Ammeter induction coil

[greggn]

Question: will a digital ammeter read the current accurately if two (2) conductors are passed through the induction coil but with only one conductor active at any time ?


Scenario: I'm building a new power controller (120VAC) and I'm using a DPDT switch to select either SSVR control or to bypass the SSVR and run full power. I'd like to be able to see the current in both scenarios.

My guess is that the displayed current will be lower than the actual due to the presence of the other passive conductor, which is 12 AWG, but I also suspect that the difference will be minor at the operating range of 10 - 12 amps. I can test this using my current controller but will need to open the case dig around in the wiring.

[Aux]

Just put the ammeter on the active side of both loads (before any switching) to measure total current. That is unless you are using both at the same time.
If you wanted to know total load and load on each leg of your circuit get 3. You can get them for like $10 on aliexpress.

[Steve Broady]

Disclaimer: I’m not an expert, just a guy with a hack level grasp of several things.

As I understand it, the coil detects the field generated by flowing current. That field will be the same regardless of the presence or absence of inactive wires in close proximity. Therefore, what you propose ought to work just fine. It’s exactly what I’ve done, though in my case I’ve run two wires for different voltages through the same coil. I lack the test equipment needed to verify that the reading I am getting is accurate, but it makes sense to me at least.

[Yummyrum]

I’d agree with both answers.
And add that so long as the unused wire is totally unable to pass any current from one end to the other that is passing through the CT .

[Steve Broady]

I’m assuming that both circuits would feed a single connection to your heating element. You could also tie the two together internally and put your coil on the resulting single lead. That way you’re measuring whatever current goes to the element regardless of how it gets there.

[Yummyrum]

Thats correct Steve . I think thats what Aux was saying too .
But this may help . The current Transformer can be used at any place in the circuit as shown .

Also ,you could simplify the curcuit by just using a SPDT switch as there is no point wasting a second set of contacts to switch effectively the same wire.

It can be even simplified more by just using a SPST and then there is no need to have double wires through Current Transformer anywhere

[Aux]

This is what I understand what you want to do.
Switch between full power or controlled power to the element. If so the correct placement of the ct for ammeter would before the switch.
You mention different voltages, I'm not sure what you mean by that.
I wouldn't put the ct after the ssvr as the sine wave gets chopped up to change the rms voltage. Ie it switches the sine wave and it becomes spikes. The ammeter may not get a true reading as it is no longer a sine wave.

Don't put a switch across the 2 terminals of the ssvr, just noticed that after posting

[Yummyrum]

Aux

You can put the CT anywhere in the circuit . The current in a series circuit is the same in all places . It is chopped up before the SSRV , after it , on either side of the element or in the Neutral lead . ( or other Live if you are running 240V )

The only precaution is to make sure the Voltage that is running the meter is supplied before the SSRV to save it burning out .

You are correct that most cheap Current meters don’t read accurately when measuring chopped up waveforms . Only True RMS reading meters will display correctly.

Also , there is no problems simply placing a SPST switch across the SSVR terminals . It will not damage the SSRV or cause any other issues . And a SPST switch is much cheaper.

However your version is equally functional
Redrawn to remove my switch for clarity . Also shown correct place to supply voltage to the Ammeter . ( while the current will be the same and chopped up anywhere in the circuit , the voltage at the input will not .

[Aux]

I have to strongly disagree Yummyrum.
Many circuits can be wired incorrectly but still work. Placing a switch across the SSVR does not isolate the SSVR so the mosfet is still being driven by the variable resistor thus it will still be producing internal heat and it will still be outputting a chopped waveform. Where as isolating it the SSVR has no power to it and will not produce any heat.
I would also put another switch before the ammeter, this would isolate all components incase of a failure.
A SSVR has a sine wave input (left terminal) and the output (right terminal is chopped) the mosfet that controls the waveform is an internal component so it cannot chop the waveform before it get there. Sine in - Chopped out.
As an electrician of 40 yrs experience I rarely give people wiring advice and I'm kind of regretting commenting. We have a saying in the trade "A little knowledge is a dangerous thing". There are many reasons wiring is regulated and most of these stem from how to correctly wire things so other "potential" hazards can be avoided.

