# HotTop B2-K RCD trip problem



## nirgal

I have a problem with my HOTTOP KN-8828B-2K. I've been using the roaster for seven months now and it's 38 roasts old.

I always roast 250g batches. And then during the 28th roast, somewhere between 200-210 degrees Celsius the RCD in my shed tripped (this is where I roast coffee).

I could not switch it back on while the machine was physically connected to a socket. I had to wait several minutes before I could turn it on again and dispose half-burned batch into cooling tray. Same story happened during the following roast few days later.

My first thought was that it was heat related issue so I decided to replace the back filter to improve airflow. I washed the old filter before in a coffee machine cleaner solution after 12 roasts before.

Having new filter installed I could enjoy another 6 roast from the beginning to the end.

Then the 36th roast was unsuccessful again - the RCD has tripped in similar temperature range as before (200-210 degrees Celsius).

This time I decided to align the heating element because it was too close to the wall of the roasting chamber. It was nearly touching it looking from the front side of the roaster. It was aligned like that from the very beginning so I didn't alter the factory alignment for quite a long time.

37th roast. I finished roasting just after the first crack. The temperature was 210 degrees Celsius when I disposed the beans to the cooling tray.

I was happy that there was no RCD trip this time and then during the cooling phase it tripped! My first thougt was - it is not heating element failure because it was off during cooling phase.

38th roast. I decided to warm up the shed before roasting. It was 5 degrees Celsius inside and quite high level of moisture. I warmed up the air to about 18 degrees. Moisture level dropped to about 60%. RCD has tripped during the first crack...

I keep my HotTop in my house in dry and warm environment. I take it out to my shed only for roasting. I have no idea what is wrong. Can anybody help me?


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## Thecatlinux

RCD trip due to 'earth leakage'

by the sounds of it something is expanding and shorting out on the chassis due to heat,

the logic behind this thought is that the problem only seems to appear when the machine is hot

where is the RCD located .


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## nirgal

I have exactly the same thoughts although I didn't write explicitly before. The more precise question is - how to find the leak point while the roaster is not operating? Anybody else experienced something similar with HotTop roasters? Where the leak spot is possibly located?


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## MrShades

Have you taken the drum out and had a good look inside? The element may have distorted and it could be touching the case when getting hot... just a thought.

I've seen hottop elements that have even heavily used and they can distort aignificantly. You can buy replacement elements as spare parts.


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## DavecUK

Probably heating element.....


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## nirgal

DavecUK said:


> Probably heating element.....


How to explain that there was one roast where the RCD has tripped while the roaster was in cooling mode (heating was set to 0)?


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## grumpydaddy

Step back a moment and think about which components are ON at the various stages of the roast.

My guess, not knowing anything about the machine is that there are 3 maybe 4 to consider

1. heater

2. drum motor

3. fan

4. thermostat

cross off the heater for now as it happened in the cooling phase when the heater was not on. It is not a dead cert to be good however

think about the airflow. if the fan blows air into the heater there is less chance it is breaking down under heat load than if it extracts hot air

Where does the drum motor sit ?? in a very hot part of the roaster ?? If not then that lowers the chance of it being the culprit. Is it possible to further heat shield the motor?

The thermostat has to sit in the high temperatures so it or its associated wiring would be my first choice of likely candidate. Perhaps you could ensure it is not itself earthed and then test again?

Like I said, I know nothing of these machines but maybe this can point you in the right direction


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## nirgal

Thank you for your suggestions. The fan is placed in the back of the roaster and it extracts the air from the drum placed in the front part. The drum motor is in the middle. I'll have a closer look on the motor in the coming days.

The hot air passes the motor on the left side of the motor visible on the picture below:

https://www.hottopusa.com/top2/top2-2.jpg


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## nirgal

Quick question? How does dirty thermocouple behave? Does it show lower voltage than it should or higher?

The roaster automatically dumps the beans into cooling tray at temperature 220C unless I decide to do it earlier. If the reading is too low then the actual temperature in the drum could be higher. This could be the cause of overheating and ultimately current leakage. Am I wrong or right?


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## Thecatlinux

The most likely cause is a phase or neutral conductor touching the chassis when hot.

( expanding metal )

the thermocouple is likely for temperature control and most likely of the sealed cappilarory type so dirt will have no influence


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## Thecatlinux

Thecatlinux said:


> The most likely cause is a phase or neutral conductor touching the chassis when hot.
> 
> ( expanding metal )
> 
> the thermocouple is likely for temperature control and most likely of the sealed cappilarory type so dirt will have no influence


is there a permant source of electricity in the shed or you trailing a lead to the house

picture of RCD would be helpful


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## nirgal

Thecatlinux said:


> is there a permant source of electricity in the shed or you trailing a lead to the house


There is a permanent source of electricity. There is a ceiling light and two wall sockets. The installation in the shed has its own fuse set including an RCD. My washing machine uses one of these sockets daily but never at roasting time.

UPDATE: Yesterday I connected the machine to a wall socket in my house and the RCD in the house tripped immediately before I even touched the ON button on the control panel.

Then I unplugged all the wires responsible for electrical elements mentioned on the picture in the lower left corner

https://www.hottopusa.com/base2/base2-1.jpg

I connected the roaster to mains again and this time it was ok. Then I figured out that RCD trips when the eject solenoid is connected to the board.

Today I am going to roast another batch of coffee with the eject solenoid unplugged. I can dump roasted beans into cooling tray manually with an eject knob.

For now I do not know why the RCD trips as soon as mains plug is plugged in a socket (unless I unplug the solenoid). It used to trip in the late stage of roasting. It means that things got worse. I do not understand how the solenoid affects the behavior of the machine if anyway it is supposed to be in off state when I start the roaster.


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