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Topic: Triac ratings (26 msgs / 686 lines)
1) From: John Abbott
Major considerations when specifying a triac are:
(a) Forward and reverse breakover voltage.
(b)Maximum current
(c) Minimum holding current
(d) Gate voltage and gate current trigger requirements.
(e) Switching speed
(f) Maximum dV/dt
--

2) From: John Abbott
Not directly Ed, but I wouldn't put my finger on it while its powered up =
-
you'll smoke your finger. I have finally given up on the triac control to=
 my
Fresh Roast and have gone to relays.  The semiconductor part of me hates
relays -but they are cheap and if you don't have a scope they solve a lot=
 of
problems. 
A little off topic but we were discussing the electronic controls of
roasting.  Which we all no is Exothermic :O)
--

3) From: John Abbott
The conversation had been on the application of triacs to control roastin=
g.
One of the questions indicated a lack of familiarity with triacs.  Having
been a part of the 3 lead device group at National Semiconductor (where w=
e
proved we couldn't make high current anything) I just thought I'd flop th=
at
data on the table.
Ummm  probably shouldn't have.  I just went through a lot of failure on m=
y
SCR controlled Fresh Roast and replaced them with relays (hate relays).
--

4) From: John Abbott
Dan,
I said "National Semiconductor" couldn't make a high current device.  The=
re
are what are fondly called "Hockey Puck" devices that can handle much mor=
e
current than anything we could build.  But I'd be surprised if a "giant"
motor is run directly from the throughput of an SCR.  Breakdown and Dwell
voltage is a very strange beast.  But I don't know that its not.
--

5) From: John Abbott
Because I foolishly gave away most of my lab instrumentation when I retired.
It is VERY hard for me to figure out what's going on with just a digital
meter.   All that to say "I'm a weak designer" and maybe always was.  I had
a pile of five volt relays with some good current carrying ratings.  So I
just gave up on the SCR refusing to turn off from time to time.  My signal
conditioning wasn't all that good for a 12" cable into the motor/heater
lines.
Bottom line: It was just a feasabilty model to begin with and it proved what
I was trying to prove.
--

6) From: John Abbott
I just re-read this.  A switch to me IS an SCR or Triac :O)    The right
answer is probably - I'm using a home made controller to do the roasting
profile. The computer steps that heat according to the ramp. With the
computer doing the work it needs to be a solid state switch.
--

7) From: Kevin DuPre
There will be no problem. The heater is largely
resistive rather than inductive. If it will drive a
light bulb, the heating coil will be no problem - as
long as it is rated.
For example the Fresh Roast draws 1200 watts so at a
nominal line voltage of 120 that is 10 amps - A LOT OF
CURRENT!
I would need a 1500 watt dimmer just to ahve some
headroom.
You should size yours accordingly. A 25% margin above
the roaster rating should be sufficient.
<Snip>
=====
--
Kevin DuPre
obxwindsurfhttp://profiles.yahoo.com/obxwindsurf"The real voyage of discovery consists not in seeking new landscapes but in having new eyes -- Marcel Proust"
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8) From: AlChemist John
Sometime around 19:07 9/12/02, Kevin DuPre typed:
<Snip>
Thank you all for the consistent answer.  I figured that was the case that 
a heating coil and incandescent light were virtually the same.
I have a  10 amp dimmer.  That is what I plan in installing in my WB.  The 
no load is 6.3a (I think that is what it was).  I am going to verify full 
bean load before it goes in and give my self some margin also.
The next step to my profiling...
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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9) From: Dan Bollinger
<Snip>
John,  Just so you know, a dimmer rated at 10A means that it can handle all
of 10A (It can probably handle more for short durations)  They have already
taken a safety factor into consideration before giving it a rating.  Dan
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10) From: EskWIRED
<Snip>
Cool.  What is the brand and model?  How much did it cost?
I'm wondering what the differences are between the various dimmers with
different ratings.  Do they use different triacs, but the same parts
otherwise?
My limited understanding is that the heat given off by the triac is the main
concern WRT longevity (and current rating?). Lutron brags that they use a
much heavier aluminum mounting plate/heat sink than the cheaper brands.
In order to fit my dinner into my WEPP, I cut off much of the mounting
plate, and as a result, I have much less heat sink attached to the triac.
If it causes premature failure, I don't really care, because it is a cheap
part.
But what my fevered little mind is considering is taking a regular dimmer
switch, demounting the triac, bolting it onto a CPU heat sink, and mounting
it inside the popper where it would get a lot of airflow.  My theory is that
inside a wall-mounted electrical box, it gets no airflow whatsoever, and so
I could push the limit using airflow, and still get decent life out of a
cheap part.
Any EEs here to disabuse me of my folly?
Are there any newsgroups which cater to electrical experimentation where I
could ask?
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11) From: AlChemist John
Sometime around 06:57 9/13/02, EskWIRED typed:
<Snip>
Actually, after looking at it, it appears to be rated at 14.5a and my WB 
has loaded load of 5.4A
<Snip>
Specifically it has the following information on it
KB Electronic, LTD.
Model:  KBWC - 16
Rated           6.0 A FLA (fluorescent load my EE at work says)
                 14.5 A  LRA (lighting load  - number I need for a heater 
my EE says)
                 120 VAC
Cost, , free, my EE at work thought it sounded like a need project and 
said, "here, try this.  Should work.  If it burns out, oh well, its cheap)
BTW, it is very light and is solid state (I don't know if all triac are).
Hope that helps.
So, will this work?
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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12) From: Dan Bollinger
<Snip>
John, I believe that stands for Lighting/Resistance Amp load.   Your heater
is a Resistance Load.
<Snip>
Yep, a Triac is a solid-state device. :)  Dan
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13) From: Dan Bollinger
John,  You lost me on that one!  :)  Dan
  