[NormandieStill]

A SSVR has a sine wave input (left terminal) and the output (right terminal is chopped) the mosfet that controls the waveform is an internal component so it cannot chop the waveform before it get there. Sine in - Chopped out.

This is true for the voltage but not the current. For a thought experiment imagine a really slow sine going in (0.1hz for example). And replace the SSVR with a switch. When switched on the current measured either side of the switch would rise and fall with the sine wave (At zero volts there's no current flow). By watching the voltage at the input I can turn on and off the switch to produce an average current (averaged here over a minute or more giving the cycle speed). Each time I throw the switch the current will be "cut" as measured on either side of the switch... unless the switch is performing some current smoothing function beyond that of a simple air gap.

[Yummyrum]

I have to strongly disagree Yummyrum.
Many circuits can be wired incorrectly but still work. Placing a switch across the SSVR does not isolate the SSVR so the mosfet is still being driven by the variable resistor thus it will still be producing internal heat and it will still be outputting a chopped waveform. Where as isolating it the SSVR has no power to it and will not produce any heat.
I would also put another switch before the ammeter, this would isolate all components incase of a failure.
A SSVR has a sine wave input (left terminal) and the output (right terminal is chopped) the mosfet that controls the waveform is an internal component so it cannot chop the waveform before it get there. Sine in - Chopped out.
As an electrician of 40 yrs experience I rarely give people wiring advice and I'm kind of regretting commenting. We have a saying in the trade "A little knowledge is a dangerous thing". There are many reasons wiring is regulated and most of these stem from how to correctly wire things so other "potential" hazards can be avoided.

You maybe an electrician , and I totally get your stance on safety and I would not suggest anything that was not safe.

Me , I’m a TV technician ( well was for over 25years )we were trained to understand how electronic circuits work and what happens at component level as that is what we would need to be able to fault find ,locate and replace to get circuits working again , so I know very well how these SSVRs work .
For one thing , they use a TRIAC not a Mosfet as the switching device .

Secondly , if the switching terminals are shorted (bypassed) with switch , then the SSVR can never switch on .So never generate any heat and certainly not supply a chopped waveform .

OK , heres a schematic of a SSVR ….. yes its the same as those light dimmers that have been used for years .

The triac is the thing on the right . It’s the switching device . It is triggered into conduction when current flows into its Gate terminal . The Gate is connected to a device called a Diac . Diacs have a breakdown voltage around 25-35volts .
The lefthand side of the DIAC is connected to the capacitor which is charged via the pot . Every half cycle , the capacitor starts to charge .When the voltage across the Capacitor is above the Diac breakdown voltage , the capacitor discharges into the Gate and the Triac conducts for the rest of the half cycle . The position and therefore resistance of the Pot determines how fast the Capacitor charges up to the trigger voltage . That is how the phase angle switching occurs .

But …..If there is a closed switch across the SSVR then there can be no Charging of the capacitor ( obviously because there is no voltage across a closed switch)
So the Triac will never get to conduct and even if it did , there is a short circuit across its Main terminals anyway .

So re orientating it so it looks like it’s an SSVR , we get this .

Tell me how , when the switch is closed , that there is any voltage across any part of the SSVR to make it work ?


Sorry Greggn, didn’t mean to derail your OP .This hasn’t directly answered your initial question but it may have given you some alternatives .

[greggn]

I can test this using my current controller but will need to open the case dig around in the wiring.

I was able to test this using my current controller and, yes, two conductors through the coil was measured accurately.

You could also tie the two together internally and put your coil on the resulting single lead. That way you’re measuring whatever current goes to the element regardless of how it gets there.

Well, I'm embarrassed to say this never occurred to me. Placing the coil on the single hot going out to the heating element accomplishes what I need. Thanks.

It can be even simplified more by just using a SPST and then there is no need to have double wires through Current Transformer anywhere

In my old line of work this would have been called an "elegant solution." Simpler, less wiring, and easier to assemble.
For better or worse, I purchased all the components (including the DPDT) at the beginning of Covid when I saw the logistics and delivery issues and worried that I had no backups to critical elements of my distilling process. Now, nearly four years later and retired, I have the time to build it.

Sorry Greggn, didn’t mean to derail your OP .This hasn’t directly answered your initial question but it may have given you some alternatives .

This is a discussion forum and this is discussion. It's all appropriate.