Amps v Amp hours v Amps/Hr

[StuM]

Originally Posted by valhalla360

amp/day, amp/sec, amp/min, etc... essentially the same thing being measured. Same as feet and meters are both measuring distance.

I saw the comment about seeing the change in amps as the sun sets but what value does it provide? What would you use it for?

Examples:
- Amps: Allows you to determine appropriate wire or circuit breaker size or select a starting battery that can produce enough cranking amps.
- Amp-hr: Allows you to select appropriate battery bank size.
- Amp/time period: ?????

OK, hypothetically:
If my morning draw is around 5 amps and I get 2 Amps/hr from sunrise to mid morning from my solar panels, my batteries will start charging about 2½ hours after sunrise

[Wotname]

Originally Posted by Factor

What is a dozen, sounds like a silly old english concept.

Originally Posted by Wotname

Stay tuned, the answer will be forthcoming but in another thread ( to be advised). I have drifted Stu's excellent topic too far already - sorry mate!

Here you go

http://www.cruisersforum.com/forums/...en-154418.html

[valhalla360]

Originally Posted by StuM

OK, hypothetically:
If my morning draw is around 5 amps and I get 2 Amps/hr from sunrise to mid morning from my solar panels, my batteries will start charging about 2½ hours after sunrise

True but only if the rate of change of amps is linear. Which I don't believe it is. A passing cloud can cause it to drop off quickly then rebound. If it's an overcast day, it may never hit 5amps.

Also on a typical cruising boat, you don't have a constant draw. As the sun comes up, lights go off. Maybe there is a spike of 20-30amps if you have a 12v coffee maker. Then you plug in your phone to charge drawing an extra amp. Etc...

So as a means of determining when the batteries will start charging it's not very useful.

But from a systems point of view, why do you care when they start charging? If you have an estimate of the total amp-hrs used and the total amp-hrs generated, what use is charging start time?

I'm not challenging that it's a real unit of measurement. I'm challenging that it doesn't have much use to your average cruising sailor.

It's getting a bit beyond my expertise but I could maybe see where someone designing an induction motor may have a use for it to assess the inrush of current when power is applied but your typical cruiser doesn't care about that as long as there is enough to get the motor going without damage.

[Zil]

Use the thumb of one hand to point at each joint of that hand's fingers. Counting to 12. I believe it was the Babylonians, or their neighbors, that gave us the base 12 numbering system. Along with 60 minutes, 360 degrees, and I'm sure there are other examples. The dozen started as an extra measure from 10, something like a coupon offer. The king decreed smaller bread rolls, and bakers made their own dozen as a protest.

[StuM]

Originally Posted by valhalla360

True but only if the rate of change of amps is linear. Which I don't believe it is. A passing cloud can cause it to drop off quickly then rebound. If it's an overcast day, it may never hit 5amps.

Also on a typical cruising boat, you don't have a constant draw. As the sun comes up, lights go off. Maybe there is a spike of 20-30amps if you have a 12v coffee maker. Then you plug in your phone to charge drawing an extra amp. Etc...

So as a means of determining when the batteries will start charging it's not very useful.

But from a systems point of view, why do you care when they start charging? If you have an estimate of the total amp-hrs used and the total amp-hrs generated, what use is charging start time?

I'm not challenging that it's a real unit of measurement. I'm challenging that it doesn't have much use to your average cruising sailor.

It's getting a bit beyond my expertise but I could maybe see where someone designing an induction motor may have a use for it to assess the inrush of current when power is applied but your typical cruiser doesn't care about that as long as there is enough to get the motor going without damage.

I think we've both said on several occasions that while Amp/hr is a valid unit, it's has little use in the real world.

Methinks Wottie is stirring again

[barnakiel]

Talking metric or imperial units?

I am always puzzled when posters try to convert inches to lumens.

;-)

b.

[exMaggieDrum]

Originally Posted by valhalla360

No they are the same units.

The only issue is you need to account for inefficiencies in the system.

This is similar to filling a 5gal jug. In reality, you have account for the accuracy of the measurement lines on the jug, you have to account for temperature expansion and other variances. It doesn't change the units.

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.

[sailorchic34]

Originally Posted by StuM

This one was thrashed out fairly comprehensively in the drifted thread which prompted this one http://www.cruisersforum.com/forums/...omestic+fridge

The Actual SI definition of the Ampere is not as a derived unit of Coulombs and seconds. It is a Base unit defined as:

"The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per meter of length."

In SI, the Coulomb is the derived unit (one Amp sec).

