Ammeter Wiring

[Sailvayu]

First my apologies for not getting back sooner but unfortunately making a living take priority over this fun.
I also have done a really crappy job of trying to explain my position. So with that in mind I will get back to this in a day or so when I finish some reports and do a much better job of explaining my logic. I hope I can help at least some of you understand why I think it is wrong to use Ah as a unit of power used. Stay tuned.

Oh and I will review the information provided i need time to look that over as well.

 

[Ross]

Does anyone keep account of power consumption to two decimal places?

 

[walt]

Im repeating something I heard on the internet (which makes it questionable) but I understand we use amp hours because the amp hours into the battery is more closely matched to the amp hours that you get out of a battery for equivalent state of charge.

If you were to look at watts (which is more technically correct), you charge a battery with some amp hours but its typically at a voltage in the 13 to 14 volt range. When you discharge a battery the same amount of amp hours, its at a voltage in the mid to low 12 volt range. So power* time into the battery is more than power* time taken out. But amps*time in is closer matched to amps*time out..

why not... its only misleading if anything other than 12 volt batteries are considered (which does happen with solar panels and electric motors on boats)

 

[Stu Jackson]

Wayne

I hope I can help at least some of you understand why I think it is wrong to use Ah as a unit of power used. Stay tuned.

Oh, so you have a "day job", too? :dance:

It will be interesting to learn of your thoughts on this matter. Please recognize a few things, though. No one is saying ah is a unit of power. We all recognize that the power is the amps, or as some have mentioned, it's actually the watts. All anyone has been saying is that this is the accepted measurement tool when it comes to battery monitors (which as I've already noted is really watts converted to amps inside the monitor algorithms) and battery sizing, and it's a measurement of power over time. Sometimes it's counterproductive to tilt at windmills, although I'm sure we're going to be all ears and can learn something new.

Thanks for getting back to us.

Mega watt hours anyone?

 

[Ross]

Re: Wayne

The unit Amp Hours is applied to all batteries and simply indicates a capacity for energy. When I was a kid we had a room full of glass cased single cells, lead acid type, connected in series to provide a 32 volt DC power supply for the house. That battery weighed about a ton. It had an amp hour capacity exactly equal to the amp hour capacity of a single cell. It could have been connected in a series/parallel configuration to make a six volt battery with an amp hour capacity of 5x the single cell rating. We also used to get drycell batteries for radios that were boxes of cells connected in series to provide 90 volts for the high voltage side of the radio. Some cells were 2 inches in diameter and 6 inches long. Those were often packaged four in a case with two screw terminals and they supplied 6 volts.

 

[Ron20324]

Does anyone keep account of power consumption to two decimal places?

Sure we do. It's as easy as Pi .

 

[walt]

An "amp" is charge per time. So when you multiply (charge per time) * (time), you get charge ie, number of electrons.

Specificially, one amp hour is 2.24 E 22 Electrons. I think we should stop using the term "amp hours" and only talk in terms of number of electrons.

Then there would be no confusion at all. For example, I could say I left the LED light on for two hours and used 1.344 E 22 electrons.

 

[Sailvayu]

Ok putting aside the electron group, you guys are a bit too far out there any way lol.

Let dip my toe back in and look at the offending statement then we can dive in a bit deeper.

"There is very little need to every monitor a starting battery, starting a small diesel uses less than .5Ah,"

I read this as stating it only requires .5 amps for a period of one hour to start your engine. So it would appear this is being used as a statement of Ah as "energy used" or a unit of energy used. This we all seem to be in agreement is wrong. So this means this number used this way has little meaning. If it does has meaning please explain how it would be practical. (And I am not trying to be difficult please do not miss understand I am just trying to clarify and understand.)

So let me restate this and you tell me if it is more correct. lets restate this to say it will require a .5 amp charge for 1 hour to return the battery to its fully charged state.

Am I reading this right and can we agree on this? if so I will move forward with what I was trying to explain.

 

[Stu Jackson]

Amps & amp hours

"There is very little need to every monitor a starting battery, starting a small diesel uses less than .5Ah,"

1. I read this as stating it only requires .5 amps for a period of one hour to start your engine. So it would appear this is being used as a statement of Ah as "energy used" or a unit of energy used. This we all seem to be in agreement is wrong.

2. So this means this number used this way has little meaning. If it does has meaning please explain how it would be practical. (And I am not trying to be difficult please do not miss understand I am just trying to clarify and understand.)

3. So let me restate this and you tell me if it is more correct. lets restate this to say it will require a .5 amp charge for 1 hour to return the battery to its fully charged state.

1. I believe you are beginning to understand. It is not necessarily only 0.5 amps for one hour, it is the "equivalent" value per earlier post discussions. Could be 1 amp for 30 minutes.

