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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Drum Roasters

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2kg drum roaster - help me design one! ;)
stuartgrant	#1 Posted on 09/20/2009 6:57 AM
Newbie Posts: 36 Joined: September 01, 2009	Okay, so I've been thinking about roasters and I'm currently having a go at designing a 1.5-2.0kg (~4#) drum roaster. I live in Australia but I'm overseas until mid-2010 which means that this design can only be theoretical (for me, at least!) until then - but I know some of you guys love theorising about the best ways to build a roaster so I invite you to help me think about it. Here's my wish-list for a roaster: 1. Powerful enough to bring 1.5-2.0kg (~4#) of green beans to second crack in 15-18 minutes; 2. Consistent and controllable ? able to reproduce a given roast profile; 3. Highly adjustable and reactive heat source(s) (with some radiant and/or conductive as well as convective); 4. Gentle, preferably adjustable air flow; 5. Adequate removal of chaff from heat source(s); 6. Efficient use of heat. IN THEORY, the theoretical design I've come up with below will theoretically meet the above requirements. In theory. You know, theoretically, at least. ;) Here's where I went from there: How Much Heat? - My Corretto, KK's TO roaster and presumably many other home/commercial roasters can achieve approx. 1500W/kg or 5200BTU/hr/kg (700W/lb or 2400BTU/hr/lb). Based on this, for 2kg (4.5#) green, I will allow 4000W (14000BTU/hr) to be on the safe side. - I want to use a 2000W heat gun to provide half this wattage, along with some airflow (more expensive heat guns also allow you to safely throttle back the airflow which would be a big plus). - I will use 2 x 1000W IR-ceramic elements for the remainder of the heating. I'd also consider halogens. - In order to achieve this level of heat efficiency I will need i) a small roasting chamber, and ii) good insulation around the roasting chamber. What Size Drum? - The drum will be perforated or mesh, so as to allow the max IR through onto the beans. - On surveying drum dimensions, I found that most drums allow about 6L/kg (166 cu.in/lb) so I would need a drum volume of about 12 litres (730 cu.in). - Again, looking at drum dimensions, a reasonable average for this size drum seems to be that the length is double the diameter. To make it easy (in metric!) I settled on 20cm (8") diameter and 40cm (16") length. This is quite similar in size and dimensions to a 6lb RK Drum, as it turns out. What Size/Shape Roasting Chamber? - I think it makes sense to put the cylindrical drum inside a hexagonal chamber. Thus, when the drum is rotating, one of the hexagon's sides will be approximately parallel to the bean mass as it "rides" up the drum wall. I will mount the IR-ceramic elements on this wall. - I designed such a chamber based on giving the drum a minimum clearance of 1cm (3/8") from the sides of the hexagon. - I then needed to slightly modify the side which would be used to mount the IR-ceramic elements, making it slightly longer (wider) so that it could fit two elements on it. I also made it slightly further away from the drum (2cm=3/4"). - the elements are a minimum of 12cm (5") from the centre axle of the drum, which means they'll be about 15cm (6") from the bean mass. This seems good to me? How to Do Airflow? - The other advantage of the hexagonal shape of the chamber is that it will allow the air to cycle around (and through) the drum quite effectively. The fact that the roasting chamber is also quite small also helps here. - The main idea was to have the heat gun pointing down onto the drum at one end of the roaster while air/smoke could only escape at the diagonally opposite end. - Chaff will no doubt exit the drum and fall beneath (where it should be safely separated from the heat sources). There may or may not be enough airflow to push the chaff out the air/smoke exit. I'll design some sort of chaff catcher accordingly. What haven't I done yet? - I have no idea about how to design the vanes. I like the idea of being able to run the drum in the reverse direction to unload it, but that seems to require a certain vane configuration and I'm not sure if that configuration is going to be best for mixing evenly in a small(ish) drum. What can people share with me here? - I haven't thought about the front door of the roaster, except that it will have to include a loading funnel, a viewing glass, a trier, a thermocouple hole AND a dumping chute/door. I'll consider that later, but any thoughts would be appreciated. - A motor. I haven't reserched this, though I did notice that Diedrich/Probat/someone listed the specs of the motors they use so that might be a good reference point. - Motor/drum mounting. Again, haven't looked into this yet. - What insulation is