hello everyone,

thanks for participating and thanks for letting me ask a question (or two).

i'm building a kiln controller using a controller module, solid state relay(s), and thermocouple.

i built the kiln i'm controlling and it is powered by (2) 110 volt lines coming from
a double pole breaker with a ground to 4 switches wired in series for 4 elements.

being new to building a control system i inquired about the parts needed.

i was told that using one solid state relay on one of the 110 lines would
cut the circuit to the kiln. i'm thinking that isn't true and that i need a relay on each 110 line with both relays connected to the same connector/actuator on the controller.

concurrently, when i inquired about adding a second breaker inline after the relay, a single pole one was recommended. again, i think not.

so... any thoughts on this matter?

thank you

 

Welcome to the forums! You actually don't have two separate 120 volt lines. You have a pair of wires that across both will product 240 volts. You have no neutral as one is not needed for a 240 volt circuit on heaters. You will need to use both lines in tandem to product the 240 volts needed at the elements.

Maybe you could sketch out what you propose and let us see what you are doing, or wanting to do. You won't use a single breaker anywhere you have the 240 volts present.

 

No it is not. It is 240 volts power by a 240 volt line. You would be using it on one leg of the 240 and it would kill power but it isn't considered safe because one leg of the 240 would still be live. Whoever is advising you is clueless.

Tell us what you are trying to do and we will be glad to help you.

Tech info: Your house is supplied with 240 volts from a transformer with a secondary center tap. That center tap is grounded and come to your house as the neutral. 120 volts in your house is derived from one of the 240 volt legs and the neutral. If you kilin is 240 volts there is no neutral and there is no 120 volts.

 

You can use one 240vac solid state relay to control your kiln but you'll need to know the wattage of your elements for relay capacity.

Are you building the actual controller or using an available unit ?

 

wow, thanks for the help folks.

i appreciate the clarifications regarding my statements. it helps me learn what i'm
talking about. always a good thing...

i believe my kiln pulls about 28 amps.

i have had the kiln for years. with glass kilns you need to be able hold a steady temp for
30-45 min or more at times and using 4 mechanical switches, as i have been doing, is definitely "old school".

so i researched what is needed and it appears to come to:

a digital temperature controller
a solid state relay
a thermocouple

i have purchased these items:

solo controller SL-4848-RR
SL4848-RR | 1/16 DIN dual output digital temperature controller

this solid state relay
AD-SSR640-AC-280A | Finger-safe AC solid state relay (SSR) 40A SPST N.O. SCR, puck style

this circuit breaker
WMZS1B40

here are a couple wiring diagrams for the controller



my understanding is that relay is a switch actuated by the controller.

i would like to add a secondary breaker close to the kiln.

i thought i would just cut the line and throw this stuff in.

the controller has a rs485 output for computers to have what is called

a supervisory control and data acquisition human machine interface. scada/hmi

some interfaces can be very visually elaborate. like a web page can be.

so i'm looking forward to the microsoft hololens so i can put on a pair of cool of looking

glasses and control my scada/hmi from a holodeck.

well, that's about it in a nutshell...

thank you,

live long and prosper...

 

Rather than just "adding" a breaker maybe a wall mounted disconnect switch. Your kiln should be protected for overcurrent at the electrical panel. You don't need two breakers protecting it and the one you linked to is a single pole and not correctly useable in this application.


Your controller is ok and will work with that SS relay. When I design control circuits for 240v appliances I usually use a two pole relay as opposed to a single pole like you linked to so that both legs are disconnected.

Did you get a thermocouple with the controller ?

 

You're going to need to mount that SSR on a pretty good sized HEAT SINK. It is going to get HOT. It will fail if you don't.

 

ok

would it be best to use a double pole ssr as opposed to two singles since
i have one single already?

i purchased this thermocouple


i can let the extra breaker go. i saw it recommended in a diagram where one
was used. perhaps to protect the controller. i'm not sure now.