2. Its practical use is to compare it to the available amount of amp hours in a battery bank.

3. Discounting battery acceptance, yes, with the caveat that it could well be 1.0 amp for 1/2 hour, 2 amps for fifteen "minutes and so on..." as I excerpted from the Link 2000 manual I posted before. Since most battery chargers are a minimum of 20 amps (that's D.C.) and most alternators are at least between 35 and 55 amps, the point is that it takes very little time to REPLACE the amount of amps used over that short period of time (amp hours) used from the batteries to start a small diesel engine. Yes, there is inherently a "disconnect" in phrasing there, right? Amps & amp hours. I'm an engineer and deal with the need for specificity on a regular basis. However, I do understand the difference between the amps used and its measurement over a period of time.

Think of a big jug of water, which is used in voltage and amperage discussions in many electrical books. If the tank is 50 gallons and you remove 10 gallons, the flow rate of the replacement medium (say a hose) expressed in gallons per minute will tell you how long it will take to top off the water tank. 1 gpm will take ten minutes, ten gpm will only take a minute.

Welcome back.

 

[KingAirDriver]

To give you an idea about how long it takes to recharge starting batteries, I'll cite an example using the airplane I fly.

It takes about 30 seconds of starter/generator use to start each Pratt & Whitney turboprop in my King Air 200. On initial engagement, it draws somewhere between 900 and 1200 Amps! Very quickly it drops off to a steady 200-400 Amp draw. I then start the other engine, using the same amount of battery capacity.

When I engage the generator portion of the unit, it is rated at 300 Amps of output at 100% of engine speed. I engage at 65% when battery starting. It will show about a 70% load for about 10 seconds then quickly drop to about 25-40% load depending on air temperature. It takes under 5 minutes, sometimes as low as 2 minutes, to drop to about 10%, which is what the aircraft draws to run it's normal systems.

The battery is a sealed lead acid type, 24 volts, with a rated capacity of only 44 Amp/hours at the 1 hour rate. They are 85 pounds. Oh yeah, they cost $1,895 bucks too.

Long story short, I recharge the ship's battery, after a massive draw, in under 5 minutes.

We are generally more concerned with overheating the battery. That heat is normally generated by the draw, not the charge.

The copper cables that run from the battery to the starter/generators, are "0". Due to the short duration use, they can get away with that size cable.

Moral of the story, starters draw high amps for short duration. The rate is high, the overall volume is low.

Start your engine or burn your cabin lights for 15 minutes. Probably about the same amount of capacity amps (energy) being used.

I think what we have to clarify is the vocabulary.

Amp = rate of current draw
Ah or Amp hour = rate of current draw over a specified period of time, in this case, 1 hour. This is a measure of overall battery capacity.
CCA or Cold Crank Amps = This is the MAX output amperage the battery is capable of producing when COLD.

High Ah rating gives a battery the ability to be used over long periods of time, those types of batteries will be ruined if used in high current draw situations. Golf cart and marine deep cycle are examples.

High CCA ratings are how FAST a battery will give up its amps and volts. These batteries are constructed differently than capacity batteries. And these batteries will get ruined if they are used for missions that require capacity or long duration draws. Example = starting or cranking batteries.

You generally cannot have a battery that will do both missions in lead acid style. Some Advanced Glass Mat, or AGM, batteries can to both to some degree.

My airplane battery, has a CCA of 600 at 0 degrees F. But can do almost 2000 amps in warm weather, but a capacity of only 44 amps over 1 hour.

All that BS having been said, perhaps saying a boat only uses .5 Ah to start is poorly worded. It may only use .5 Amp per start, but at a rate of 265 amps over .75 seconds. If you had a battery that was only rated at .5 Ah, it would be depleted after 1 start.

Just my 2 cents...

 

[Sailvayu]

Still working on reports but thought I would share this from the technical editor of Good Old Boat magazine.

Amps per hour, Amps/hr. and similar -- Although actually published occasionally, these are meaningless terms which only confuse the well-informed reader and demonstrate the writer's lack of comprehension of basic electricity. If amps per hour does not grate on your sensibilities like fingernails on a blackboard, you probably should not write about electricity. If you do the algebra on this, you come out with the reciprocal of time (1/time) or charge divided by the square of time (T squared). Nonsense.

Electricity and water do not mix -- Many writers eventually resort to some kind of water analogy to try to explain how electricity works. I have yet to see what I thought was a really good water analogy. If you want to explain electricity, talk about electricity. Hydraulics is another field entirely. Avoid this trap; it is already full.

Hopefully I will have more this weekend as time allows

 

[Maine Sail]

Still working on reports but thought I would share this from the technical editor of Good Old Boat magazine.

Amps per hour, Amps/hr. and similar -- Although actually published occasionally, these are meaningless terms which only confuse the well-informed reader and demonstrate the writer's lack of comprehension of basic electricity. If amps per hour does not grate on your sensibilities like fingernails on a blackboard, you probably should not write about electricity. If you do the algebra on this, you come out with the reciprocal of time (1/time) or charge divided by the square of time (T squared). Nonsense.

Electricity and water do not mix -- Many writers eventually resort to some kind of water analogy to try to explain how electricity works. I have yet to see what I thought was a really good water analogy. If you want to explain electricity, talk about electricity. Hydraulics is another field entirely. Avoid this trap; it is already full.