available in Australia? I'll get to that much later. ;) I've worked out that it'll require no more than 1/2 sq.m (5.4 sq.ft - what units do you guys use for area??) - Will it be possible to use wooden panelling on the outside of the roaster (ie. inner=metal, middle=thick insulation, outer=wood)? My theory is that this would be fine (not too hot for the wood) but I'm not sure. How hot do the outsides of people's insulated drum roasters get? The wood would also be easier to work with, cheaper, and possibly have an additional insulating effect. - There will no doubt be hundreds of other things I haven't thought about. Please let me know if you spot any clangers! Notes on the below pics: - You're looking at the front, with the front door removed so that you can see inside! - The drum is 20cm/8" in diameter. - This shows the internal walls only. There will be insulation and an outer wall later. - At the rear/top is heat gun inlet. Bottom right shows the air/smoke exit. Dimensions of these to be figured out later. - The bulky units on the top left are the IR elements. Hopefully they'll sit flush with the internal walls. Love to hear your thoughts. Keep in mind that I'm at a very early stage and very happy to completely re-design everything based on your advice!! Thanks. Cheers Stuart. stuartgrant attached the following image:
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stuartgrant	#2 Posted on 09/20/2009 6:58 AM
Newbie Posts: 36 Joined: September 01, 2009	(other pic :P) stuartgrant attached the following image:
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boom	#3 Posted on 09/20/2009 12:27 PM
1/4 Pounder Posts: 150 Joined: June 08, 2009	Hey Stuart Trust me when I say you're taking on a big project...but it's FUN! Here's what I can tell you: How much heat: I used a single 8500BTU IR burner and it wasn't enough, although I have a lot of steel to heat as my drum is solid 3.5mm SS. I can barely make a roast in under 20min. Plus, I run the burner with a high pressure regulator, resulting in a burner that essentially destroys itself over time. Drum size: Looks good Roast chamber: On paper and in simulations, 1cm sound adequate. In practice, it is VERY little space. Remember that you need to fit everything in there by hand and possibly do some welding: veeery difficult in a 1cm space. Also, manufacturing within 1cm could be difficult unless you use accurate tools, which require accurate drawings, which require CAD modeling. Google Sketchup is great for rapid prototyping and brain storming, but laser cutters etc. will require .DXF files, which I think only pro CAD software can do. I could be wrong. Remember to make your materials thick enough to weld on. Trust me, 1.3mm is too thin!!! Try something like 2mm or preferably more. Air flow: It rarely goes where you want it to! If your extraction is at the bottom, you are bound to get loads of beans in there. I grill in front will work, but it will also hold back some of the larger chaff particles. Remember that, at 200+ deg C, any chaff will quickly rise to the top of the chamber...make your extraction there. Agitation: Vane design is very important. If I could redesign my roaster, I'll start with a perspex mockup of the roaster's front and rear panels and build a drum with adjustable vanes to first figure out the exact optimal setup. Fluid dynamics can come in handy, but you'll need a very willing mechanical engineer for this. Have a look at my post "profile controlled roaster". There is a pic of a Dierdrich drum there somewhere, so you can see what the fins look like. Again, the smaller the drum the less space you'll have for welding...veeery difficult to weld those veins in a tight space!!! Front door: I learned that leaving something out of the design will surely cause it to be neglected. You'll end up with a great machine with that one part that bugs you for the rest of your life because you didn't design it properly. Also, remember that your drum will have to fit tightly to the front and rear panels. I did this by first reinforcing the drum with wood so that it wouldn't bend (it still did) an then putting it on a lathe which cut the ends exactly to within spec, leaving enough space for the expansion of the metal. My space is within 0.2mm at 250 deg C, but this took some time to perfect. Use self aligning bearings (most flanged bearing housing are, I think) to ensure that the drum spins exactly level. Motor: A standard DC or small AC motor should do. 12V DC windscreen wiper motor are incredibly powerful and cheap from any scrapyard. And they can be easily controlled through electronics. The weight of the beans does have a rather big effect on the torque required, but those DC motor can handle it nicely. Everything else: You'll find snags on every single part of your design...sorry!! :) It took me about 2 months to sort all of those out...that's full days of roaster building. Maybe it's just me, but I had my days and I'm still very much stuck with those I didn't fix while I had the chance. See to it that your model is perfect and consult guys with loads of practical experience on the design. Boiler makers are great with these things. I know the other guys on this site has build incredible machines from hand-drawn sketches and ideas. I have no idea how they did it!!...whatever you do, just have fun!! Even when everything fails, it's still a hell of a lot of fun to build a roaster by hand!!!! Edited by boom on 09/20/2009 3:24 PM A good espresso should give you hair on your chest! Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster


