Correct SSR for 240 furnace?

ScottRoush

ScottRoush

Joined
Jan 10, 2010
Messages
1,818
First... Merry Christmas!

I just came out from trying one last test on my kiln before Christmas after figuring out my element draw and nailing down the wiring in my box. For refresher.. this is a 240 volt set-up with 2 SSRs and PID.

I now know that I have three 30 amp elements in my kiln (each one measuring 8ohms with multi-meter). I decided to take one of those elements out of the picture. Two of them wired in parallel come out to 50 amps which is too big for my SSRs and would blow my 30 amp fuses. So they are now wired in series which only comes out to 15 amps.. which may be too weak??

Anyway..I fired it up the main switch and the PID comes on. But when I hit the toggle to fire up the elements all I get is a pulsing (turning on and off) of the red light indicators on the SSRs which causes a pulsing of the info on the PID.

So... I need to troubleshoot this. First.. I need to learn to understand my PID to see if it's even set in a way that will fire the elements.. and I need to check if I have the right SSRs. http://www.multice.com/bp/Solid%20State%20Relay/SSR-25DA.htm If somebody could please confirm that this will work.. I would appreciate it. I have the 40 amp.

Also.. I'm not getting power to the fan... which is wired to one leg of the DPST switch and one to the neutral.

Well... I'm getting close and nothing is fried. But I worry that I will now have an underpowered kiln when I finally do get the elements to fire....
 
We need much more info .

Do you have a drawing for the whole wiring diagram?

Which PID are you using and do you have a manual?
You need to match the power output of the PID to the inputs of the SSR

Re the fan.
What power does it need, and how are you powering it ?
 
When you say you get a pulsing of the info on the PID, can you be more specific? What is the controller?

Without the full picture, there are several things that spring to mind.

First is that the PID is controlling the output as intended; Most of the controllers I've used have an indicator on the front to show when the output is on. This should pulse, feeding the SSRs as it does so.

The output will be time-proportional and there will be a cycle time set in the programming somewhere. I usually use 2 seconds. For full power, the output will be on for 2 seconds every 2 seconds. For half power, it will be on for 1 second and off for one second every 2 seconds.

Does the on/off cycle time correspond with the setting in the controller? if you increase the setpoint, is it on for more of the cycle?

The PID terms in the controller are basically a mathematical model of the process being controlled and the control will probably be absolutely lousy until you have tuned the PID terms. Most controllers have an autotune facility.

The next 2 things I can think of are not as intended.

You are driving 2 SSRs. It is just vaguely possible that the controller cannot output enough current to trigger both SSRs. TBH, it's unlikely as the Fotek sheet in your link gives a 7.5 mA trigger current and most controllers I've come across are good to at least 25 mA, but it is worth checking.

Your current drain when the elements are on is enough to pull down the voltage at the controller below its minimum supply voltage. Again, it seems unlikely. Most modern controllers are rated for 100-264V to cover the full range of world mains voltages plus/minus 10%. On a 240V supply, you'd really have to go some to drop under 100V. If you have a multimeter, it is easy to check.
 
sorry guys.. I should've added this to my previous thread. But I'm using JT's wiring diagram seen here: http://www.bladeforums.com/forums/s...eat-Treat-Oven-Wiring-Schematic-Future-Sticky The only difference is that I've added a third SSR because one of mine is only 25 amps.. so the extra is wired into the other to bring up the total amperage.

I will add to this tomorrow when holiday stuff has settled down.. but I have a Sestos PID that is supposed to be 240/120... but I will get the specifics tomorrow....
 
Also.. It seems like the pulsing is what should be happening from what you describe.. but just no power to the elements. I will see what I can find out with my VOM...
 
I think the manual is the one at;

sestos-hk.com/english/download/d1s-en.pdf

Assuming you are running on the default values, you'll be getting the output fed on a 4-second cycle (the "Ctl" setting; factory default is 4 sec). The proportion of the cycle that is "on" will depend on how far off the setpoint the indicated temperature actually is.

It looks like it only reads in degC, so your actual temperature is likely to be around 20 degC, assuming it's at room temperature.

If you reduce the setpoint, the "on" time should reduce and if you increase the setpoint, the "on" time should increase. It may not be immediate, but you should see a significant change within a minute or two of a big change in setpoint.

First thing to establish is whether the cycle time is actually 4 seconds.

Next thing is to check the indicator lights on the SSRs come on when the output indicator on the controller is on.

If the lights come on, the SSRs are being told to pass mains. At this stage, it is probably easiest to take the setpoint to maximum, so that you have 4 seconds "on" every 4 seconds and don't need to worry about when in the cycle you are checking for voltage.

It should then "just" be a case of seeing where you have power.

