### Network

J

#### Jim Elbrecht

Jan 1, 1970
0
I'm trying to set up a digital temperature controller for a kiln.

I have the controller & it outputs 22.5 volts DC. I want to run a
15amp 120VAC heating element. [a 20A relay would be nice as it would
leave me some leeway if I change elements-- but 15 will work]

So I need a relay, but I've been looking at them at a dozen different
vendor's sites and don't see any rhyme or reason to how they are
listed.

I would prefer an electro-mechanical relay [because I've been told
they usually fail 'off' which I prefer to one that fails 'on'.

The latest website I've searched is alliedelec.com. I searched AC
relays for 15A & 20A and though I get some hits on relays that will
handle the amps, I don't see where they mention the voltage needed to
trip them-- or whethter they are e-m or solid state.

Here's the results-
http://www.alliedelec.com/Search/SearchResults.asp?SearchQuery=relay+15a+120&SearchType=STANDARD

Can someone try to educate me on how to search for the relay I need?
Or will one of these work?

Thanks,
Jim

J

#### John Fields

Jan 1, 1970
0
I'm trying to set up a digital temperature controller for a kiln.

I have the controller & it outputs 22.5 volts DC. I want to run a
15amp 120VAC heating element. [a 20A relay would be nice as it would
leave me some leeway if I change elements-- but 15 will work]

So I need a relay, but I've been looking at them at a dozen different
vendor's sites and don't see any rhyme or reason to how they are
listed.

I would prefer an electro-mechanical relay [because I've been told
they usually fail 'off' which I prefer to one that fails 'on'.

The latest website I've searched is alliedelec.com. I searched AC
relays for 15A & 20A and though I get some hits on relays that will
handle the amps, I don't see where they mention the voltage needed to
trip them-- or whethter they are e-m or solid state.

Here's the results-
http://www.alliedelec.com/Search/SearchResults.asp?SearchQuery=relay+15a+120&SearchType=STANDARD

Can someone try to educate me on how to search for the relay I need?
Or will one of these work?

---
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? 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.

C

#### Chris

Jan 1, 1970
0
Jim said:
I'm trying to set up a digital temperature controller for a kiln.

I have the controller & it outputs 22.5 volts DC. I want to run a
15amp 120VAC heating element. [a 20A relay would be nice as it would
leave me some leeway if I change elements-- but 15 will work]

So I need a relay, but I've been looking at them at a dozen different
vendor's sites and don't see any rhyme or reason to how they are
listed.

I would prefer an electro-mechanical relay [because I've been told
they usually fail 'off' which I prefer to one that fails 'on'.

The latest website I've searched is alliedelec.com. I searched AC
relays for 15A & 20A and though I get some hits on relays that will
handle the amps, I don't see where they mention the voltage needed to
trip them-- or whethter they are e-m or solid state.

Here's the results-
http://www.alliedelec.com/Search/SearchResults.asp?SearchQuery=relay+15a+120&SearchType=STANDARD

Can someone try to educate me on how to search for the relay I need?
Or will one of these work?

Thanks,
Jim

Hi, Jim. Relays are rated by their contacts (that's the switching
part) and coil (that's the part that creates the magnetic force that
pulls the switch.

You need a relay whose contacts are rated at least 15 amps at 120VAC
resistive.

The coil may be a bit more of a problem. 22.5VDC is an oddball
voltage, but it's almost 24VDC. DC relays are usually guaranteed to
pull in at 80% or 85% of rated coil voltage. So, nearly all 24VDC
relays will actually pull in at 20.4 volts DC and up. I'd be a little
would bog down with the load of the relay coil.

Before we do anything else, you should take a look at the docs on your
controller, and see what kind of output you have, as well as how it's
wired. Many temperature controllers are made to provide a voltage
output for a solid state relay (which would be a very good solution for
you, except for that "fail-off" business). That may mean it's only
capable of pushing 20mA or so into a SSR input. Feel free to contact
the manufacturer of the temp controller -- they'll probably be happy to
help you find out what you've got from the controller model number.

