another_jim wrote:Hi Rafael,

I'm not sure if this means the response on bean temperature is too slow for PID control. I was seeing lags of about 45 seconds and 2 minutes for a full response to pulses on the heat or fan during my dry runs This makes a ramp control a bit dicey. You might consider PIDing the MET at roughly the point where I'm measuring it. The response there is only 15 seconds lag, and one minute to a full response.

Hi Jim.

I can also run the roaster in manual mode as in the original configuration. And I don't always use the PID to control the roaster, maybe some phases. Sometimes I use the PID to get a solid drop temperature and then I turn the switch and go manual mode. I am still in the early stages of learning.

Yes, with the PID there is some lags but I can always go manual and then switch back jeje.

I was doing some Yemen beans (300 grams) and 4.5A was not enough do a smooth landing (the airplane goes down fast jeje). In my experience, when the roaster is 'heavy,' a little bit more power is needed at the end to get the same results as when it is light (200 grams).

Regards

I've been reading a lot of blogs and articles on people using Probats and San Franciscans, both solid drum roasters with ventilation. Roasters seem to split evenly whether to profile by varying the air or varying the heat. So today, I did a roast varying just the air.

My goal was to hold the MET between 250C and 260C (490F to 510F) throughout. I started at the 375C drop in, 7.75 amp and 4.5 air setting recommended for 225 gram roasts. This turned out to hold the MET very nicely at the target without requiring any changes. After the second crack started, the MEYT started to climb, and I had to slowly run the airflow up to 7.5 to keep it steady. This produced a 5 minute roast finish, and an overall roast of 17 minutes. In any case, using air to hold the MET steady is a simple and effective profiling strategy.

Very cool Jim. I started basing my profiles on power alone and this idea opened back new possibilities. I guess the airflow control gives faster response for cooling down if needed to. In my case, with the added insulation, this is good to keep in mind. I tried to use the fan for heating up (turning fan down) but that is not a good idea because of moisture condensation. I even saw water drops forming. So this idea of using the fan is good because the roaster reacts faster to control.

Cheers

In the M3 does more air flow always reduce the temperature of the beans?

Regards, Henry

I'm pretty sure control can also be done with constant airflow and varying the power too. At least this is what all the blogs and articles about this style of roaster say -- they just vehemently disagree which is better.

The key for me has been getting an accurate read on the environmental temperature, since this responds much faster than bean temperature to either heat or air changes. Holding it constant, like I did on this roast, is probably not the best profile, but it is the simplest.

After I get back from Thanksgiving, I'm going to run the same constant 260C environmental, but start with a higher drop in to see if I can speed the roast to around 12 to 14 minutes.

hbuchtel wrote:In the M3 does more air flow always reduce the heat transfer to the beans?

That's a very good question. I don't know the answer.

I was using airflow to hold the MET (T2 on the graph) constant at 250C to 260C. For this, more air lowers the temperature.

But more air also increases convection heating of the beans, which counteracts the lower temperature. It could be one could get a faster roast at the same MET using a combination of both higher amperage and higher airflow. This will depend on how much heat the forced air flow transports to the beans. This I don't know. Orwa or Rafael may have worked it out; but if they have, they are keeping it secret.

Actually, I'm posting this stuff more or less half baked (or half roasted) ...

The reason I'm doing this is because I anticipate going in three steps and taking about a year to get expert with the roaster. Right now, I'm not even trying to profile the bean temperature; I'm just figuring out and controlling the basic thermal properties of the roaster -- air flow, power, environmental and drum temperatures. I keep reading about all the heroic struggles drum roasters go through trying to profile, and I think it's difficult because drum thermodynamics are not nearly as obvious as air roaster's. So it's key to do the basic science stuff to make profiling less painful. I can't really start doing taste comparisons and deciding what profiles are best until I've done all that.

Since all this will take a lot of time, I want to post the basic control info as it comes in.

another_jim wrote:I started at the 375C drop in,

Jim, Did you mean 375F here?

another_jim wrote:I'm not even trying to profile the bean temperature; I'm just figuring out and controlling the basic thermal properties of the roaster -- air flow, power, environmental and drum temperatures.

Jim, air movement complicates things for these small drum roasters. Go ahead, follow the KISS principle, and try keeping the fan on OFF for your experiments; at least initially.

One more thing, you're another_jim, so I can't give you tips , but if I could, I'd suggest that when you start profiling, do it with minimal fan, if any at all.....but you're going to figure that out yourself anyway.

And, what's with the 225g!? I mean, if you're trying to understand this baby, why not experiment with the load she will eventually be profiling, like, em, 150g!

Have fun, we all are; it's nice to have another_jim join the home drum roasting club .

Hi Eric, I meant 175C (350F) drop in -- The roaster comes with a centigrade thermometer, so I've decided to do my logging in metric; but my brain doesn't always follow.

Hi Max, I'm pretty cluelss with drum roasters, but the problem with airflows below about 3.5 (roughly 40% of max) is that the smoke starts leaking out of the front, and the chaff falls into the oven. My next project will be to answer Henry's question -- do higher power and high ventilation versus lower power and low ventilation roasts, all at the same charge weight, drop in, and MET, and see how the roast times respond.

BTW, I've done roasts from 100 to 250 grams; there's enough power to do all these weights to the 2nd crack in under 15 minutes. No word on quality yet.

Instead of insulation, I'm also wondering about a Franklin stove like case around the side and back, so the air is drawn in through this case, and heated by the roaster before it goes into the port hole in the rear. That should make the roaster both faster and more efficient.

Oh, dear, this is all so tempting. Especially since this roaster looks so compact