

12102015, 16:00

#91

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Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
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Re: Amps v Amp hours v Amps/Hr
OK. Last try:
Volumetric measurement <> Volumetric rate measurement.
And it's when people conflate the two (like the 0.1 gph/day v 0.1gph above) that the confusion occurs.
I really can't see how someone as obviously intelligent as you continues to miss this point.
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12102015, 16:29

#92

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 4,812

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by StuM
OK. Last try:
Volumetric measurement <> Volumetric rate measurement.
And it's when people conflate the two (like the 0.1 gph/day v 0.1gph above) that the confusion occurs.
I really can't see how someone as obviously intelligent as you continues to miss this point.

I'm not so sure its me that's missing the point.
0.1gph/day would be the same as saying 2.4 GPD (Gallons per day). Where 0.1 GPH would be a tenth of a gallon per hour. Both are volumetric. FPS, MPS, measures velocity. Feet per second or meters per second is a Speed rate. GPH or GPM is a volume rate.
Now say 2GPH for 30 minutes and its a single gallon volume moved not a speed rate of flow. Or 2GPM/HR would be 120 gallons. 2GPH/hr is a bit redundant. Neather give you the velocity of flow.
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12102015, 17:02

#93

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Join Date: Oct 2014
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Posts: 426

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
I'm not so sure its me that's missing the point.
0.1gph/day would be the same as saying 2.4 GPD (Gallons per day). Where 0.1 GPH would be a tenth of a gallon per hour. Both are volumetric. FPS, MPS, measures velocity. Feet per second or meters per second is a Speed rate. GPH or GPM is a volume rate.
Now say 2GPH for 30 minutes and its a single gallon volume moved not a speed rate of flow. Or 2GPM/HR would be 120 gallons. 2GPH/hr is a bit redundant. Neather give you the velocity of flow.

Back to calculus, please.
Start with distance. The first derivative of distance is the rate of change of distance, distance per unit time. Meters per second. We call that velocity. The second derivative is the rate of change of velocity. Meters per second per second. We call that acceleration.
Now a quantity of fluid. The first derivative, I suppose, would be the rate of change in quantity. Liters per second. We call that flow. Then the second derivative would be the rate of change of flow. Liters per second per second. I don't know what that is called. But it is not flow, or quantity; it is the rate of change in flow.
But I've probably forgotten all this.
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12102015, 17:04

#94

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Join Date: Nov 2013
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Re: Amps v Amp hours v Amps/Hr
"0.1gph/day would be the same as saying 2.4 GPD (Gallons per day)."
NO IT WOULDN"T! (sorry about shouting, but I'm getting really frustrated by your obtuseness here!)
It would be the same as saying increasing by 2.4 gallons per day.
You can't know how many gallons per day is represented by 0.1 gph/day unless you know how many gallons per hour (or day) at the start and how many days.
Once again: gph/day is "gallons per hour per day".
The key factor you keep missing is that "per hour per day" is not a rate of change in volume, it is the rate of change in the rate of consumption of volume.
"Or 2GPM/HR would be 120 gallons. 2GPH/hr is a bit redundant."
Again  NO!
2gpm/hr means that after one hour the flow rate is 120 gallons per hour greater than it was at the start. 2gph/hr means that after one hour, the flow rate is 2 gallons per hour faster than it was at the start.
Again without knowing what the flow rate (gpm or gph) was at the start point, we cannot know the flow rate at the end of the hour or how many gallons have flowed in total.
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12102015, 17:07

#95

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Join Date: Nov 2013
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Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by Cottontop
Back to calculus, please.
Start with distance. The first derivative of distance is the rate of change of distance, distance per unit time. Meters per second. We call that velocity. The second derivative is the rate of change of velocity. Meters per second per second. We call that acceleration.
Now a quantity of fluid. The first derivative, I suppose, would be the rate of change in quantity. Liters per second. We call that flow. Then the second derivative would be the rate of change of flow. Liters per second per second. I don't know what that is called. But it is not flow, or quantity; it is the rate of change in flow.
But I've probably forgotten all this.

Absolutely correct! Why is this so hard for some people to grasp?
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12102015, 18:05

#96

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 4,812

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by StuM
Once again: gph/day is "gallons per hour per day". The key factor you keep missing is that "per hour per day" is not a rate of change in volume, it is the rate of change in the rate of consumption of volume.

I'm sorry, That is not correct. A flow of 0.1gph/day is not an acceleration, that would be 0.1gph/day/day. Just as Liters per second per second is a rate change in velocity, but liters per second is volume.
So I can have 0.1GPH which is a rate of one tenth of a gallon per hour. Since Hour is defined in GPH and a day is 24 hours we get 2.4 GPD.
An acceleration of rate change would be 0.1 GPD/D or 0.1 GPH/H That is a rate change in velocity.
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12102015, 19:27

#97

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Join Date: Oct 2014
Boat: Shopping
Posts: 426

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
I'm sorry, That is not correct. A flow of 0.1gph/day is not an acceleration, that would be 0.1gph/day/day. Just as Liters per second per second is a rate change in velocity, but liters per second is volume.
So I can have 0.1GPH which is a rate of one tenth of a gallon per hour. Since Hour is defined in GPH and a day is 24 hours we get 2.4 GPD.
An acceleration of rate change would be 0.1 GPD/D or 0.1 GPH/H That is a rate change in velocity.