boom	#4 Posted on 09/20/2009 3:19 PM
1/4 Pounder Posts: 150 Joined: June 08, 2009	I'm so glad you also use the metric system. It just makes sense. 1m = 100cm = 1000mm. 1kg = 1000g etc. against 1" = ???ft = ???yard = ???miles...it doesn't make any sense! And what the hell is a "stone" like the Brits use? And what is an ounce?? I'm confused!! A good espresso should give you hair on your chest! Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster


dBndbit	#5 Posted on 09/20/2009 9:07 PM
1/2 Pounder Posts: 268 Joined: January 13, 2007	Very ambitious, Stu! Sounds like your power is about right for a well-perforated or screen drum and a well-insulated enclosure. I would worry about using a wood enclosure. You'd need to make sure there was absolutely no tiny hole for the hot gasses to escape and make a tiny hot spot. Wood normally has about the same water content as green beans but it will get very dry after a few roaster cycles. Dry wood can flash at the famous temp of Fahrenheit 451 (233C). Can you clarify the position of your heating elements? I'm a little confused on that. IR effects drop off quickly with distance (inverse square). So 15cm from the beans you may not get as much IR effect as you want. I'm still liking my high-lift vanes that scoop the beans and carry them up to the heaters. Lifting the beans nearer to the top of the roast chamber also exposes them to the hotter air. So I don't have to waste power to generate 290C+ air in the top of the chamber to get 250C down where the beans tumble. Have you noticed where the Behmor put it's IR heater? My machine was different though, since I was working with an existing toaster oven, two 300W rods at the bottom, two 400W rods at the top. In that setup, my beans ride (at closest points) about 3cm from the top elements and 4cm from the lower ones. Not sure what to recommend for your higher-wattage elements. And HEY! What wrong with inches, feet and ounces??? I had no trouble whatever calculating my drum edge velocity in furlongs per fortnight. Don't blame the Brits. At least they've been smart enough to abandon all (most) of that silliness. It's just us crazy Americans who are still holding on to weird ancient traditions. Edited by dBndbit on 09/20/2009 9:12 PM Jim 11 years old... forever! ReeferDoor.com >home-built roasters and fair trade
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boom	#6 Posted on 09/21/2009 12:10 AM
1/4 Pounder Posts: 150 Joined: June 08, 2009	My burners are placed 1cm from the drum and I still had heat problems. I also use a highly sophisticated method of varying the distance: bang it with a hammer till it's close enough. Might be why I'm struggling with broken ceramics, but hey...this is a 3rd world country! Although I see SA as being a 2nd world country...we only get hi-jacked twice a day as opposed to 3 times. At least we're going to win the Tri-nations rugby! :P Wood in a roaster? You might need a good smoke filtration system. Although it will only be used once. Edited by boom on 09/21/2009 12:21 AM A good espresso should give you hair on your chest! Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster


seedlings	#7 Posted on 09/21/2009 7:57 AM
1 1/2 Pounder Posts: 4226 Joined: June 27, 2007	Why not add a touch of Braniac's heating method (http://forum.home...ead_id=570) and place halogen heat elements along the axis of the drum? Along with your IR from below, this may be a nice 1, 2 punch. I don't know if 1/4" (6.35mm) thick cement board is readily available in AUS, but it may prove to be a friendly, helpful transition between a metal hex chamber and a wood exterior. You may need an assembly line once this project is complete... to start taking orders! CHAD Roaster: CoffeeAir II 2# DIY air roaster Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover


stuartgrant	#8 Posted on 09/22/2009 2:36 AM
