arriflex wrote:Ed, if you had to pick two voltages to run your heating elements at, what would they be?
Your dreamroast is a great model to follow, I have acquired an 1800 watt convective fan and element assembly out of a residential oven that I hope to have two heat settings on. Assuming high is at line voltage, the real question is how much below line voltage to go for when you find yourself turning down the Variac or do you believe the Variac is a necessary tool to adjust the voltage in a more analog fashion?
I don't think you'd be happy with just 2 settings. I have been using a variac from the beginning but what Randy is talking about should certainly be considered as an alternative to a variac.
You should also realize that added wattage may not mean you can roast larger batches unless the heat transfer abilities of your roaster can utilize it without your MET (maximum environmental temp. hitting the beans) becoming too high. This will correlate with the size of your roast chamber, agitation, convection, wattage, batch size, etc.
Are you still liking the tc4 configuration? I am anticipating using a similar TC configuration to yours, any advice is welcome.
It works great for me! I work with JimG and Bill and they created exactly what I was looking for. Though again what Randy speaks of sounds like a really neat and similar option if one is starting from scratch.
OffTopic:
Regarding agitation, would you recommend a flat or curved bottom pan? Thick or thin? Are you still happy with the 200 to 300 rpm I think I remember reading somewhere?
The concept of my roaster is a bit different from a SC/TO. A SC/TO stirs the beans that lay on the bottom of the Stir Crazy. The stir mechanism must churn the beans/bean mass to allow exposure to the heat source and do it evenly to each bean. Efficiency is limited by the beans being massed where convection is unable to easily reach the bean surfaces consistently. My design lifts the beans and whirls them around elevated around the sides of the pot at a higher speed. The higher speed increases convection and increases the churning of the beans. This increases the exposure to heat and heat transfer ability and the higher speed increases the replenishment of heat(increased convection).
The concept of my design is similar to the large high tech, industrial roasters such as the
Probat Saturn Series. I like my design better than the Saturn because my heat out of the TO top flows down the sides an d up the middle where the Saturn works the other way. In the Saturn the heat is concentrated in a smaller flow that's deflected with the cone at the bottom with more risk of high MET exposure and reduced efficiency.
For my design around 200-220rpm creates the best splay of beans and heat transfer. I uses a speed control motor with the appropriate gearhead ratio made by Oriental Motor. In a typical drum roaster rpms are limited by centrifugal force that eventually just glues the beans to the drum walls. This is why the
Loring drum roaster was created with a fixed horizontal drum and moving paddles that allow higher speed agitation and increased convection.
The shape of the pot is important for the bean mass pattern achieved by the bean bats. The bats whirl around striking the beans as gravity drops them down to the bottom. If the sides are sloped the beans will be batted to the slope and fly too far up to the top. I chose a square bottom that allowed an even splay along the sides without shooting up to the top.
I went with a thin walled pot so as to not hold too much heat when I need to slow the roast around 1st crack. The insulation keeps from losing too much heat or having a cooling pot surface when my room temp. might be low.
Roaster design and dynamics are quite complicated. This is what makes some commercial roasters better than others. Off the shelf home roasters tend to be simple to keep cost down. For example, I saw the fins to be lacking in a hottop limiting efficiency. When users improved the fin size and arrangement the efficiency and roasting evenness improved.
It took me alot of thinking about what is happening in the roaster and to the beans and adjusting everything from trial and error to find the sweet spots.
hope this helps get a start,
farm
PS I'm thinking it might be useful to have a thread on "roaster dynamics" with group contributions. This would help for those thinking of designing/building a roaster or modifying an off the shelf roaster.
by farmroast on Sun Apr 03, 2011 10:15 am 
