On 24/11/2019 04:18, Bill Wright wrote:
I want to put some LED lights on my sliding gate. I wondered if I could
power them inductively, with a power 'transmitter' fixed to the gatepost
and a power 'receiver' on the gate, positioned so when the gate's shut
they are close together and the LEDs come on. The power requirement of
the lights is 24W at 12VDC. The positional accuracy of the gate is good.

Bill

My electric toothbrush has a base which is connected to the mains and a
toothbrush which sits on the base to charge it. Effectively there is a
coil in the bottom of the toothbrush that charges the toothbrush battery
via a diode, and I imagine (I haven't dismantled one to find out) that
there is a similar coil in the base, though as it is connected to the
mains it will be a lot more turns of a much finer wire. When in close
proximity they form an air cored transformer, and the mains going in the
base charges the battery in the toothbrush.

In theory, a similar arrangement could light the diodes on the gate by
having one transformer coil on the gate and one on the gatepost.

There are some snags:
In order for a transformer to work (whether air cored or the more
efficient iron cored), you need alternating current going into its
primary winding. You will need either power originating from the mains
or a DC supply with an oscillator between power and transformer coil.

LEDs require DC, so you are going to need a rectifier in the gate
circuit, and unless you are prepared to put up with a 50Hz flicker it
will need to be a full wave rectifier, and ideally a smoothing capacitor
to protect the LEDs from spikes in the power input.

This is an outdoor gate, so you will have to make sure everything is
weatherproof. It can be done, but I would be inclined to look for an
alternative configuration: perhaps a battery pack for the LEDs on the
gate charged by a solar panel, and a proximity switch based on a burglar
alarm "door open" detector between gate and gate post? Or even a simple
plug and socket arrangement between gate and gatepost so that DC
arriving at the gate post gets to the LEDs on the gate when the gate is
closed and the plug and socket marry up?

Just as an aside, 24W is a lot of light from LEDs (it is roughly the
lumens equivalent to 4x60W incandescent light bulbs). Anybody shutting
the gate in the dark is going to get suddenly dazzled. Anybody opening
the gate and thus turning the previously lit LEDs off is going to find
themselves night blind for a couple of minutes.

Jim