Communication problems with PowerOne Inverter

[Russell Manson]

For the last 9 months I have been using Aurora Communicator to monitor my wind turbine's output . I am connecting through a RS485 to USB to a PowerOne 6Kw inverter. Last week it lost the connection and I cannot get it to reconnect. When I do a scan it does not find the inverter. The panel on the front of the inverter still shows all the correct readings. I have tried the RS485 to USB lead on another inverter and it works fine. I have a friend that has a similar problem - his communication will reset if he shuts down the inverter and restarts it. Any ideas of what the problem could be?

[Rob Beckers]

Russell, if the same PC, software, and wire works OK on another inverter I would suspect a hardware issue with the inverter. If you want you can open an RMA case with Power-One, to get it fixed/replaced. I can help you get that started. FYI, the one time I have seen a similar issue Power-One tested the inverter after they received it back, and it worked fine (in other words, this is an unusual issue).

Alternatively, you can do away with USB and the somewhat flaky Windows drivers by using RS485 directly. This also allows much longer wiring lengths. I've been using this RS485 adapter with success: http://www.robotshop.com/ca/devantech-usb-rs-485-interface.html

-RoB-

[Russell Manson]

Thanks for your help.
It seems rather drastic to send the whole unit back -it is on a wind turbine and presently I am producing around 100kW per day so for me it is the wrong time of year to send it back! I would like to try the USB connection on the side of the inverter but I have had no success in installing the driver. I am using Windows 7.
Strangely enough, I think I am using the same USB to RS485 converter
http://proto-pic.co.uk/usb-to-rs485-interface-module/
I appreciate that it is not a common fault but it is a real miss not having the facility to monitor it remotely.
There is another strange problem on the inverter - as soon as the daily total reaches 65kW it resets itself back to zero. The figure in the General Status for the daily production is wrong(it doesn't add on the 65kW) but the total production is correct.

[Rob Beckers]

Hi Russell,

I misunderstood your original post; thinking you were using the USB interface on the inverter. It's rare that people use RS485, most use the USB interface. The Devantech converter looks to be the same I'm using.

The issue regarding a reset of the daily production count at 65 kWh sounds like a firmware bug. Keep in mind that these inverters were originally designed for solar PV, and it would be very hard to get anywhere close (even in the sunniest location on the planet) with solar on a 6kW inverter (we see around 45 kWh at best for an oversized array on the most sunny/cold day late spring when maximum production occurs). Could be there's a 16-bit counter, counting Wh, since that would wrap around at 65,536. I'll pass it on to Power-One tech support, though unless they are particular bad there is no desire desire there to fix firmware bugs (something about having to go through part of the certification again if they make changes to the firmware). It could help prevent the same bug in future inverters though.

Not sure what to tell you regarding the RS485 communications. I assume you've tried cycling the inverter (both grid and wind power off for a few minutes, so everything powers down). The USB interface is in essence in series with the RS485 one (it talks RS485-over-USB), so if RS485 is broken there's a good chance USB won't work either. It's unlikely for RS485 to fail, so be sure to test thoroughly before giving up on it.

-RoB-

[Bryan Inkster]

Russell, Since it worked previously it is a case of finding what changed and most importantly, if it is the inverter.

2 wire RS485 is not very easy to fault find but there are some checks that can be done. If the link has only "degraded" then it is possible that it will work at a lower baud rate. Try setting it to the lowest baud rate (at both ends). Note that my 3.6Kw Aurora allows setting baud rate on the buttons but the settings only stick until the next power down. Then it reverts to the default 19.2 Kbaud. This may be the same on the 6Kw?

The inverter normally listens for a data request from the PC so there will be no voltage on the pins when disconnected. There will be 120 ohm resistance to ground when the Termination switches are closed and my 3.6Kw shows 10Kohm with switches open. Check both with a multimeter. The PC sends quick bursts of data requesting information from the inverter then listens for the inverter's reply. The best way to check this is using an oscilloscope. You will see "activity" using a multimeter. Check that the signal is there, on the PC wires, when not connected, then connect them to the inverter and check that they are similar levels (to the disconnected state) and not loaded down by a fault in the inverter. Note that the data+ line normally sits at +5v and goes to 0v during data and the data- line sits at 0v and goes to +5v during data.

I traced the circuit of my 3.6Kw unit and replaced damaged components after a lightning strike. There is a MAX485 driver ic and a SO727 surge arrester ic in the circuit.

[Bryan Inkster]

Russell, Afurther update. I just rechecked my figures.
The termination resistance is between data+ and data- (not to ground) 120 ohm when on and more that 10K when off.

With the RS485 disconnected and the inverter powered up and running, my 3.6Kw unit gives a dc reading on the data+ line = 1.5v and data- line = 0.3v both with respect to gnd.

[Russell Manson]

I did some measurements today and for both the 6Kw and 3.6Kw inverters - the termination resistance was about 120 ohms with switch on - with the switch off it was in the meg ohms so that looked ok. For the 6Kw inverter gnd to +ve 2.6V and gnd to -ve 2.6V - for the 3.6Kw inverter gnd to +ve 1.047 V and gnd to -ve 0.095V. I tried adjusting the baud rate at the computer end but that didn't work - in fact it failed to connect to the 3.6 KW inverter when set at a lower rate - it didn't look as if I could adjust the rate on the 6Kw inverter at the inverter end. Still not having any success with the USB to RS485, I connected the old setup that I had using the serial port on the computer and Aurora RS485 to RS232 adapter and it immediately saw both inverters - very strange. It is working perfectly and I am very relieved! Could it be the Devantech converter? (but it works fine with 1 inverter and I believe I have the terminations correctly set.)

[Bryan Inkster]

Russell, It sounds like it may be the Davantec usb/RS485 converter.

The point here is that these 2-wire converters have to swap from listen to send and back again and there is always a compromise involved in the timing of the switching back to listen. You might think that the faster the better but i it is too fast then the stop bit of the previous data might be chopped short. On the other hand if it is done too slowly then received data might be missed. This can only be analysed on an oscilloscope and it is not that easy to do because you have to synchronise the scope to the exact moment of changing from Transmit to Receive. Even then, if you find a timing overlap problem, there is nothing you can do because the converter has no adjustments.

Presumably your RS232/RS485 converter has timing which suits the Aurora. I have, in the past, adjusted the timing in RS232/RS485 converters to match my Aurora 3.6. The timing is set by a C+R time constant circuit so you can tweak component values while watching performance on a 'scope.

[John Szegda]

Thanks for your help.
It seems rather drastic to send the whole unit back -it is on a wind turbine and presently I am producing around 100kW per day so for me it is the wrong time of year to send it back! I would like to try the USB connection on the side of the inverter but I have had no success in installing the driver. I am using Windows 7.
Strangely enough, I think I am using the same USB to RS485 converter
http://proto-pic.co.uk/usb-to-rs485-interface-module/
I appreciate that it is not a common fault but it is a real miss not having the facility to monitor it remotely.
There is another strange problem on the inverter - as soon as the daily total reaches 65kW it resets itself back to zero. The figure in the General Status for the daily production is wrong(it doesn't add on the 65kW) but the total production is correct.

Hi Russell,
Can you tell Me what type Generator and capacity you have, that is producing 100KW per day.

John

[Bryan Inkster]

John,
I can reply for Russell because I have the same machine as his which is an Eoltec 6KW. I can add that the best days are over 120KWh. Russell and I are lucky enough to have our installations in the Orkney Islands which are windy. Last year I had 18000KWh and some of the more exposed units get 24000.