Forum Replies Created
-
AuthorPosts
-
Hi Steven,
Did you see the Video Player Controls page? We link to it under the first video in the course (Mod 2, unit 2 – “IMPORTANT VIDEO TIP”)
https://my.mastersamuraitech.com/video-player-controls/
Every original MST video in the course has a searchable transcript.
The intention is that students treat videos as if they are in a classroom. Meaning, paying attention and taking notes. The nice thing is that you are in control of the video. You can adjust the speed up and down, you can pause to take notes, back up to re-listen to a portion, etc.
Your notebook should have a page (or more) for each unit in the course where you list the video(s) and topics covered in it. That becomes a reference for you when you want to go back to find a particular discussion.
Most of our students want more videos, not fewer, which is unfortunate for the occasional student who would prefer to have more text.
There are no reading assignments in the Kleinert book until Module 4. You’ll see them listed in some of the units.
I did! Just replied.
Hi Danny,
Unfortunately it is too big of a file to email (56 MB) so some kind of drive has to be used.Hi Blake,
The answer is “power and control”.
There’s a lot of info in Unit 7! Including this section:
In general, the two types of voltages you will measure (aside from AC and DC) are:
– Power voltages: these are used to drive the loads that do the appliance’s work– motors, heaters, lights, etc. These are usually AC line voltages.
– Control voltages: these are uses to control power voltages. Examples are digital data logic lines. These are usually DC voltages.
Hi Lucas,
Is this for Unit 4, the image that goes along with the audio clip? If so, it showed up for me, which suggests you might need to refresh your browser, maybe clear your cache, etc.Here’s the image- does it work for you?
No worries!
Questions are always encouraged and welcome! When there are a number of them, it may just take us a bit to get our reply together 🙂
Hi Darci,
Good question! The Kleinert book is used as a supplement to our course, not as a primary text. It has some good diagrams, images, and info that are helpful. But it is not reliable as a stand-alone instructional text (even in 2013). The vast majority of what you will learn in the course is the exclusive material delivered in our course units.
Appliance technology does not change anywhere near as rapidly as computer or similar tech. The few things that are newer (say, linear compressors in fridges, R600 refrigerant, a few of the control configurations, induction cooking, internet connectivity) are covered in our courses, which we update as needed. But much of what an appliance tech needs to know is the same as what a tech would have learned 20 years ago.
I hope that helps!
Glad to be of help!
The only thing I get different from your calculation is that I get an Req for loads A and B of 68.6, which I round up to 69 to use in the calculations (Rt = 319 ohms). But that does not make a significant difference in the resulting numbers, so nothing to have any concern about.
The reason my Req is slightly different probably has to do with how many decimal points are preserved during the calculation.
Hi Stephen,
If there were another resistor in the circuit, we’ll call it R2, in series with the parallel set and R1, it really doesn’t make it that much more complicated. The total resistance in the circuit would be R1 + Req + R2, and then current in the series portion would be It = E/Rt. Then the voltage drops for the loads would be E = I x R, etc., just like I show in the video.
Most of the time we’re going to be dealing with AC loads/circuits in appliances, but there are some DC applications.
Whether the circuit is AC or DC doesn’t change the basics of what I demonstrate in the video. Electrons “feel” the total resistance in circuits, and that (along with voltage) affects the rate of electron flow (current). And the rate of flow through each resistance will generate a voltage drop and power (work).
And, FYI, it’s not likely that you’ll need to do more complicated series-parallel calculations like I’m showing as part of doing appliance repair, but being able to follow these calculations and play around with different scenarios can give you a feel for the behavior of electricity in different configurations, which is important for being able to read schematic diagrams.
If you want to try adding a resistor as you described and assign it a resistance, then do some calculations, show me what you get and I’ll check your work!
Hi Bryan,
On some old-school or low-end refrigerators you are often manually controlling the damper door. If you set the freezer to the absolute coldest setting, you can actually prevent the damper from letting in enough cold air to keep the fresh food compartment at the appropriate temperatures.Does that help?
This is from the lesson:
This ignitor is wired in series with the gas valve, meaning that current is flowing through both whenever the circuit is powered.
So – if the burner has a flame, the ignitor also still “on”.
That explanation is there because we changed the question a couple of years ago, so if someone came back to look over the results it might have looked confusing because they would see the new question but the old answer. Sorry for any confusion!
Hi Lucas,
There are two ways that you can get a voltage difference in a circuit.
One is regular voltage (or voltage “potential”). This type of voltage is measured with your probes on two points that are not both on a circuit with current flowing through it.
Example 1: measuring across an open of some sort (for example, an open switch, or an element that failed open), and reading voltage “potential”. That would be Line on one side and Neutral on the other, in a 120v circuit, or L1 on one side and L2 on the other in a 240v circuit.
Example 2: you could be measuring voltage with one probe on a point in the circuit, and another probe on a known-good neutral somewhere. This would also be “potential”, because the two measurement points are not both on the same circuit with current flowing through. Some of the measurements in the video are done like this (L1 wrt N, for example).
Two: Voltage Drop, which is the difference in voltage across a load that occurs when current is flowing through it. In the video, when we measure across the element (L1 wrt L2) we are looking for voltage drop. The fact that we don’t get any indicates that there is no current flowing, which means the circuit must be open somewhere.
In a 120v, L1-N circuit, if you have 120v potential at the load, then you know that the L1 side cannot be open, because that’s where your hot voltage comes from. Neutral doesn’t supply any voltage.
But because both sides are supposed to be “hot” in a 240v circuit, you can’t tell which side is open until you disconnect one side and see what happens.
When there is an open fault in the circuit, no current is flowing, and the voltage that is coming from the power supply will be present in the circuit up to that open point. So, with the open on the L2 side somewhere, L1 is able to be present from the power supply and through the element (which just acts like a wire) up to the point where the open fault is.
When we disconnect L1 from the element, that prevents the L1 voltage from being present through the element, and thus we see the change in the L2 wrt N reading in Fig. 2.
Does that help? Maybe try drawing out the scenario on paper and see if that helps.
Let me know if you are still unsure.
Hi Lucas,
I’m glad you asked!
An open switch has infinite resistance. Current will not flow across an open switch in a standard 120v or 240v circuit. (* See note below)
One of the challenges to understanding electricity is that we tend to picture electrical current like water flowing. Water is an independent substance that can run through pipes or in a river bed, etc. Electricity is different.
To put it simply, electric current is made up of electrons that are part of the material of the circuit itself. In a copper wire, voltage puts pressure on the electrons in the copper atoms so that they want to move. This movement is electrons hopping from one copper atom to the next. An open switch breaks this ability for the electrons to move. The electrons to the left of the open switch feel the pressure of L1 voltage, but they have no where to go. They are not going to jump through the gap to the other side.
Review the second video in Unit 2, What is Electricity? Current and Voltage.
*Note: with very high voltage and a very small gap, we can get electrons to jump across an opening. That’s what spark modules do.
Let me know if you have any other questions.
-
AuthorPosts
