How Can You Convert AC Amperage to Voltage?

[Averagesupernova]

ALL analogies have flaws. ALL analogies make more sense if this is kept in mind. It's somewhat up to who is doing the explaining using the analogies to determine if it fits well enough to use.

 

[russ_watters]

There are problems with using water analogies.

If you say current is like water flowing in a hose, you come to grief when you say the current has to return to the other side of the battery. Water in a hose ends up on the garden so why would it go back to the reservoir?

You probably could pump water around in a circle to give a true analogy of what an electric circuit does, but it isn't a situation most people are familiar with.

Most people don't deal with them much, but I would think they are at least familiar with the concept: You can talk about a closed system such as a chilled water plant. You have the pump working as a battery, then multiple loads in the system.

If you say that voltage is like the "head" of water, or the pressure due to the height of the water source above ground, then how do you then explain that the only voltage that matters is the voltage between the terminals of the voltage source?

I'm not quite following. Though head is used for easy conversion to height, all pumps have a head pressure rise whether there is a rise in height or not. The delta in head across the pump is very analagous to the voltage rise across a battery.

No, of course it isn't perfect but if care is taken in the construction of the analogy it can be quite useful.

 

[vk6kro]

A pump is only a good analogy for voltage in a closed loop. If the pump takes water out of a lake and squirts it in the air, where is the analogy then?

Analogies are like teaching a kid baby talk. You teach "choo-choo" then you teach "train". The kid learns two things instead of one.

So, we say current is like water flowing, sort of.
Then we say it is a flow of electrons.
Then we say it is conventional current so it flows the other way.
Then we say it isn't even electrons flowing, it is a wave passing through electrons. Individual electrons hardly go anywhere.
Then it is a wave of electrons flowing the other way. Got to have conventional current.

Why not just start off with the real story and cut out the stuff that isn't true?

 

[stewartcs]

A pump is only a good analogy for voltage in a closed loop. If the pump takes water out of a lake and squirts it in the air, where is the analogy then?

The water falls from the air and back into the lake and the pump repeats the cycle.

Why not just start off with the real story and cut out the stuff that isn't true?

Because it is typically easier for most people to build upon concepts they already understand. I'm sure you weren't taught differential equations before basic addition and subtraction right? Imagine how confused you would be if you had not learned those basic concepts first and built upon them to eventually understand differential equations.

CS

 

[sophiecentaur]

The water falls from the air and back into the lake and the pump repeats the cycle.



Because it is typically easier for most people to build upon concepts they already understand. I'm sure you weren't taught differential equations before basic addition and subtraction right? Imagine how confused you would be if you had not learned those basic concepts first and built upon them to eventually understand differential equations.

CS

The only problem with teaching by analogy is that you have to be reeeeealy careful to ensure your pupil realizes that it is an analogy and that extending the analogy beyond what you told them may be very dodgy. It should always be:

"Analogy - Caveat - Caveat - Conclusion / Prediction"

and it seldom is, in fact, taught that way.
The fact that there are so many confused questions from non-cogniscenti about electricity and pressure analogies simply proves my point.

Geez, there are enough problems and misconceptions with actual water flow and pressure to show that the whole thing is pretty fraught. I think that, of the dozen or so Plumbers I have dealt with, not one of them had a 'safe' understanding of pressure so heaven help the Electricians with the same model in their heads.

 

[stewartcs]

Geez, there are enough problems and misconceptions with actual water flow and pressure to show that the whole thing is pretty fraught. I think that, of the dozen or so Plumbers I have dealt with, not one of them had a 'safe' understanding of pressure so heaven help the Electricians with the same model in their heads.

Plumbers (in the US at least) generally don't study fluid mechanics (maybe some basic Plumbers fluid course if any). So I'm not surprised that they don't understand those concepts all that well.

Nevertheless I agree that analogies should be treated as that...a tool for helping to build an understanding of some other concept...hence the name.

CS

 

[sophiecentaur]

I wasn't talking "fluid mechanics". I was talking simple static head concepts and the 'obvious' stuff that occurs in everyday Central Heating systems. It's done (apparently) completely 'by numbers' and there never seems to be any System Analysis when fault finding. That sounds very elitist, I know, but I have had to bite my tongue on a number of occasions and let the guy do the 'wrong thing' first before he got things to work - and all because of some simple misconception about pressure and flow.
Hence my reservations about giving someone a water analogy and expecting them to treat it with due care when applied to Electricity. Believe me, I have seen / had to rectify the results!

 

[stewartcs]

I wasn't talking "fluid mechanics". I was talking simple static head concepts and the 'obvious' stuff that occurs in everyday Central Heating systems. It's done (apparently) completely 'by numbers' and there never seems to be any System Analysis when fault finding. That sounds very elitist, I know, but I have had to bite my tongue on a number of occasions and let the guy do the 'wrong thing' first before he got things to work - and all because of some simple misconception about pressure and flow.
Hence my reservations about giving someone a water analogy and expecting them to treat it with due care when applied to Electricity. Believe me, I have seen / had to rectify the results!

