24V dc lighting circuit

mhar · Apr 4, 2023

I am having a flat roof constructed with solar panels over. As it is a cold, vented flat roof I will be having 175mm of Cellotex insulation immediately above the ceilings which I am reluctant to dig into to fit downlights (which I have never been the world's biggest fan of anyway). My thoughts are to have plaster in led profile and led ctt tape which I have used to good effect in the past.

In order to avoid bulky power supplies everywhere would it be practical to run a 24V dc circuit (powered by two batteries in series with a voltage regulator to maintain the output). The dimmers and ctt changers that I have fitted in the past have been separate items after the driver. I intend to use a fair bit of tape for lighting.

Has anyone done this before or are there good reasons why not! Thoughts and practicalities would be appreciated

Lucien Nunes · Apr 4, 2023

The wiring can all run at 24V, starting from a PSU and distribution point somewhere convenient. Beware voltage drop, which is 100 times more severe at 24V than 240 (10 times the current, but 10 times less total volts to lose) and ensure that the OCPD on the 24V side will work (although like dimmers, the PWM controllers rather scramble any attempt to calculate fault current which will be tiny)

I'm not sure about the significance or function of the batteries; is this part of a UPS scheme?

mhar · Apr 4, 2023

Thanks for the reply. I have access to EnerSys Powersafe SBS C11F batteries removed from ups systems, they have about 10 years of anticipated life in them. Converting from dc from solar pv to ac for a power supply which then converts back to dc seems unecessary. Also the cost of the psu is a consideration as is the bulk of the things, concealing a number of these would be an issue especially if I was running a standard 240V ac circuit and required multiple drivers.
I note your comments on volt drop. Luckily I am unlikely to have any run much over 10m. I envisaged using 3182Y flex and each circuit going back to a vehicle type fusing system.
These are initial thoughts, if there is a good reason not to have a dc circuit then I won't, I would be intersted to discover why this isn't done though. Since the adoption of led lighting it seems sensible to me though

DPG · Apr 4, 2023

mhar said:
Thanks for the reply. I have access to EnerSys Powersafe SBS C11F batteries removed from ups systems, they have about 10 years of anticipated life in them. Converting from dc from solar pv to ac for a power supply which then converts back to dc seems unecessary. Also the cost of the psu is a consideration as is the bulk of the things, concealing a number of these would be an issue especially if I was running a standard 240V ac circuit and required multiple drivers.
I note your comments on volt drop. Luckily I am unlikely to have any run much over 10m. I envisaged using 3182Y flex and each circuit going back to a vehicle type fusing system.
These are initial thoughts, if there is a good reason not to have a dc circuit then I won't, I would be intersted to discover why this isn't done though. Since the adoption of led lighting it seems sensible to me though

The losses in your regulator may well be nearly as much as the losses in the LED driver that steps 240VAC down.