Scott Brown

[Scott Brown]

Yes, exactly!

Here’s the reality: you simply cannot understand electricity with “stories,” “tech myths,” or “gut feel.” You have to run the numbers. This is exactly why we teach it the way we do.

Because you can’t see electricity, we understand it in exactly two ways: Math and Measurements.

The math explains how it works.

The measurements show us that it really works the way the math tells us it does.

Electricity is 100% described by math. There’s just no getting around the math.

Another way to think of parallel circuits is that they represent additional paths for current (electrons) to follow. Or additional loads that the power supply must supply electrons to.

Take away one of those paths and the power supply has to supply fewer electrons (less current) to the remaining load.

Make sense?

[Scott Brown]

…why the overall current decreases when one parallel branch opens… and the total R decreases…

If one of the branches in parallel circuits opens, then what happens to the total equivalent resistance? Run the numbers yourself using two, 10 ohm resistors in parallel.

1. Calculate the equivalent parallel resistance of the two 10 ohm resistors.

2. Now imagine one of those branches opens. What is the new total resistance in that circuit?

3. Does the total circuit resistance increase or decrease?

[Scott Brown]

Hi Javin,

I still have that Radio Shack meter– always good to keep a spare around!

I hear a lot of techs get all into which type of meter has which features or is the best to use. The irony is that most of these techs don’t understand basic circuits, how to read schematics, or the proper use of the meter. For example, when to use the DMM and when to use a loading meter.

There’s a common tech myth out there that a tech is only as good as his test instruments. I call complete BS on that! Just the opposite is true: a test instrument is only as good as the tech using it.

If you take a master tech who knows electricity and circuits like breathing, he can troubleshoot even the trickiest appliance problem with the schematic and $10 meter.

On the other hand, you could have a tech with a $400 Fluke meter who doesn’t know the difference between Line for Neutral. Sadly, this is not an overstated example– *most* techs don’t understand this distinction along with many other aspects of AC power and electric circuits.

Bottom line: your Radio Shack meter is just fine. I got the Fluke for some extra features and functions. It also gives more stable readings when I’m checking DC voltage on a data line which has pules on it rather than a steady DC voltage.

By the way, if you haven’t already, you need to watch this webinar recording:

https://mastersamuraitech.com/webinar-recording-voltage-measurements-loading-meters-ghost-voltages-triac-controlled-neutrals/

[Scott Brown]

You betcha! Glad to help! 🙂

[Scott Brown]

…there are no other components between Neutral side of the ignintors and the Neutral of the supply range.

I think you’ve just answered your original question!

So, line is traveling up to the ignitors

To the other (non-Neutral) side of the ignitors, yes.

the gas valve is not considered a load.

The gas valve actually has two components: a bimetal that opens to let gas through and a small heater that heats the bimetal. The heater is a load and that’s what’s shown in series with the ignitor on the schematic. For a detailed analysis of this system, watch this webinar recording:

https://mastersamuraitech.com/webinar-recording-gas-oven-hot-surface-ignition-systems/

[Scott Brown]

The terminals are on the line side of the ignitors and when the switches close they complete a neutral path to the ignitors.

Let’s take a look at what you said here– it is contradictory!

The terminals are indeed on the Line side of the ignitors. How then can they complete the Neutral path for the ignitors?

Do you see components between the Neutral side of the ignitors and the Neutral supply to the range?

[Scott Brown]

Appliantology is a fantastic information tool for any appliance tech! Glad you found what you need there.

I would just urge you to read your auto insurance contract carefully– many have specific exclusions for a vehicle used in commercial work. If you have a claim and the adjuster gets wind that the vehicle was used for commercial work, even part time, he may have grounds to void your coverage right there on spot and leave you high and dry.

We have commercial auto insurance on our service vehicle. Covers replacement value of tools and parts. We pay less than $800/year but this will vary by your area and company.

