Hello….I need some help.
I'm developing a DC circuit which will sit behind a wall mounted light switch and perform a function not related to my call for help.
The DC circuit will derive its power from the available AC conductors which exist in the back box at a generic light switch location; these conductors are part of a lighting circuit. The available conductors will be an AC unswitched, an AC switched and a ground - I am assuming that a neutral conductor will not always be available (at least it is not common in the UK) and I do not want my circuit to require a rewire to provide a neutral conductor where one is not available.
I therefore need to generate power from the AC unswitched conductor which I will do so by using a PCB mounted isolating transformer, like the Block VB 1.5/1/6, which I will connect the primary coil in series with the AC unswitched conductor. This will generate a 6Vac supply which I will rectify to DC to power the DC circuit.
In other words I’m aiming to ‘harvest’ energy from the AC lighting circuit to power a DC sub-circuit which operates independently of the status of the AC load.
I have a few sticking points I am seeking a bit of inspiration to move my design forward:
I’m not a newbie to electronics however I have little practical experience of what works in the real world so I’m looking to you guys for some guidance to help me move one step closer towards my proof of concept. These are honest queries and I really would appreciate open and honest responses.
Many thanks,
Neil
I'm developing a DC circuit which will sit behind a wall mounted light switch and perform a function not related to my call for help.
The DC circuit will derive its power from the available AC conductors which exist in the back box at a generic light switch location; these conductors are part of a lighting circuit. The available conductors will be an AC unswitched, an AC switched and a ground - I am assuming that a neutral conductor will not always be available (at least it is not common in the UK) and I do not want my circuit to require a rewire to provide a neutral conductor where one is not available.
I therefore need to generate power from the AC unswitched conductor which I will do so by using a PCB mounted isolating transformer, like the Block VB 1.5/1/6, which I will connect the primary coil in series with the AC unswitched conductor. This will generate a 6Vac supply which I will rectify to DC to power the DC circuit.
In other words I’m aiming to ‘harvest’ energy from the AC lighting circuit to power a DC sub-circuit which operates independently of the status of the AC load.
I have a few sticking points I am seeking a bit of inspiration to move my design forward:
- The AC supply is intermittent such that power is only available to harvest when the light switch is closed. When the AC supply is available (light switched closed) the DC circuit will store energy in a battery however when periods when the AC circuit is not available (light switch open) the DC circuit will consume more power than can be held in the battery. I have not been able to come up with a way to enable permanent AC supply irrespective of the status of the light switch therefore have I missed something blindingly obvious as to how I can derive a permanent supply without wiring in a neutral? In my mind this must be possible as this product by LightwaveRF (http://lightwaverf.com/product/400-dimmer-lw400/) powers an electronic lightswitch, dimming electronics and a wireless transceiver from the AC unswitched conductor without a neutral.
- If the isolation transformer approach is a feasible one then as the primary coil is in series with the AC load the full load current will pass through the primary coil. I am concerned that the primary coil will burn out when under full load, is there a way I can calculate the current rating of the primary coil?
- An alternative to subjecting the primary coil to the full load current would be for the load circuit to bypass the primary coil therefore the bypass would carry the full load and the primary coil circuit would only draw the power it requires. However as there is no neutral present would bypassing the primary coil just in effect short both sides of the coil together with a voltage waveform of the same potential and phase?
I’m not a newbie to electronics however I have little practical experience of what works in the real world so I’m looking to you guys for some guidance to help me move one step closer towards my proof of concept. These are honest queries and I really would appreciate open and honest responses.
Many thanks,
Neil