 

i asked the dude at the web site about this. he was like, oh no, ours dissipate
heat effectively enough through the base plate. not good. double pole ssr seems a little hard to find and maybe expensive. if i return the breaker, another 15 gets me a second ssr.

 

You need a high heat thermocouple as it sits inside the kiln. Usually it will be stainless steel with a metal jacket.

Yours looks like plastic or rubber ?

 

it's nickel-chromium with a ceramic sleeve. rated to about 2280 degrees.

 

It is my experience that solid state relays should always be sized to double the expected amperage as well at a minimum of fifty percent higher than expected voltage ratings. Always use a heat sink with an SSR. Two pole SSRs are difficult to find so instead use a three pole (three phase) SSR. Ebay is a good source of inexpensive SSRs as well as controllers.

 

thank you furd for your suggestion. could you elaborate on your experience that a 60 amp ssr should be used on a 30 amp draw. that becomes a much larger investment.

the 3 phase ssr seems like an economical approach.
how would i wire it to my circuit?

ebay is where i initially started looking at controllers. i saw what packages where being offered and wanted to be sure the components where quality. there are some good prices for single set point controller packages with ssr, heatsink, and thermocouple.

i'm glad i ended up choosing a solo controller as they have free software for the controller. if the average joe wants to be able control their kiln from a computer, that's huge.

 

You would use two of the three poles.

At the amp rating you need it is more common for it to be a 3 phase circuit therefore being more common cheaper then single phase (what you have).

 

my controller is ac powered and the connection to the ssr is ac.

does this mean i need a 3 phase ac-ac 40a ssr?

something like this
Q00029 Hoymk SSR3 A4840HK 40A 3 Phase Solid State Relay AC AC SSR3 A4840HK | eBay

is it okay to use two single pole ssr's?

i want to put this together this week and don't want to wait for china post.

any good suggestions where to buy in the us online?

 

Your controller has only relay outputs. Ideally for SSRs you want a DC voltage output. With the voltage output the controller can pulse the SSR to more closely control the temperature. With relay control you need a "dead band" to keep the output relay from cycling too often. I would try to return the controller you have for the SL 4848-VR model.


I would far prefer that you use a 60 ampere SSR. Something like this Three Phase 3Phase DC AC Solid State Relay SSR 60A 60A | eBay

The 60 ampere will better withstand the 28 amperes of your heater and provide better heat dissipation. I would couple it with this heatsink. 1 Pcs Aluminum Heat Sink for 3 Phase Solid State Relay Heat Dissipation Cooler | eBay

The ratings on Solid State Relays are ultimate ratings. Using only 50% of the ultimate rating is not too conservative in my mind.


Theoretically it IS possible but it is really frowned upon in practice.


Sorry, anything bought in the US is likely to have a price three to four times that of Ebay.


Well, if that is really important to you then go for it. In the vast majority of cases it is unnecessary and just an added expense and something more to fool with.

 

aw gee whiz...lol

guess i'll have to get those ants out of my pants...

so the wisdom of using a 60a ssr finally makes sense. thank you

it's all about ample capacity (no pun intended), heat dissipation, and safety.

will you explain further,
"With relay control you need a "dead band" to keep the output relay from cycling too often"

if i return the controller i would like to get this one. it seems like it is the same one you pointed out, just in a 1/8 din size.
SL4896-VRE | 1/8 DIN dual output digital temperature controller

i find a computer screen much easier to interface with then the controller panel and the software adds to the ease of use. my investment was 10.00 for a rs-485 to usb module. i have an inspiron mini all ready to go with the software. plug and play. besides, i'm a geek.

 

Outside my skill set but would mechanical relays be a cheaper solution for
Urglik?

 

Sure. Dead band is the range around the set point where no controller action takes place. Example: If your set point is 100 degrees and you have a ten degree dead band the heater will stay energized until the temperature reaches 105 degrees and will then shut off. The temperature will have to drop to 95 degrees before it is turned on again. This cycle will then repeat in an attempt to hold the "average" temperature to about 100 degrees. If you shorten the dead band to say, 1 degree the heater will turn off at 100.5 degrees and turn on at 99.5 degrees. Obviously the shorter (tighter) the dead band the closer to set point the controller will control.

