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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » David and Alchemist Roaster Building Project

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Part 2 and 3 - heating and control
Alchemist	#1 Posted on 08/28/2007 7:34 AM
1/2 Pounder Posts: 287 Joined: November 02, 2005	We have the option of a few different mods of heating control and heating itself. For simplicity, I think the very easiest would be tubular heating and a variac. Over in our comments area, there are some pro's (from me) and con's of tubular heating. The only real issue (if you like the response time of the heater) is if we can bend the heaters to fit the shape we need. I will make a call and report back. I also have one here I have already bent up and will test for survival. At some point you mentioned a halogen light. I think this would be a great way to illuminate the beans (mount it in the front out of the way) and add a heat source. When I roast, I always have some heat on to the end. This could be it in this roaster. Great idea s:2. Maybe 400 watts or so. The other heat source I lean heavily toward is nichrome coils. We could either make the insulators of sealed kiln refractory (mold and cast - I have all of that) if we want a custom fit, or round porcelain insulators if we don't mind the extra space they take up. Coupled with a variac (or dimmers, see below), this is also pretty simple. Control. I have looked up triacs and a ) they are not what I thought and b ) I am not sure how they work (yet). As you know, I am for simplicity (where possible) and I like a variac. I fought kicking and screaming and in the end like the simple dial nature of it. It is your call on both. I will happily discuss the pro's and con's as I see it, but I am helping YOU build. One other solution that almost seems too simple that I will toss out. We are already discussing a halogen lamp (400-500 watts). If we broke the remaining available heat into two parts (say 500 watts), we in theory could control two elements with two cheap 5 amp dimmer switches. Fitting the length of coil needed might be an issue. We would have to crunch some numbers to make that final decision. What say you sir?


David	#2 Posted on 08/29/2007 10:16 AM
1 1/2 Pounder Posts: 690 Joined: October 27, 2005	Let's split up the heating sources. I would like one of the elements to be halogen, both for heat and light. 400 or 500 watts. These often come with their own dimmer switch. Would we be using this? or would the halogen simply be "on/off." For the second heat source, I'd like to give the nichrome wire a try. I like the idea of fabricating our own insulators, but our larger audience would probably like to know if there are off-the-shelf insulators that would be a good-enough fit, or will be be fabricating our own? If the nichrome turns out to be too awkward or unsuitable for our purposes, I could go with the tubular or even a second halogen. Variac is good. i have one we could use. Triac is good also. I'm researching the circuitry required. I have learned that having a way to dissipate heat is an issue, so attaching a heat sink might be involved. I will probably build one of these for my own interest, regardless of whether we use it in Zen 4.2


Alchemist	#3 Posted on 08/29/2007 1:12 PM
1/2 Pounder Posts: 287 Joined: November 02, 2005	OK, I kind of want to treat this as a small lesson. I mentioned to David off forum that I needed to wait for input a little before I could kick out the next item for consideration. Too much hinged on decisions. The information I used above was that we are going to go for nichrome coils and good insulation. To keep it simple for the moment, and most approachable for everyone else, I am going to go with the ceramic insulators I saw in Dan's sample roaster. Also, as a best/worst case, I have put in comfortable tolerances and completely sufficient insulation room. Taking all that into consideration (7" drum, 1" clearance, 1" insulators, 2" insulation, plus metal dimensions), the overall maximum width of the roaster is 14.5". David, can you live with that or do we try and shave off inches? As places we could "trim", tubular elements would take off an inch off both sides (2" total), and we could also reduce insulation to 1" (another 2") for a width around 10.5", but we sacrifice heater response, make it a little more complicated and waste more heat (which translates to less beans we can roast). And David's response is..... Alchemist attached the following image:


David	#4 Posted on 08/29/2007 2:05 PM
1 1/2 Pounder Posts: 690 Joined: October 27, 2005	No problem with the larger dimensions.


