Sanity check on SCR / controller wiring please!

[rockystill]

Hello all,

I'm in the home stretch of completing my first still, a CCVM design with a keg boiler and single 5500w heating element running on 220v. I'm building a controller box based on a lot of threads I've seen here. I thought everything was looking good but when I plugged in my box and flipped the switch, my SCR popped/smoked from the Voltage Output connections - pretty sure its a goner. Can someone check out my wiring diagram below?

A couple notes:
I didn't have an element connected yet - the cable coming out of my box terminates in an L6-30 receptacle at the moment. There was no load on the SCR.
When I plugged in to the dryer outlet, I got display on my meter right away and it was reading 245v. As soon as I flipped my power switch, the SCR popped.
The breaker never tripped.

I'm using a 4-wire dryer outlet, but Neutral is not wired. I bought one of these power plugs (convertible from 30A dryer/50A range) and just wired ground and the two hots. I took the time to dismantle my dryer outlet to ensure red/black were wired correctly on either side of the plug.

Convertible power plug

powerplug.JPG (20.44 KiB) Viewed 7233 times

[still_stirrin]

The Leviton switch is a "double pole", I assume...hence the connection to both "hot" wires, correct? It should be OK.

When you flipped the switch, did the fan start?

Obviously, the voltmeter is powered from the line voltage, not the switched circuit, so it would be "on" when plugged in. However, your ammeter reads the current through the torrid transformer, so without a heat element connected to the circuit, it shouldn't read any current flow.

The circuit looks OK to me. I wonder if you got a cheap underrated SCR module that smoked upon power up. Did you buy an extra?
ss

p.s. - if you disconnect the SCR module, and switch the circuit "on", does the fan run? Measure the voltage at the +V & -V terminals on the switch...same as the voltage "rail" that the voltmeter displays?

[Pikey]

Have pm'd you RS.

It looks like the output side has fried to me. That has to mean there was a Big current flowing however briefly.

I'm assuming it was NOT a faulty board to start with, so you have a big power draw - such as a short on the output side.

Can you rewire it as you had it and photograph the actual wires coming out of the unit as well as where they connect to the load ?

[rockystill]

The Leviton switch is a "double pole", I assume...hence the connection to both "hot" wires, correct? It should be OK.

When you flipped the switch, did the fan start?

Obviously, the voltmeter is powered from the line voltage, not the switched circuit, so it would be "on" when plugged in. However, your ammeter reads the current through the torrid transformer, so without a heat element connected to the circuit, it shouldn't read any current flow.

The circuit looks OK to me. I wonder if you got a cheap underrated SCR module that smoked upon power up. Did you buy an extra?
ss

p.s. - if you disconnect the SCR module, and switch the circuit "on", does the fan run? Measure the voltage at the +V & -V terminals on the switch...same as the voltage "rail" that the voltmeter displays?

It is definitely a double pole switch, it's this one: Leviton 3032-2W switch

It's quite possible was a bad SCR - I have another sitting here to replace it, but I wanted to have some other eyes on my schematic before I installed it.

I switched the circuit off so quickly when I saw that flash, that I'm not sure if the fan came on or not. But that's a good test - I'll remove SCR completely and see if it runs.

[bronctoad]

before you turn it back on, take a minute to open up your 30 amp cord cap and check those wires
its awful easy to flip flop one of those wires
good luck

[Pikey]

I'm pretty sure the fault is on the output side.

With no current draw, there is no reason why the output side of the triac should, would or could fault.

You have said that there is no current draw (No load connected) - yet the output side has fried !

Go looking at switches all you want, I'm pretty sure you'll find a fault on your L6-30 wiring or a logic fault in your mains connections - causing a short somewhere.

But make no mistake, the output cannot fry, unless it has a high current flowing !

[rockystill]

Removed the SCR, just leaving the fan connected, still with no element load yet (power out is terminated in a L6-30 receptacle), and everything looks perfect! Fan comes on when I flip the switch, and obviously turns off when I switch it off. I'm pretty confident that L6-30 receptacle is all good. Ground is clearly marked (green) and the way the wires come in to that receptacle, there's no way they could touch each other.

Maybe I'm ready to try out the replacement SCR. I'm going to make sure I have no loose wires/strands anywhere - I took apart my wall plug (pictured above), and cleaned up the wiring a little better there. I really don't think that was the issue, but I'm cleaning everything up to be sure.

