Scott Brown

[Scott Brown]

One of the quiz question’s answer is that: it is true we probably wont ever measure DC current… but why?

It’s a practical thing. To measure DC current, you need to put your meter in series with the circuit. As a practical matter, you will never do this as an appliance tech. It’s not that the DC current doesn’t exist. It’s just that you will never do this as an appliance tech. I’m imparting to you practical experience as an appliance tech.

But if there is an open in the DC circuit between negative and positive, wouldn’t that cause the current to cease and therefore you would need to determine that there is indeed an open by testing for the DC current?

You could do this but it’s a PITA. Much easier to check for opens with a continuity test.

Make sense?

[Scott Brown]

The reference in your topic title– which asks about wire depictions in schematics– doesn’t seem to relate to your question. But I think I get the gist of what you’re asking.

It’s probably not helpful for me to speculate on how a particular lab kit may have functioned based on vague recollections. But if you can get me details on the kit you worked with in school, I may be able to provide more explanation.

Of more immediate importance is addressing some of the fundamental, conceptual points you raised:

…but instead increasing the voltage drop on the second bulb by dropping a full 12vdc (assuming its a 12v battery) across the only remaining load (the other bulb) at which point the bulb should then glow brighter and the ammeter would still read 12vdc?

First, you would not read voltage on an ammeter. You measure the voltage across a load (light bulb, in this case) with your voltmeter. Your ammeter is used to measure circuit current in amps. More on electrical measurements in a later unit.

I think the gist of what you’re getting at is differences in voltage drops and current flows in series and parallel circuits. You’ll get into fun-filled details on this these important topics in later units. Meanwhile, here are a couple of new Doodlecasts added to Unit 4 that may help clear this up:

https://www.youtube.com/embed/HG3d46zkDvY

 

https://www.youtube.com/embed/mRV6OM7DgUA

 

[Scott Brown]

Hi Gene,

This is a good question and testing for a valid power supply would always be your first move in a DOA appliance so your thinking was exactly right!

After reviewing quiz question 4, I can see why this would have confused you because the question does not specifically state that the washer is plugged in to a valid power supply. I have edited that question to make that clear by adding this phrase to Question 4:

After verifying that the washer is plugged in to a good power supply…

Thanks for pointing this out!

[Scott Brown]

So my misconception has been identified and eliminated (right?)

Indentified: Yes. Eliminated: Maybe.

Start with this fact: Shunts are NOT parallel circuits!

Equivalent resistance in parallel circuits is exactly and completely defined by this equation:

This is one of the Laws of Electric Circuits. It is settled science, basic physics, not open for debate or interpretation. It’s like a water is wet or grass is green kind of thing.

In a shunt circuit, one of those branches– the shunt– has no load in it; its resistance is 0 ohms by definition.

Let’s pretend we have a shunt circuit configuration. The shunt’s resistance is 0 ohms (by the definition of a shunt) and the other branch with the load has a resistance of, say, 100 ohms (just as an example).

Now plug the numbers 0 and 100 into the governing equation for equivalent resistance in parallel circuits. What happens?

You should be seeing an error in your calculator because, as you know, only Chuck Norris can divide by 0. 🙂

What does this mean? It means that the governing and defining equation for equivalent resistance in parallel circuits DOES NOT APPLY to shunt circuits! In a shunt circuit configuration, 100% of the current flows through the shunt and 0 current flows through the load. But this not for the reason given by the common tech myth: “Electricity follows the path of least resistance.” It’s because in a shunt circuit, to the electrons there is only ONE path to be followed!

Thus the math shows us that shunts are their own unique type of circuit configuration.

Another tip: since we cannot see electricity, we learn how it works in exactly two ways 1) math and 2) measurements. BOTH are essential for us to understand electricity; neither is optional.

The math tells us how electricity works and the measurements make it real to us and keeps us grounded in the physical reality of what we’re dealing with.

You cannot avoid math and hope to understand electricity. Just can’t be done. Anyone who says otherwise is either lying or deluding themselves.

So the take-away point is that you begin your analysis of electric circuits with an understanding of the mathematical equations that define and explain how it works. The measurements make it real to us and your application of that math is done with an understanding of the physical properties of electricity and circuits.

An example of the latter is your markup of the dryer circuit in another forum topic where you were trying to understand the voltage drop across the three loads in series with each other. You were applying the Ohm’ Law equations but your application of them was not connected to physical reality because you were showing three different current flows through each of the three loads. This is physically impossible because the current flow in a series circuit is the same at every point in the circuit.

[Scott Brown]

Great answer, Mrs. Samurai! The only other thing I would add for Chris is to encourage him (and all other students!) to come to Office Hours this coming Monday where we’ll specifically be going over power, voltage, resistance, and current in series and parallel circuits. It’s a great opportunity for students to ask questions live, real-time, and nail down these important concepts as well as ask any other questions pertaining to their coursework.

