Susan Brown

[Susan Brown]

Zachary – do you want to run it by me to make sure?

[Susan Brown]

A thermistor is a load, since as you noted, it has a voltage drop. Any switching that is done as a result of the thermistor’s sensing is done by the board.

Make sense?

[Susan Brown]

Your calculations tell the story!

“Equation 2” has 3 parallel branches, each with 10 ohms, and a *total* current of 36 amps.

Now, if one of those 3 circuits fails open, you are just left with two circuits. This is what you show in “Equation 1”, where you found you had 24 amps when there were just 2 circuits with 10 ohms each.

The other, and simpler, way to think about it is that total current of parallel circuits equals the sum of the current in each circuit. So, it’s easy to see that if you loose one branch, the total decreases.

[Susan Brown]

Hi Patrick,

See if this helps:

1/(1/80 + 1/480) =

1/(0.013 + 0.002) =

1/(0.015) =

66.7 ohms

The rule of thumb is that the Equivalent Resistance of loads in parallel will be something less than the smallest resistance. So, this answer makes sense – it is less than 80 ohms.

Note – to change a fraction into a decimal number, to make it easier to add them, you just do “1 divided by 80”, etc., on your calculator.

Try this yourself to make sure you get the same answer. Depending on how many decimal points you preserve when you change the fractions into a decimal, your final answer can vary by a bit. For example, I just got 68.6 ohms by doing it a slightly different way on my calculator. That is not a significant difference.

[Susan Brown]

Hi Andrea,

During the continuity testing, the dryer was unplugged. But for the voltage measurements, it had to be plugged in. About halfway through the video look for the slide that says “Live Test of the Element or Coil” with a safety warning in red.

Also can the motor run with the L2 wire is disconnected from the spade on the heating element ?

Yes – if you look back at the schematic, the motor is in a L1-N circuit – it just runs on 120v. So, it is not connected to L2. This is why *occasionally* a customer will have an electric dryer that tumbles but has no heat, and the problem turns out to be that the circuit breaker partially tripped, leaving L1 connected but not L2.

[Susan Brown]

Hi Kaley,

Good job – you’ve got it. Oh, and remember that voltage does not move or “run.” Voltage is best thought of as being “present.” [rest of answer hidden]

• This reply was modified 2 years, 4 months ago by Susan Brown.
• This reply was modified 2 years, 4 months ago by Susan Brown.

[Susan Brown]

I understand that only current flows through a circuit.

Yay! That’s the point of that question – to really make sure a tech has that distinction very clear.

And you are correct – the higher the resistance, the higher the voltage drop. Good job!

[Susan Brown]

Hi Bill,
Do use the formulas correctly, you have to understand certain things about how circuits work.

For example – if you have a single circuit with two or more loads in series, you need to understand that the current will be the same throughout the circuit (in other words, the same amount of amps will be going through each load). And that the total resistance in the circuit is part of what determines what the current will be.

Then, when finding the Power for a load (the heat generated by it, for example), there is more than one way. Look at the various formulas for P. They use two of the following: E, I, R. So, for example, if you know the amps going through a load and the resistance of that load, you can calculate P for that load. Or, if you know the voltage drop across the load and the current going through it, you can use a different equation to find P.

Rewatch the second video in Unit 4 where I do some of these calculations for series circuits.

If you are dealing with parallel circuits/loads, then there are other considerations (see Unit 5).

If you have a more specific question you want help with, let me know.

[Susan Brown]

Would 4 be stuck at 0 volts cycling around the shunt (detector switch)?

[answer hidden]

• This reply was modified 2 years, 4 months ago by Susan Brown.

[Susan Brown]

Modern fridges with a split-phase compressor use PTC thermistors as start devices, but the devices are still often labeled as “relays” because those used to be used and the jargon got carried over. If you listen to around the 11 minute mark of the first video, that’s the point he’s making. Bottom line: for most fridges we encounter these days, we should assume the “start relay” is actually a PTC start device.

[Susan Brown]

😀

[Susan Brown]

The Question: Which of the following is NOT one of the points made about voltage and current in the video for this lesson?

There is no absolute 120 volts out there somewhere
All voltage measurements must be made in comparison with some other point.
There is no absolute 10 amps out there somewhere
We arbitrarily designate the earth as having a charge of zero.
Voltage is a difference in charge between two points in an electric circuit.

In other words, which one of those statements is not a valid statement about voltage or current?

What do you think?

[Susan Brown]

Hi Terrance,

It isn’t intuitive based on the name of the valve. See the 3rd video in the 3-way valve unit, starting approximately 11 minutes in.

[Susan Brown]

Hi Derrick,
Yes, you can see your quiz results at the end of each unit that you have completed.

[Susan Brown]

Hi again, Mohammed,
Some of the questions you are asking are based on material that is taught in the Core course. As I mentioned earlier, you kind of skimmed through much of that course. The Advanced Courses assume that you know the material in Core, so it would benefit you if you went back to Core and worked on earning your Certification in that course before taking the Advanced courses.

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