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Hi Jessica, are you referring to a mechanical thermostat or an oven that uses an RTD?
The old skool mechanical thermostats used a gas filled bourdon tube connected to the thermostat body. The gas in the tube expands and contracts in response to temperature. The expanding/contracting gas opens and closes contacts inside the thermostat body, thus controlling power to the heating element or gas ignitor.
If that’s not what you’re after, let me know.
The main take away from that section is the paragraph right above the gauge table. Note particularly the injunction against joining copper and aluminum wires.
Wire GAUGE is inversely related to wire DIAMETER. The higher the gauge, the smaller the diameter. Wire gauges are stamped on the insulation. It’s good to have a familiarly with these things since there are lots of wires inside an appliance!
Ampacity– the amount of amps a particular gauge wire can carry– is also inversely related to gauge. The higher the gauge, the less amps it can carry.
. Do you assume that all of those are connected to the control board? or to each other? In other words, do you have to have the appliance torn apart to fully understand which connetor connects to what?
“Molex” is the name of a company that has become used as a generic. Like Kleenex or Coke. So it’s a generic term used to refer to any type of multi wire connection, whether that connection is at a board or at a door hinge or wherever.
The relative location of molex connectors is usually shown on the schematic or wiring diagram. GE is especially good at denoting molex connections anywhere they occur right on the schematic without having to use messy wiring diagrams. They do this because someone at GE at one time understood that any molex connector is a weak point in a circuit because it is subject to corrosion, mechanical failure, etc. that wires are not vulnerable to.
I just had a question in regard to thermal fuses vs thermal cut outs.
Watch the first minute of the first video in Module 4, Unit 5. Thermal fuses and thermal cutoffs (TCO) are different names for the same physical component.
There is a distinction between TCOs and hi limits. Hi limits are bimetals and function differently from TCOs.
Even though TCOs and hi limits are in different electrical circuits, they are still physical components placed in locations in the dryer where they can monitor and respond to overheat conditions.
The big electrical thing that both TCOs and hi limits have in common is both are switches. The whole purpose of a switch is to control the power supply to a load. In an overheat condition, these switches do what switches do: they switch! In this case, they go open, killing power to the load they control, be it motor or heating circuit.
Ok, so in DC circuits when you measure +5VDC you’re really measuring that sucking force of the positive polarity whereas in AC you’re measuring the “pushing” force, is that a good way to put it?
Not quite. Remember that electrons are pushed a circuit around by a voltage DIFFERENCE between two points in a circuit. Those two points creating the voltage difference in the circuit are the power supply. In a complete circuit with a driving voltage difference, electrons will move in accordance with the same principle: like charges repel, opposite charges attract. This fundamental law of electricity is called “electrostatic attraction” or “electrostatic repulsion.”
Electrically, the only distinction between AC and DC circuits is that the DC power supply polarity does not change over time. So the negatively charged electrons will always travel in the same direction in the circuit: from the relatively negative polarity to the relatively more positive polarity. In AC circuits, the electrons “jiggle” back and forth as the polarity of the voltage supply switches 120 times a second (in a 60 Hz supply, which is North American grid standard power).
So whether you think of it as pushing or sucking, electrically AC and DC voltage supplies operate on electrons in the exact same way: electrostatic attraction and repulsion.
For example, if I were to measure voltage between the red wire and some other random neutral, I’d see +5 VDC (or whatever the power supply voltage is) and if I do the same for the white wire and some other random neutral I’d see 0v? or would it be the other way around? Thanks!
Remember that the definition of voltage is the DIFFERENCE in potential between TWO points IN THE SAME CIRCUIT and FROM THE SAME POWER SUPPLY.
How many leads does it take to measure voltage? Two, right? So we do not measure voltage “at a point” in a circuit. We measure voltage BETWEEN TWO POINTS in a circuit. The SAME circuit. The circuit powered by the SAME power supply.
DC and AC circuits function independently from each other because they use different voltage supplies. DC ground (or common or negative terminal of the battery) is NOT AC Neutral or chassis ground. If you’re measuring DC voltage, you need a DC reference. It makes no sense electrically to measure the voltage difference between a DC circuit and an AC circuit.
In the above exaxmple it seems that VCC is DC ground?
In DC circuits, VCC and DC ground are the two sides of the voltage supply. In AC circuits, the two sides of the voltage supply are L1 and Neutral or L1 and L2.
VCC also goes by various other names. We discuss those in this video: https://appliantology.org/topic/101611-strip-circuits-dc-terminology/
Making more sense?
