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Name any time tomorrow
No problem, I’ll set it up for 10 AM ET tomorrow. Look for the Join.me invitation in your inbox. If you haven’t attended an Office Hours before, watch the short video on how to use Join.me:
Talk to you tomorrow morning!
Yes, it is unfortunate that Whirlpool chose to use the word “pulse” in their description of how the drive motor works because it easily misleads someone into thinking they’re talking about data pulses. They are not. They are simply talking about turning on and off the triacs which are supplying AC power to the motor windings.
These are good questions, Dale, and I’d like to explain this to you in a web meeting where we can look at schematics together and talk about them real-time. Are you available today? If so, let me know a good time and I’ll set it up.
They seem to be using a PSC on the VMWs? Whirlpool Modular Washer?
Yes, that is a PSC motor, too.
They seem to run so smooth. Sounds and functions to me so much like A BLDC motor in operation?
PSC motors are single phase, split phase motors. BLDC motors are three phase motors. They are completely different animals.
This thing is AC?
Yes, of course. Even BLDC motors are AC motors because of the electronic commutation switching the polarity of the voltage at the motor windings.
How’s that pulsed from the board?
There is no “pulsing” going on with a PSC motor. It runs off regular single phase line voltage.
If you take the time to watch the webinar recording I posted in my last reply, most if not all your questions about PSC motors will be answered.
I see triacs.
Triacs are just solid state switches used to supply AC to a load. Think of them as solid state relays. Watch this other webinar recording for more details on how triacs are used and how to test loads with a triac:
I must be really missing something big time somewhere.
All your questions will be answered if you watch both the webinar recordings I’ve posted for you. Yes, it takes time to watch them but they will clear up lots of things for you.
And read the link to the topic at Appliantology that I posted in my last reply.
Let me know if you still have questions after you have watched both videos.
PSC stands for “permanent split capacitor.” To understand the real meaning of this name, you have to think back to the other types of split phase motors (of which the PSC is one type).
All split phase motors have one thing in common: they all use a second winding to create a second phase that is “split” from the main single phase supplying the motor (single phase, 120 VAC power supply).
Remember the start devices and start relays used with all the other types of the split phase motors that you studied (like start devices on old skool compressors)? the whole purpose of that start device is to take that second winding out of the circuit after the rotor starts turning.
The difference between the PSC motor and the other types of split phase motors is that the PSC motor doesn’t have a start device. This is because the second winding stays in the circuit the entire time, both starting and running. A run capacitor is permanently connected between the main and auxiliary windings during both starting and running. Hence the name “Permanent Split Capacitor Motor.”
For more info, see this topic at Appliantology:
https://appliantology.org/topic/56698-dishwasher-motor-type/
And watch this webinar recording on split phase motors:
Lemme know if you have any other questions.
September 4, 2016 at 5:55 pm in reply to: Unit #5 Using Schematics to Troubleshoot Appliances, Part 2 (quiz) Question #6 #10717My pleasure, glad it helped!
And thanks for taking the time to ask questions to make sure you understand these fundamental and crucially important concepts. There’s a lot tech mythology out there about electricity and this is the place to get those myths de-bunked!
September 4, 2016 at 5:07 pm in reply to: Unit #5 Using Schematics to Troubleshoot Appliances, Part 2 (quiz) Question #6 #10715You still seem to have a fundamental misunderstanding of voltage drop across loads and I suspect this has to do with the commonly-used term, “current draw.” I’ve made a little Doodlecast just for you that I hope explains this better for you. Let me know.
September 3, 2016 at 10:24 am in reply to: Unit #5 Using Schematics to Troubleshoot Appliances, Part 2 (quiz) Question #6 #10713My first question is would I leave the wiring harness connector plugged into the main PWB when checking for 120 vac.
With few exceptions, when checking power supply to a load, you want the load connected. This is especially true when the power supply has a triac in the Neutral because the triac needs a certain minimum current flow through it in order to “turn on” and close. Watch this webinar recording for lots more details on this:
My second question is, if the drain pump were bad wouldn’t I get less than 120 vac because the pump is bad and not using current?
It doesn’t work that way. The voltage will be the same whether the load is open or closed. The only thing that would change is current.
If the load is closed, there will be current and you will be measuring voltage drop across the load.
If the load is open, you will not have current and will measure voltage supply at the source.
Voltage drop vs. voltage supply.
Voltage drop: caused by current flow through the resistance of a load. E = I * R
Voltage supply: a source of voltage that has the potential to push electrons (current) through a circuit. If the circuit is closed, then that current potential becomes a current reality.
Does that clear things up?
Ah, yes– that’s your basic freeze spray. You can get a can at the hardware store or on Amazon: http://amzn.to/2bDdooG
Most of these freeze sprays use pressurized refrigerant, like HFC 134A gas as in the case of the linked product above.
Learning a lot man. Thank you so much.
Great to hear! Let me know if you have any other questions.
Hi Quick,
There are 5 videos in that Unit. What’s the title of the video you’re referring to?
This is a great question, Quick! The short answer is Inductive Reactance.