(See Essentials of the SI: Base & derived units)

Anyhoo, I didn't write this post for physicists, but as an attempt to explain amps and amp hours to a non-technical cruiser. It necessarily contains a number of simplifications. Trying to introduce Coulombs would have just raised the complexity without adding anything of substance.

Ah, I see where you are correct. Ampere is a base unit as defined by the General Conference on Weights and Measures, (CGPM) committee. They could just have easily have used Coulonbs as the base unit and made Ampere derived.

That definition of ampere needing conductors of infinite length sure sounds like it came out of committee and is somewhat cumbersome to say the least.

From a strictly physical standpoint, that is, not something hashed out by committee, both ampere and coulomb are derived from electron flow.

Both one ampere and one coulomb are equal to 6.241×10^28 electrons per second. And that dear sir, will be the definition of an ampere by 2018 or so. Seems the SI committee did not quite pass that in 2014, as there were to few votes. (Or is that volts ).

So while the SI standards as agreed to by the CGPM committee has set the ampere as a base unit. That base unit is derived from the flow of electrons. Much like kilogram is defined by an artifact rather than a fundamental physical property. We could have had Pounds or stones as a base weight unit , if enough of the committee agreed to it.

Just because the SI has defined Ampere as a base unit of measure, does not mean its not ultimately derived from other physical properities.

[sailorchic34]

Originally Posted by barnakiel

Talking metric or imperial units?

I am always puzzled when posters try to convert inches to lumens.

;-)



b.

Lighting photometrics are often defined as lumens per square foot or square meter. The question is how many lumens per pound or kilogram.

[Privilege]

[QUOTE= In what context would you care about the amp/day?[/QUOTE]

Thanks for the thread Stu. I'm not challenging anyone here, I'm just checking out my understanding.

I've recently built a freezer and wanted to work out its energy usage. There's little use in knowing how many amps it uses whilst running as it cycles frequently. Also, the cycling periods will depend on ambient temperature, how many times I open it, etc... This will also vary from hour to hour so again, there is little use in knowing the amp/hr useage. What I'm really interested in is the average useage or amp/day. This is the same for my water pump...it will depend on how many showers I take, how often I flush the fresh-water head etc... So, if I can work out my amp useage per day (amp/day) I can work out how much I need to get out of my solar panels without going into the red.

Is that about right?

[colemj]

Originally Posted by Privilege

So, if I can work out my amp useage per day (amp/day) I can work out how much I need to get out of my solar panels without going into the red.

What you are looking for is your Ah usage per day (Ah/day).

Mark

[colemj]

Originally Posted by barnakiel

I am always puzzled when posters try to convert inches to lumens.

The real question is how many RPM's are in an inch/lumen?

Mark

[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".

[hellosailor]

But Stu, that leaves me so confused. I've never found a proper ISO reference for converting the speed of electrical flow, from foot-furlongs per light-second into ay other more conventional measure of speed, nor for accommodating the incremental speed changes in any conductor type when subjected to localized gravitational relativistic field effects. And of course, that difference in acceleration and speed can result in the electrical flow in different conductors becoming out of phase, as well as unbalanced in speeds.


Then too, there are so many countries that aren't even in the UN, that haven't signed the various international standards and use their own terminology. Which ignores the few that still ban "electricity" as being witchcraft, not to say they've got it wrong and we've got it right.


I'm so confused.

[StuM]

Originally Posted by Privilege

Thanks for the thread Stu. I'm not challenging anyone here, I'm just checking out my understanding.

I've recently built a freezer and wanted to work out its energy usage. There's little use in knowing how many amps it uses whilst running as it cycles frequently. Also, the cycling periods will depend on ambient temperature, how many times I open it, etc... This will also vary from hour to hour so again, there is little use in knowing the amp/hr useage. What I'm really interested in is the average useage or amp/day. This is the same for my water pump...it will depend on how many showers I take, how often I flush the fresh-water head etc... So, if I can work out my amp useage per day (amp/day) I can work out how much I need to get out of my solar panels without going into the red.

Is that about right?

As colemj correctly says. You need Ah/day or (aka Ampere hours per day)

Re-read the initial post. There is no place for expressions like "Amp usage" and "Amp/hr usage". An Amp is an instantaneous measure of rate of current flow, you don't "use up" amps. You use up Amp hours (Ah)

You are incorrect is saying that there is little use in knowing how many Amps your freezer, water pump etc uses when running. That is exactly what you need when drawing up an energy budget.

You need to combine that figure with an estimate of the average and/or maximum times that your various electricity consumers are drawing power over an hour, multiply the amperage of each unit by the number of hours your estimate it will actually be running to get Ah/day for each unit and then add then together to get your total estimated Amp hours per day.