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LED lighting system is totally waterproof..but is there a problem?

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Flyback

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Hello,

We have been tasked with lighting up another huge system of outdoor architectural water fountains with coloured LED lamps. In previous jobs, we find it’s a massive problem with moisture getting into all the connectors and contacts.

Therefore, for this build, we are going to use our new contact-less LED lighting system. For this, there is a single power supply, which puts a high frequency (100khz) sinusoidal current into a 30 metre cable (twisted pair). Its only the power supply we have to keep waterproof. All the downstream LED lamps have no metal contacts, and so they are waterproof. Each LED lamp comprises a ferrite coupler which “clips” over the 30 metre cable wires, and the secondary is embedded in this ferrite as a PCB “printed” secondary. –No contacts! – each lamp can very simply be clipped or unclipped, from anywhere on the cable that we like. It’s a perfect system. Why is no one else doing this? Its so incredibly simple. Its not even original, its just a series parallel resonant converter with its "guts ripped open" along 30 metres.

The current in the 30 metre cable is a beautiful sinusoid due to the resonant topology chosen. The voltage waveform is also smooth.

Can you see any problems with our new setup? What about RF interference? The 30 metre cable wire will be a twisted pair of multi-strand conductors.

Schematic and LTspice simulation as attached.
 

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dknguyen

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Maybe because it somewhat defeats the efficiency advantage of LEDs?

Do you guys use contact lubrication to seal against the moisture ingress? It's possible other people have found a way to make the contacts last.

Neat idea though.
 
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Flyback

Well-Known Member
Thanks, but this is more efficient than other methods for driving LEDs, because the driver stage is soft switching.

Do you think our inductive couplers are ok?
We will have to find some way of making the secondary embedded in the lamp casing so that it doesnt get exposed to atmospheric water. The coupler will be embedded in the lamp...so we have no metal contacts.
We will sweep the world with this design, as contact corrosion is a major grief point for electronics with DC voltages above about 24V that get wet or even a bit damp.

I think the best way for us to do the dimming is to simply reduce the input voltage to the power supply. Would you agree?...eg make it less than 390V.

The alternative is to increase the dead time of the fet switching.

The critical point is to avoid the switching stage going into the capacitive region, because that will mean severe reverse recovery of the fet diodes.
We are going to have to find the frequency below which the switching stage sees a capacitive impedance.

In effect, all we have done here is very simple indeed….we have just taken a series parallel resonant converter, and “ripped its guts open” and spread them out along 30 metres, and then simply connect secondaries along it. Its so incredibly mind-blowingly simple that you wonder why its not a commonly spoken about technique? ..with off-the-shelf couplers available etc etc.
 

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