Static head, air flow through ducts, etc. are fluid mechanics concepts. HVAC technicians don't design those things, Mechanical Engineers do. The technician only needs to know enough to troubleshoot and repair them, not design them or do any kind of system analysis. Of course there are some technicians through self-study or other means who can do it but they are the exception to the rule.

I wouldn't give a person the water flow analogy if they were trying designing an electrical system, I'd expect them to be properly trained as an Electrical Engineer. In fact, that seems to be what happens most of the time (especially on the internet forums)...people come here looking to do some type of engineering but aren't trained to do it and ask opinions from anonymous people about how to do it. Naturally, a lot of analogies are used because it doesn't take a lot of effort and the person ends up applying them the wrong way.

The moral of the story is: make sure you know what you're doing by being properly trained.

CS

 

[russ_watters]

A pump is only a good analogy for voltage in a closed loop. If the pump takes water out of a lake and squirts it in the air, where is the analogy then?

Yes, if you use an analogy in a situation where it doesn't work, it doesn't work. So what? That's why you only use an analogy in a situation where it works. It is a strawman to try to criticize an analogy for not working in a way that it isn't used anyway.

Analogies are like teaching a kid baby talk. You teach "choo-choo" then you teach "train". The kid learns two things instead of one.

No, the purpose of an analogy is to use one thing that has already been learned to learn another that hasn't. It is a way to avoid having to start from scratch.

Why not just start off with the real story and cut out the stuff that isn't true?

Because people won't know what the heck you're talking about, it'll take longer to learn and you'll have to work backwards learning a lot of the more basic stuff anyway.

Part of my problem with your method is that when you hit someone with a piece of information far outside their understanding, they don't learn it, they memorize it and sometimes fail to really understand it. By linking similar concepts, you have have less to learn and a wider base on which to put it - two connected facts are easier to learn than two disconnected facts.

 

[russ_watters]

Static head, air flow through ducts, etc. are fluid mechanics concepts. HVAC technicians don't design those things, Mechanical Engineers do. The technician only needs to know enough to troubleshoot and repair them, not design them or do any kind of system analysis. Of course there are some technicians through self-study or other means who can do it but they are the exception to the rule.

Agreed. A technician who'se job it is to solder pipe and start-up a piece of equipment doesn't really need to know anything about thermodynamics or fluid dynamics, so it isn't surprising that many don't.

 

[sophiecentaur]

Agreed. A technician who'se job it is to solder pipe and start-up a piece of equipment doesn't really need to know anything about thermodynamics or fluid dynamics, so it isn't surprising that many don't.

It matters if he's come to your house to troubleshoot a problem with your plumbing system and you are paying him by the hour. That's the level of technician that is sent by the Gas Company or the Emergency Plumbing service and I am just making the point that even the simple concepts of pressure and water getting around the house successfully are actually much more difficult than you / we, as probably well informed and fairly Science - literate will appreciate. A simple air lock due to a horizontal run of pipe is much harder to comprehend than you might think.
So what you may think of as a perfectly straightforward model to use as an electrical analogy may be, in itself, quite problematical BUT, because it appears familiar, it can easily be taken up wrongly.
At least, when you give 'em Ohm's Law, they will realize just what difficulties they're up against.

 

[russ_watters]

It matters if he's come to your house to troubleshoot a problem with your plumbing system and you are paying him by the hour.

No, it really doesn't. He measures the refrigerant pressure and compares the reading to a table. He looks at fans and makes sure they are spinning (and in the right direction!). He looks at error codes on the system board, etc. There is no need for him to know thermodynamics or fluid dynamics.

If on a commercial system, he suspects something out of normal bounds (and he's got a table with the design drawings that tells him what all of the operating parameters designed by an engineer should be), such as too much air pressure at the fan outlet and not enough pressur and can't figure out why, he calls-in an engineer -me - to troubleshoot further.

You'll almost never see an engineer working on a residential system, but maybe you should: there is a reason why most residential systems contain either design and/or installation/operational flaws. But it currently isn't considered important engough in most places to have an engineer on the project. Conversely, you're required by law to have an engineer design a commercial system because the fluid and thermodynamic concepts involved are too important to leave to a technician who'se expertise is based mostly on rules of thumb.

That's the level of technician that is sent by the Gas Company or the Emergency Plumbing service and I am just making the point that even the simple concepts of pressure and water getting around the house successfully are actually much more difficult than you / we, as probably well informed and fairly Science - literate will appreciate.

You're arguing against your own previous point here. You were right when you said none of the plumbers or electricians you've dealt with have a good understanding of these concepts. You're wrong to think they should. Heck, you're now basically arguing that every technician you've ever run across is underqualified for their job!