March 17, 2018 00:24:17


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View Thread » ALL ABOUT ROASTERS » Other Roasters
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Imex Digirosto 1500 Power teardown and rebuild
I picked up a VERY disused Digirosto 1500 yesterday for a very good price, but wasn't able to test it before taking it home. I took it on faith when the seller told me it had been in service until very recently when it was abandoned by his tenant when they skipped out on their lease. Shame on me for being so trusting.

When I got it home and started tearing it down for inspection, it became clear that it had been out of use for quite a while and it was never properly maintained. It had obviously roasted quite a lot of coffee, but I doubt they ever cleaned it and from sitting idle for what I assume was a couple years the residual sugars from roasting grew an impressive colony of mold. On. Everything.

There's very few resources online for this roaster, even though it was sold pretty widely. I have been able to reach the manufacturer and have inquired about spare parts, but now I have to roll up my sleeves and do the dirty work of cleaning it. My plan is to take the whole thing apart, completely, and scrub it all while checking the component functions along the way. I will give Imex credit, this thing is a pretty marvelous piece of engineering and very well built.

I'm starting this thread to document the work as I go so that others may benefit from my labor of love. I know the work will be worth it, but it's daunting.

I will be away for work the next couple days, and will start updating the thread on Saturday when I get back to work.

If anyone here has ever worked on one of these things, chime in and let me know what your experience has been with it.

perhaps post a picture or two, I don't know what they look like.



just did a google search and there is a lot of talk, older but talk just the same on your roaster.

looks cool...
Hi Sam,

IR roasting can produce some amazingly good coffee. I'm not very knowledgeable about the Digirosto 1500 and it's roasting capability but if it can be used in manual mode you should be able to steer it through typical 5-4-2 profiles and achieve great roasts from it.

Do you know what a typical cooling cycle looks like with this roaster?

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
I'll add some pictures later today, my web host is giving me fits!

It's been a while since I rolled my sleeves up as far as I did this weekend. I ended up tearing the whole thing apart, literally. I decided that if I was going to clean it, I might as well go all in. My fingers were crossed the whole time as I didn't even know if it would work once I put it all back together but late Saturday night I fired it up and did a little fist pump when the drum started spinning and the halogen lamp came on inside.

My model actually has two heating elements: the halogen lamp inside the drum and a 1500W resistive element outside the drum. This means I'm getting both IR and conductive heat into the beans and I'm eager to see how this mix effects the flavor profile of the roasts.

I will share a few observations on the roaster now that I've gone over every square inch of it. First, it's extremely well designed and built. Every part is solidly fastened with tight tolerances, every surface that the coffee touches is heavy gauge stainless steel, every component is overbuilt and the mechanics are extremely well thought out. There are one or two design choices that I may have done differently, such as the auger that moves the beans from the dump door on the rear of the drum into the cooling tray since it tends to drop a handful of beans into the bottom of the machine every time. The electronics are extremely straightforward and user serviceable, and I'm pretty sure it's all run off an Atmel microcontroller which means it's likely I can rewrite the software if I'm feeling ambitious. Either that or I can easily retrofit it with an Arduino and run my own software.

I was able to put about 20lbs through it Sunday and the learning curve was a little steeper than I anticipated. In the end I got about 12lbs of what I think will be great beans after they're rested. This was purely using the Automatic mode just so I could get familiar with the operating principles and heating characteristics of the machine. So far I'm pleased with the results, and running it manually should allow me to really dial in the roasts.

Allenb, to your question the cooling is pretty good using the built in blower and cooling tray. At the end of each roast, the dump door opens on the rear of the drum and the beans are pushed out into an auger, that then deposits them into a perforated stainless tray. Under that tray is an 85cfg blower that pulls outside air down through the beans and exhausts it out the back. The 2-3lb roasts I ran were just barely warm to the touch after 4 minutes, of course that was with an ambient temp around 40 degrees so we'll see how well it cools in the summer.

I'm moving the roaster to its permanent home this week, and then I'll start roasting in higher volume and can report in more detail how it performs. I'm also going to be installing an additional pair of thermocouples to mirror the current ones so I can simultaneously run RoastLogger and track the profiles as I go.
So I've done about 60 roasts with the Digirosto since setting it up, and I thought I'd report my findings.

Bean Cooling - Seems to be a common question/concern and I have to say I've been relatively happy. A FC roast will get cool enough that you can stick your hand into the beans and hold it there within 4 minutes. Ambient temp plays a big part in how quickly it cools, so during the summer I might have to use an external cooler. For folks who are trying to roast a high volume with this machine will probably want to cool externally anyway because it saves the 4-5 minute cooling cycle and it avoids cooling off the drum and waiting for it to reheat each time.