[Pikey]

Removed the SCR, just leaving the fan connected, still with no element load yet (power out is terminated in a L6-30 receptacle), and everything looks perfect! Fan comes on when I flip the switch, and obviously turns off when I switch it off. I'm pretty confident that L6-30 receptacle is all good. Ground is clearly marked (green) and the way the wires come in to that receptacle, there's no way they could touch each other.

Maybe I'm ready to try out the replacement SCR. I'm going to make sure I have no loose wires/strands anywhere - I took apart my wall plug (pictured above), and cleaned up the wiring a little better there. I really don't think that was the issue, but I'm cleaning everything up to be sure.

Put a multimeter (Ohms) across the two output wires (where they were connected to the triac unit) and test the resistance of the L6 - it should be infinite at this stage. Then test the resistance of each to earth (ground) - again should be infinite.

No chance something shorted out the board terminals of your triac unit I suppose ?

IN fact why not put your load in place and wire straight through from the "input wires" through your L6 and through the load (Keep well out of the way when you turn it on though ) should trip out if there is a fault - or just heat the element if not. I sometimes use my own kit in that configuration during "Heat up" - works fine if your wiring is right !

[rockystill]

IN fact why not put your load in place and wire straight through from the "input wires" through your L6 and through the load (Keep well out of the way when you turn it on though ) should trip out if there is a fault - or just heat the element if not. I sometimes use my own kit in that configuration during "Heat up" - works fine if your wiring is right !

You read my mind! Before putting the SCR back in, i just wired the output from the switch directly to my output/L6. Worked like a charm. I'm going to connect the element now, and see what happens. Fingers crossed!

[rockystill]

Connected up my element, and water is now heating up - exciting! I think I'm ready to install the replacement SCR now.

[MtRainier]

I agree with everyone saying you must have had a bad SCR. Your diagram looks good to me assuming you wired it how you drew it.

I might have gone ahead and wired in the neutral since you had one and then you could power some 120V devices in your box too. You'd have more flexibility in fans, for instance, or could drop a 120V outlet on the outside of the case for things like utility pumps for cooling.

[Pikey]

IN fact why not put your load in place and wire straight through from the "input wires" through your L6 and through the load (Keep well out of the way when you turn it on though ) should trip out if there is a fault - or just heat the element if not. I sometimes use my own kit in that configuration during "Heat up" - works fine if your wiring is right !

You read my mind! Before putting the SCR back in, i just wired the output from the switch directly to my output/L6. Worked like a charm. I'm going to connect the element now, and see what happens. Fingers crossed!

Not really - just elemental and logical fault finding (well done - btw )

Now since you're new to all this - The terminology "SCR" is completely wrong in this context. AN SCR is a "Silicon Controlled Rectifier" - which these are not ! - An SCR is a Thyristor which is a sort of diode with an electronic "switch" called a gate and when a voltage is applied to the gate, a current can flow in one direction only.

However that is no use at all for our purposes as you would only use one half of the wave. So what they do is to put two of them back to back in a package and when an alternating gate voltage is applied it allows current to flow in both the positive half of the wave and the negative half of the wave.

Thus it is no longer a "Rectifier" at all.

It is called a TRIAC !

Annoying use of lazy language it may be - or just a lack of understanding - I don't know or much care, but VERY irritating to those of us who Do actually know the difference !

[HDNB]

well, the pictures are not clear enough for me to say with certainty, but that looks like a SSR i have used which only switches (or controls) one side of the 220vac. (even though it has connections for 4 wires like that one.)

meaning the black OR the white go through it, not both. one conductor goes direct to element.

prolly saying the same thing as Pikey, but in a less technical way...so what is this device exactly anyway? did it come with a schematic, or at least a searchable part number?

[shadylane]

Connected up my element, and water is now heating up - exciting! I think I'm ready to install the replacement SCR now.

Sounds like a logical idea

[rockystill]

Wired in the new controller and everything works great now! Weird, I'm going to assume a bad first controller - didn't change much else.

Thanks everyone for checking out my setup and offering advice. Can't wait to get some finished still pics posted, and to make that first run!

[Pikey]

..so what is this device exactly anyway? did it come with a schematic, or at least a searchable part number?