However, there is also the lag in the heating element to heat up and cool down to consider. This is called hysteresis and can really throw off your temperature control in that there is a time lag between the heater being turned on and it actually raising the temperature of your kiln. During this time the temperature may drop more than the 0.5 degrees if you are using a 1 degree dead band. That lag could be several degrees depending on the size of the kiln, the size of the heater and the temperature of whatever you have in the kiln. It works the same way on the upper end as well so even if you have the dead band set at 1 degree you could get a temperature swing in the kiln of several degrees over and under the desired (set point) temperature. Also, the smaller the dead band the more you will be switching the heater on and off and IF using mechanical relays the more wear and tear on the contact points. Because SSRs have no contacts there is no arcing or wear of the relay no matter how fast it is switched.

The above is a description of an "on-off" control scheme. Almost all electronic controllers have what is called PID control in addition to on-off control. PID stands for proportional-integral-derivative and when properly set up will control to a gnat's eyelash of the set point. Proportional control will adjust the on/off time of the heater so that the farther from set point the longer the heater will stay on or off as needed. The integral portion will give an extra "kick" the farther the temperature is away from set point but at the same time will retard the proportional action when close to setpoint. [Integral action was one time called reset as it "shifts" the proportional band in order to compensate for the action of the particular circuit.] Derivative control is a further enhancement that looks at how fast the variable is changing and in what direction to compensate for the integral action, in short, derivative works to minimize "overshoot" of the setpoint. [Derivative was once called "rate" as it slows down or speeds up the control action to compensate for the extra kick of the integral action.] Most systems do not need derivative action.

Now, by using proportional action (probably won't need integral or derivative) you can "pulse" the heater on at differing rates to quickly come up to set point and then maintain that temperature. These pulses can only be made using an SSR driven by a pulsed voltage from the controller as a mechanical relay would soon fail, either mechanically or electrically.


Ray, do you see why a mechanical relay is not a good idea in this application?

 

thank you furd.

i think i have enough of a grasp of the essentials to get the proper equipment and why.

though this is a little off topic, perhaps i can finish this thread with how to build the appliance.

- how would you mount the ssr/heatsink?
- how would i determine wire gauge for the controller-ssr connection and ac power for the
controller?

thanks everyone for your help. it's nice to be able to get solid electrical advice.

 

The SSR is bolted to the heat sink. Heat sink probably has metric tapped holes but you can re-thread for either 6 or 8-32. Use some heat conductive paste between the SSR and the heat sink. The heat sink can be mounted on some kind of base with machine screws or sheet-metal screws. You do need to allow free circulation of air around the heat sink.


Both are relatively low power so #18 is sufficient, I might use #16 only for mechanical strength.

 

i went ahead and purchased the ssr and heatsink that you recommended furd.

and returned the other items and will be getting the appropriate controller.

and that's that. thank you.

 

Let us know how it turns out.

 

will do...............................................

 

howdy folks,

nice to be back to the best do-it-yourself forum in this quadrant of the galaxy.

the delay in having anything of substance to report was acquiring the heat sink for the ssr. i was sent the wrong item from china (a ten second timer) that took many weeks to arrive then awaited a replacement which never came and my money was refunded. i found one in texas! and received it within a week. the ssr took awhile to arrive but appears to be well worth the wait due to it's cost of 34.00 delivered. i currently use four 30 amp mechanical switches on my kiln which would cost more to replace.

the picture shows my configuration for power switch, thermocouple, ssr, and data with the rs 485 to usb module.

i've thought about how to mount the ssr a bit. so far, the fact that it's 5 inches tall with the heat sink has presented a problem. i'm thinking about just mounting the heat sink to the brick wall next to my kiln. open air. probably not code, but good for heat dissipation. also, i'm going to use a thermal paste but have never tried to cover such a large surface before. with computer cpu's, one generally places a dot or short lines depending on the cpu and let compression spread it out. i'm not that fond of trying to spread out an even layer with a credit card, etc. any suggestions regarding these matters?

and if i may, a last concern came to mind. the ground wire to the kiln in regards to the ssr. can i attach the ground to the third pole on the ssr?
i imagine they are all isolated switches.

thank you

 

Mounting the heatsink to the brick wall is not a bad idea. The brick will dissipate the heat from the heatsink. I would build a screen type cage to over it as long as it has exposed electrical connections.