Newbie Posts: 36 Joined: September 01, 2009	Quote boom wrote: Roast chamber: On paper and in simulations, 1cm sound adequate. In practice, it is VERY little space...[] Air flow: It rarely goes where you want it to! If your extraction is at the bottom, you are bound to get loads of beans in there...[] Agitation: Vane design is very important...[] Front door: I learned that leaving something out of the design will surely cause it to be neglected....[] Hey Boom - thanks a lot for those comments. Thanks for the general "warning"/advice that this project will be big. That's not a worry for me at the moment because I'm OS until May and won't be able to even start sourcing materials until then. This is very much a thread of ironing out any design issues and aiming for the best/easiest approach! 1cm clearances - no worries, I can easily increase that in the design. 2cm ok, you think? I'm not dead-set on making my own roast chamber either - if I find something ready-made that's about the right size (for example, I do have a 50L SS beer keg at home...). Air: I'm still trying to work out a simple way of getting the airflow to move around/through the bean mass... I suspect that you're right and that the air will do whatever it wants (!) and that I'll probably have to modify the design to optimise it. As for chaff - you say the chaff will rise to the top even if the only air exit is at the bottom? Hmm... I'll have to have a look at this feature in some other designs. Vanes: welding onto perforated (or even mesh) is probably not going to work. I think it'd be best (as I've seen others do) to fasten the vanes onto the perf/mesh with screws/rivets/whatever. I had a good look at existing vane designs yesterday. I like Jim's scooping vanes a LOT! These look like they'd optimise the amount of contact the beans have with air and with IR (more exposed beans). Question about vanes: at this stage I'm hoping to use the traditional drum roaster dump mechanism - once the door is open, the vanes push the beans out. Simple. BUT, here's what I can't work out: if that's what the vanes do (push the beans forwards), won't the bean mass mostly gather up one end of the drum during the roast? I'm confused on this point. Front door: yeah, you're right - I will need to work this out. The most complicated part (in my head) is the way the door acts as the front wall of the drum - ie. it needs to be very accurate, especially vane design. Anyway, I'll have a closer look at some designs. This relates closely to how the drum is mounted... another thing I haven't thought through yet. That a long list of things I haven't considered yet/much, you may notice! I suppose the reason for that is that my design is based solely around my research into the optimal thermal properties of a drum roaster and not all those other pesky details! Don't worry, with the help of you guys, I'll get there! Cheers Stuart.
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stuartgrant	#9 Posted on 09/22/2009 2:51 AM
Newbie Posts: 36 Joined: September 01, 2009	Quote dBndbit wrote: I would worry about using a wood enclosure... [] Can you clarify the position of your heating elements? I'm a little confused on that. IR effects drop off quickly with distance (inverse square)...[] Have you noticed where the Behmor put it's IR heater?...[] Hi Jim, thanks for the comments. I had another look at your roaster - great stuff. Yeah - not sure about the wood outer. It would make it nice and easy to make, and I like the idea of the extra insulation, but not at the expense of safety! I think if the insulation between the metal inner and the outer wood is good enough, it should be safe enough. Hmm, I deliberately placed the elements as far from the beans as I could, but I suppose that might not be necessary or desirable? How close is too close to a 1000W element, in your opinion? As I said above, I really like your scooping vanes! I only saw the pic of them yesterday - something like that would be highly suitable for this design, I think. I haven't looked at the Behmor design much! I shall do so... Cheers Stuart.
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stuartgrant	#10 Posted on 09/22/2009 2:57 AM
Newbie Posts: 36 Joined: September 01, 2009	Quote seedlings wrote: Why not add a touch of Braniac's heating method (http://forum.home...ead_id=570) and place halogen heat elements along the axis of the drum? Along with your IR from below, this may be a nice 1, 2 punch. I don't know if 1/4" (6.35mm) thick cement board is readily available in AUS, but it may prove to be a friendly, helpful transition between a metal hex chamber and a wood exterior. You may need an assembly line once this project is complete... to start taking orders! Hey Chad, Yeah, I'd forgotten about brainiac's design! It's great. I saw it a while back but forgot to check it again. There are several aspects of that design that I like! I may consider halogens as well/instead of the IR elements. But I think I'd rather keep them outside the drum. The cement board sounds good. Be a while before I get to that stage, though. Production line? Aw, thanks. ;) Cheers, Stuart.
