Lighting LEDs- PWM dimming from a distance?

[GaelZorro]

Hello All,

I'm working an idea here and I'm trying to understand if it would be 1/ feasible and 2/ a good idea: to control 24VDC LEDs and (small) LED strips from 4W to max about 30W, right now I have the PWM dimmers (about 20kHz frequency) right next to the LEDs.
My idea would be to move all the PWM dimmers to one location in the switch box. Let's say one big unit, with 24 outputs for max 20 amps total.
For the bigger LED strips the PWM dimmers will stay right where they are.

The issues as I understand them:
1/ deal with the inductance of the wire, about 90µH for maximum 40 meters total round-trip: I can add a flyback diode to the outputs
2/ EM radiation from the 40 meters of unshielded wires with about 1 amp and 20kHz frequency through them: that's a total unknown for me. What are the consequences?
3/ Voltage drop: that's not an issue, I run the LEDs with 24V and in the worst case scenario the voltage drop is less than 0.5V: 2%, that's fine for me.
4/ Maybe other issues that I don't know about?

I'm asking because I haven't found a commercial product that does this, so maybe there's a reason?

Thanks for any advice!

[kvet]

@GaelZorro Hi, have you found answers on your questions?

[I wanted a rude username]

Last year I chatted to a guy whose business makes variable message signs ... the type you might see by the side of the road when there is construction ahead, with a big LED matrix. EMI is a huge problem even in that application where the cable lengths are much shorter. He had some proprietary solution that he didn't go into details on, but this is likely a major reason why you don't see it being done.

[ajb]

Local PWM with a well decoupled power input would be better in terms of EMI, but you have to be realistic about the dI/dt and dV/dt you're throwing around either way.  Soft switching the transistors (don't just slam the gate open and closed with a big gate driver at least) can help at the expense of increased power dissipation at the dimmer.

As far as the flyback diode goes, remember that the flyback current is equal to the initial current so you don't have to go crazy.