HomeRoast Digest


Topic: controlling a 240v roaster heating element with (9 msgs / 256 lines)
1) From: Ed Needham
A technician with Hearthware, several years ago said the thermister was set 
to allow 500F air into the roast chamber of their Hearthware 'precision' 
fluid bed roaster.  That sounds like a good starting point anyway.  Build a 
machine that can control the heated air from around 400F to maybe 550F and 
you'll cover all the bases.
*********************
Ed Needham
"to absurdity and beyond!"http://www.homeroaster.com*********************

2) From: Michael Dhabolt
Ed,
Do you remember where the long conversation concerning monitoring
roast chamber air inlet temp vs. monitoring bean temp happened at?
Was it Alt.coffee?  I've been searching and can't find it archived
anywhere.  Sounds like something that Dave may be interested in.
Mike (just plain)
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3) From: Ed Needham
Oh my.  Is that the one where we went off on inserting a probe in a
bean-like material and placing it in the bean mass?  Whew.  That was a wild
thread.
I have absolutely no clue where that took place.  I'm thinking it would
likely be here, back when a few others were developing a universal control
board for coffee roasters.  I know there was some conversation over on
alt.coffee involving myself, Barry Jarrett and a few others where we
described a system that compared heat input temps with exhaust temps to come
up with how much heat was absorbed by the beans.  That involved doing dry
runs without beans to develop a baseline heat curve over time, then adding
the beans and calculating the difference between the two for a given load.
That seemed to be a great way to monitor bean roast progress to me.  Barry
just used exhaust temps on his Diedrich roaster to monitor progress.
*********************
Ed Needham
"to absurdity and beyond!"http://www.homeroaster.com*********************

4) From: Michael Dhabolt
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5) From: Bob Hazen
There's been lots of talk on this one - some right on the mark, some... 
well... scary.  Some folks have said it's OK to switch one hot with the SSR. 
Nobody, as far as I can tell has said "use a single pole circuit breaker." 
Several people have emphasized the safety issue and that would dictate a 
double pole breaker (whether you switch one side or both with the SSR) and a 
solid unswitched ground (not neutral!) to the chassis of this creation.
Certainly there are building electrical codes that don't apply directly to a 
homebrewed Frankenstein roaster, or anything else you plug into the mains. 
They define the building requirements.  Electrical usage equipment is nearly 
always certified to standards from a test lab such as UL or ETL.  This is 
ostensibly for safety.  I say "ostensibly" because if one had a mind to, 
they could pull the wool over those labs' eyes.  Not good, even if you 
could.  They are there to help save your (and others') collective hides.  My 
profession is aircraft electrical power.  It >has< to work correctly.  It 
 >has< to work safely.  You can't call 911 at 35,000 ft.  While it is a bit 
different with ground-based, hobbyist/experimental stuff, you could still 
burn your building to the ground or find some other way to fry yourself.  It 
has to be taken seriously.
Tom is probably OK playing with this stuff if 1) he uses a proper circuit 
breaker upstream.  2) He listens and learns before he dives in (he's a smart 
guy, who'd expect anything else?  3) he keeps his mitts out of it with the 
power on.  5) he doesn't leave this thing while its in operation or even 
just plugged in.  And 4) he keeps a good fire extinguisher nearby.
Just my 20m$
Bob*
(Not Ray's "Bob" but my real name)

6) From: Ira
At 10:28 AM 4/20/2008, you wrote:
<Snip>
The discussion started with something like how do I get power here 
and control the heating element with a PID. For that a single 
properly rated SSR is on the edge of OK. Probably want it backed up 
with a dual pole switch or dual pole power relay to cut both sides of 
the power to the whole mess when the heater is not supposed to be 
hot. Personally, I'd never trust a SSR to keep me safe as even 
essentially nonexistent leakage currents can be a problem for a 
human. I'd assume in working around a machine like this that if the 
lights are one, it's not safe.
While it's all well and good to try and make things safe until you 
get to the place where the GPF is built into the power cord of a 
hairdryer or toaster, you can still kill yourself using a hairdryer 
in the shower or freeing stuck toast with a metal knife.
The point of the SSR as I understand it was to control the heat of 
the heating element, not to power it down. One could argue that if 
you set the thermostat to 50 that the heater would never turn on and 
the element would still be hot which is a fine reason for switching 
both sides, but in the environment of Toms shop controlling a coffee 
roaster it likely will never be an issue.
If it was me, I'd put a double pole switch between the power cord and 
everything else, a big double pole power relay to control the power 
to the heating circuit with a light to indicate it's armed and an SSR 
to control the heat.
Ira
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7) From: Rich
I would tend to agree with the suggestion that has been made by Ira.  If 
you have a major problem with this then you need to remove all 
electrical outlets from your home as you might stick a bobby pin into a 
socket...  Common sense is not a disease.
Ira wrote:
<Snip>
  SNIP
<Snip>
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8) From: Michael Mccandless
I agree.
Many safety procedures are there to prevent DEATH.
A half-assed design is likely to eventually kill someone or one of their
kids.
I don't care who does the design.
Where will the device be in 10 years?
Who will you be putting at risk?
Is saving a life worth the extra $10 investment?
Many safety codes have been implemented as a result of a death.
It's not a joke or something to be taken lightly.
In hindsight would you rather be saying "good thing that wasn't powered" or
going to a funeral saying "oops - sorry - should have listened to the
experts"?
I ride a Harley & one thing that really ticks me off is a driver putting my
life in jeopardy through sheer ignorance "Oops - I was texting on the cell
phone & didn't see you".
Shouldn't even be considered as an option.
What ever happened to common sense?
'nuff said
McSparky
On Mon, Apr 21, 2008 at 10:54 AM, Rich  wrote:
<Snip>
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9) From: Ira
At 05:20 PM 4/21/2008, you wrote:
<Snip>
When I ride that I'm really careful to not be where someone else 
wants to be when they get there. It was way worse before cell phones 
and good stereos when people actually paid attention to their 
driving, now they just drive like zombies and you can always figure 
out what they're going to do before they do it. No one has actually 
tried to kill me in 10 or 15 years, before that it was reasonably 
common.  You ride a motorcycle, it's your responsibility to figure 
out what the people around you are doing, not theirs to watch out for 
you. If you think it is, you won't last very long.
Ira
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