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stuartgrant	#11 Posted on 09/28/2009 11:52 AM
Newbie Posts: 36 Joined: September 01, 2009	Ok guys, I've made some further progress... as long as "thinking about it" counts as progress, that is! 1) For simplicity's sake, I'm going to limit the total heating to around 2200-2400W so that it can be operated off one 10A socket (Aust is nominally 230V now, according to my electrical engineer buddy). That will mean limiting the max bean load to about 1.2-1.5kg. I'm okay with that - I'll upsize it later if I feel the need! 2) I'm looking at these 1500W halogen tubes OR these 1200W infrared ceramic panels but I honestly don't have a good idea of their suitability for such an application. I've emailed them to ask... who knows what they'll think of us roaster-builders using their products! The comment against the halogens stating that oils from your fingers can reduce their life may be a problem - although at operating temps I guess the oils wouldn't actually get close (they'd burn up!)... Any thoughts? 3) In my design, I've moved the heating elements to the opposite side so that they're right next to the beans (2cm away, with elements at 900C/1650F)... was that unwise? It seems really close to me, but I did see Jim's point about heat efficiency... What kind of distance should I aim for, ideally? Anyone know the gap in the Behmor, Hottop or Deidrich? 4) I've done away with the heat gun for air flow/extra heat. Too much airflow (500L/min = 18 cu.ft/min) plus heat guns aren't really designed for back-to-back roasting and I want this roaster to be able to handle that. I'll work out the actual fan later, but can anyone tell me what kind of airflow I should be aiming for? Jim uses ~1cu.ft/min (30L/min) I recall... Anyone have figures on other/commercial roasters' airflow rates? 5) Crazy idea: how about having fins on the outside of the drum to encourage even, circular airflow within the roasting chamber? Coupled with a small fan drawing air/smoke out of the roaster, I think this could produce a nice even temp within the roaster. Good idea? Overkill? Stupid idea? :P 6) Vanes: I'm stuck here. Can someone explain to me what the job of the vanes is, exactly. Are they supposed to move the beans from one end of the drum to the other, and back again? OR, are they supposed to bunch them up one end where they tumble back some of the way (ie. the beans aren't evenly spread along the drum)? Related question, how does the dump work? From watching some vids of commercial roasters, it seems to me as if all the beans are bunched up the dumping end just waiting for the door to open. True/untrue? Thoughts welcome, guys! Thanks again, Stuart. ps. I've found plenty of ceramic fibre matting (Kaowool equivalent) available in Aust for quite cheap so that shouldn't be a problem. Should I go 1/2" or 1"?
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boom	#12 Posted on 09/28/2009 2:01 PM
1/4 Pounder Posts: 150 Joined: June 08, 2009	Hey Stuart Halogen lamps: As far as I know, some of the coffee oils are vaporized during the roasting process and end up in the air in the form of Volatile Organic Compounds. I'm not sure about this, but I do know that roasting is an oily business. My rear panel is so full of oils that some of the chaff tends to stick to it...maybe not the best idea for those lamps. Why not gas? I also considered investing in industrial burners that are used in chicken farms. They keep the chicks hot and are designed for dirty and difficult environments. They are more expensive, but it's worth a try... As for the vanes: In my drum, I have two sets of vanes. The first is the smaller outer veins, which moves the beans to the front. They are welded to the inner side of the drum itself. Secondly, we have the helix axle fins (cool name eh?). My drum has "cross-braces" in the front and rear: a simple cross shaped thing to keep the drum's shape and to mount the axle to the drum. On it, I have welded 4 helix shaped fins that moves the beans to the rear. In theory, the outer fins moves the layer of beans closest to the drum wall towards the front. Once they reach the front and start piling up, the inner fins sends only the top layer of the bean mass towards the rear. This motion allows you to dump the beans if you open the front door, since the bottom layer of beans are constantly being pushed forwards. If the door is closed, the beans heap up at the front door and are moved backwards by the helix shaped inner fins. It took me some time to figure it out. Unfortunately, I don't have a computer model that I can show you: it was too difficult to model! Have a close look at the pics of my drum in my other post. It's difficult to visualize, i know!! A good espresso should give you hair on your chest! Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster


stuartgrant	#13 Posted on 09/28/2009 11:17 PM
Newbie Posts: 36 Joined: September 01, 2009	Excellent info on vanes, thanks Neil! I looked back and found your vanes photos. I understand the concept, but you're right; it's hard to visualise! Just to clarify, what your vanes design means is that the bean mass is primarily up the dump-chute end of the drum during the roast, correct? I know designs like the RK Drum, Behmor and others have vanes which simply move the beans around - but then they both involve removing the drum to dump the beans... I guess that means there are those two main vane/dump designs, then? Does anyone have estimates of what level the beans will come up to when the drum is in operation? I guess it depends a lot on how large the vanes are and what rpm the drum runs at, but I'm looking at where to put holes for the thermocouple, the trier and maybe a sight glass on the front door. As for gas - that would be better, IMO, but I'm sticking with electric for this one just because I'm more familiar with it. I suspect any larger than this and I'd want gas. Cheers Stuart.
