Maximum acceptable Voltage for Control Outputs
Cinch
Posts: 40
Well I'd like to use a Soundweb to Control some switches of an old \"ELA\" (100V lines based Speaker System). The Systems logic is build up with 24V Relays, a powerfull 24V PSU is also integrated. So it should be possible to use the control ports of the soundweb to drive the relays. But... I can't find any documentation telling about the maximum Voltage on a logic out port in sink mode. The only value given is 60mA, wich is enough for the relays.
Is there somebody able to confirm that 24V are ok?
Is there somebody able to confirm that 24V are ok?
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\"The logic output can source 10mA at 5V DC, or sink 60mA up to 50V DC.\"
This information is in the Installation Guides which can be downloaded from the BSS website.
The Installation Guides are also found in the London Architect Help.
that's exactly what I wanted to know
I always thought that the logic outputs can light up an LED or energize a small relay as explained in the installation guide.
The drawing in the help file shows a coil in series with the port and only the positive side of the power supply. Where does the negative part of the power supply go? On the common port? What happens if the DC power supply happens to have a different ground reference than the Blu unit? The newer switchers often float the neutral. Could that cause false readings on input ports that are referenced to the same common?
As you know, the 0v can be accessed on the 'C' terminals of the Logic Output block.
When using an external 24v PSU for the relays, then its 0v reference must be tied to the BLU's 'C' terminals (and not to any other point with a voltage ref ground).
When using multiple units, it is (empirically, but without access to and study of any diagrams) adequate to link the 'C' terminals between units and thereafter to return any relay coil current to any unit's ground.
While I have succesfully driven several 24v relays by sinking their coil curent into a Soundweb control port, I have preferred to be safe by reducing the BLU's exposure to external currents and voltages, and so I've installed a high current transistor between the BLU's port and the 'low' end of the relay's coil. It only required a 2 resistor divider to bias the base of a TIP2955 between ground and the coil.
Hope this might be of some assistance.
As I was asking the question, I'll try to explain it to you...
I wouldn't have understood it by DeltaXRay's post (even though the post is quite interesting anyway...)
Well the sinking feature is used if you have an external power supply, and you want to use soundwebs control port to switch on and off an external consumer powered by your external power source.
So what you would do is take your 24V eg. and wire it to a relay coil. The other side of the relay coil to soundweb control port and the 0V side of the power supply to the \"C\" port. Then you are in \"sink mode\". If the control port is triggered by your program, the impedance of the port is gowing down (measured to \"C\"), so your external power can flow and your relay is activated.
But be careful, the soundweb uses little transistors inside, they are getting warm, if they have to drive more current, thats why the sink mode is limited and why DeltaXRay suggests using external transistors.
Technical I think soundweb uses a so called open collector, with a pull up resistor. The resistor is supplying the limited power in souce mode and the open collector part is pulling down the resistence to 0 when the output is activated. This would explain why the output acts inverted in sink mode...
Hope you understood it now, if not ask again :-)