Mechanics - Nearly flawless, with one really annoying exception. The bean dump door at the rear of the drum occasionally gets a bean lodged in it that prevents the door from closing completely. If you don't notice it, when you dump the next batch in the beans start falling out the back. Clearing the stuck bean requires access to the rear of the machine, which would normally be covered with a metal panel. I never put the panel back on when I reassembled it, so I can reach inside and cycle the dump door solenoid by hand a few times.

Heating - This thing takes FOREVER to preheat for the first roast when it's cold. I've had it take as long as 25 min to reach the 230C ET recommended start temp. This is compounded by the fact that the machine seemingly randomly decides that it needs a cleaning cycle, which takes another 25 min. In my 60 roasts I've had to run four cleaning cycles, but none of them were at regular intervals. No idea what that's about, but at least it's keeping the buildup in the drum under control.

Roasting (Auto) - Automatic mode on this machine is excellent, as long as the roast curve that's programmed into the unit is to your liking. Two of my roasts use the auto mode, the other three I run manually. The unit preheats then makes you weigh the beans before dumping them in. It uses the weight to adjust the target temps for each ramp, compensating for the bean mass so it doesn't go too fast or slow. The start temp is always 230C though.

Roasting (Manual) - Gotta have quick fingers to roast in manual on this thing. There's a lot of waiting around to hit a temp, then you furiously have to press lots of buttons to set the next ramp to keep the roast moving. I'm sure with more practice I'll get better at it, but I just always feel rushed. Otherwise it works exactly as you'd expect, which is to say it does exactly what you tell it to do.

Gripes - My only real gripe with the machine is the reversible rotation of the drum, for several reason. In both Auto and Manual mode, the drum will rotate in one direction for a while, then pause for 4-5 seconds and begin rotating the other way for a while longer. It keeps doing this throughout the roast, and there's two reasons I really don't like this.

First, the pause between switching directions can scald the beans on the top of the pile when the halogen lamp is on. I have made a habit out of inspecting the beans after they're cooled to pull out any that are significantly darker than the rest, and there's always a few of them.

Second, when the drum reverses the agitators inside it pull the beans to the front or back of the drum. I'm sure this is to help with keeping them well mixed, but when the beans go to the front of the drum it exposes the BT probe at the rear. The built in controller seems to compensate for this somehow, perhaps with some really aggressive smoothing, but I installed a second BT probe in the rear to hook to my TC4/RoastLogger and every time the drum reverses it throws my curves waaaaaay off.

Since the plan all along was to have a roaster with an Arduino controller, I've decided to build an interface board between the built-in controller and an Arduino so I can run my own software instead. I've ordered all the headers needed to plug the existing wire harnesses into the new board, so I can switch back to the built-in controller by just moving the wires. The setup seems pretty straightforward as everything either runs off 9VDC, 15VDC or 120VAC and other than the heating elements nothing draws more than 1A-2A. I've got SSR's for the heaters, and a bank of relays for the rest. I can tap into the existing transformer to pull the 9V and 15V then run them through a rectifier to get DC.

Once I start putting the interface board together, I'll post more pictures.
I had one of these for a few years before selling it last year. I had reasonable success running it in a manual mode. It seems that you've torn into your more than I did with mine, but I'm happy to share what I learned.

My biggest complaint was cooling. I learned to dump the beans without burning myself and cool them outside the machine. The machine has an option for injecting water for cooling, but it was hard to control.

I didn't have any problems with heating the machine. It only took a few minutes to 120C. I didn't try to go higher than this because the radiant heating from the halogen goes directly to the beans. I was more annoyed with the machine not being willing to start a new roast unless it cooled below 35C.
Quest M3, IMEX digirosto 1500, various popcorn popper roasters, with TC4 logger, Quick Mill Vetrano, PIDed Rancilio Silvia espresso, Presso, Chemex, Hario, and Melitta drip, Cory and Yama vacuum/siphon, bodum french press, aeropress; Mazzer Major, Hario mini, and PeDe Dienes grinders - and a Nuova Simonelli Aurelia rebuilder in pieces
Happy new owner of a similar disused Digirosto Pro 1500 machine, but I wouldn't say VERY disused, I can imagine even worse :)
A proof is that today, after 3-4 hours of cleaning the deposits I found all over inside, including cleaning the glass window as new, well... it worked at first attempt.
Machine is still open, needs even more cleaning, so I can do a lot of pictures, if interest, at least to inspire someone interested to build a clone.

The only major difference versus the above coffeedragon description is the heater, a single 1550W internal halogen lamp.
Didn't noticed anything rezistive outside drum, nor connections suggesting such element hidden somewhere.
The back panel plate say also clear there is only a 1550W halogen heater, and a second 1000W resistive element for the smoke burner system.
DIY: TO based IR to bean 800g
Moded commercial: Dieckmann RoestMeister, Nesco, popcorn.
PID/ramp/soak controllers, MS6514 USB/Artisan/App
Grinder: mod'ed Porlex to 47 conical burrs
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