Nothing comes out of asia with a wiring diagram nowadays HDNB - Even Sony can't give you or even possess themselves a wiring diagram for any modern Sony TV ! - they can't mend their own TV's ! (except by "Board swapping" )

Basically - this is a moderner version of it and what they refer to as a "Two way thyristor" - is a TRIAC !

Simple enough principle _ GATE voltage has a "Trigger level" of say 5 volts. After that it lets All the current through until the wave goes negative when it shuts off.

By putting Two Thyristors back to back, you can use both parts of the wave.

Less than 5 volts on the gate - no electric.

So to get to 5 volts you have a potentiometer (the turny knob) and that lets electric through quickly or slowly depending on the position of the knob. After the "electric" gets through the "Pot" it charges a capacitor (Like a very quick battery") and when the capacitor gets charged to the 5 volts, the gate "Opens" (because it is wired in parallel with the capacitor ) and lets all the rest of the "wave" through. Similarly the negative half of the wave has it's own Capacitor and charges exactly the same but opens at say -5 volts. so by just twiddling the knob, you can adjust the rate of charge of the two capacitors which trigger the TRIAC - and therefore the amount of "electric" which gets through to your element.

https://www.ebay.co.uk/itm/10000W-AC-22 ... SwQb5bUDwN

[rockystill]

I'm glad YOU answered that one, Pikey.

[Pikey]

well, the pictures are not clear enough for me to say with certainty, but that looks like a SSR i have used which only switches (or controls) one side of the 220vac. (even though it has connections for 4 wires like that one.)

meaning the black OR the white go through it, not both. one conductor goes direct to element.

prolly saying the same thing as Pikey, but in a less technical way...so what is this device exactly anyway? did it come with a schematic, or at least a searchable part number?

Yes I think so HNDB - I'm assuming SSR means "Solid State Relay " ? - not a term I'm familiar with (being "foreign" an all ) - I think a "Solid State Relay" would have much the same properties as a thyristor and in fact they're probably different names for the same thing. So with needing to conduct on both halves of the wave, there would need to be two of them as well - one for the positive, one for the negative. ie back to the old TRIAC

And yes you're right again, they only need to operate on one half of the circuit. If there is not a continuous path, the electric stops so no need to switch it twice.

[petepipes]

I have a similar scr, just wondering where you are attaching your ground?

[Yummyrum]

I have a similar scr, just wondering where you are attaching your ground?

Relavant to grounding , the OP’s wiring diagram is good showing a common ground point ....( however the colour coding of the rest of the diagram is wrong IMO ... regarding the red hot connection .)... regardless ....

If its a metal case then it is common practice to connect all ground connections to a common bolt which is secured to the metal case with star washers and nuts so that a positive connection is made .

When the SCR controller ( yes Pikey ... that name shits me to tears too ) is mounted on the metal case it is grounded by the mounting nuts and bolts . .... to the already grounded metal case . .... again star washers help with a positive electical bonding .But there is nothing wrong with running a seperate ground wire from the common point to the controller case as well .

In the instance that you use a plastic case ....( and incidentally I hate that option) ... then you need to run a ground wire from your common grond connection to the metal case of the controller .

[rockystill]

The controller didn't actually have any real ground connection marked at all. With the first controller (the one that fried) I just picked a screw on the back of the case and used that. It was a small screw and tough to get my thick 10 gauge wire under it (yeah, could have picked better parts). I also wasn't sure exactly why the controller blew, so when I wired up the new one I did not connect a ground to that controller box. Maybe that's something I'll go back and do now that its working.

[shadylane]

A ground lug like this makes the job easier
https://www.amazon.com/Skywalker-Signat ... ground+lug" onclick="window.open(this.href);return false;" rel="nofollow

[rockystill]

A ground lug like this makes the job easier
https://www.amazon.com/Skywalker-Signat ... ground+lug" onclick="window.open(this.href);return false;" rel="nofollow

Yep, that'll do the trick!

[Bigvalveturbo]

ok so i have the same set up but my meter(i have the same one) shows only 120v, it shows 20a draw and its a 5500w element so that is correct. When i test at the element i get 120 on each leg... i tried running both legs and a single leg thru the ring (induction meter?) no differance.it probably makes no difference but i like things to read correctly. any help?

[shadylane]

I'd use it as is to measure current.
The wiring can easily be changed but.
Cheap digital meters don't last very long when connected to measure output voltage of a SSVR controller.