Alchemist	#5 Posted on 08/29/2007 3:38 PM
1/2 Pounder Posts: 287 Joined: November 02, 2005	Quote David wrote: No problem with the larger dimensions. You are so easy to work with! s:2


David	#6 Posted on 08/29/2007 10:22 PM
1 1/2 Pounder Posts: 690 Joined: October 27, 2005	Quote Alchemist wrote:You are so easy to work with! s:2 That's what you say now. Just you wait!! ;) Did I tell you I want a roaster I can touch without gloves?? :@ So, I'm cooool with the larger dimensions for the sake of better insulation. David attached the following image:


Alchemist	#7 Posted on 08/30/2007 2:43 PM
1/2 Pounder Posts: 287 Joined: November 02, 2005	Without gloves - no problem. I want to be able to lay hands on the top and feel virtually no heat. OK, I have run with the timer module. Here is the low down. It is from ssac.com. It is NHPD-CA-31-31-RXE. It has a variable cycle time between 0.1 seconds and 10 seconds, as determined by the potentiometer used. A 50 K ohm pot will give a cycle time of 5 secs. 100 K 10 secs. You get the idea. It calls for two pots, but if a dual-ganged pot is used, as the on time goes up the off time goes down, maintaining the constant cycle time. Pros: Small, pretty elegant, slightly less expensive than a Variac. Cons: A little fussier, less plug and play, only a little less expensive than a Variac. List price is $74.47 plus another $5-10 for a pot, and 2-3 for a knob and we are near (but not there) the variac price. I recall the one Dan has and the ones I have were less expensive. Seems to get the lower cycle time, and with newer models, prices have gone up. So, Timer modual or Variac? Questions? Edited by Alchemist on 08/30/2007 2:44 PM


Alchemist	#8 Posted on 08/30/2007 8:12 PM
1/2 Pounder Posts: 287 Joined: November 02, 2005	At some point we talked about a halogen lamp for illumination (btw, I know we have a trier, but a window is quite doable since we will have the light - I am thinking a pair of watch glasses). How do you feel about doing the leg work for specing that out. We have about 11" across in the drum area. We could make the drum area exact to fit a given fixture or see if any will fit. 8-10" ? 300-500 watts? Your turn.


David	#9 Posted on 08/30/2007 10:17 PM
1 1/2 Pounder Posts: 690 Joined: October 27, 2005	Quote Alchemist wrote: So, Timer modual or Variac? Questions? Let's go ahead and build ours around a variac. I'm still committed to gathering info on a triac as a lower cost alternative to a variac. But there's no need to wait on that info for our current project. Onward!


David	#10 Posted on 09/02/2007 7:30 PM
1 1/2 Pounder Posts: 690 Joined: October 27, 2005	Braniac gave me a source for the halogen lamps that he used. Coincidentally I found a very similar no frills 500 watt worklamp at Lowe's today for $10. There were pricier ones, but the cost seems to be in the stand. Purchase made. i didn't buy a dimmer for the halogen because, as it will be on throughout the roast. [As we discussed, we will be actively controlling the other heating elements via the variac.]


Alchemist	#11 Posted on 09/02/2007 7:45 PM
1/2 Pounder Posts: 287 Joined: November 02, 2005	Good initiative. I considered piecing together the component parts, but at that price, we can't beat it. Good job. The only comment I will make is we may or may not use the 500 W bulbs. We may find we need to drop to 300 W considering we need to get an after burner in there, plus the main coils. I just fear even 500 w at the end of the roast may be too much in a well insulated roaster. But we will deal with that a little later. I suspect we could get a 300 w element to fit that model. If you have the part number, would you go update the parts list please.


Alchemist	#12 Posted on 09/21/2007 7:13 AM
1/2 Pounder Posts: 287 Joined: November 02, 2005	I picked up one of these for the Zen II. I think we also now have the source for our view glass. That from tempered glass is perfect I think. I hope you have yours still. I was really thinking about putting in two layers of glass for insulation purposes. The halogen light glass would be good inside. We then just need to source another (maybe thinner) piece for the outside glass. I think hacking any old thrift store toaster over would be the way to go for that unless we can find small inexpensive pieces of tempered heat resistant glass.


David	#13 Posted on 09/24/2007 8:26 PM
1 1/2 Pounder Posts: 690 Joined: October 27, 2005	Uh Oh! Am I expected to cut tempered glass. I have heard such stories about that. Oh my! :\| c:2


Alchemist	#14 Posted on 09/24/2007 9:51 PM
1/2 Pounder Posts: 287 Joined: November 02, 2005	Quote David wrote: Uh Oh! Am I expected to cut tempered glass. I have heard such stories about that. Oh my! :\| c:2 Oh heavens no. We just install it in the front "wall" as is and make the front opening as large as we want the viewing port to be. A bit of visual fakery as it were.

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