I got an RS485 USB adapter so I can read the data from my solar inverter (Aurora PVI-2000-OUTD-AU). It’s just 3 screw terminals. The manual says the wire must be capable of 600V. I have some old phone extension cable I thought I would use, is this going to work or burn my house down?
Also there is an IP65 cap for the cable. I would like to make it permanent and waterproof, so where can I get one of these caps that I can run cable through?
Thanks!
Hmm. Connected up phone line to test and not getting anything. Assuming + should be connected to + on both ends. Solar has RTN (ground) but usb dongle doesn’t, so I left it disconnected, not sure if that should matter.
Ensured inverter has address set (2). Not sure if I need some software to tell the device what address to listen to - just assuming it merges it all into a single serial port like RS232.
Finally, not quite sure if a single inverter needs the terminator set on - manual isn’t clear but indicates it only needs to be on, on the last unit if in a chain.
Have tried the 4 options - terminator on/off, + and - swapped around, no luck.
I found Aurora Monitor which is FOSS and lets you configure com port and address. However still no response from inverter #2 (that’s its address) 
http://auroramonitor.sourceforge.net/
So, something’s wrong… possibly the really cheap USB device. Maybe it only works for low voltages.
The phone cable shouldn’t have any issues, chances are the 600V requirement is only for a fault condition, it won’t be operating the line at that voltage.
In regards to the ground/RTN, see if you can connect it to any metal parts of the RS485 adapter. Apparently if the two devices have a different ground potential, it can throw the signal out of the voltage range of either device (see here). Might just be a stab in the dark. Looks like the positive of one device should connect to the positive of the other device, same for the negative.
Good luck!
WOW! So when it does have said fault condition and 600v appears, vaporizes the wire, causes a fire and burns the house down, we can all drive round and toast marshmallows.
It might work fine right now, but do you want to risk your house/life on it when rated wire probably isn’t that expensive.
If there’s a fault and you’ve got 600V on that wire the insulation rating is going to be the least of your worries. Remember there’s going to be a computer and associated devices on the other end of the line, and I can guarantee that the USB port won’t enjoy sitting at 600V above the ground of the computer.
As a side note, the voltage rating of the cable is just what the insulation can withstand. If it’s exceeded the wire won’t vaporise, it’ll just arc through the insulation (mind you the voltage is too low to cover any real distance in air). The protection circuitry on the inverter, or even laptop will kick in well before the rating of the cable becomes an issue. So yeah, it could do damage, but there’s lots that will happen and have to happen before it can.
Today I got this basically working - I used cat5 twisted pairs, tying one of each pair together as ground and soldering that to the USB sheath. Then I was able to read data with aurora monitor and log it to PVoutput.org!
However, it was arranged with an old laptop outside on an extension cord, with the wire hanging out of a side panel on the inverter, so… not ideal. Need to figure out how to make this more permanent. Either run a long cable, or some wireless solution. An R.Pi could work but is a bit overkill. I also thought maybe Arduino could read from it and output over Nordic radios as I’m playing with those for other projects. In either case it’s not going to work from inside the inverter, so I have to pipe it out to somewhere.
Yeah you will get problems with those cheap USB rs232 converters. You also
need to run shielded cable and earth the shield to drain the interference
you her. You can get a rs232/rs485 to eathernet bridge and use that for the
long distance. But for the same price you can get a rasp-pi and stick it
next to inverter with a WiFi connection. Another good hack you can do is if
you have an electronic power meter the have an led that pulses for every
kWh you use. Just tape an ldr onto the meter to detect the pulse and you
can chart your consumption too.
Thanks for your help. When I get another chance to try it (probably next
weekend) I’ll use cat5 twisted pairs (one of each pair to ground) on a
shorter run and see if that helps. The phone line was pretty long and
unshielded so maybe it was interference.
I wouldn’t have used the phone line permanently, it was just the longest
cable I had handy - it had to run about 15m. I’ll have to get one of my old
laptops with Linux running closer to the inverter to test it. Once that’s
established I’ll need to get appropriate cable (probably cat5) to run to
wherever it’s going to end, and I’m not sure about that yet. I’d like to
run it to the R.Pi in my office but there’s no convenient way to run the
cable there, except maybe up through the floor and carpet.
Whatever cable I get, I’ll have to get an appropriate IP65 cap with it for
the inverter.