Major considerations when specifying a triac are:
(a) Forward and reverse breakover voltage.
(b)Maximum current
(c) Minimum holding current
(d) Gate voltage and gate current trigger requirements.
(e) Switching speed
(f) Maximum dV/dt
--

14) From: Ed Needham
Does that have anything to do with exothermic?
Ed Needhamhttp://www.homeroaster.com
ed
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15) From: Dan Bollinger
Absolutely, Ed, absolutely. Didn't you know, EVERYTHING is exothermic.
Otherwise we wouldn't be having global warming, eh?   ;)    Dan
<Snip>
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16) From: Dan Bollinger
This is a multi-part message in MIME format.
Wait a second, John.  Don't they use SCR's to control giant electric =
motors?  I thought they did.  Dan

17) From: Jeffrey A. Bertoia
Ed Needham wrote:
<Snip>
Yes! If any of those ratings are exceeded then the triac will
exotherm in a very large way!
I happen to have a very large body of experimental data that
conclusively proves it too!  :->>
jeff
<Snip>
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18) From: dewardh
Ed:
<Snip>
Only if the triac burns while/after failing . . . 
Deward
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19) From: EskWIRED
<Snip>
"Should work.  If it burns out, oh 
 well, its cheap"   :)
I'd give it a shot.
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20) From: EskWIRED
This is a multi-part message in MIME format.
Not directly Ed, but I wouldn't put my finger on it while its powered up -
you'll smoke your finger. I have finally given up on the triac control to my
Fresh Roast and have gone to relays.  The semiconductor part of me hates
relays -but they are cheap and if you don't have a scope they solve a lot of
problems.
----
Why do you use a relay instead of a switch?

21) From: Ben Treichel
John Abbott wrote:
<Snip>
Our 1 Mw dyno controllers use triac's.
<Snip>
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22) From: EskWIRED
<Snip>
Ah. Now I understand.  I thought you were somehow doing it manually.  That's
how I currently control the temperature of my coils, by turning them on and
off with a SPST switch.
But I just got back from an appliance repair shop, and learned about
"infinite switches", which are used in electric stoves.  The guy told me
that they had small heating coils and bimetallic switches built into them.
According to him, they are built to control up to 15 amps.  Interesting!
I need to find out how hot they get, and what the dimensions are.  I'm
waiting to find an old stove in front of somebody's house on trash day, so I
can nab one.
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23) From: Ed Needham
Keep in mind that the stove circuitry is 220v.  That might have an effect if
you run them on a 110 circuit.
Ed Needhamhttp://www.homeroaster.comed
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24) From: EskWIRED
<Snip>
While the burners are at 220, the rest of the stove, including the control
knobs, runs at 110, according to the guy at the appliance repair place.
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25) From: Ed Needham
That may open up some inexpensive ways to control these beasts if true.
Report back for sure!
Ed Needhamhttp://www.homeroaster.comed
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26) From: Dan Bollinger
<Snip>
That makes sense.  Stove wiring carries the neutral and the ground to the
receptacle (220V, 3-wire plus ground).  Connecting to the neutral and either
the red or black wire will give you 115VAC.   Dan
<Snip>
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