Hopefully I will have more this weekend as time allows

Amps per hour or Amps/hr are NOT the same an an ampere-hour or Ah...... I have discussed this with Jerry and fully agree with him. Many writers write Ah incorrectly, amps per hour is NOT the same as Ah.......

1 amp for 1 hour = 1 Ah

 

[jviss]

Ah = ∫A dt

 

[Bill Roosa]

If this is all you are having trouble with then stick to sailing and rent an electrical engineer!!!
Amp- hours is amps times hours or A*h. General mat convention is don't show the multiplication sign so Ah
A/h is a horse of a different color altogether and has no application that I know of as it is just the number of electrons "used". You would (again) have to specify a voltage (which we assume) to determine anything from A/h
a starter that draws 100 amps for 1.4 seconds consumes:
Ah=100 amps * 1.4 seconds * (1 hour/3600 seconds) = not very much

 

[Sailvayu]

MS
Ok now I am at a complete loss
In an early post you said you are using Nigel Calders math to arrive at Ah correct?
He does not give a formula but uses the example of a 400 amp motor running for 15 seconds.
400/(4*60)=1.66
So we can extrapolate this to a formula of A/H=Ah, A being Amps and H being hours.
But in your last post you said Amps/Hours is NOT Ah
" Amps/hr are NOT the same an an ampere-hour or Ah"
Don't get me wrong here I am not trying to be a ass I am just trying to understand what you mean so we can all be on the some page for further discussion.

 

[weinie]

Ah = ∫A dt

close:
Ah = ∫A(t) dt

 

[Sailvayu]

To all those reading please understand I am not trying to be difficult or stir crap up. (Well maybe just a little lol) I feel this is a badly miss understood subject and by playing devils advocate and challenging some assumptions I am hoping it will make all of us think a bit more about how we express these things. This is an interesting subject and not always so clear cut as we can see. It helps to force all of us to think about this in larger terms and I include myself in that. Discussions such as this help keep us all sharp. I honestly feel using amp hours for expressing power used is not very accurate and can often be misleading. It is a fair method for determining how much stored energy you may have available but it is not so good at understanding power used. That said I know there are times when we need to fall back on it and methods that might not always be good but are sometimes the best we have. If we are to really understand a subject it is useful to fully debate it.

 

[weinie]

close:
Ah = ∫A(t) dt

Public service message: Boat responsibly: Don't drink and derive.

 

[Warren Milberg]

Since this thread long ago stopped being about anything the original poster inquired about, I feel free to add here my concerns about quoting Nigel Calder. He may be an expert on some things, but he left a lot to be desired when he wrote about how we all should commission our new boats (I've never had one). He then reversed the polarity on his main panel on his new Crealock, hit start, and fried most of his newly installed electronics. Unlike most of us, he was able to get them all replaced free of charge by the manufacturers. As the saying goes, don't try this at home.

Calder is also the "expert" who wrote in Sail Magazine that you need to make sure you installed your raw water impeller in the "right" direction. He was called on that one and reluctantly admitted it made no difference which way the blades faced as they sort themselves out on the first revolution of the engine.

Now, as to wiring an ammeter....

 

[weinie]

To all those reading please understand I am not trying to be difficult or stir crap up. (Well maybe just a little lol) I feel this is a badly miss understood subject and by playing devils advocate and challenging some assumptions I am hoping it will make all of us think a bit more about how we express these things. This is an interesting subject and not always so clear cut as we can see. It helps to force all of us to think about this in larger terms and I include myself in that. Discussions such as this help keep us all sharp. I honestly feel using amp hours for expressing power used is not very accurate and can often be misleading. It is a fair method for determining how much stored energy you may have available but it is not so good at understanding power used. That said I know there are times when we need to fall back on it and methods that might not always be good but are sometimes the best we have. If we are to really understand a subject it is useful to fully debate it.

Sailvayu,
With all due respect, how we quantify things and the units we apply to them are things covered in the first chapter of any 101 science class. There is NO debate here and nothing to discuss!

AmpHours is simply the most convenient unit for dealing with storing electricity in batteries. We have tools to measure current (Amps). We can easy measure electric potential (Volts). We can easily measure Time (hours).
If you consider it, energy is a pretty tough topic to grasp! I mean, What is Energy?
Sometimes we are talking about mechanical energy and we can use units like joules.
Sometimes we are talking food energy so we can use units like calories.
Physics uses units for energy called the Electron Volt.
Bombs are measured in lbs. of TNT like kilotons.
Airconditioners are measured in Therms.

etc etc etc

Amp Hours is practical because if we know the value a battery in Amp Hours and we know the amount of time we are using those Amp Hours, we can simply divide by the amount of time to calculate the Amps (or current) we are using. We can then use the amount of current to determine voltage of a system if we also know the resistance or vice versa.

So if you have two different batteries, each one with a different AH value, you, know that if you draw the same current from each battery, one will last longer than the other. This way, we have a way to compare battery A to battery B.