Solid State Relay - Voltage

I am not surprised at the leakage.
I open the circuit breaker serving my kilns just to be sure there is nothing energized.

Solid state devices are not perfectly clean in operation, and they do not work like a mechanical relay with an air break; they are more like fuzzy logic, ie: "Off for all practical purposes".

That is one reason I don't like them, but it is hard to argue with the controllability that they provide an electric kiln/furnace.

 

Kelly, do you have a circuit available?

 

I do the same....Call me a chicken, but I'd rather change out a tired CB than take a 240 poke.

 

More traffic here than at AA apparently. I replied there this morning, and having bothered popping in here till now.

Guess I should just follow the crowd and start using AA as a secondary site.

 

I just wish I could remember that it is not Vilbert.
For some reason that is what I see visually; its an automatic hard-wired thing.

Glad you are here.

 

Triacs or 'SSR' need a draw down or you will get a leakage that will read on the meter, LED loads are to small to 'run off, that leak. Don't stick fingers on anything that is likely to go live is a simple rule. (as my sadly departed mentor taught me, fuse in the pocket)

 

How much current does your meter show with the circuit in the open position?

Disconnecting both 110V phases is a good idea.

Travelling now. Will respond in detail when home.

 

I remember looking at a lot of wiring diagrams when I was setting up my kiln controller, and reading a lot about the in's and out's of various arrangements online with single and dual SCR's, but now I forget what I discovered.

I can say that in general, I don't like to mix my power circuits with my control circuits, ie: I would have one 2-pole breaker for powering the SCR's and another 1-pole breaker for controls only, but again I need to go check how I set mine up because I don't recall using two breakers.
I don't like having the possibility of getting feedback through anything.

I will try and dig that stuff out and post it.

Edit:
Here is some online info I found:
https://www.phidgets.com/docs/Solid_State_Relay_Primer

https://en.wikipedia.org/wiki/Solid-state_relay


As I recall, the controller is just switching the SSR on and off quickly at varying rates to control the power flowing to the load.

 

I found the sketches I made for my kiln controller hookup.
I remember playing around with the controller and putting it on the scope, but I don't think I have actually run it on the kilns yet.

I looked up several heating element controller wiring diagrams, and I don't see the need for two SSR's unless you are using a 3-phase power source, or perhaps if one SSR cannot handle the entire load.

But why use two SSR's when one works?
Seems like I have read some doomsday posts on other forums about the need for using two SSR's always, but I don't believe it, or rather have no reason to believe that one SSR would not work safely and well.

Below are some photos of the equipment I bought (I also bought a beefy heat sink for the SSR), the instructions, and my wiring diagram sketches (un-tested, use at your own risk).
And be aware that wiring diagrams vary greatly depending on the exact equipment you are using. There is no single wiring diagram for SSR heating element controls that works in all situations.

The instructions are written in Chinenglish; so a bit of a challenge to interpret (the price was right).

And there are some meltdown/burnup photos on the net of SSR's, so perhaps not a good idea to leave them unattended.
As I mentioned above, I open the two-pole breaker serving the kiln when I am not using it.

And as I recalled above, I do use a separate 120 volt breaker to feed control power, so that I don't get any feedback from tapping one line of a 240 volt circuit.
I always use a separate 120 volt control source unless I am using a control power transformer on a 3-phase circuit, but you need labels to warn that both breakers must be turned off to safely work on the equipment if you choose to use a separately derived control power source.

Edit:
Don't ask me what the waveform means; I was just playing around with it and I assume that is a junk signal of some type, or maybe that is the output, and it is showing some clipping.

 

I understand about independent control. I don't see a problem with doing that.

But if I understand you correctly, it is as if you want to be able to have physical contact with a coil (either an accidental touch, or perhaps contact with metal lifting tongs, etc) while the SSR circuit is on, but with the SSR in its non-conductive (low-conductive) state?

I would not reach into a kiln with the power on, whether the SSR was conducting or not.
If I had to reach into a kiln, I would either open the 2-pole circuit breaker feeding the kiln, open a wall-mounted disconnect switch, or if I am going to work on the unit, unplug it from the 240 volt receptacle and turn off the 120 volt control circuit.

You could use your main contactor to turn off 240 volt power to the unit, but contactor contacts can weld closed, and there is no guarantee that they will actually open when you think they are open.

So I guess I don't see why you could not just turn off the 240 before opening the furnace?
I suppose I don't understand your operation exactly.

 

I am very familiar using single-phase 240V in the UK for as many years, and a single line being "hot" is the norm for me. Neutral in my experience has always been at 0V potential.
USA seems to have the Neutral being the center tap of the utility transformer, with the two split-phase 120V hots 180 degrees out of phase with each other, giving 240V. The Neutral is only used if 120V is required. The Neutral is not used if 240V service is needed. Safety Earth must be used in all cases.

Isolation of power to Kelly's heating coils is the objective, with a means of reducing leakage current to a minimum.

I will be testing my setup which uses the same SSR to a resistive heating element. If an SSR is not isolating power sufficiently to make it safe, another means of powering the coils should be investigated i.e. ye olde contactors.

 

If you need to keep power to the rest of your system while handling material in/out of the furnace bore (temperature?), I would go for a three-pole isolator between the SSR output(s), both split-phases and the heating element connections.

In the nature of KISS, it does require you to make it safe each time, but it allows you to keep your independent control.



Randomly got this 4-pole one from Amazon UK...

https://www.amazon.co.uk/Gewiss-GW70436-Rotary-Isolator-Neutral/dp/B008OQLOO8

Space depending of course.

 

Small error in the last circuit which would have isolated everything. Now corrected.



Phew!

 

Seems like in your second diagram, if you touched he left side of either coil/hour meter connection, you could complete the circuit to ground and get 120 VAC.

 

Pat,

Agreed however those connections should be in the control cabinet and not in the furnace bore.