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Brainiac	#14 Posted on 09/29/2009 12:25 AM
1/4 Pounder Posts: 89 Joined: July 27, 2007	Quote boom wrote: Halogen lamps: As far as I know, some of the coffee oils are vaporized during the roasting process and end up in the air in the form of Volatile Organic Compounds. I'm not sure about this, but I do know that roasting is an oily business. My rear panel is so full of oils that some of the chaff tends to stick to it...maybe not the best idea for those lamps. The quartz envelope temperature of halogen lamps is about 600 degrees Fahrenheit (needed to maintain the Halogen cycle). My experience (lots of 2C+ roasts) is that there are no oils deposited on the lamps (plenty everywhere else that the vapour and smoke touch though..). I think that, like any condensation process, the oils and other compounds deposit onto surfaces whose temperature is lower than the vapour temperature and/or where the velocity of the gas flow drops. Brian


boom	#15 Posted on 09/29/2009 12:44 AM
1/4 Pounder Posts: 150 Joined: June 08, 2009	Hey Stuart Jip, the beans heap up in the front. I found that my design isn't perfect, because the beans are less at the rear than in the front; i.e. the axle vanes don't do their job too well, but it's good enough for a first attempt. The efficiency of your vanes will also be subject to the amount of beans in the drum. The axle vanes only work with a batch size of above a certain amount...So you have to design your drum around a fixed amount of beans for optimum agitation. Or you could just guess (worked for me). The space between the axle and outer vanes determine your optimum batch size of your drum...that's the theory. The bean level is sooo hard to calculate or estimate, because of the doubling in the bean's volume during roasting. Again, the vanes' placement will determine this to a large extent. A good espresso should give you hair on your chest! Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster


Koffee Kosmo	#16 Posted on 10/04/2009 4:45 AM
Administrator Posts: 1620 Joined: December 31, 2008	Quote As for gas - that would be better, IMO, but I'm sticking with electric for this one just because I'm more familiar with it. I suspect any larger than this and I'd want gas. Cheers Stuart. I had a similar thought with another KK design you can use 2 x oven circular elements around the outside of the drum These elements are normally used for the rear fan forced system But for Australia the total current draw for a power point circuit is 2400W total KK Koffee Kosmo attached the following image: Edited by Koffee Kosmo on 10/04/2009 5:21 AM I home roast and I like it. Designer of the KKTO Roaster Build information https://homeroast...ad_id=1142 https://docs.goog...lide=id.i0 Blog - http://koffeekosm...gspot.com/ Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex, (KKTO) Turbo Oven Home Roaster.
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stuartgrant	#17 Posted on 10/04/2009 1:37 PM
Newbie Posts: 36 Joined: September 01, 2009	I like the concept, KK. I've seen those elements for sale - not too expensive even brand new. Though you'd have to think that there'd be a whole lot of them available for next to nothing (ie. in trashed ovens!), along with the fans and variable controllers, for that matter. Might be worth looking into for an inexpensive starting point. Leads to another question, though. Given that we Aussies have 2400W or 10 Amps to play with, how much could we reasonably allow for the heating? I couldn't find much info on windscreen wiper motor wattage, but I know that they can pull as much as 1.5A, leaving 8.5A for the heating and fan. That's equivalent to about 2000W. I think a fan would be 50-100W, leaving 1900W for the heating. Does that sound accurate? 1900W isn't a whole lot; I suspect that would limit the batch size to 1.2kg (2.6#) at a guess. A related question: If my heating power is limited to ~1900W, would it be unwise to install a 2000 or even 2400W element? I wouldn't be able to run them at 100%, obviously... Is there a simple way of limiting the max output of something like that? Still thinking... enjoying trying to nut out this design. Cheers, Stuart.
