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You would only ever want to use a cheater cord on a load that is intended to receive line voltage. If a load is, for example, supposed to run on 12 VDC, then it could definitely be damaged if you connected it to a 120 VAC power supply.
Does that answer your question?
Exactly! Dealing with missing information is a big part of being a technician, so we do our best to prepare you for that.
This is one of those situations where the manufacturer hasn’t explicitly stated some information, so you have to make an educated guess based on other clues.
For example, there are certain conventions concerning the wire colors of line and neutral. Do you remember what those are?
Don’t sweat it! Learning to catch every little detail is part of becoming a top-notch appliance tech. You’re well on your way. 🙂
The abbreviation is given right there in the unit — reread the material closely and you’ll find it.
May 9, 2019 at 3:23 pm in reply to: ADVANCED TROUBLESHOOTING – MOD 5: UNIT 1: EXAM QUESTION #4 #15805Hi JP,
I highly recommend that you rewatch the videos in this unit (especially the second one), because they spend most of their time covering this exact question.
Keep in mind too that, while both legs of the power supply might go through timer contacts, only one of them is really ever switched by the timer during operation.
Let me know if you’re still confused after rewatching the videos.
What type of voltage is applied to BLDC motor windings?
Think of what that inverter is doing. It’s taking DC current and sending it through the windings in one direction, then the other, switching the direction many, many times a second. What kind of voltage do you have when its polarity is constantly reversing like that?
How many windings are polarized at a time to do work in a BLDC motor?
There’s a diagram showing the answer to this about halfway through the video on electronic commutation.
And could this actually be considered 3-phase
Why yes, it is 3-phase power. That’s the kind of power that the inverter board is producing by switching the voltage to each of the three windings like it does. That doesn’t disqualify the motor from being a BLDC motor. In fact, that’s how all inverter-driven BLDC motors work. It’s why they don’t need start devices to get going from a dead stop.
Wouldn’t a longer duty cycle actually contribute to slowing down a motor at high RPMs, despite its voltage increase?
I’m not quite sure what you’re getting at here. Are you thinking about the duty cycle of the PWN signal that gets sent to the inverter from the main control? That’s just a data signal to tell the inverter what to do. The inverter then interprets that data signal and decides whether to run the motor faster or slower.
After reviewing Multisim in a bit more detail, I can already see that it wouldn’t be of much help for your situation.
If I understand correctly, what you’re struggling with is finding on a schematic where you should make your measurements — identifying EEPs, in other words. Multisim doesn’t teach how to find troubleshooting points on a schematic. It’s simply a tool that you can use to create simulations of circuits, without instructional features.
Multisim would only be useful for people who deal with much more complicated circuits than we do — with reactive components, P-N junctions, etc. That’s a whole other level of electricity that we don’t get into as appliance techs. The kinds of circuits we deal with are always, at the end of the day, just loads and switches (yes, even control boards simply function as intelligent switches).
If you were working in electronics or as an electrical engineer, Multisim might be a helpful tool. But for an appliance tech, it’s overkill.
Glad you’re enjoying the courses! Interactive troubleshooting training materials are definitely something we’re looking into right now. We don’t have any personal experience with Multisim, so I can’t give you a recommendation for or against them.
We do have tons of videos that are focused specifically on the area of selecting the correct electrical measurement to troubleshoot a problem. Here are a few that I think you’ll find particularly instructive:
April 15, 2019 at 4:51 pm in reply to: Question about schematic used in quiz question 4 and 5, unit 5 part 2 #15704A check from one of the output terminals to one of the input terminals would not be useful here. As part of the setup for this question, you already have as a given that your power supply up to the noise filter is good. So you know the component has a good input. The only test you need to make is from L2 wrt N2, since those are your two output terminals. That will tell you if the noise filter is capable of putting out a good 120 VAC.
The question is supposed to throw you off your game, so don’t worry — it’s just doing it’s job! 🙂
The point of it is to teach you to always pay attention to text in schematics. If the engineers took the time to write a special note for you, you can bet it’s something important. In this case, they tell you exactly which two wires provide the input, and which two provide the output.
Since they’ve given you this info, you don’t need to know anything about the inner workings of the noise filter. You can just treat it like a black box. Check that it’s getting a good 120 VAC power supply. Then check that it’s putting out a good 120 VAC power supply. That’s it.
I believe that the concept of inputs and outputs is covered in Fundamentals, and it’s definitely covered in detail in the Advanced Troubleshooting course’s material on control boards.
The concept isn’t too complicated. An input is just whatever is supposed to be supplied to a particular component, and an output is just what it’s supposed to do in response to the input.
As a very basic example, let’s think of a motor. The input is just the power supply: 120 VAC on one side and neutral on the other. In response to being supplied with power, the motor outputs mechanical motion. Another example is that noise filter we’ve been talking about elsewhere in the forum. Its input is the power supply coming from the wall outlet, and its output should simply be that same power supply.
We talk about inputs and outputs the most when we’re talking about control boards. This is because boards are programmed with logic that’s supposed to produce certain outputs in response to certain inputs.
Whether a particular component that’s connected to the board is supposed to send the board an input or receive an output from the board is rarely called out explicitly — but it’s not hard to figure out by common sense. Just think about what a particular component’s intended function is.
For example, a control board in a refrigerator will receive input from thermistors telling it the temps in various places around the refrigerator. If the board receives an input telling it that the freezer compartment is too warm, then it will probably send power (an output) to the compressor. The thermistor sends input to the board, and the compressor receives output from the board.
We’re not always privy to exactly how a control board is programmed to make decisions — that’s a place where we’re at the mercy of the manufacturer to provide that info. But identifying what’s supposed to be an input and what’s supposed to be an output is relatively simple.
And a Wiggy is just a brand of loading meter. Amazon is probably the best place to get one.
They are both physically located on the motor, but they are in fact two distinct switches with different purposes.
The centrifugal switch in the motor’s circuit is there to take the start winding out of the circuit once the motor has begun to spin. This is pretty standard stuff for split-phase motors.
The other centrifugal switch in the L2 side of the heater circuit is there as a safety. The engineers put that there to keep the heater from running if the motor fails to start. If the motor doesn’t start spinning, the heater circuit will never close.
April 11, 2019 at 9:09 pm in reply to: Question about schematic used in quiz question 4 and 5, unit 5 part 2 #15694You’re correct that you should make your test at L2 wrt N2, but it’s not to check for voltage spikes — you probably won’t be able to detect the kind of noise that this device is supposed to filter out. All you need to do is make sure that, if you have a good 120 VAC power supply going into the filter, you get a good 120 VAC coming out.
Hi Jason,
Let’s go through your questions one at a time.
1. “Cam” is just the term used to refer to the physical switch inside of the timer.
2. For a switch to be “made” is just a common phrase that means for the switch to close — exactly as you thought.
3 (and 4). Probably why that diagram is throwing you is because you’re trying to look at it as a transformer, when it’s actually a noise filter. I saw your response to another topic in this forum which seemed to indicate that you had mostly figured this out, but just for clarity…
You don’t need to worry about any of the funky stuff (coils, capacitors, etc.) that you see in the diagram. All you’re concerned about is that, if you’re getting a good 120 VAC power supply in, you’re also getting a good 120 VAC power supply out. There’s even text in the diagram telling you which side is the input and which is the output.
The L1/L2 nomenclature in this case is not referring to a 240 VAC configuration. In this particular diagram, the manufacturer (for whatever reason) decided to mark the inputs to the noise filter as L1 and N1 and the outputs as L2 and N2. A little confusing, but again, there’s text right on the diagram saying what’s the input and what’s the output.
Make sense?
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