S
Simon Pettitt
Hello,
Sorry if this isn't the right forum for this. Didn't look to be far off...
So I'm looking for some advice please with regards to interaction between loads sharing a circuit. I understand (or think I do!) a lot of the composite concepts and I think I have an idea of what my answer might be - but I want to bounce this off those with more experience and see where I'm wrong. I work in the entertainment industry with lighting and audio systems. I have a fairly good understanding of electrical principles but have no actual electrical qualifications (although I've considered training soon, that's another story).
So...
In several instances in our industry and outside it, I often hear people exclaim that a given device on a supply is affecting the power delivered to others on that supply. Take the scenario of a TRIAC-based lighting dimmer and an audio amplifier, both taking power in parallel from a given supply, with the amplifier buzzing when the dimmer is at certain dimming values. Often someone will say something to the tone of 'that dimmer is sending c**p back down the line'. SMPS supplies are said to do the same.
Now, on a conceptual level this makes sense - switching noise generated in the TRIAC on each dimmer channel is affecting the amplification stages in the amplifier and becoming part of the output signal. However, I can't seem to fully understand the electrical details behind this.
(For the moment, I'm discussing noise/distortion transmitted through mains wiring - not signal-level interconnection between two devices - I know Ground Loops are another story)
Both devices are connected to earth and the supply via suitably low impedance wiring, so why would any noise generated in load 1 (an SMPS/dimmer/other noisy supply) affect the power supplied to load 2? How can load 1 actually distort the waveform delivered to load 2 if load 1 is directly connected to the mains?
(I guess part of the confusion also lies in the difference between noise on the earth and noise/reactance on the circuit conductors superimposed on the mains waveform, maybe there are two different answers...)
The answer that I've came up with in my head is down to the natural impedance of the wiring in the system forming a voltage divider - so although load 2 is connected straight to the mains, it is done so through wiring with a finite impedance that will 'drop' a voltage, meaning the supply voltage and the voltage measured at the input to the device will be different - they are either side of a given impedance of wiring, thus different nodes in a circuit.
Or put another way, the voltage at the socket outlet feeding the affected device will be a summation of 1) mains voltage (through the impedance of the supply wiring) and 2) noise/distorted power from another load (through the impedance of whatever wiring affects the two) - with the affected load sitting at a given node in a voltage divider.
One last point - a lot of venues have 'Sound Power' supplies, Technical Earth etc. Again while I broadly understand the concept of separating noisy dimmers/SMPS from audio equipment, surely the fact that they all common back to the same earth would introduce interference? ...or again, is it the fact that because you're lowering the impedance between earth and the affected load (giving it a good direct connection) and increasing the impedance between noisy load and affected load (putting it on a different radial earth branch) then it naturally puts the affected load at a better point in the theoretical voltage divider?
Would appreciate if someone could steer me in the right direction, not sure how many other people end up thinking the same.
Thanks,
Simon
Sorry if this isn't the right forum for this. Didn't look to be far off...
So I'm looking for some advice please with regards to interaction between loads sharing a circuit. I understand (or think I do!) a lot of the composite concepts and I think I have an idea of what my answer might be - but I want to bounce this off those with more experience and see where I'm wrong. I work in the entertainment industry with lighting and audio systems. I have a fairly good understanding of electrical principles but have no actual electrical qualifications (although I've considered training soon, that's another story).
So...
In several instances in our industry and outside it, I often hear people exclaim that a given device on a supply is affecting the power delivered to others on that supply. Take the scenario of a TRIAC-based lighting dimmer and an audio amplifier, both taking power in parallel from a given supply, with the amplifier buzzing when the dimmer is at certain dimming values. Often someone will say something to the tone of 'that dimmer is sending c**p back down the line'. SMPS supplies are said to do the same.
Now, on a conceptual level this makes sense - switching noise generated in the TRIAC on each dimmer channel is affecting the amplification stages in the amplifier and becoming part of the output signal. However, I can't seem to fully understand the electrical details behind this.
(For the moment, I'm discussing noise/distortion transmitted through mains wiring - not signal-level interconnection between two devices - I know Ground Loops are another story)
Both devices are connected to earth and the supply via suitably low impedance wiring, so why would any noise generated in load 1 (an SMPS/dimmer/other noisy supply) affect the power supplied to load 2? How can load 1 actually distort the waveform delivered to load 2 if load 1 is directly connected to the mains?
(I guess part of the confusion also lies in the difference between noise on the earth and noise/reactance on the circuit conductors superimposed on the mains waveform, maybe there are two different answers...)
The answer that I've came up with in my head is down to the natural impedance of the wiring in the system forming a voltage divider - so although load 2 is connected straight to the mains, it is done so through wiring with a finite impedance that will 'drop' a voltage, meaning the supply voltage and the voltage measured at the input to the device will be different - they are either side of a given impedance of wiring, thus different nodes in a circuit.
Or put another way, the voltage at the socket outlet feeding the affected device will be a summation of 1) mains voltage (through the impedance of the supply wiring) and 2) noise/distorted power from another load (through the impedance of whatever wiring affects the two) - with the affected load sitting at a given node in a voltage divider.
One last point - a lot of venues have 'Sound Power' supplies, Technical Earth etc. Again while I broadly understand the concept of separating noisy dimmers/SMPS from audio equipment, surely the fact that they all common back to the same earth would introduce interference? ...or again, is it the fact that because you're lowering the impedance between earth and the affected load (giving it a good direct connection) and increasing the impedance between noisy load and affected load (putting it on a different radial earth branch) then it naturally puts the affected load at a better point in the theoretical voltage divider?
Would appreciate if someone could steer me in the right direction, not sure how many other people end up thinking the same.
Thanks,
Simon