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Koffee Kosmo	#18 Posted on 10/04/2009 5:45 PM
Administrator Posts: 1620 Joined: December 31, 2008	Its probably best for even heat distribution to use 2 or 3 elements to achieve your total wattage needed KK I home roast and I like it. Designer of the KKTO Roaster Build information https://homeroast...ad_id=1142 https://docs.goog...lide=id.i0 Blog - http://koffeekosm...gspot.com/ Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex, (KKTO) Turbo Oven Home Roaster.
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Brainiac	#19 Posted on 10/04/2009 6:11 PM
1/4 Pounder Posts: 89 Joined: July 27, 2007	Quote stuartgrant wrote: I couldn't find much info on windscreen wiper motor wattage, but I know that they can pull as much as 1.5A, leaving 8.5A for the heating and fan. Stuart, A wiper motor runs on 12 volts via a transformer-type power supply. This means that the POWER requirement is only about 20 to 30 watts, which for all intents and purposes can be ignored as far as mains supply rating is concerned. Brian


boom	#20 Posted on 10/05/2009 1:16 AM
1/4 Pounder Posts: 150 Joined: June 08, 2009	Be carefull of those little wiper motors. When I tested them, they pulled around 4A at startup. It could be even more if your drum is fully loaded. I have burnt 2 of my electronic circuits because the drum scraped against the sides and eventually got stuck. A good espresso should give you hair on your chest! Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster


stuartgrant	#21 Posted on 10/05/2009 2:11 AM
Newbie Posts: 36 Joined: September 01, 2009	Quote Koffee Kosmo wrote: Its probably best for even heat distribution to use 2 or 3 elements to achieve your total wattage needed Hey KK, That's the plan. I've emailed a few places and they recommended those ceramic infrared elements as being appropriate for the environment. They tend to come in 500-600W half-size and 1000-1200W full-size. I'm far from working out the final element configuration, but there's plenty of flexibility there. Cheers Stu.
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stuartgrant	#22 Posted on 10/05/2009 2:23 AM
Newbie Posts: 36 Joined: September 01, 2009	Brainiac, I remember from grade 12 physics that P = I.V... doesn't that mean that 25W running off 12 volts is actually pulling 2 Amps?? Or is my understanding wrong? Boom, Yeah, I'm a little worried about that. If I have the heaters on when I start the motor, voila, un probleme. But I'd love to have a setup which didn't have any of those potential issues every time I roasted... Similar to if I ran 2400W-worth of elements when I only had ~2000W available; it would be a blown-fuse waiting to happen. Any thoughts on solutions to that one? Thanks for the replies! Cheers Stuart.
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boom	#23 Posted on 10/05/2009 5:19 AM
1/4 Pounder Posts: 150 Joined: June 08, 2009	Get a bigger fuse! :) The answer is....GAS! A good espresso should give you hair on your chest! Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster


seedlings	#24 Posted on 10/05/2009 7:09 AM
1 1/2 Pounder Posts: 4226 Joined: June 27, 2007	Yes, stuart, but that's 2 amps at 12 volts. 25 Watts will only draw 0.11A at 220V, so if you put your current meter on the 220V leg going to your stepdown transformer, you'll see 0.11 amps. If you put the current meter on the leg from the transformer to the motor, you'll see the 2 amps. Brainiac won't lead you astray. And, gas is not a bad idea - although I share your desire for the instant control that electricity allows. You're on the right track, and remember even the best laid plans require some post-engineering. Build it, test it, adjust it. CHAD Roaster: CoffeeAir II 2# DIY air roaster Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover


stuartgrant	#25 Posted on 10/05/2009 11:16 AM
Newbie Posts: 36 Joined: September 01, 2009	Duh! Haha - I get it now! Thanks Chad. And Brainiac - I knew I could trust you! :P In that case, as for boom's warning about the starting current for a WW motor spiking to 4 Amps, that will means that the PC power supply will have to be up to providing ~4A - albeit momentarily. Correct? Would most PC power supplies be able to handle that? Neil - of course gas would provide a simple solution to lack of power! But I'm fairly determined to stick to electric for now - it's almost a key design parameter... Give the above advice, I'll actually have more like 2300W available to the heaters, so that's a lot more likely to handle 1.5kg (3.3# ... 45.78 shekels) which would be ideal. Bigger fuse, tho? If our circuits are (nominally) 10A... I can't exactly exceed that, can I? Thanks again, everyone! Cheers, Stuart.
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