Jim, no I have not wrapped the drum with insulator yet. Mine is a 220V so the power rating may be a bit different but performance should be similar to the 110V version. With less heat loss, I assumed it would be similar to the effect of increasing the power of the heater. Any views?

Jammin, believe it or not, the "standard" straight line ramp is not easy to achieve due to the varying endothermic/exothermic behavior of beans during the roast. I couldn't make the BT line straight every time but was just showing those successful cases here. To make the BT ramp straight, I need to predict the timing when the endothermic behavior will occur, and to match it with the delayed heat up behavior of the drum/hot air. Vice versa is also needed before the exothermic moment of the beans or temperature would go up too fast.

I was curious because you are getting fast roasts with relatively low ETs. The ROR(BT) is going to proportional to (ET-BT), and insulation will increase the ROR(BT) for a given ET-BT. It could be that the 220 volt version has more air and heat, or it could be that you are measuring the ET at a different spot from me.

Jim, from your previous posts I learnt that you had spent some effort to locate a good ET position for probe installation. Mine was just the default location which came with the machine. I think the default position is good for measuring purely the air temperature that was flowing into the drum. However, it did not reflect much of the drum temperature. For drum temperature, I'm currently settled with using the power reading (A) of the heater as a clue. After all, I am only concerned about the BT (MET could not be too high since the ET was always below 230'C and I had never see scorching so far). The "ET" reading in my M3 only gives a clue as to how the Delta-BT was going to react to my changes of inputs.

The port they provide is obviously the best place to read it (I installed mine before they made this change). I was just envious of your fast roasts at low ETs, since that speaks to an efficient roaster. Perhaps the newer models have been improved compared to mine.

another_jim wrote:It could be that the 220 volt version has more air and heat

More heat - I don't know, it goes up to 5A with 220V. More air - probably not, as 220V most often means 50hz instead of 60hz, so the drum motor and fan motor turn ~17% slower with 220V/50hz, which is slightly annoying as the drum could really be turning a bit faster for me.

another_jim wrote:Perhaps the newer models have been improved compared to mine.

I believe the only change is the thinner drum.

--
Lukas

farmroast wrote:Wouldn't the thinner drum transfer heat more quickly? The advantage of the thicker drum being more even heating and a little more stored energy for say the drop-in turnaround.

I'm not a physicist, but as far as I know stainless steel is a rather poor heat conductor, but still good in retaining the heat. In relation to drum size, this could simply mean that a thicker drum is actually more prone to scorching the beans than a thinner one:

For the same mass of beans, the 2.5mm drum of the older quest has nearly double the heat capacity than the current 1.5mm drum (if there's a linear correlation). If you heat both drums to, say, 250degC, and then fill in cold greens, the thicker drum would take longer to cool down to a non-scorching temperature while at the same time transfer more heat to the beans than the thinner one, thus more risk of scorching. It doesn't magically distribute the heat more evenly or some such, because both drums are turning constantly and there'll probably be no hot spots on them anyway (other than the front being hotter than the back side).

I hope I'm not totally off on this one, any phyisicist on here?

Edit: some numbers on this from random internet sources for copper and stainless steel:
Heat conductivity:
copper: 400 W/m*K
stainless steel: 16 W/m*K

Heat capacity:
copper: 385 J per Kg per Kelvin
stainless steel: 510 J per Kg per Kelvin