[Scott Brown]

I think this may be what’s tripping you up: No new connection or re-wiring was done to establish the alternate Neutral path for the loads in the freezer! The new Neutral path was there all along, it’s just that electrons did not use it as one because the Neutral wire to the freezer effectively shunted the compressor and condenser fan motor. When that Neutral wire to the freezer broke, it removed the shunt.

The only thing that had to happen in this circuit to make it behave the new way was for the Neutral wire supplying the loads in the freezer to break. Period.

No new wires were added.

No wires were touching anything they shouldn’t be touching.

No misplaced connections.

No new connections.

The compressor and condenser fan motor still had its original Neutral wire intact.

Just a broken Neutral wire in the wire harness to the freezer (defrost heater and evaporator fan motor). That’s it.

When that Neutral wire to the freezer broke, it removed what amounted to a shunt of the compressor and condenser fan motor.

When that happened, the circuit was “flip-flopped” so that the evaporator fan motor was now being supplied with Neutral through the low resistance of the compressor windings and condenser motor (in parallel with each other, which lowered the equivalent resistance to almost nothing) and the supplied Line through the low resistance of the defrost heater.

Net effect: three equivalent resistances in series: two of them of such low resistance compared to the resistance of the evaporator fan motor that they dropped hardly any voltage so the evaporator fan motor was still able to run.

Using an unusual real-world example, this unit illustrates a basic circuit principle: electrons follow ANY and ALL valid paths to reach that positive voltage.

Does this make more sense?

[Scott Brown]

Please tell me the time in the video player (minutes:second) you’re referring to so I can scrub ahead to it.

[Scott Brown]

I am probably missing something very simple.

These are often the most subtle and important things to understand! So it’s good you’re asking the question.

Let’s try seeing through this another way: Where in the video do I lose you? Tell me the min:sec in the video. This will tell me exactly which part of the instruction in the video wasn’t clear for you.

[Scott Brown]

I’ve split the topic into its own, new topic in the Basic Electricity forum.

[Scott Brown]

Up to this point in my studies I have been taught that electron can not travel if there is an open in the circuit.

And this is still true! But just because there’s an open in the intended circuit doesn’t mean that the electron won’t seek that positive charge through an alternate, unintended path, as shown in the video in that unit.

So, how is it possible that the evaporator motor find itself in series with the defrost heater when there is a broken neutral?

Just because the intended Neutral is broken doesn’t mean that the electrons can’t find another path to the positive charge. It all depends on where the physical wires break.

Loads in series, such as the defrost heater in series with the evaporator motor, is a common configuration in appliances. You’ll see this frequently in older dryers where the timer motor is series with the heating element as shown in the schematic below, which should look familiar to you from Module 3, Unit 2:

The exact same principle is at work here. In this case, this is done by design. In the refrigerator case in Unit 3, it occurred by accident. But, in both cases, the same principle applies.

The relatively much lower resistance of one load to another makes it act, essentially, as a wire, such as in this case with the evaporator motor in series with the defrost heater or a dryer timer motor in series with the heating element. The electrons don’t care if they have to go through another load to return to the power supply. Electrons will follow all valid paths in their quest for electrical neutrality.

How then is line now traveling through the heater threw broken neutral wires to the evaporator motor when the circuit is open because of broken wires?

This is the way circuits work! The point of this unit is to bring that concept into sharp focus using a real-life example of this. You also saw this concept in Module 3, Unit 2, and Module 5, Unit 2. I encourage you to re-watch the video in those units as well as this video in this unit.

[Scott Brown]

Hi John,

All capacitors work essentially the same way whether they’re ceramic disk or electrolytic. See if this video helps you understand capacitors mo’bettah:

https://youtu.be/l4Fl84tTnXs

[Scott Brown]

These should work nicely: http://amzn.to/1VbYtp9

[Scott Brown]

As a practical matter, we as appliance techs will never measure DC current. So no need for a meter with this function.

However, we should still know how to calculate DC current using Ohms Law. In fact, the Final Exam has a question on this and if you answer, “we never measure DC current as appliance techs” it will be marked wrong. Word!

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