[Scott Brown]

1440 Watts = 6amps(squared) x 40ohms

Your statement “From this equation you can see that increased resistance can increase the heat generated” if I am working this equation right, you are wrong. Increased resistance LOWERS Watts which is your heat.

In the above equation, double the resistance– make it 80 ohms– while leaving current the same and recalculate the wattage. What do you get?

[Scott Brown]

Hi Chris,

I think that’s a wise decision that will serve you well in the long run. And remember about Office Hours every Monday evening! We cover lots of interesting topics and it’s a great enrichment to the course.

[Scott Brown]

Yes, the Annual Service Training Institute put on by the United Servicers Association. We go every year. This year it’s in Miami. You can read details here: http://mastr.tech/1ZKMlec

Maybe we’ll see you next year!

[Scott Brown]

Hi Chris,

Couple of points here:

1. You’re getting ahead of yourself in the courses by working the ASAT course without first completing the Basic Electricity module in Fundamentals. The ASAT course was developed with the assumption that students have the necessary electrical background. Otherwise, you could get lost, especially in later units.

2. You are making some fundamental conceptual errors in your calculations that are specifically addressed in the Basic Electricity module. One big one is that the current in a series circuit is the same through the circuit. You show three different currents through the three different loads that are in series with each other– a physical impossibility!

I strongly recommend to hold off on the ASAT course and resume work on the Basic Electricity module in Fundamentals. After you’ve done that, review your work with your newfound, empowering wisdom and let’s take this back up.

[Scott Brown]

Hi John,

That’s great news it’s working for you now! And thanks formletting me know. Chrome is very aggressive about caching– it’s a big reason they can claim to be so fast. Safari is my main browser, too, and I usually don’t have problems with it.

We heard from other people that the video on the sample course wasn’t playing. We were also having problems with some of the course videos not playing. This was back when we used Vimeo for hosting. We switched everything over to YouTube and those problems disappeared. That’s why I wanted to make sure this was fixed for you.

Looking forward to meeting you, too! Will you be in Miami for the upcoming ASTI?

[Scott Brown]

Hi John,

All videos in the Academy streams from Youtube. When a Youtube video gives the message, “this video is restricted. Try signing in with a google apps account” when attempting to play it, it means that the video owner has categorized the video as “private” which means that only specific Google users can view the video. This would not be a desirable setting for videos used in the Academy because no one would be able to play them!

So I checked the settings on that video to make sure it wasn’t accidentally set to “private” and it is not. I then verified that the video plays by signing out of Google myself (including Youtube) then logging into the Academy and played that video. This means the permissions on the video are set correctly since Youtube didn’t know who I was and played it for me anyway.

I’m thinking that somehow Google’s wires got crossed. So let’s try a couple of things:

1. Signout of all your Google accounts, including Youtube.

2. Close Chrome completely and re-start it.

3. Try playing the video again.

If still no joy after this, then the next thing to try is a different browser altogether. Firefox is a good choice (in fact, Firefox is my standby browser).

Please report back and let us know either way. If the video still isn’t playing for you, would it be possible for you to take a screen shot of the just the video player showing the exact error message you’re getting?

If you do get the video to play, please tell us what finally worked for you.

Thanks!

[Scott Brown]

Awesome, glad you got it!

Always feel free to post any questions you have about your coursework in these forums. Interactive help is part and parcel of your course!

Also, keep in mind the weekly Office Hours web meetings where you can stop by and ask questions.

Happy New Year!

[Scott Brown]

Hi Chris,

First off, DO NOT worry about taking up my time! I LOVE doing this and especially love it when I see complicated circuit concepts clicking with students.

My reason for asking for you for a markup was so I could see exactly what you where thinking and where you were going wrong. And your markup showed it.

GREAT job on your markups on the Delicate cycle, BTW! I can see clearly what you’re thinking and you almost got it right. There was one little mistake that made all the difference. But this was such a good question that you merited your own private video reply! Here it is, let me know if you’re still confused:

https://www.youtube.com/embed/b6QWImjLTTQ

 

[Scott Brown]

Your pictures showed up fine but those are MY markups. I’m asking you to post NEW images with YOUR OWN NEW markups. Please re-read my reply carefully.

[Scott Brown]

Hi Chris,

I think what’s happening is you’re trying to trace out the circuit in your head and confusing yourself. Although this is a simple circuit, it takes experience before you can do accurate circuit markups in your head.

Keep in mind that the timer chart shows which cam is active during which cycle but also WHICH CIRCUIT that cam is activating.

Since this is a lab-oriented course, this is a great opportunity for a lab exercise!

Let’s do this:

1. Get the original image of the tech sheet included with the lesson. LINK (JPG file), LINK (PDF file)

2. Starting with a blank copy of the tech sheet, draw out two different versions of the load analysis on the motor: one for Delicate cycle and one for Regular cycle. So, to be clear, you will make TWO different markups: one for Delicates and another for Regular. Do not put both markups on a single drawing.

3. Post nice, big copies of your two markups here so I can review them. I’ll review them and this will let me see exactly how you are misunderstanding the timer chart and schematic.

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