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As per standard DALI power supply should be 15 V at 250 mA. In the same time standard says that there can be up to 64 devices on the bus. So I can suppose that each DALI slave SHOULD cunsume 4 mA from the bus as the maximum.

Is this correct?

If so, is it OK to incorporate power supply in the controller with less current capabilities (let's say, 10 mA) for cases one controller - one luminare to avoid using of separate power supply?

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    \$\begingroup\$ The spec says that each device can take a maximum of 2mA from the bus. The 64 device limit comes from using 6 bits to define the address. \$\endgroup\$
    – Finbarr
    Mar 13, 2019 at 13:39
  • \$\begingroup\$ Thank you! That clears many things. However: what do you think if I put weak power supply (< 2 mA) in the controller for use in pear-to-pear cases? \$\endgroup\$ Mar 13, 2019 at 13:45
  • \$\begingroup\$ You can get DALI supplies with lower outputs, e.g. 70mA or 200mA; the maximum is 250mA and any supply must be current limited to that. I've no idea what the minimum would actually be but I would suggest 2mA is too low. \$\endgroup\$
    – Finbarr
    Mar 13, 2019 at 14:03
  • \$\begingroup\$ @Finbarr, you've stated that one DALI slave should take no morre than 2 mA. So if I will make my only-one-slave controller with 2 mA power supply it should work. Or not? :))) \$\endgroup\$ Mar 13, 2019 at 16:13
  • \$\begingroup\$ Maybe, maybe not. I wouldn't design it with such a low output. Are you so desperately short of power that you need to? \$\endgroup\$
    – Finbarr
    Mar 14, 2019 at 0:06

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Assuming the DALI device doesn't have an integrated bus power supply - that is to say, it is not providing the voltage on the DALI bus, there are two options. If it is powered by another input (not just the DALI one), usually a mains input, like an LED driver is, then it is subject to the limit of drawing 2mA from the bus. That limit applies over the range of bus voltages and other conditions, so you will probably find devices drawing 1.5mA at 16V, but don't rely on it being much less than 2mA.

If it is powered by the DALI bus then it can draw any current up to the 250mA limit whilst in the non-transmitting state (not pulling the line low). This option is typically used for occupancy sensors, light sensors, switch input devices and similar. The current rating must be stated by the manufacturer and as a system designer you have to ensure the sum of the currents in the non-transmitting state is less than your power supply current limit (the voltage remains high).

You can have just one bus power supply which keeps things easy, as a separate device from the other products (sensors, control gear etc) or multiple power supplies as long as they meet the overall requirements together, total current limit below 250mA. Or you can integrate the bus power supply into the controller (sensor, control plate etc) or into the control gear (LED drivers etc).

Wherever the power supply is located, there is also a minimum current limit of 8mA required by the standard.

So, no, each device is not allowed to consume 4mA from the bus unless it is classed as bus powered and has no other power terminals, and yes, a 10mA supply is acceptable.

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