Hours and days are both units of time. So 0.1 gallons per hour per day could be expressed as 0.1 gallons per hour per 24 hours.
In my mind, gallons per hour per day is not the same thing as gallons per hour FOR A day. One is division, the other multiplication. We seem to be using "per" differently.
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12102015, 19:30

#98

Registered User
Join Date: Apr 2012
Posts: 570

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
I'm sorry, That is not correct. A flow of 0.1gph/day is not an acceleration, that would be 0.1gph/day/day. Just as Liters per second per second is a rate change in velocity, but liters per second is volume.
So I can have 0.1GPH which is a rate of one tenth of a gallon per hour. Since Hour is defined in GPH and a day is 24 hours we get 2.4 GPD.
An acceleration of rate change would be 0.1 GPD/D or 0.1 GPH/H That is a rate change in velocity.

Whoa...
You're right...gph/day is not an acceleration...it is a rate of change of flow.
Liters per second per second is not a rate change in velocity. It is a rate of change in volumetric flow rate.
Liters per second is not volume, but volumetric flow rate (which you described accurately in a previous post...you're just messing with StuM, aren't you?)
Continuing...0.1 GPH is a volumetric flow rate of one tenth of a gallon per hour, and if that flow rate continues for 24 hours, you do get 2.4 GPD. But that is simply another way of saying the same thing...but using a different time period for the constant volumetric flow rate.
And if you change the flow rate by 0.1 GPH/hr, the flow rate would be 0.2 GPH after the first hour, 0.3 GPH after the second hour, 0.4 GPH after the third hour, and so on. The volumetric flow rate is changing...getting higher...and could be said to be accelerating.
I'm not sure why you continue to discuss the velocity of the fluid in the discussion. Flow rate is a function of velocity, specifically the mass flow rate is equal to the fluid density times the cross sectional area of the pipe times the average velocity of the fluid in the pipe...and the volumetric flow rate is equal to the product of the average velocity and the cross sectional area of the pipe.
And if the flow rate is increasing, the velocity is increasing, which means the fluid particles are accelerating.
And amps/hr still has little practical meaning.
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12102015, 19:50

#99

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Join Date: Oct 2014
Boat: Shopping
Posts: 426

Re: Amps v Amp hours v Amps/Hr
Quote:
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.
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.

"When we started our voyage, to meet the water requirements of the crew, we had to operate the water maker at a rate of 1 gallon per hour. As we approached the equator, and the crew increased their consumption, we found we were having to increase the flow rate of the water maker about 0.1 gallons per hour, each day. By day 10 of the voyage, we were operating the water maker at a rate of 2 gallons per hour."
I think that's a rate of change in the flow rate of the water maker of 0.1 gph/day.
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12102015, 19:54

#100

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Join Date: Oct 2014
Boat: Shopping
Posts: 426

Re: Amps v Amp hours v Amps/Hr
But I really wish everyone would use watts and watthours for power and energy.
When people talk about their 120v fridge using 10 amphours each day, I am left confused by not being sure if they are talking about 120v amps, or 12v amps.
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12102015, 20:11

#101

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Join Date: Apr 2015
Location: NC
Boat: 1974 Morgan Out Island 33
Posts: 552

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by colemj
Also:
"When at idle, the tach shows a range of RPM's between 500 and 1000. Do I have an air leak somewhere?"
Yet another valid use of "RPM's"
Mark

LOL, how about RsPM?
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12102015, 20:13

#102

Registered User
Join Date: Apr 2012
Posts: 570

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by Cottontop
But I really wish everyone would use watts and watthours for power and energy.
When people talk about their 120v fridge using 10 amphours each day, I am left confused by not being sure if they are talking about 120v amps, or 12v amps.

I've never heard anyone discuss energy use in terms of AH except when the power source is a battery, whose ratings are given in AH, allowing approximating the remaining capacity of the energy source (dependent on discharge rate, of course).
Submarines have large main storage batteries that can be used for hotel loads or propulsion. Ship electricians are charged with (heh) maintaining the batteries and carefully evaluating the their capacities around the clock. They do that with by continually monitoring an amperehour counter. For a more accurate determination of the capacity remaining, they check the specific gravities of the battery cells.
They do calculate KWhrs used, but only in conjunction with equalizing charges and test discharges, when determining actual capacity and battery health. Calculating KWhrs or watthours used continually would be of little utility.
Knowing the AH ratings of my batteries and the discharge rate, with knowledge of the discharge rates used to determine the ratings, I have a pretty clear running approximation of the states of charge and can compare my mental estimates with the battery monitor as a backup to it. Using watthours would not be useful.
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12102015, 20:15

#103

Registered User
Join Date: Apr 2012
Posts: 570

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by jwcolby54
LOL, how about RsPM?

No. That would be Revolutionss Per Minute.
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12102015, 20:29

#104

Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
Posts: 6,707

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by Cottontop
"When we started our voyage, to meet the water requirements of the crew, we had to operate the water maker at a rate of 1 gallon per hour. As we approached the equator, and the crew increased their consumption, we found we were having to increase the flow rate of the water maker about 0.1 gallons per hour, each day. By day 10 of the voyage, we were operating the water maker at a rate of 2 gallons per hour."
I think that's a rate of change in the flow rate of the water maker of 0.1 gph/day.

Absoutely. That is exactly what my example shows after 10 days: 2 gph or 48 gallons per day. So you were indeed increasing your usage by 0.1gph/day and using the dimensions correctly. My apologies for doubting you. I mistook your correct usage of the units for the way SC insists on trying to use it.
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12102015, 20:56

#105

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Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 6,385

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by 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.

Lars,
WADR, whether it is peas or a water analogy, Voltage is always pressure and Current is always flow. This is in every single boating electrical and/or electrical 101 books I've ever seen.
I think you may have gotten them backwards.
Now back to our regular dimensional analysis program, starring StuM and sailorchic!!!
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