Also remember that when we talk about current, we’re talking about the movement of negatively charged electrons directed in a wire. This is key to understanding the function of DC ground or DC negative pole in a circuit’s power supply. The DC ground (or common or negative terminal of the battery) becomes a reservoir of electrons that are pulled out of ground (common/negative terminal) by the positive polarity. I think of it as the positive polarity (DC supply) as “sucking” electrons out of the negative pole (common, DC ground, negative polarity) and draws them to itself because, in electricity, opposite polarities are attracted to each other. Same polarities repel each other. So negatively electrons are always going to be attracted to a relatively more positive charge.
Why does the white wire get the power from the battery if thats DC Ground?
You need a complete circuit from the power supply, through the load, and back to the SAME power supply for electrons to move and make the load do its work. If you’re going to cheat a load, you have to supply your own DC power supply– that means DC voltage supply AND DC ground. Both need to come from the same power supply source. In this case of cheating a BLDC motor with a 9 volt battery, that means the battery must supply BOTH DC voltage supply AND DC ground. Hence the white wire connected to the negative terminal of the battery.
If you’re still confused, you may find it helpful to attend the upcoming Live Dojo workshop on 12/21. We have live discussions about all things pertaining to appliance repair, current repair problems and questions about fundamentals of circuits and technology. Here’s the link to the next Live Dojo: https://appliantology.org/events/event/946-appliantology-live-dojo-saturday-12212024-10-am-et/
Hi Noah. You’ll get into BLDC motors and their configurations more in the motors module of the Core course. But some short answers to your questions:
– The red wire is the DC supply voltage
– White is DC Common, which is another label for DC Ground and this is how it functions in the circuits
– Yellow is the Pulse Width Modulated (PWM) speed signal generated by the main board computer telling the inverter inside the motor housing how fast to make the rotor spin. The more DC pulses on that line, the faster the inverter will make the motor run. You’ll also see this on your meter because your meter reports an average of the voltage pulses. Higher voltage (on your meter) means more pulses and faster RPMs. So tying yellow to red is effectively telling the motor inverter to make the motor run at full speed. That’s why red and yellow were jumped together.
– Battery polarity is positive to the red wire and negative to the white wire.Here’s a blog post from Appliantology that explains/illustrates all this in detail: https://appliantology.org/blogs/entry/1095-bldc-motor-configurations-fg-signals-and-pwm-signals/
the AC2 which is on the heater relay board CN1 Pin 2 switches between a Line and N via the Relay on that board
No. Neutral does not play a role in this part of the heater circuit. We’re dealing with a simple relay that is either open or closed. When closed, the heater relay at connects Line from CN1-2 to CN1-3. When open, it’s just like any other open switch: just open. Which means the heater is no longer supplied with Line and so cannot do any work since there is no longer a complete circuit on the Line side of the heater circuit.
I know it will lowest resistance
If you’re saying that current takes the path of least resistance, then I need to correct you on that. This is a half truth. The full truth is that current (a directed stream of electrons) also takes the highest path of resistance. This is why parallel circuits work.
Shunts are a special case because a shunt does not create parallel circuits. Why? Because the shunt itself has no load. What three things do all valid circuits have? 1) power supply 2) a load 3) conductors connecting them together. Shunts, by definition, do not have a load therefore do not create a circuit in themselves. It’s just a jumper wire that is typically used to bypass a load and can reconfigure the larger circuit.
“Since current takes the path of least resistance.”
This is only a half truth. The full truth is that current (a directed stream of electrons) takes ALL valid paths regardless of resistance. The resistance just limits the number of electrons per second (amps, current) going through the load. This is, in fact, why parallel circuits work.
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This reply was modified 4 months, 3 weeks ago by
Susan Brown.
If you connect a
positive voltage to the anode (negative side of the diode) and a negative voltage to the cathode
side (positive side of the diode), the diode becomes forward-biased (Figure 7-17a).Good question! Kleinert’s explanation is confusing because he is not talking about the PN junction INSIDE the diode. He is only talking about the EXTERNAL voltage applied to the diode. Hang with me…
PN means “positive-negative.” This is specially “doped” (technical term– that’s what they really call it) semiconductor material INSIDE the diode; half of it is positively doped (has a net positive charge) and half is negatively doped (has a net negative charge). The JUNCTION (where the P and the N material meet– all inside the diode) is the interesting part. The whole trick of semiconductors with PN junctions is either collapsing the junction so the material conducts electrons (current) or expanding the junction so that it blocks electrons.