The manual seems a little cryptic;

"Operation Procedures:
1/ Press SET key 2 second into the function mode, after return to the operation mode. If no any change
after 10 second automatic return.
2/ For temperature setting, press the UP or Down key change the value, after 10 second operate the new
setting.
3/ First operate the Auto adjustment, press AT key 2 second, SV display blink AT, finally into PID control
mode. Press the AT key 2 second to abandon Auto adjustment.
4/ If successful the first Auto adjustment, can not use AT key for Auto adjustment again. It need change
function setting Ctrl to 2 to operated again.
5/ Auto adjustment needs from few second to few hour."

I assume it means that you can adjust the setpoint whilst in normal operating mode, but that it will not accept the change until 10 seconds have passed.

I also assume that the way to autotune it is to start from room temperature, set the setpoint to the desired tuning value and as soon as the change is accepted, press the autotune button for 2 seconds then release it.

I don't know what the display will show during the autotune.

Usually, during autotune, a controller applies full output until the setpoint is reached, then zero output. It then measures the overshoot temperature and time as the temperature falls back to the setpoint, or sometimes a bit less than the setpoint. It then applies an output and repeats for several cycles until it has calculated the PID values. Most controllers I have used will then carry on controlling at the setpoint with the calculated values.

I'd recommend tuning at a reasonable tempering temperature (perhaps 200 degC), rather than at Austenitizing temperature. There are a couple of reasons for this:

First, you can be pretty sure of actually reaching tempering temperature in a reasonable timescale. I'm sure I'm not the only person to have aborted an autotune because it seemed like nothing was happening, when in fact it was. Not knowing what information this controller will give during autotune doesn't help; some show the temperature and the output, others just flash AT at you as if to say "get lost, I'm busy".

Second, it's harder to control the overshoot at low temperature because of the relatively fast temperature rise and slow cooling.
Overshooting tempering temperature makes a bigger difference to the finished blade than overshooting Austenitizing temperature by a similar amount.
If we tune for the low temperature, we'll get no overshoot at the high temperature, where the rate of rise is slow and the rate of cooling is fast.
If we chose to tune at the high temperature, we'd get overshoot at low temperature, where it does the most harm.
 
Thanks a lot... I'm headed out right now to check a few things. For one thing.. the PID lights DO come on at the same time as the SSR lights.. but the period is certainly less than 4 seconds. But I've been using the PID as a 110v thermocouple readout.. no control.. and I'm sure that I messed with settings at some point.

I also need to track down why the fan isn't coming on... since that may be linked.

You've helped me on the other forum with the programming of this PID.. but I never got around to needing it programmed till now.. so thanks for the review.

edit: after checking.. the 'pulse' is indeed 4 seconds. And another thing I forgot to mention... when the lights on the SSR go out (after 4 seconds).. the readout on the PID goes completely dark.. no indication of any power at all on the 4 second cycle.

Also... when I turn on the main DPST swich.. which just provides power to the box and only should turn on the PID and fan.. the PID has an 'out' light on. When I hit the toggle to power up the elements... that is when the 4 second 'pulse' starts.
 
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Sounds like you need to get your voltmeter on AC range across the power input terminals to the controller and check whether you are losing supply voltage when the display goes dark.

It's not clear from your description whether you are just getting one shot after hitting the toggle switch to power the elements, or whether you are getting multiple shots on the 4-second cycle, albeit with no display during the "off" part of the cycle.

If the loss of display only happens when the elements stop being fed, you might try powering the controller through the main DPST switch, raising the setpoint to maximum to that you have a continuous output to the SSRs, then hitting the toggle switch to power the elements. That way, the SSRs should be fed continuously, giving you a bit of time to fault-find.

It sounds like there's probably a wire out of place. Here, I'd have half an idea of what to look for, but I'm not even going to guess at what's going on with your wiring, as I'm not familiar with the US mains supply system.

What I try to do when I have a suspected wiring fault is put away the diagram, sleep on it, then trace the wires out and draw a diagram of what is really there without referring to the original diagram. Then I sit down with a cup of coffee and both diagrams and play spot-the-difference. It's the only effective way I've found to ensure I see what is really there, rather than what I expect to see (of course I don't do it right away, I usually faff about for an hour or five, getting progressively more frustrated, first).
 
Once I hit the toggle switch the SSRs begin to go through a 4 second cycle... light on, light off. The PID goes on then dark on the same cycle.. continuously. So it's not just a one shot deal.

I've just gone through all the wiring and I just don't see anything amiss.. unless I'm misinterpreting the slight differences between my PID and the one on JT's diagram. But I will do as you suggest and make a diagram of my current set up.

I'm not sure I understand about powering the PID through the main DPST. I'm already doing that. The toggle only powers the SSRs and elements....

egads....

