RS485 power configuration

[alainc]

Hi !

I'm building a control system that uses RS-485. I have a master controller

display that communicates with remote sensors and output boxes. My idee

is to have an isolated power supply in the master controller that powers the

remote sensors (i can't put a power supply on the sensor nodes, too small).

My question, is it possible to supply power to remote nodes at more then

1000' and what could be a good (for industrial controller) approch for

powering the remote nodes, should i have a isolated power, say 6V in the

master and then have a small footprint voltage regulator on the nodes, or

maybe i don't need iso power on the master controller. Help would

really be appreciated. Thanks !

Alain

 

[JimB]

You need to find:

The current taken by each node

The resistance of the cable to each node

Then calculate the volt drop along the supply cable.
Depending on that volt drop,
If the drop is low, just wire it up and the job is done

If the volt drop is high,
consider using a thicker cable
or, put regulators at each node, and put a higher voltage supply at the master.
The voltage at the master must be at least equal to (regulator minimum input + cable drop).

Dont forget that you will have to allow for the volt drop in both supply and return wires from master to node.

JimB

 

[alainc]

Hi Jim, thanks for your inputs. Ok i figured on a 5V supply comming from the master i could go about 800' before the voltage gets to low(4.8v) for the rs485 driver (MAX13487E), so my option to go further would be to output maybe 6v from master and regulate to 5V at the nodes using a small volt reg.
thanks.

Alain
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[blueroomelectronics]

What wire guage are you using?

 

[alainc]

Hi Bill,

I'm using 3 twisted pairs 26 gauge CAT5, one pair for data and one for power and ground.