Sciencemadness Discussion Board

Can we infer what is broken in the hot plate given the following?

6dthjd1 - 8-2-2024 at 14:39

This used hot plate was working near the high setting for a few hours last night until it was turned down from hi to setting of 8. Sometime during the night it broke and stayed broke for about 16 hours..

During the daytime every five or so seconds interference in the bandwidth of VHF channel 2 (54-60 MHz) was noted on an analog television. Interference was also noted on a frequency on 1.210 Mhz on a very sensitive AM radio.

The hotplate was the source of the interference because the interference on the am radio coincided with a clicking noise the hot plate makes. This clicking noise is correlated with the start of heating when the hot plate is turned on.

fx-991ex - 8-2-2024 at 15:38

Quote: Originally posted by 6dthjd1  
This used hot plate was working near the high setting for a few hours last night until it was turned down from hi to setting of 8. Sometime during the night it broke and stayed broke for about 16 hours..

During the daytime every five or so seconds interference in the bandwidth of VHF channel 2 (54-60 MHz) was noted on an analog television. Interference was also noted on a frequency on 1.210 Mhz on a very sensitive AM radio.

The hotplate was the source of the interference because the interference on the am radio coincided with a clicking noise the hot plate makes. This clicking noise is correlated with the start of heating when the hot plate is turned on.


Its hard to tell without make/model, schematic and picture, is it a relay controlled model or triac?

From the description the clicking and the interference could be from the relay switching.
Sound like the heating element is shorted or open.

Best way to find out is to open and take some measurement.

Measure the heating element resistance(unplugged of course!) and check that the heating element is getting power(be careful with live line voltage!).


Usually the resistance of the heating element should be equal to the square of voltage divided by the wattage.

ie 120volt 1440 watt
120*120/1440=10 ohm.

[Edited on 8-2-2024 by fx-991ex]

Sulaiman - 8-2-2024 at 22:10

My first guess is that the 'temperature' controller contacts are burned/pitted/piled/fucked,
A new one should be quite cheap and easy to replace.
How to test?
Unplug,
open,
short circuit the two wires to the temperature controller,
Power up.
The mantle element will immediately be at full power.
If this works it proves that it's just the controller.
If so then some choices are;
1) repair the controller - my repairs usually work - for a while.
2) buy a new controller
2.1) an original from the mantle manufacturer
2.2) a compatible/oem unit from online sites
2.3) IF you intend to do fine fractional distillation
AND you feel comfortable with a mains wiring
Then I recommend replacing the on/off bi-metallic controller with an electronic 'dimmer' module.

Loptr - 9-2-2024 at 11:33

With the interference it sounds like it might be on the high voltage side. I would check for any signs of burns or physical damage to components from a visual inspection.

The click might be from a relay, however, I would expect it to use a solid state relay, and clicking is usually from a mechanical relay.

It would help if you would open it up and post pictures.

Personally, I think its going to be somewhere in the relay circuit.

khlor - 10-2-2024 at 06:51

Any PWM(Pulse Width Modulation ) stuff burned or SMPS(Switched Mode Power Supply )?

6dthjd1 - 24-6-2024 at 22:16

Quote: Originally posted by khlor  
Any PWM(Pulse Width Modulation ) stuff burned or SMPS(Switched Mode Power Supply )?
I'd say no because there wasn't broadband hash on am broadcast radio

Sulaiman - 24-6-2024 at 23:59

Analysing harmonics of rfi could lead to a diagnosis,
but it's much easier if you just open it up and test stuff.

Rainwater - 25-6-2024 at 18:10

Quote: Originally posted by 6dthjd1  

During the daytime every five or so seconds interference in the bandwidth of VHF channel 2 (54-60 MHz) was noted on an analog television. Interference was also noted on a frequency on 1.210 Mhz on a very sensitive AM radio.

Thats called switching noise, or square wave harmonics. Its actually a good sign that your devices control circuits are working. Tho your measurment of the signal is rather questionable.
Assuming the frequency range is accurate that would put your switching speed around 16.6ns~18.5ns. These could also be 3rd or 5th order harmonics. So a minimum switching speed of 83ns. For this type of device this sounds right.
You can eliminate both mechanical relays, solid state relays, and triacs. As those switch in the range of ms, and we are 2 orders of magnitude above that.
So a mosfet transistor is sounding about right. High current, medium switching speed, likly a 5-14v gate threshold voltage, most likly with an overcurrent circuit disabling the device because of a short circuit.

Now i want to see some pictures of the layout and boards.
Your am radio signal can masure the power output, but not the frequency. For that you need an fm modulation(where signal power is meaningless). You will hear tye am noise on almost all frequencies. Just get a AAA and short it out repeatly for an example.

6dthjd1 - 30-6-2024 at 06:03

Quote: Originally posted by Rainwater  
Quote: Originally posted by 6dthjd1  

During the daytime every five or so seconds interference in the bandwidth of VHF channel 2 (54-60 MHz) was noted on an analog television. Interference was also noted on a frequency on 1.210 Mhz on a very sensitive AM radio.

Thats called switching noise, or square wave harmonics. Its actually a good sign that your devices control circuits are working. Tho your measurment of the signal is rather questionable.
Assuming the frequency range is accurate that would put your switching speed around 16.6ns~18.5ns. These could also be 3rd or 5th order harmonics. So a minimum switching speed of 83ns. For this type of device this sounds right.
You can eliminate both mechanical relays, solid state relays, and triacs. As those switch in the range of ms, and we are 2 orders of magnitude above that.
So a mosfet transistor is sounding about right. High current, medium switching speed, likly a 5-14v gate threshold voltage, most likly with an overcurrent circuit disabling the device because of a short circuit.

Now i want to see some pictures of the layout and boards.
Your am radio signal can masure the power output, but not the frequency. For that you need an fm modulation(where signal power is meaningless). You will hear tye am noise on almost all frequencies. Just get a AAA and short it out repeatly for an example.

'
'
'Hi
'
'What math did you use to derive switching speed from frequency?

fx-991ex - 30-6-2024 at 07:55

Quote: Originally posted by 6dthjd1  

'Hi
'
'What math did you use to derive switching speed from frequency?


frequency = 1/speed
and speed = 1/frequency

ie
60hz = 1/60=0.016666.. S(16.666...ms)
16ms = 1/0.01666... = 60Hz

[Edited on 30-6-2024 by fx-991ex]

Rainwater - 30-6-2024 at 09:56

The interference on the tv was caused by unwanted EMI. Which is determined solely by a transistors(really any circuits) rise and fall time.
The once every 5 seconds implies an operating frequency of .2hz but the device itself can switch much faster.
Its gonna be a bad heating element. Nice long coil of conductors with lots of inductive reactance getting smashed by a dc pulse strong enough to release an emp wave. No other circuit on tye hotplate will have that much potental power.
If the heating element was fine tuned to a reasonable resonance frequency(swapped out for an antenna) , and assuming the hotplate has about 300W of heating power. A signal like that could be detected for a a few hundred miles

Sulaiman - 30-6-2024 at 11:14

The spiral heating element could also form a spark-gap transmitter,
If there is a spark somewhere (switch or relay contacts, a break in the heating element etc.)