Susan Brown

[Susan Brown]

Hi Nihar,

I think what he said is that it is a type of closed circuit. A circuit with zero resistance is definitely “closed” (it is not open somewhere) but also is a short circuit, because there is no load (resistance) in it.

Circuits in appliances will always have a load in it by design – an element, fan motor, light bulb, etc. When the circuit is closed, current will flow through it and power the load(s). If a short circuit occurs, that is a fault.

You’ll learn more about these things as you go along.

Does that help?

[Susan Brown]

See the last video, starting around the 20 minute mark. It discusses the water valve being in series with the drain pump, and the implications of that. One thing it means is that if the drain pump winding has failed open, then the water valve would not be able to work. So – if water comes in, that means the drain pump (motor) winding is fine.

Winding: the drain pump is a motor, and motors have windings that the current goes through.

Does that help?

[Susan Brown]

Good catch! We reorganized some things since that video was recorded. Sorry for the confusion! I just added a link to the webinar recording – it is over at Appliantology.

https://appliantology.org/topic/62258-mst-office-hours-362017-neutral-vs-ground-inverter-microwave-digital-communications-more/

[Susan Brown]

FYI – here’s the part of the schematic that shows the circuit:

To get your Appliantology account set up, just go to Appliantology.org and click the red “Sign Up” button in the upper right. Let us know what your username is, then we’ll upgrade your account.

[Susan Brown]

Scott created this sketch for you. First he took the pertinent part of the circuit from the original schematic and drew it as a strip circuit, to make it easier to focus on.

The Heat Sense circuit opens the triac or relay for the test while the motor is running, and uses L1 as the reference for the voltage measurements.

You can see the three conditions that it is designed to sense for below. For the grounded element scenario (where the element has broken and part of it is contacting the chassis), L2 is out of the picture, but there is a circuit from L1 to chassis/ground with current flowing. The resistor in the heat sense circuit has a much higher resistance than the part of the element that is touching the chassis, so essentially all of the voltage will be dropped across it. That is why when you measure voltage at the heat sense location with respect to L1, you get 120v, because you are measuring the voltage drop across that resistor. (Alternatively, if you measured voltage from the heat sense with respect to N, then you would get 0v.)

Take a look and let us know if you have any questions. This is a great example of a modern appliance using some old-school series circuit concepts to accomplish a task. We are planning to do a video stepping through it. Thanks for asking about it!

NOTE – you can right click and open in another tab to get a larger view.

• This reply was modified 2 weeks, 3 days ago by Susan Brown.

[Susan Brown]

Okay, I’ll pass that along to our tech team and see what we can figure out. I understand about your Saturdays. Right now that is the only time we are able to do them. We do post recordings afterwards at Appliantology – did you ever get your membership set up there? I saw that my assistant was working with you to get that set up.

[Susan Brown]

Better to overthink than to underthink! 😀

[Susan Brown]

The correct answer is: Turn on broil and see if you’re getting 120 vac between P20-2 and P1-N at the electronic control board.

[Susan Brown]

When I say “the current here will be different than the current here”, “Here #1” is in the top circuit of the set of 3 parallel circuits, and “Here #2” is in the series portion, as labeled below. As soon as we go past the green dot (up, right, or down), we are in one of the parallel circuits.

The current will be the same along the L1 side of the circuit from the power supply (“L1”) to the green dot. (And, on the neutral side, from the other side of the parallel circuits back to the power supply.) Does this help?

• This reply was modified 2 weeks, 6 days ago by Susan Brown.

[Susan Brown]

First I pointed to one of the parallel circuits, then second to the series portion of the circuit, before the set of three. They will have different current.

Is that the part you were looking at?

[Susan Brown]

Hi Andrea,
You are correct. I reset you. FYI – it’s always best to use the Quiz & Exam Reset Request when needed 🙂

[Susan Brown]

Hi Ronnie,

You actually don’t need to calculate the watts to answer this. We know that power is directly proportional to resistance*.

R1 is 5 ohms and R2 is 5000 ohms, which is a 1000 times difference.

The question is “how much work is R1 doing compared to R2?”

The answer is “1000 times less work”

But, to show you the calculation:

I = E/Rt = 120/5005 = 0.024 amps

P1 = I^2 x R1 = 0.024 x 0.024 x 5 = 0.0029 watts
P2 = I^2 x R2 = 0.024 x 0.024 x 5000 = 2.9 watts

* How do we know Power is directly proportional to resistance? One way is that we know voltage drop is (E = I x R) and that power and voltage drop are also directly proportional to each other: P = I x E. The formula P = I^2 x R also shows that P and R are directly proportional.

[Susan Brown]

Hi Trevail,

There are at least a couple of ways they can do this. One is current sense, the other is a sensing line (a switched line that goes back to the board with information). If you give us the model number, we can look up the schematic and see what we can infer from what they show.

By the way – this is the kind of thing we often talk about at the Live Dojos. The next one is Saturday morning at 10am eastern.

[Susan Brown]

Thanks! I assume you mean this line:

Water leaks and/or ice build up at the bottom of the refrigerator

We mean the bottom of whichever compartment is at the bottom of the appliance. If it is a freezer, then it will be ice. If it’s the fresh food compartment, then it will likely just be liquid water. Side by side – depends which side!

Does that answer your question?

[Susan Brown]

I can’t see the image that you’re referring to.

Can you either quote it, or email the image to me?

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