Navitron Renewable Energy and Sustainability Forum

Energy/Electricity Storage and Use/Grid Connection => Low Energy Computing => Topic started by: Ivan on July 20, 2013, 01:39:41 PM



Title: long distance rs485 for connecting inverters?
Post by: Ivan on July 20, 2013, 01:39:41 PM
Does RS485 really work over long distances? I've got to try to monitor 7 samil inverters. I'm planning to daisy-chain them with RS485 cables (RJ45), then the last one needs to connect to a PC. The nearest safe place I can leave a PC set up is about 80metres away - can I run this cable in CAT5 over that distance? I've read it works over 1200m- but that sounds like quite a long way! Also, when running the cables daisy-chaining the inverters, do these have to be run away from the mains cables (if so, how far?), or can I just cable-tie alongside the AC cables? Finally, is it ok to use the RS485 (cat5) cables to join inverters up to 25metres apart?


Title: Re: long distance rs485 for connecting inverters?
Post by: Mostie on July 20, 2013, 01:50:43 PM
hello Ivan, I have 3 Aurora's daisy chained with 4 core screened cable with an ebay RS485 to usb converter, that cable might be a better option.
however, I also ran 40-50 mtrs of cat5 to a Soladin with the DIY converter from this forum.


Title: Re: long distance rs485 for connecting inverters?
Post by: Ivan on July 20, 2013, 01:53:51 PM
I've got a roll of cat5 cable, twisted pair - would be handy if I can use this. the inner cores are wrapped in a silvery-coloured plasticy layer - not sure if that counts as screening or not.


Title: Re: long distance rs485 for connecting inverters?
Post by: Tinbum on July 20, 2013, 02:28:59 PM
I have my SMA inverters and  a webbox connected together using Cat6 cable that has about 75m between them. This works very reliably. The CAT6 cable is also run parallel and close to mains cables, no way to avoid other than by digging another 75m long trench.


Title: Re: long distance rs485 for connecting inverters?
Post by: knighty on July 20, 2013, 03:44:18 PM
Ivan, if you check your cat5 cable, it should have a letter after the cat5 bit... cat5 E is the best

(sometimes called cat6... but there is no 'legit' cat6 standard, not last time I checked anyway)


the better stuff is screened

it's better to run it away from the AV cables, doesn't matter on short runs, but it can make a difference on long runs

it sounds daft, but avoid any kinks/tight bends too, it messes up the twisted pairs


I'm guessing there only a very small amount of data to transmit, and it will be done quite slowly ?  do you know what kind of speed the inverter end runs at or if you can change it ?

running slower massively improves reliability :-)


Title: Re: long distance rs485 for connecting inverters?
Post by: Ivan on July 20, 2013, 05:18:46 PM
yes, small amount of data. I've just checked, the cable is CAT5e


Title: Re: long distance rs485 for connecting inverters?
Post by: Tinbum on July 20, 2013, 05:32:21 PM
The Cat 5e spec doesn't have any requirement for screening as far as I can see.

I recently wanted to extend my Ethernet temporarily so I just put an RJ45 connector on each end of a spare roll of outdoor cat5e cable (unscreened) I had. It caused problems so I had to shorten it.

Go for screened, its not that much more and check if its solid, stranded, copper or CCA (copper clad aluminium).


Title: Re: long distance rs485 for connecting inverters?
Post by: knighty on July 20, 2013, 07:38:33 PM
hi, yes there's cat5e screened and not screened, i should have pointed that out a bit better

with only a small amount of data, and slow transmission, you should be fine over 80m

I've got longer cables, running inside the house, around AC cables and running at gigabyte speeds :-)