But assuming you really do need a 24VDC coil relay, let's see if we can
give you a hand with your immediate problem here. The
Tyco/Potter&Brumfield T92S11D22-24 is a great relay for industrial
control applications. It's DPDT (double pole, double throw) contacts
are rated for 30 amps at 120VAC resistive, and has a 24VDC coil that's
350 ohms. It's also available at Allied as Stk.# 886-0149. I like it
because the contacts aren't open to the air (nothing messes up relay
contacts faster than ceramics dust -- it prevents them from closing
fully and leads to a miserably short life), and it has faston
connectors. Bolt it down with two screws, plug in the faston
connectors, and you're done. I like that kind of solution.

You can download the P&B data sheet from the website. This will help
you wire it up, as well as giving you a bit of an intro to how relays
are spec'd.

By the way, see if you can get a 330 ohm, 3 watt or more resistor
before you order your relay. Put it across your 22.5VDC source and see
if it bogs down below 21VDC. If the voltage holds up there, you're
good to go. If it does bog down, it's probably a SSR driving output.
In that case, you might want to consider a smaller relay with a higher
ohm coil or look to some other means of driving the relay coil
(possibly a transistor).

Also, you should put a 1N4002 diode across the relay coil to absorb the
inductive kick of the relay coil when it turns off, so whatever's doing
the controlling won't have to.

Feel free to post again with any additional questions, especially if
you have a SSR output on your controller. There are ways to get around
that so you can use a relay instead.

Good luck
Chris

J

#### Jim Elbrecht

Jan 1, 1970
0
-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

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 ]

C

#### Chris

Jan 1, 1970
0
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

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
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
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

J

#### John Fields

Jan 1, 1970
0
-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 ]

---
Yes, those are "EV"ents 1, 2, and 3. SPST NO relay contacts rated for
250VAC or 30VDC at 5A into a resistive load. It doesn't look like
there's an internal supply that you can use to activate your external
relay, so I'd recommend that you get a relay with 120VAC 20 amp
contacts and a 120VAC coil and run the relay from the mains in series
with the controller's relay contacts, like this:

120HOT>-----------------+
|
|
+---------+ |
| | |
| | <--O------------+
| | | |
| O----O---------+ |
| | | O--> |
+---------+ [COIL]- - -|
CONTROLLER | O
| |
| [HEATER]
| |
| |
120NEUT>-------------+-------+

A good relay to use would be a P&B (Tyco) T92P7A22-120.
(Digi-Key, $8.83) Sealed, 30A 120/277VAC DPST NO contacts, 120VAC coil, chassis mount with faston terminals. With the extra set of contacts as spares, when the first set burned out all you'd have to do to get things working again would be to move the terminals over to the other set, as long as the first set hadn't welded closed. Or, if you wanted to switch both mains hot and neutral you could do that. 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 think that might be a time-proportional (or ON-OFF) SPDT relay output, but I'm not sure. Take a look at page 3-6 of the manual and also the top of page 8-6. --- 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. --- It looks to me like 8-9 is your sensor input and 10-11-12 is the SPDT relay output. --- 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] C #### Chris Jan 1, 1970 0 John said: --- OK. --- As I have understood the manual. [100 pages of mostly 'greek to me' stuff] - I will hook the relay to EV1, EV2, or EV3. --- Yes, those are "EV"ents 1, 2, and 3. SPST NO relay contacts rated for 250VAC or 30VDC at 5A into a resistive load. It doesn't look like there's an internal supply that you can use to activate your external relay, so I'd recommend that you get a relay with 120VAC 20 amp contacts and a 120VAC coil and run the relay from the mains in series with the controller's relay contacts, like this: 120HOT>-----------------+ | | +---------+ | | | | | | <--O------------+ | | | | | O----O---------+ | | | | O--> | +---------+ [COIL]- - -| CONTROLLER | O | | | [HEATER] | | | | 120NEUT>-------------+-------+ A good relay to use would be a P&B (Tyco) T92P7A22-120. (Digi-Key,$8.83) Sealed, 30A 120/277VAC DPST NO contacts, 120VAC
coil, chassis mount with faston terminals. With the extra set of
contacts as spares, when the first set burned out all you'd have to do
to get things working again would be to move the terminals over to the
other set, as long as the first set hadn't welded closed. Or, if you
wanted to switch both mains hot and neutral you could do that.

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

---
I think that might be a time-proportional (or ON-OFF) SPDT relay
output, but I'm not sure. Take a look at page 3-6 of the manual and
also the top of page 8-6.
---
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.

