Susan Brown

[Susan Brown]

I have multiple electronic books, but I have yet to find any sinusoidal drawings of our 120/240 split phase systems. At the moment, I do not have one to reference that system.

Most electronics books don’t spend much time talking about AC power supply, since electronics are generally only concerned with DC.

If you do a search for split phase power you can find all kinds of sine wave graphs. Here’s another cool one:

[Susan Brown]

Hi Ian,

The black sine wave is the resulting voltage from L1 and L2. The x-axis is labelled: “240 volts AC = (Phase 1) – (Phase 2)

Note that it is not drawn with a mirror image of itself like the waves for L1/L2 are.

Does that help it make sense?

[Susan Brown]

Even though you got it correct on the quiz, I commend you for taking the time to make sure you understand it!

Let’s make sure we’re talking about the same thing.

If everything was working as it should, you should be getting 120vac supplied to both sides of the element – 120vac from L1 and 120vac from L2.

We carefully disconnect L2 from the element while the dryer is still plugged in, and measure 120vac from that disconnected L2 wire wrt N. That means there is not an open along that side of the circuit.

Then we measure the L1 side of the circuit and get 0vac wrt N. This means there is an open somewhere up the L1 circuit, preventing the L1 voltage from being felt at the element.

I’m not sure where your confusion is coming in. Remember, we’re measuring voltage (L1 or L2) with respect to a neutral point, not measuring two points along the wire.

If this doesn’t make it clear, please let me know where you are getting hung up and we’re happy to help you further.

[Susan Brown]

Yes, and you can see that P2 is 1000 times higher than P1.

This supports what I said in my first reply to you that since P and R are directly proportional to each other, you could answer this question just by seeing that R2 is 1000 times higher than R1.

It’s great to do the calculations to understand it all better, but it’s also good to know the relationship of P and R!

[Susan Brown]

It’s not where you were posting, it’s what. You were asking questions about reading schematics. Unless I’m mistaken, these were not for a job you were going on, but just to practice reading schematics.

My point is that you will get a lot more practice reading schematics in the Oven & Range course as well as Advanced Troubleshooting. These courses will help you get better, and you can ask us questions here about those schematics without worrying about posting a picture, because we’ll be talking about schematics that are included in the courses.

[Susan Brown]

Hi Mike,
Questions about refrigeration or Refrigerator technology, like what you asked above about the ADC board, are fine to ask.

It’s the questions about reading schematics that we’d prefer you wait on until you’ve taken the other courses, which will give you more instruction and practice on reading schematics. You’ll benefit a lot from taking those courses! And it would be better if you asked us questions on the schematic exercises and case studies in those courses – it would make for more fruitful dialog.

[Susan Brown]

The question shows two loads in series: R1 and R2
R1 = 5 ohms
R2 = 5k ohms

It’s asking how much more work is done by R2.

[Susan Brown]

I have 120 volts
I enter 5 ohms of resistance
I get current of 24 and power of 2880

This is not correct?

This would be correct only if the 5 ohm load is the ONLY load in the circuit.

The current in a series circuit, which is the same throughout the circuit, is determined by the total resistance of the loads in the circuit. In this case, that is 5005 ohms.

If you have 5005 ohms and 120volts, what will the circuit current be?

Then use that current to figure out how much wattage is produced by each load.

(There’s no record of a Reset Request from you, but I did just set you back to this unit.)

[Susan Brown]

How do you do that quote thingggy?

1. Copy and paste the text you want to quote into the reply box.
2. Highlight it.
3. Click “B-Quote” in the tool bar at the top of the reply box.

[Susan Brown]

Hi Desert,

The easiest way to figure this out is to just look at the Ohm’s Law equation for Power that involves resistance and circuit current, P = I^2 x R (current squared times resistance)

Power is directly proportional to resistance. When resistance goes up, power goes up.

Then all you have to do to answer this question is see how much R1 is greater or smaller than R2, and that will be the same amount that P1 is greater or smaller than P2.

The reason we know that your approach was mistaken in some way is that you got a much higher wattage for a very small load – that doesn’t make sense. If you were trying to use the formula P = E^2/R, the value for voltage (E) has to be the voltage drop across the load in question. The voltage drop across a 5 ohm load will be MUCH smaller than the drop across the 5k ohm load.

[Susan Brown]

HI Bailey,

Yes, with NTC, if the temperature goes up, the resistance decreases. Or if the temperature decreases, the resistance increases. In other words, they move oppositely.

So when you dunk the probe in ice water, you are making the temperature decrease. This means the resistance will increase.

That’s what we’re saying in the question. Does that make sense?

[Susan Brown]

Hi OwlGuy!
Are you looking at the Household Electrical Power Supply video? (Some people mistakenly count the “Safety, Mon!” photo as a video.)

It’s at about the 11 minute, 50 second mark of that video.

[Susan Brown]

Hi Ali,
Thanks for posting in the Forums!

Question 10 is asking about AC voltage, not current. You can figure out the answer to this if you think about polarity. Remember, DC is “direct current”. It has one direction, thus a positive and a negative side to the power supply (like a battery). AC is “alternating current”, and moves back and forth, as you have learned. When you read DC voltage, as the video in this unit showed you, you’ll either get a + or – sign as part of the measurement. Do you also get that with AC voltage measurements?

Question 21 – from unit 7

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.

[Susan Brown]

Hi Jared,

Thanks for posting a question!

Question #2 asks about DC current. The part you copied from the lesson is talking about DC voltage.

Very different things!

From Unit 7:

The three most common electrical measurements you’ll be doing as a professional appliantologist are:

– Voltage, either DC or AC
– Resistance and its daughter test, Continuity
– AC current, which is always done with a clamp-on amp meter (or ammeter). (Note: You will never need to measure DC current in appliance repair.)

[Susan Brown]

Okay – it sounds like you’ve got it figured out. I’ll reset that quiz for you. Feel free to ask more questions in these Forums as needed!

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