mile is a 1 dimensional unit (meters) and speed in meters per second or knots is a two dimensional unit (meters and seconds).
Note that these do not have to all be different units: acceleration for example has 3 dimensions even though it only uses two different basic units, since it uses one unit twice (meters per second per second)
Even more complex units such as the Volt can still ultimately be expressed in basic units. (The volt is actually a 7 dimensional unit which can be expressed as meters x meters * kg / secs / secs / secs / Amps )
A plain number by itself, without any specified unit is called "dimensionless" (i.e. numbers like dozen or 42).

NAMES AND ABBREVIATIONS

Unit names are frequently abbreviated. It is a convention that where the name of a unit comes from the name of a person, the name or abbreviation is capitalised, all other units are not.
So we have Ampere, Volt, Watt and their abbreviations Amp or just A, Volt or just V and Watt or W, but meters (or m), seconds (sec or s), kilograms (kg), gallons (gal or g) etc

As mentioned previously derived units comprise two or more units which are multiplied or divided by each other. A great deal of confusing arises where these operations are not expressed properly.
When two units are multiplied together, the resultant unit name is written as the basic unit names without any intervening mathematical or other symbol.
(i.e The commonly used unit of "energy" stored or used in an electrical system should always be written as simply Ampere hour (or Amp Hour, Ah).
When one unit is divided by another , the two words are separated by a slash (divide sign "/") or the word "per" (or just p)
(ie gallons/hour, gallons per hour or gph).


FINALLY - AMPS, WATTS, VOLTS AND TIME
There are a number of different aspects of electricity that we are concerned with:
Current Flow, Force, Power and Energy

The basic SI unit of electrical "current flow" is the Ampere (Amp or A). It is the measure of the rate at which current is flowing through a specific point in a circuit at a specific point in time. It is equivalent to the rate at which elementary electric "charges" are passing the point (charges per second)
The derived unit of electric "force" is the Volt (V). It is a measure of the "potential difference" between two points in an electric circuit.
The derived unit of electrical "power" is the Watt (W) It is a measure of the amount of energy flowing (Amps) through a point where this is a certain potential difference (Volts) across the point. So: Watts = Volts * Amps and Amps = Watts / Volts
(Example: A solar panel generating 48 Watts at a point in time will generate a current of 4 Amps at 12 Volts or 2 Amps at 24 Volts.)

Note that Amps, Watts and Volts are all measures of different aspects of electrical force at a single point in time.

The final aspect of electricity above is "Energy" and this is where time finally rears its head. It is the amount of "work" that a given amount of electricity can do such as how long it can provide the required power (Watts) to a specific piece of electrical equipment and is expressed in Watt seconds.

Rather than Watt seconds, it is more practical to talk about Watt hours (1 Watt hour is equal to 3600 Watt seconds)
Also, if we are working with a nominal 12 Volt system, it is often easier to work in Amp hours where the voltage is assumed to be a constant 12V. Since Watts = Amps x Volts, 1 Amp Hour is, in this situation, the same amount of energy as 12 Watt hours (if we are working with a 24V system, 1 Amp hour is the same as 24 Watt hours)

THE BOTTOM LINE.

If we are working in Amps rather than Watts, then:

The "capacity" of a battery, the amount of power used or needing to be replaced is a number of Amp Hours or Ah.
It is not a number of Amps, Amps per hour or Amps/hr which as we see above are totally different things.

There is no such thing as a 100 Amp battery. (Some batteries are rated in CCA or Cold Cranking Amps - but that is not an indication of its capacity, it is an indication of the maximum rate at which energy can safely be drawn from it )

There is no reasonable practical meaning of Amps/hr or Amps per hour (which is actually a measure of how fast a current is increasing or decreasing.)


If we all use the correct units and abbreviations, we can avoid confusion and misunderstanding in our forum discussions. If we use them incorrectly, there is endless room for misunderstanding (and massive thread drift )

The use of the term basic I find confusing to students. Fundamental better describes how we can use units of force, length and time to derive all other units. Hence the term derived.

I've found the water hose analogy useful to explain Volts, Amps and Resistance in the context of DC electrics 101. Volts is analogous to water pressure, Amps to water flow and Resistance is due to restrictions or loss.

Comparison units like CCA, Amps consumed over time, etc provide a repeatable, but not often a realistic means of comparing apples to apples. They also typically include a time component which allows us to interpolate 'the area under the curve' of measured data.

This interpolation makes it relatively simple for the layperson to choose components without having do their own experiments.