---
It looks to me like 8-9 is your sensor input and 10-11-12 is the SPDT
relay output.
---

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]

If I could add something, Mr. Fields. The EV outputs are SPST relays,
and they can be set to turn on or off at a set temperature (with a
programmable hysteresis in this controller). They're made for a number
of ancillary purposes, like overheat alarm, turning on an internal oven
convection fan, and other things. You could use one of the event
relays as the main control output. However, this turns a self-tuning
PID controller into a bang-bang ON-OFF controller. Not sure that's
what the OP needs, even though it's tempting as the simplest solution.
In my experience with kilns, anyone who's trying to make ware make
money needs any advantage he can get.

(Actually, the thermal mass of the stack will even out the temperature
on the inside, but there will be overheating on the outside, and on
corners. They respond very quickly to the slightly higher peak
temperatures from bang-bang controller oscillation.)

Might be wrong, but the way I see the full manual, I believe the output
that has self-tuning PID control is at pins 10 and 11, and is made to
drive a SSR.

Thanks
Chris

J

#### Jim Elbrecht

Jan 1, 1970
0
Thanks to both of you-- since I started this reply both Chris and John
have posted some great info that will take me a couple days to absorb.
I'll be back.

On 13 Apr 2005 09:42:00 -0700 said:
Hi, Jim. Relays are rated by their contacts (that's the switching
part) and coil (that's the part that creates the magnetic force that
pulls the switch.

Thanks. [and if anyone was reading that & rolled their eyes thinking
he was being too elementary--- I read it three times before I really
'got' it.]

-snip-
The coil may be a bit more of a problem. 22.5VDC is an oddball
voltage, but it's almost 24VDC. DC relays are usually guaranteed to
pull in at 80% or 85% of rated coil voltage. So, nearly all 24VDC
relays will actually pull in at 20.4 volts DC and up. I'd be a little
would bog down with the load of the relay coil.

I think the 'Events' will drive the relay as they say +/- 15% which
brings them right into the ranges you mention. But now I also think
you're correct to think I'm trying to get power to the wrong terminals
and that the EVents are there for 'accessories'- not necessarily the
element.
Before we do anything else, you should take a look at the docs on your
controller, and see what kind of output you have, as well as how it's
wired.
-snip-
I'm re-reading that manual this weekend. Each time I read it I have
another 'Eureka' moment.

You can download the P&B data sheet from the website. This will help
you wire it up, as well as giving you a bit of an intro to how relays
are spec'd.

Hmm-- I found 'Tyco Relays and Circuit Breaker - Databook' under free
literature & they'll ship it with my order.

http://relays.tycoelectronics.com/solid_state.asp that should keep me
reading until the next millenium. Something is bound to sink in.
By the way, see if you can get a 330 ohm, 3 watt or more resistor
before you order your relay. Put it across your 22.5VDC source and see
if it bogs down below 21VDC. If the voltage holds up there, you're
good to go. If it does bog down, it's probably a SSR driving output.
In that case, you might want to consider a smaller relay with a higher
ohm coil or look to some other means of driving the relay coil
(possibly a transistor).

I'll conduct that little experiment just as soon as I can get some
power to that terminal. I'm still struggling with the programming.
Also, you should put a 1N4002 diode across the relay coil to absorb the
inductive kick of the relay coil when it turns off, so whatever's doing
the controlling won't have to.

Will do-- I recall the manual mentions a Zener diode being an option
someplace--- might this have been the spot? [nope-- I just went
back to the manual. That's what 7-8-9 are for. It does still
look optional- 'resistance thermometer'? Is that the same as a
thermocouple?]
Feel free to post again with any additional questions, especially if
you have a SSR output on your controller. There are ways to get around
that so you can use a relay instead.

I'm sure I'll be posting again. You & John have given me a lot to
digest & clarifie da few things so the manual makes a bit more sense.
Thanks for the translations.

Jim

R

#### Rich Grise

Jan 1, 1970
0
On 13 Apr 2005 09:42:00 -0700 said:
Hi, Jim. Relays are rated by their contacts (that's the switching
part) and coil (that's the part that creates the magnetic force that
pulls the switch.

Thanks. [and if anyone was reading that & rolled their eyes thinking
he was being too elementary--- I read it three times before I really
'got' it.]

This is sci.electronics.basics. We don't roll our eyes at newbies.
Sometimes at each other, but never at newbies. ;-D

Cheers!
Rich

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