Posted Wed May 20, 2009, 9:25pm Subject: Hottop Temperature Monitoring
I'm thinking about getting the Hottop programmable model, but I'm reading about how the temperature readings aren't very accurate unless you put a probe in the bean mass. So I've got some questions:
are the temps the Hottop sensor reports linear with the bean mass probe? That is, could you safely say "the hottop claims its 400F, given the constant 20F discrepancy, its really 420F"? Or does it fluctuate inconsistently across the temp ranges you'd care about?
why get a programmable model if you're programming it against inaccurate readings? (if its linearly off, I'm guessing you can just compensate for that- but if that were the case then I suspect there wouldn't be so many modders :))
Do you really need to the additional bean mass probe once you 'calibrate' the machine, say, for a particular bean and total weight?
Coffeerick Senior Member Joined: 5 Apr 2007 Posts: 45 Location: Harrisburg Expertise: I love coffee
Espresso: ViValdi II Grinder: Rocky Roaster: HotTop
Posted Thu May 21, 2009, 7:06pm Subject: Re: Hottop Temperature Monitoring
rama Said:
I'm thinking about getting the Hottop programmable model, but I'm reading about how the temperature readings aren't very accurate unless you put a probe in the bean mass. So I've got some questions:
are the temps the Hottop sensor reports linear with the bean mass probe? That is, could you safely say "the hottop claims its 400F, given the constant 20F discrepancy, its really 420F"? Or does it fluctuate inconsistently across the temp ranges you'd care about?
Nope. The HT sensor is best described as "slow" since it is really reading the temperature of the back wall rather than the beans. Since you drop the cold beans into a hot drum, HT starts out much hotter than the beans. The beans are playing catch-up until about 360F, when they overlap. Then the bean temperature will pass the HT temp but it is variable depending on the bean and how much you slow down the roast between cracks. I run a much smaller load of beans than most people and my BT at completion will be around 440 with the HT reading about 410. But it could read as high as 420 or as low as 405 depending on the profile, load size, bean type, etc. In other words, it is pretty useless unless you are doing the exact same roast. It will also vary depending on whether the roaster was already warm from a prior roast or stone cold from sitting all night.
why get a programmable model if you're programming it against inaccurate readings? (if its linearly off, I'm guessing you can just compensate for that- but if that were the case then I suspect there wouldn't be so many modders :))
I have a "P" and you have hit on some of the fundamental issues. An even more serious limitation is that the heater control is either full on or full off. This, combined with the thermal lag of the sensor, means that if your program hits one of the programmed temperature points the heater will turn completely off. But the HT sensor will continue to rise for the next 45 sec as it catches up with the bean temp. And the heater is not going to turn back on until it reaches the next program segment since it would take about 1.5 min of coasting before the HT sensor would show the beans cooling. This is the perfect recipe for a stalled roast. The "B" model has power adjustment which lets you dial back the heaters to slow things down without shutting anything off. It is a much better solution. I finally broke down and modded my "P" with a dimmer control that lets me do the same thing and the difference is amazing. The only other way to slow down the later stages of a roast in a "P" is to continuously adjust the temperature up and down to cycle the heater manually. It is a pain and you need a bean probe and a current monitor (so you can tell if you are on or off). Get the "B".
Do you really need to the additional bean mass probe once you 'calibrate' the machine, say, for a particular bean and total weight?
If you are happy with what you get, the repeatability is not too bad. But if you have any intention of learning and improving your abilities you will need to see bean temp. I found that some beans virtually run away during first crack with as much as 15° more temp rise than others yet there is no indication from the HT sensor. Without BT you are roasting blind. But the HT is a good basic roaster, everything can be replaced/repaired. I have over 1000 batches through mine. And it has all the key elements to do great roasts. It just needs some help from you.
Posted Thu May 21, 2009, 7:19pm Subject: Re: Hottop Temperature Monitoring
Thanks, helpful information. I really didn't want to stay in the business of temperature surfing (coming from a Poppery), nor do I really want to spend that much on a machine that *needs* mods just to work well.
The programmable functions do appeal to me however. Would it be possible to splice a bean mass probe in place of the HT sensor, so the control panel reads correctly without the need for external bits like a multimeter, dimmer, etc? Dunno if thermocouple outputs are universal/interchangeable.
Coffeerick Senior Member Joined: 5 Apr 2007 Posts: 45 Location: Harrisburg Expertise: I love coffee
Espresso: ViValdi II Grinder: Rocky Roaster: HotTop
Posted Fri May 22, 2009, 5:45am Subject: Re: Hottop Temperature Monitoring
I wouldn't tackle that mod. I think the HT sensor is a temperature sensitive resistor (thermistor or varistor) rather than a thermocouple. The interface to these would be completely different than a TC and specific to the application. It would probably be easier and more effective to completely replace the HT controller with a PID system, but that is more than I care to undertake.
rama Said:
Thanks, helpful information. I really didn't want to stay in the business of temperature surfing (coming from a Poppery), nor do I really want to spend that much on a machine that *needs* mods just to work well.
