Jim said:
-snip-
You don't say what the 22.5 VDC output from the controller does, or
how much current it can supply. For instance, does it go to 22.5V
when the kiln temp is lower than the setting on the controller and
then drop to zero when that temperature is reached, or does it do
something else?
I *think* that's how it works--- but to tell the truth I still haven't
been able to figure out how to program the thing to test it. The
wiring diagram on the side shows those contacts with a normal closed
switch on them.
[here's the diagram
http://home.nycap.rr.com/elbrecht/sdc21termi-small.jpg ]
As I have understood the manual. [100 pages of mostly 'greek to me'
stuff] - I will hook the relay to EV1, EV2, or EV3. But now as I
look at that diagram for the 100th time, I wonder what terminals 10-11
are doing. .. vpulse sounds promising.
I searched the manual [its a pdf file- ] and found no mention of
vpulse -- and I looked through the chapter where I thought it
explained all those terminals, but it skipped those. I'll go back to
reading.
I'm not sure what 8-9 or 10-11 do. The others are power in- [1-2-3]
and the remote switch and computer connection options.
Also, if the current is small, (that is, used for
signal purposes only) then the relay will need to be driven by
something else and there may need to be another power supply added for
the relay.
I think the current will just trip the relay-- The current is 22.5VDC
+/- 15%, internal resistance 1.1 K ohms. [page 20 of 100- second
diagram as mine is the 6D]
Thanks-
Jim
[if anyone is a glutten for punishment- the 100 page manual is
http://www.yamatake.com/products/control_products/control_products/manual/CP-UM-1470E.pdf
the 8 page overview is
http://www.yamatakeusa.com/pdf/Specifications/CP-SS-1471E.pdf ]
Hi, Jim. The correct term is "glutton", and I guess I qualify. Mmmmm,
temperature controller manuals...
It wasn't necessary to look at the full manual, though -- the info was
on the 8-page blurb. Honeywell is usually good about that kind of
thing. You have what's called the Model C21 6D, which has
time-proportional voltage PID output. It specifies 22.5V in series
with a 1.1K resistor -- in other words, it's a SSR driving output. If
you put the 350 ohm load resistor on the output, you would see it bog
down to around 5.4 volts. Not good for driving the T92 relay.
In addition, the output is time-proportional, which means our relay
would probably bang itself to an early grave if you could use it.
Let's say the controller has a 2 second time constant (I'm not
downloading the entire manual to check), and it's calling for 50%
power. That would mean the output is on 50% of the time, and your
relay would turn on every 2 seconds, remaining on for 1.0 seconds each
time. If your relay is good for a two million mechanical operations,
your relay would be good for a month and a half of continuous use near
the set point. Sorry, no go on the relay.
I would guess the SSR (Solid State Relay) is the way to go for this
controller. They're not as bad as all that, if you make sure to heat
sink them well (you'll need to dissipate about 20 watts) and use some
kind of external safety. Of course, you should do that with a relay,
too (relay contacts _do_ stick sometimes). What to do with this
depends on your setup. One possible is to use a thermal fuse which has
been made to fuse at a temperature past that which you expect to use in
the kiln. Another setup is to use a second thermocouple and temp
controller as a safety. Unfortunately, most of this stuff is very
dependent on your local electrical codes as far as safety requirements.
But if you've already got an overtemp safety, you can just tie into
that, and not worry about the SSR at all.
So here's the drill: install a 25 amp SSR that has DC input to 32V
(don't get the low voltage 3-8VDC input -- it might be high, depending
on the circuit in the SSR.) Make sure the output is AC, can switch
your AC voltage, and is _not_ "zero-crossing". That degrades
resolution on time-proportional outputs that have a small time
constant. Connect your + (pin 10) to the + input of the SSR, and the -
(pin 11) to the - input of the SSR. Connect the SSR output in series
with the heaters. Use a heat sink made for SSRs, and be sure to use a
very thin coat of thermal grease (also called transistor heat sink
compound) between the alcohol-cleaned SSR back surface and the
alcohol-cleaned heat sink front surface. Make sure the heat sink can
breathe, too. Heat related failure is by far the number one cause of
SSR death. As far as safety considerations for the dreaded "fail
shorted" problem, you'd have to let us know a little more about your
setup.
Feel free to post again if you need more help.
Chris