Thanks for trying to help...
 
Purely resistive loads can be tricky going from series to parallel. They are not additive in nature.
 
The third SSR is my main concern. If that makes sense to you or someone else here that has successfully wired one of these, then maybe that's fine, but that's what I'd be focusing on to start with.
 
well... it works! I didn't change anything other than securing wiring. So something must've just been loose. It auto-tuned to 170 C just fine. Which brings up another question... I don't see any way to switch which decimal place I want to change on the setpoint. i.e. right now it only changes in 10ths. It will take forever to increase to austentizing temperature!

Other issues.... My 220 source is in the unheated section of my shop.. an attached pole building where I also have my hot working/forge area. Living in Northern Wisconsin this can mean my kiln will be starting up from freezing temperatures. I plan to keep my control box in the heated area of my shop.

Also.. due to the element arrangement (see above)... I'm only operating at 15amp. I suppose I will find out tomorrow morning when I attempt to fire this to austentizing temps... but will this be enough? What can I do increase amperage? One thing would be to run a separate set of SSRs to fire the third element that has now been taken out of the picture? As I said above... if I run all three elements in parallel then I'm at 50 amps.. which is more than what my current SSRs can manage. I do have a 50 amp circuit.. so I suppose I could get 50 amp SSRs and a bigger buss fuses for the power cord?
 
We posted at the same time fellas...

Ron_M80... I went from parallel to serial actually. Not sure what you are getting at? It has to be one or the other??

Mike.. I got that idea from a knowledgeable member of this forum. But I do plan to just purchase all 40amp SSRs so I don't have to mess with that... unless it makes sense for me to run 50 amp SSRs so I can run my third element....
 
You need to set:

dIP (decimal place) to zero (factory default is 1)
dIL (lower end of range) can probably stay at -50
dIH (upper end of range) to 1300

I always set the lower end of the permissible setpoint range to zero, so I don't waste time overshooting into a range I'll never use. The Sestos doesn't have the facility to restrict the permissible range of setpoints and will allow a setpoint anywhere in the input range. You could set dIL to zero, bit if you might see real temperatures that low, you'd better leave it as it is.
 
Just as an example, if you take two 800 ohm loads and connect them in series they are 1600 ohms. Two 800 ohm resistors in a purely resistive circuit wired in parallel make total of 400 ohms.

I don't know all the rules. But echoing 12345678910 a wiring diagram is necessary to see the rules that apply.
 
Scott,
I think we all need to see your wiring diagram. You have made so many changes and modifications, that it isn't clear what you have done. Draw up a detailed sketch of the actual wiring and post it.

Just a suggestion - It may be best to stop trying to get around not having the right components by making parallel/series circuits.....and just get the right components.
Failures will be far more likely and catastrophic with cobbled together solutions.
 
Okay.. will do. But as I said before.. the only difference is that I wired in a third SSR. Everything else is the same. Also.. I did mention that I was ordering new SSRs. I'm on the gun to finish this sword.. and the third SSR is allowing me to run this kiln for right now.

ScottRoush said:
But I do plan to just purchase all 40amp SSRs so I don't have to mess with that... unless it makes sense for me to run 50 amp SSRs so I can run my third element....
Click to expand...

I'm running the kiln right now... so I will know more later today if I need more amperage or not.

Thanks again to those who have helped me on this (both here and on the phone) and have taken the time to read and understand what I'm going through. I know I'm a difficult case... but I've learned a ton and I believe I now have a working sword kiln. Just need to make it long term. :-)
 
I'd guess that 3600 watts or thereabouts (15A at 240V) could just about manage a sword oven for Carbon steels. Time will tell...

I was almost sure 3 kW would be enough for my first attempt at a sword oven if I just went for a 36" extended version of my 18"L x 7"W x 6"H knife oven, using the same Morgan Thermal Ceramics JM23 IFBs.

Then I got lazy and cheap, so I built it 42"L x 9"W x 6"D using cheaper, but denser, grade 23 IFBs and a 3 kW element per side for 6 kW total. The lazy meant only 2 bricks needed cutting, as I had picked up some 1" ceramic fiber board and 3" Calcium Silicate slab for the roof and door, which let me use a full brick for the floor width without having to worry about the roof span. The extra area and thermal mass of the cheap bricks seemed too much to risk trying for 3 kW in the end, particularly as EN45 steel seems popular for swords over here and the specs call for 870-930 degC Austenitizing temperature; quite a bit hotter than most other Carbon steels.

Let us know how you get on.

If you do find you need more power, there's a guy from Portland on ebay who I get my elements from. He's been very helpful to me and will probably wind 16 ga Kanthal A1 elements to your spec if you contact him (search for Kanthal).
 
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