The programmable functions do appeal to me however. Would it be possible to splice a bean mass probe in place of the HT sensor, so the control panel reads correctly without the need for external bits like a multimeter, dimmer, etc? Dunno if thermocouple outputs are universal/interchangeable.
Posted Wed May 27, 2009, 7:56pm Subject: Re: Hottop Temperature Monitoring
For the record, I inquired with Hottop USA and Sweet Marias about the inaccuracy of the built in temperature monitoring. Hottop USA couldn't satisfactorily answer that, and Sweet Marias- after some nagging- suggested the Hottop B is indeed superior to the Hottop P (with no details as to why).
I ended up getting a Hottop B (arrives tomorrow). Given all the F.U.D. around what the best roaster is, I'm quite anxious to see if I'm even able to detect a difference between my cheapo Poppery I...
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 1,372 Location: Philadelphia Expertise: I love coffee
Espresso: N.S. Oscar Grinder: Vario, Preciso w/Esatto,... Drip: pour over Roaster: Diedrich IR-1, HT B
Posted Thu May 28, 2009, 4:20am Subject: Re: Hottop Temperature Monitoring
I am glad I went with the B instead of the P. The B gives full adjustment of heat control at any given time in the roast where the P is a profile you create and save and the heat can't be changed during roast. The B allows 3 saved profiles so I keep them stored with different heat profiles for hard, medium, and soft beans.
I have a problem with my stock temp sensor no longer giving me accurate readings, up till this sensor went bad I was happy with the readings it gave. However I am adding a thermal coupler for bean mass temp when I replace the stock sensor for more data. Hottop was unclear why my sensor went bad, it stopped being accurate after a deep scrubbing but they had never heard of this being a problem before, $15 to get a new one.
I consider it the best roaster since I can order and replace every part on the unit down to the screws, my research before buying made this a clear winner over the gene cafe for this reason.
I think you will notice a significant difference in your roasts, hot air roasters taste different then drum roasters.
Posted Thu May 28, 2009, 5:17am Subject: Re: Hottop Temperature Monitoring
germantownrob Said:
I am glad I went with the B instead of the P. The B gives full adjustment of heat control at any given time in the roast where the P is a profile you create and save and the heat can't be changed during roast. The B allows 3 saved profiles so I keep them stored with different heat profiles for hard, medium, and soft beans.
While I do prefer the control of the B panel over the P it is not true that you can't adjust the heat during a roast with the P. You can use the Advanced Manual Control explained on pg 32 of the B/P manual to lower the heat & extend the roast time between 1C & 2C.
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 1,372 Location: Philadelphia Expertise: I love coffee
Espresso: N.S. Oscar Grinder: Vario, Preciso w/Esatto,... Drip: pour over Roaster: Diedrich IR-1, HT B
Posted Thu May 28, 2009, 9:38am Subject: Re: Hottop Temperature Monitoring
JVBorella Said:
While I do prefer the control of the B panel over the P it is not true that you can't adjust the heat during a roast with the P. You can use the Advanced Manual Control explained on pg 32 of the B/P manual to lower the heat & extend the roast time between 1C & 2C.
I went and read that in the manual and it sparked the memory of being told this when I was making my decision, my eyes didn't glaze over as much this time. LOL. You spurred me on to finish reading about the P, I like the fact that I can just swap out the face plate and upgrade.
When you do this advance manual control does the power shut off completely? The B heating element can turned down in 10% increments and I never tried taking the power to 0 after 1C.
Coffeerick Senior Member Joined: 5 Apr 2007 Posts: 45 Location: Harrisburg Expertise: I love coffee
Espresso: ViValdi II Grinder: Rocky Roaster: HotTop
Posted Thu May 28, 2009, 12:46pm Subject: Re: Hottop Temperature Monitoring
germantownrob Said:
When you do this advance manual control does the power shut off completely? The B heating element can turned down in 10% increments and I never tried taking the power to 0 after 1C.
Yes, that is the real problem with the P. Unless you cycle the heater on and off in short cycles you end up with a major swings in the environment temperature going from too hot to cool. I used this technique (with a bean temp probe and current monitor for guidance) for almost a year and tried to keep my off cycle times to less than 5 seconds to approximate a steady environment. The ability to back down the power with the B or with a dimmer mod on the P really makes a difference, especially in the lighter roasts.
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