In a diode, the P-type material (positively doped) is called the anode and the N-type material (negatively doped) is called the cathode. If you apply an EXTERNAL positive charge to the P-type end and a negative EXTERNAL charge to the N-type end, then the PN junction collapses and diode will conduct electrons. This is called “forward biased.” If you switch the external charges and apply a negative charge to the P-type end and a positive charge to the N-type end, then the PN junction expands and electrons cannot get through. This is called “reverse biased.”
With this in mind, here are some resources to watch/read for further elucidation:
1. Read this article on “Diodes in AC circuits”: https://appliantology.org/blogs/entry/1093-diodes-in-ac-circuits/
2. Watch this video on “Diodes in Appliances”: https://appliantology.org/topic/102375-diodes-in-appliances/
3. For a deep dive on semiconductors and PN junctions, watch this webinar: https://appliantology.org/topic/57328-webinar-pn-junctions-and-semiconductors/?do=findComment&comment=339413&_rid=4
When I went to diagnostic after reset the refrigerator I found a frost on the section line.
You should never see frost on the suction line in a properly functioning refrigerator. Frost on the suction line means mixed phase refrigerant (liquid and vapor) is reaching the compressor. The liquid refrigerant can damage the compressor. The inverter (if equipped) will detect this as an overcurrent and kill power to the compressor.
Has this refrigerator sealed system been serviced before? If so, may be an overcharge.
If not, then the heat exchanger (capillary tube adhered to the suction line) may be disrupted.
In a radiant heating element, the thermal limiter is part of the element– it’s the rod you would see sticking inside the element. So the entire element would be replaced.
do I test for amps to see if it’s working properly or am I just testing to see if it is getting power or not.
Remember that power, P, is volts times amps. P=I*E. I don’t carry a watt meter but always carry an amp clamp. So amps are a proxy for watts– if I know the supply voltage and the amps, I know watts. Also remember that loads require watts to function properly. for some loads, like heating elements, you may be given a wattage spec either on tech sheet or on the part itself. If that heating element is not getting hot or not getting hot enough, I’ll proceed this way:
- Identify the heating element circuit on the schematic
- Find a convenient EEPs for that circuit such as at the timer or control board
- Measure voltage supply for that circuit (without voltage, nothing else happens because volts drives amps (electrons))
- If the voltage supply is good, then I measure amps and compare with specs
Here’s where real techs are separated from PCMs. The PCM looks at the manufacturer specs which usually give a resistance spec. I ignore this because they are dumbed-down specs. They do this because they know that most techs don’t understand amps and watts and aren’t comfortable or competent to work on live circuits. But most understand ohms. So they give ohms specs for liability protection because you make an ohm measurement on a dead circuit.
So I measure amps and compare with the wattage spec (which is usually given either on the tech sheet for on the part itself. You usually don’t need to tear down the appliance to get the wattage spec stamped on the part because you can simply look up the part at an online parts site and look at the picture of the label to get the wattage spec). If the amps are in spec, then I know that circuit, including the load, are functioning per design. If amps are too low (usually the case) then I know there’s a problem with a connection in that circuit or the load itself. If amps are zero (and I have a good supply voltage for that circuit) then I know I’m dealing with an open in the circuit somewhere. If you do it this way, measuring resistance of the load is irrelevant.
Remember, too, that a “good” ohms test is not diagnostically conclusive because circuit switches, connections, and loads can (and do!) fail under load (when electrons are moving though the circuit). Ohms testing is ONLY diagnostically conclusive if you measure open. Amps, however, ARE diagnostically conclusive.
If you suspect a switch (such as a hi limit) is failing under load, the best way to test it is NOT ohms! Instead, jump the switch out of the circuit and then run it again to see if you get normal operation. If the circuit works normally, then you have proven the jumped switch is the problem and you replace it. If not, then the problem lies elsewhere.
Ohms are useful in some situations. For example, a dishwasher drain pump in a computer-controlled dishwasher is not working. In this case, the computer may may be sensing a grounded winding in the pump due to current sensing. You would verify this by checking ohms from the pump winding to chassis ground. Should read open. If you get some resistance, even in the K-ohms or M-ohms, then, Houston, we have a situation and you should replace the pump. If the path from winding to ground reads open, then you can confirm the pump is capable of running by using your cheater cord to hot wire the pump. Measure pump amps when you do this. If the pump runs and amps are in spec, then the problem is NOT the pump but instead is the computer board (not supplying voltage to the pump circuit).
Have you watched the video on “Voltage and Voltage Drop, Loads and Switches, Jumpers and Cheater” yet? If you haven’t yet, you will– it’s in the Core course. I explain this in detail in that video.
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This reply was modified 4 months, 3 weeks ago by
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