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RS485 Bus Power Help

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rrb011270

New Member
Mabuhay!

I am new to this forum...

Anyway, I have a project on RS485 network for 6 devices and one master which is the host computer.

I have successfully develop a simple protocol just to test if my RS485 network can send/receive data from master to slave device or vice versa..

My question is:

Would it be possible to have a bus power on my RS485 network since I have an 3 extra wire on my 6-wire bus...

I guess it would be cheap if I am going to implement it this way.. wherein all the slave device will get its power from the host computer thru the network bus...

Anybody on this forum who can provide help.. a schematics, tips, suggestion and/or any information will do.

Thank u
 

crust

Member
Do you have 3 extra wires? Doesnt RS485 typically have a twisted pair each for transmit and receive? In any case, it depends on the distance and your current draw. If it is CAT5 (ethernet) or phone cable, you will have quite a bit of voltage drop from the host to each slave device that is distance/draw dependent.. You could perhaps use AC rather than DC, and just have some simple rectifier circuit on your slave devices. If you have a larger gauge wire, you will be better off, but still might not work.
 

Camping

New Member
Hey,

I don`t know of its posseble because of the cable and the distens between master and slave and how much power a slave need.

I have worked with a RS232 protocol with RxD & TxD. But I had a 6 line telefoon connector so I put a GRND and 2 times a 12V line. And I have 1 line free now. With that I can gif a slave some power but its only 30 to 50 mA or so. So you can put a microprocessor in it and some leds not much.

Cya
 

rrb011270

New Member
I plan to use the CAT5 of a LAN cable which has 8-wire.. my RS485 uses one ground and two data lines coz this is a differential output... with this I still have 5-wire use for my application for a bus-powered RS485 network.

I am planning to implement this on a 48Vac or 48Vdc...

I don't know which of this two sources I am going to use? can u provide me some light on this?

What would be a better solution for my RS485 network with 6 slave and a host computer?

Thnx

crust said:
Do you have 3 extra wires? Doesnt RS485 typically have a twisted pair each for transmit and receive? In any case, it depends on the distance and your current draw. If it is CAT5 (ethernet) or phone cable, you will have quite a bit of voltage drop from the host to each slave device that is distance/draw dependent.. You could perhaps use AC rather than DC, and just have some simple rectifier circuit on your slave devices. If you have a larger gauge wire, you will be better off, but still might not work.
 

Sebi

Active Member
I also use this method with CAT5 cable. One twisted-pair for communication, 3-3 wires parallel for supply. My supply is 36V, and each slave device have buck regulators.
 

rrb011270

New Member
The 3-3 wires parallel is 36Vdc or each pair is 18Vdc?

Would it be possible if u can share the schematics of power supply circuits?

Sebi said:
I also use this method with CAT5 cable. One twisted-pair for communication, 3-3 wires parallel for supply. My supply is 36V, and each slave device have buck regulators.
 
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