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HotTop wrong temperature (momentary switch)
Rallen
Hey there.

I have bought a broken HotTop KN-8828P that I am repairing and modding at the moment. I received my new main circuit board today, which seems to make everything work!!

I have faced another problem now, though..

When having the roaster disassembled, I decided to add a momentary switch to the temperature sensor as described in this post: http://forum.home...post_40018. As described on the homeroasters thread, the purpose is to be able to disable the temperature sensor for a moment, thus being able to do back to back roasts. I know it isnt the best thing for the machine, but I'll prefer changing the heating element a bit more often, instead having to wait 20 minutes between roasts.

After assembling the roaster again and testing it of, it became clear that the temperature sensor is now somewhat confused. It does somehow work, since it measures a temperature when im not hitting the switch and instantly drops to 0*C when I hit the switch. So far, so good.

The temperature that it reads is not good, though. After turning on the roaster, I preheated about a minute or so. Doing that time I could feel the roaster become very hot, but the temperature didn't change more than a degree or three (from 25C to around 28C). After hitting eject, cooling for half a minute and turning it on again, it suddenly showed 58 degrees. Thats about how it works every time I run it - it drops when cooling and raises when heating, but no where near fast enough to show the real temperatures though.

I am thinking there might be too much resistance in the switch, which is making it unstable.. On the other hand, I dont think it sounds reasonable that there should enough resistance in a small (normal) switch that it actually matters..

Any thoughts?

Thanks already!
 
ginny
sounds like perhaps you should have not changed the switch before testing.

can't you go back and undo that?

ginny
 
Barrie
The other aspect that interests me is the question of which component is at risk with back-to-back roasts? I had thought that excess heating of the motor was an issue?
Barrie (San Diego, CA)
"So much to learn, so little time."
Hottop 2K+., Artisan, Jura Capresso ENA 3 (i.e. espresso).
 
smico
This is normally-closed switch that disconnects the circuit when pressed.
1. Check if you have thee pole switch and mixed up connections.
2. Shortcut the switch and see if everything is back to normal. If everything works, replace the switch.

Back to back roasts should have no impact on the life expectancy of your heater.

Let us know if you fixed the problem. You will need to do few more mods in order to roast back-to-back, but let's do this step by step.

Regards

Miroslav
Hottop B2 + HTC, Cremina 83, OE Pharos, Brewtus IIIR, Baratza Vario
 
Rallen
Thanks for all your answers!

Quote

1. Check if you have thee pole switch and mixed up connections.


What do you mean by this? Is it possible that the connection should go the other way through the switch? - I have tried switching the cables between the two poles on the sensor without result, but I might try turning the switch aswell..

I will also try to remove the switch and shortcircuit the wires to bypass it, as you recommends. If it still doesn't work, I guess I will have to replace the sensor?

I actually thought this switch was enough to be able to do back-to-backs. Can you reveal what more I have to do at a late stage? Ofc, I will get this part working first..

Can you
 
snwcmpr
The temperature the HT reads is a combination of environment temperature (ET) and roaster wall until the beans expand. Then it is a combination of bean temperature (BMT) and roaster wall. I don't believe the roaster wall will change as rapidly as the ET.
Could that be what leads you to believe the temp is not right?

Ken in NC
--------------
Backwoods Roaster
"I wish I could taste as well as I wish I could roast."

As Abraham Lincoln said "Do not trust everything you read on the internet".
 
Rallen

Quote

snwcmpr wrote:

The temperature the HT reads is a combination of environment temperature (ET) and roaster wall until the beans expand. Then it is a combination of bean temperature (BMT) and roaster wall. I don't believe the roaster wall will change as rapidly as the ET.
Could that be what leads you to believe the temp is not right?

Ken in NC


Hmm. Maybe.. Only thing I know for sure is that it doesnt change very much during more than a minute of preheat, though I could feel the machine getting burning hot. I didn't have the nerve to see what happens if I let it preheat for more than a minute, since the fan isnt turning during preheating, and I was afraid of everything getting too hot.

How long should it normally preheat? And what makes it stop?
 
Rallen
I've now tried again, while shortcutting the momentary switch. The result is exactly the same as earlier. A temperature starting on 23C, not rising for about a minute when the machine is getting very hot, then changing to 24C during the 30 seconds cooling period.

Is it safe to assume that the temperature sensor is dead, or am I just being too afraid of letting the machine run long enough to actually get hot?
 
Randy G
The "add beans" signal is at around 165F. (74C.). I usually add beans at between 250-300 (120-148C.) depending on what coffee I am roasting and how the coffee will be used (and how the mood hits me). At the low end of the sensor's range they do take some time to respond if they have been cooled or are starting out cold. ]

And as mentioned previously, the component that will suffer the most from insufficient cooling is likely the main motor. Specifically, the reduction gear box which is not available separately from the motor.

You can thread a K thermocouple wire into the roaster or do this:
http://www.frcndigital.com/coffee/HowToHottopTemp.html

Life's too short to drink bad coffee.
 
Rallen
Thanks for the input!

I am starting to think that I should maybe try a last time, while giving the roaster more than a minutes time to preheat. I am still very afraid of the machine overheating if the sensor really is broken.

How long would it be safe to let it run in order to test if the temperature starts rising at some point?
 
Randy G
The "B" board has automatic safety points that will signal you. I suggest that you go to http://www.hottopusa.com and download the owners manual.

Life's too short to drink bad coffee.
 
smico
Rallen,
If you have doubts about the sensor, you can stick barbique termometer in if you have it handy.

Other mods that I was talking about would insure that your components are cool enough to start the new roast and avoid temperature build up and certain distruction of your roaster. I can describe them again over the weekend, but if you go through Ciel's enhancement series you will get it for sure.

But first mod should be bean temperature (and ET) monitoring. Randy's legendary mod is a good start.
Hottop B2 + HTC, Cremina 83, OE Pharos, Brewtus IIIR, Baratza Vario
 
smico
Rallen,
Any news or clues or solutions?
Thanks,
Miroslav
Hottop B2 + HTC, Cremina 83, OE Pharos, Brewtus IIIR, Baratza Vario
 
ginny

Quote

Thanks for the input!

I am starting to think that I should maybe try a last time, while giving the roaster more than a minutes time to preheat. I am still very afraid of the machine overheating if the sensor really is broken.

How long would it be safe to let it run in order to test if the temperature starts rising at some point?


did you make a decision here or find the issue?

-g

we would like to know.
 
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