There are really 3 types of units. Fundamental (aka your basic, derived and industry, market or standards norms.

It is possible to take any derived units from any system, SI or otherwise, and resolve them to fundamental units. Some of the third type of norms are just marketing terms. These are of little value to us consumers. Beware wary of these.



Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[hellosailor]

Stu,
I'll assume that's sarcasm, since you surely know those meters are designed to be used and then moved elsewhere, after you've got a typical 24 hour (etc) consumption number for the "problem children". Running lights, VHF, stereo, all that good stuff really doesn't need actual measurement. Although, there are totalizing wattmeters you can install in the primary power line if you REALLY like to avoid sharp pencils.(G)


Any battery marked as a VRLA battery for UPS use is probably an AGM battery, so the house system may need to be designed for AGM rather than wet lead. MaBell and her offspring used to change the backup batteries in their exchanges every two years, regardless of other factors, regardless of wet lead, wet NiCad, or other types.


In the computer industry UPS batteries are inevitably AGM, and typically changed out in the same two years because the standard charging and use pattern kills them after a four year life. At two years (installed) they're down to half capacity, and the way the systems are spec'd, that's time to change them. The charging systems are rough on them, and what many folks never know is that on a hot summer day, they have to be de-rated 25% simply because the ambient temperature is too high. (Air conditioners being one of the first casualties in a blackout or brownout.)


So...UPS battery as house battery? Not really. High impulse power may also mean THIN PLATES and low durability compared to a deep-cycle "traction" design. They'll work, but probably not a bargain compared to a "right" battery.

[Lars_L]

I compare electricity with airflow of peas. (The peas are the electrons). The speed of the flow is the voltage. The density of the flow is the current. If you multiply the speed with the density you get a amount of peas per time, that correspond with the power. If you let that flow for a time, you have the energy. If you shall fill a bucket with peas you need a power over some time. Increase the power and you can short the time. You can increase the power by increase the speed of the flow or/and increase the density of the flow. (The bucket is the battery).

If the flow goes thru a tube, the friction against the walls will slow down the speed. That corresponds with the resistance. That will not affect the density of the flow. But a higher density will slow down the speed even more.

If you have a wire it will have some resistance. That resistance will slow down the speed of the electrons and that’s the same as a lower voltage. That will not effect the density and that means that it will not effect the current. But a higher current will give a higher voltage drop. A thinner tube will have more friction and slow down the speed even more. It's the same with a thin wire, the voltage drop will be higher.

[StuM]

Originally Posted by Lars_L

To say A/day is like saying gph/day. There are situation where it make sense but it is seldom used, for example you can say: When we come closer to the equator the water consumption increased with 0.1 gph/day.

Sigh!! I don't think you appreciate the implications of 0.1gph/day.

A gph is not a volumetric measurement, regardless of what one or two forum members still insist.

Let's put some numbers into your statement :

Assume that just before you "come closer to the equator" you are using 24 gallons per day or 1 gph and it then increases by 0.1gph/day

The next day you would use 1.1 gph = 26.4 gallons per day.
On the second day you would be using 1.2 gph = 28.8 gallons per day.
10 days later you would be using 1 + (10 *.1) = 2gph = 48 gallons per day.
After 30 days you would be using 1 + (30*.1) = 4 gph = 96 gallons per day.
After 100 days you would be using 1 + (100*.1) = 11 gph = 264 gallons per day.
After a year in the tropics? 900 gallons per day.

I think not. Your water consumption may go up by 0.1 gph but not by 0.1gph/day.

[sailorchic34]

Originally Posted by StuM

Sigh!! I don't think you appreciate the implications of 0.1gph/day.

A gph is not a volumetric measurement, regardless of what one or two forum members still insist.

And here we go again.

From the internet: "The volumetric flow rate of a system is defined as a measure of the volume of fluid passing a point in the system per unit time". Also we have: "GPH = a unit of volumetric flow rate"

So gee, sure sounds like GPH is a volumetric measurement of flow. If nothing else, you need to know the volumetric flow to get GPH. It could also be a GPH for 5 minute duration, where only the time units change and the volume does not.

But wait there is more. A flow rate could also be a measurement of velocity and I think that is where StuM is coming from. So in SI units for volumetric flow rate are cubic meters per second, although many other units are commonly used depending on the industry, such as cubic feet per second or liters per second.

So GPH is a volumetric measurement, but so is FPS, CFS or CMS which are volumetric rates for velocity.