You're talking about silicone grease..... didn't the SSR already come attached to the heatsink ?
If not than just use a qtip to spread it between the SSR and the heatsink. You wouldn't use any grease on the brick wall.

The ground wire needs to be connected to one of the SSR mounting screws so that the heatsink is grounded. The ground cannot be connected to the extra SSR pole.

(Use the two outside poles for your control..... keep the center one as a spare)

 

thank you, i will make a cage to cover the ssr.

the stuff i was going to use between the ssr and heatsink is a compund
for cpu's and heatsinks called ceramique 2 because i have it laying around.
it may be thicker than silicone grease and spreads like a ceramic paste. yuk.
since a q-tip wouldn't work with this stuff (would rip it apart i think), maybe
i should get the silicone for a more consistent layer. i'm only running about 28 amps on a 60 amp switch, but it is fun to try and optimize. i lapped the cpu and heat sink for a computer i had. the cpu ran about 5 degrees cooler at boot time. the heat sink for the ssr sure could use a lappin'
the ssr is nice and smooth like a cpu.

i'll use your suggestion about using the outside poles for the ssr and the ground. i should read up on ground. the ground wire for the kiln is attached to the switches. they are attached to a metal grate attached to the metal frame. is this sufficient?

can i bring smaller ground wires to this ground wire? like the controller power cord ground? the controller doesn't have a separate ground screw. the box is plastic.

always things to think about on a project, eh?

thanks again!

 

I would suggest using a non-hardening heat conductive compound between the SSR and the heat sink. I think I got a small tube at Radio Shack for about five dollars a few years ago. It doesn't take much, just enough to fill the gaps between the back of the SSr and the heat sink.

Equipment grounding conductors for a 30 ampere circuit are, by code, supposed to be #10 copper. I would feel adequately protected using #14 although technically it would be a code violation. ALL metallic parts that could potentially come in contact with the current-carrying parts of the installation need to be connected with this equipment grounding conductor.

Looking forward to the completion and testing results.

 

hi all,

i'm adding a digital controller to my kiln which is currently operated by 4 mechanical switches in series for 4 elements. i'm wondering if there is any concern leaving the switches and if i wanted to replace the mechanical switch module with an item that i can bring the power to and then feed to the elements, what would that item be?

thank you

 

thanks for the help. sorry for the late response. i should be finished in a day or two. always curious as to why things are i was wondering why a #14 wire for ground would be adequate. what the electrical physics are and regarding using the outer poles on the ssr. is this to assist with heat dissipation? i have other other questions but since this forum isn't titled "let's help urglik with his kiln" i posted a new thread. thanks again for your help. it's made a significant difference in the outcome.

 

I moved post 29 here from your newly started thread. Best to keep all the questions on a topic in the same thread. It eliminates all the "get acquainted with" posts.

 

thank you.

a question about real names. i noticed you signed a reply to me with what i thought was your real name. but now i don't see it in the regular forum dialogue. is it appropriate to refer to you by that name in the open forum?

 

Sure..... my name is Pete and my friends all call me Pete. The only reason my posting name isn't Pete is because there are many Pete's. I'd be Pete29 or something like that.

If a person has a real name in the signature line.... feel free to use it.

 

PJmax is definitely better than pete29...

 

here is video i made regarding the kiln controller.

thanks everyone!

https://youtu.be/c2wZVMYnsys

 

Thanks for letting us see the product of your work.

 

my pleasure. a serious thank you to you all.