All motor windings are inductors. Inductors have a special property of resisting changes in current. It’s not the same kind of resistance as a pure resistor that slows down the stream of electrons (current) and, as a result, gets hot. The resistance that inductors offer to current flow has a special name, called reactance. Reactance is denoted with the symbol, X (capacitors also offer reactance to current but it works differently). This reactance changes with frequency according to the equation you learned in Fundamentals: X=2 x (PI) x F x L
where:
PI = the constant, PI (about 3.14, rounded)
F = frequency, Hz
L = inductance of the inductor, HenrysWhen you measure resistance with an ohm meter, you’re just measuring the resistance of the motor windings, not the inductive reactance of the winding. So the inductive reactance at Line voltage (60 Hz frequency) will only manifest when AC current is flowing through it.
Impedance is total resistance to current offered by a component like an inductor (such as a motor windings). It is noted by the symbol, Z. The total reactance of the motor windings is the sum of the resistance of the wire and the inductive reactance at the Line frequency.
Z = R + X
The specs given in the tech sheet for watts and current account for the inductive reactance of the motor when it is running off Line voltage. So the calculated resistance based on Ohm’s Law won’t work unless you also include the inductive reactance.
Here are a couple of videos that may help explain this:
Let me know if you still have questions.
What are your thoughts on TRMS? Luxury or necessity?
Good to have for things like verifying that Line voltage supply is in spec (+10/-5%). So get this feature. It is also an indicative feature of all better quality meters.
How about frequency?
Good feature to have as another check for things like pulse width modulated data lines. Some manufacturers even give a frequency spec for these lines.
How much resolution should we look for in amp readings? 0.001 milliamps?
For AC measurements in appliance repair, we’re usually only interested in amps to the tenth of an amp resolution. If your meter reads one order of magnitude beyond that, you’re good. So 0.01 amp resolution is sufficient.
But, there’s more to any measurement than just resolution. There is also accuracy (how close to the actual is the measurement) and precision (how repeatable is the measurement of the same actual quantity) to consider. Better meters will have both higher accuracy and precision.
Is temperature measurement a good thing to include on a clamp meter or should that be a separate instrument. (seen a lot of fluke bashing for temp calibration on some units)
First, consider the source of the “Fluke bashing” crowd. These are usually low-information and low-income techs (and I use the word “tech” loosely here). So the basis of their Fluke-bashing is almost always about the cost of the meter alone and is not based on actual technical arguments. And most don’t do the sophisticated troubleshooting measurements to justify the extra expense of a Fluke anyway. Any test instrument is only as good as the technician using it so the extra features and capabilities of a Fluke would be wasted on them anyway.
I’m not necessarily advocating getting a Fluke. There are legitimate technical reasons to not get one: don’t need a meter rated at CAT III, don’t need high accuracy and precision, don’t need the durability. And there are legitimate financial reasons: don’t have the money.
As for temperature measurements, this is purely a preference option. Personally, I use a separate, dual-channel digital thermometer because 1) it is only used for oven cell temperature calibration and 2) my particular Fluke meter (the 117) does not have this functionality (has others, instead).
Most of my temperature measurements are done with my Raytec IR gun.
Hi Tom,
I’m assuming in your example that all four resistors are in series with each other. In this case, yes- you would simply add all four resistors together to get the total circuit resistance. For this particular calculation, you would not need R=E/I.
But suppose your circuit had a power supply voltage of 120 VAC and you wanted to calculate the power (heat) dissipated by R1, the 5 ohm resistor. How would you do this? (HINT: calculating the total circuit resistance is the first step and the next step would be to calculate the total circuit current using a variation of R=E/I)
Glad that helped. Good to see you’re asking questions about things you’re not clear about– that’s exactly what the Student Forums are for.
The current doesn’t actually go negative.
Exactly. This is the subtle yet key distinction.
DC voltage comes in lots of different forms: could be a perfectly steady DC voltage (such as from a battery), could be a series of square wave pulses from 0 to 5 VDC (such as in a serial digital data line), could be rectified but not-yet filtered AC (such as what you saw in the video). The voltage can vary between 0 and some other value (either positive or negative) but as long as it never actually goes to the opposite polarity, the electrons will never reverse their direction of travel and we still have DC (direct current). If the voltage actually changes polarity, then the electrons will change or “alternate” their direction of travel and, in this case, we would have AC (alternating current).
In the case of an unfiltered DC voltage, as shown in the Doodlecast, the voltage is not steady, it is varying between some maximum and minimum level. As the voltage changes, either decreases or increases, the charged stored on the capacitor also changes to counteract this.
So, for example, if the DC voltage out of the rectifier decreases (becomes more negative), the capacitor plate will attract electrons. As a result of it attracting electrons, it is resisting that decrease in voltage from the rectifier.
Then, as the rectified voltage increases (becomes more positive), this will attract electrons from the capacitor plate.
The net result is that the capacitor responds to changes in voltage in such as way that is resists changes in voltage. THAT is the key take away point with what capacitors do.
Note that in the example in the video were were talking about rectified but unfiltered DC. That is key- it is still pulses of voltage, not yet steady. That’s what the capacitor responds to. If the voltage were already steady and not changing, the capacitor wouldn’t do anything.
Don’t get too hung up on capacitors. You just need to understand what they are and what they do.
Re-watch the video two more times (I’m watching the view counter!), pausing as needed, and let me know if you still have questions. If you do, note the exact time, minutes:seconds, where you get confused and we’ll take it from there.
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