Waterproof LED lighting system with no contacts.

[treez]

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?

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.

 

[betwixt]

It is used in other contactless systems, your application isn't unique but it is technically sound.

Twisted pairs of wires tend to cancel their magnetic fields so RF radiation from the cable should be minimal. I run long lengths of CAT5 cable carrying high speed RS422 data parallel and about 3m away from antennas receiving microvolt level signals and transmitting 100W+ without them interfering with each other. A good sine wave also helps because it is (hopefully) free of harmonics. Double check that you are not producing much at 200KHz so you don't produce a 2KHz beat note with the BBC transmissions on 198KHz if these are used in the UK.

Brian.

 

[treez]

Thanks, also we would do the inductive couplers as in the attached. -Just standard E cores.
We believe that the best way to do the dimming is simply to vary the input voltage of the power supply.
Would you agree?
eg make it less than 390V to dim it.
The only other way is to vary the frequency of switching, or vary the dead time.

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.

 

[Easy peasy]

We did this for a tunnel way back in 1998, 1.6km, separating the feed wires just underneath the LED lights - done this way so cable could be buried in road and lights replace-able if destroyed... we used a plastic disc to separate the cable at the lighting points, glueing the lights in place after cable burying easy as they were brightest in the right spot. 250kHz to 100kHz depending on exact load and dimming ( less bright at midnight ) single freq sinusiodal current giving single freq RFI emissions.

 

[volker@muehlhaus]

We believe that the best way to do the dimming is simply to vary the input voltage of the power supply.

In Qi wireless charging (about the same frequency range) they have a resonant pickup loop, and vary source frequency to control secondary current.

 

[treez]

We did this for a tunnel way back in 1998

… Thanks, I see, because there’s no way of knowing how far apart the tunnel lights should be, you do it by trial and error with this “clip-on-off” inductive coupler lighting system.

they have a resonant pickup loop, and vary source frequency to control secondary current.

Thanks, I could be wrong, but I think resonant pick-up loops are for when you’re doing it wirelessly….when you have tightly coupled couplers like we have, there is no need for this resonant method I believe. In effect, all we have done 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 simple that you wonder why its not a commonly spoken about technique, with off-the-shelf couplers available etc etc.

By the way, what sort of coupling coefficient do you think we will get by the inductive couplers shown in the thrid post #3? (I doubt we will really get k=0.99)

 

[betwixt]

You can vary the voltage to control the brightness or you can send a signal down the wires in the same way as the power to operate individual controllers in each lamp. Phase modulation of the 100KHz is easiest at the receiving end but might be a problem to generate at the PSU. There is no reason why a second frequency can't be carried down the same wires as a signaling channel as an alternative method.

Brian.

 

[Easy peasy]

obviously it is far easier to have all the lamps the same brightness if you control a current loop....

 

[treez]

obviously it is far easier to have all the lamps the same brightness if you control a current loop....

Thanks, what do you make of the third lamp down in my schematic of post #1, which could use the shorting fet to pwm the secondary side bus and give dimming operation to an individual lamp?
I heard of one place where they literally pwm’d the output of the parallel resonant PSU, but that sounds like a bad idea.

 

[betwixt]

You can use that approach but the changing impedance across the transformer might influence other lamps in the chain. You would be essentially shorting out the transformer secondary to make the primary appear as a lower impedance.

What I had in mind was something more akin to outgoing DALI commands. You already have an isolated supply that can power a small micro and a fairly clean drive waveform that can carry modulation or a second control channel. You have to produce a control signal to the MOSFET anyway so why not utilize what is already there.

Applying PWM to an AC power waveform and sending it any distance, even on twisted wires sounds like a recipe for EMC disaster to me!

Brian.

 

[treez]

Thanks, ..One situation I see is that when an inductive coupler is suddenly clipped on to a live bus, then the bus suddenly “sees” the inductance of the inductive coupler, and this causes an overvoltage across the primary. There is not much that can be done about this because the bus isn’t accessible to put capacitors/snubbers across it etc.
LTspice sim of this overvoltage as attached.

 

[volker@muehlhaus]

Thanks, I could be wrong, but I think resonant pick-up loops are for when you’re doing it wirelessly….when you have tightly coupled couplers like we have, there is no need for this resonant method I believe.

Qi wireless charging uses two closely coupled inductors operating at around 100KHz. The different to yours is that you have a ferrite core, whereas they use coils with a small gap in between. The challenge in the Qi system is get high Q factor (low losses) is the coils. That's what you should also study: what happens if you add realistic losses for ferrite core and coil resistance?

 

[FvM]

I wonder if the product violates patents or trade marks of existing inductively powered lighting systems? A point to consider is also skin effect of the cable at 100 kHz, have you calculated it?

 

[treez]

Thnks yes skin effect, we have a special multi stranded cable. I am just thinking, copper thieves would love it. Maybe this is why nobody does this technique i show here, which is so incredibly simple.

 

[FvM]

Dimming of the average bus current isn't a problem. But it should be done in a way that ZVS operation of the driver stage is maintained. Pulse packet can be an option.

- - - Updated - - -

"Special multi stranded", do you mean litz wire (strand of enamelled wire)? Otherwise no skin effect reduction.

 

[volker@muehlhaus]

A point to consider is also skin effect of the cable at 100 kHz, have you calculated it?

Agreed, losses is a major limitation and might kill the idea. I worked as a consultant on optimizing 100kHz coupled coils for wireless power transfer, and yes, everything looks great until you start including losses in the system simulation.

 

[treez]

I wonder if the product violates patents or trade marks of existing inductively powered lighting systems?

Thanks, essentially the system i show here, as you know, is absolutely nothing knew...its simply a modified Seris Parallel resonant converter with its 'guts dragged out' so that the multiple ferrite couplers can be clipped on. It really is no more than that. -Just a standard topology.

Yes the bus cable is 7 strands of 1mm diam copper in a sheath.

The idea looks good, as these guys over in the States are already at it...
http://www.heicolighting.com/

 

[FvM]

As a follow-up to post #13, suggest to review US2012001564, US2016165685 and related EP applications.

 

[treez]

Thanks for the patent info.

I put your first patent number in and it came up with this
http://data.epo.org/gpi/EP1845755A3
..but it doesnt really explain it fully.

It is a fact though that only compnay in the world that seems to be doing this is heico lighting
http://www.heicolighting.com
...strange that theyre the only one.....though Easy Peasy says he did a likewise system for a road tunnel.
I doubt if this can be patented?...its just Faraday's Law, a primary coupled to a secondary...surely nobody can patent that?

 

[FvM]

Yes, these are HEICO patents, the applicator EMD technologies is named on the HEICO web site. It's not my job to evaluate the patent validity, but your company would be well advised to check it. If you can prove that the "invention" is 100 percent prior art, you may decide to simply ignore the patents, but must be aware of possibly law suits.