December 2009

A matter of attitude (1)

Practical knowledge about SMA system communications

The Sunny Matrix on the wall displays the current power output of the PV plant which you built in a neighboring area. The operator will be informed every evening about the daily yield via SMS. And during your vacation, you can solve a small problem by reaching the plant's WebBox via the Internet and making an adjustment to the inverters. Examples show that: with the modern system communications by SMA, a multitude of possibilities are opened. With the following practical indications, which are organized according to products and themes, we would like to help you to use them optimally.

1. Bluetooth® NetID: the electronic picket fence

Abb. 1: Im Handumdrehen eingestellt: Wahlschalter für die Bluetooth NetID am Sunny Boy 5000TL...

With the SMA Bluetooth wireless communications standard, solutions for system monitoring are especially easy to realize. This is because devices compatible with Bluetooth are easy to network, independently and rapidly, to form a reliable wireless network. In order to separate systems which are adjacent to each other, however, first you must establish a standardized network ID (NetID) for all inverters within one system. All inverters with the same Net ID then form a common wireless network.

Simply configured, simply connected

At the inverter, you set the NetID using a small rotary switch, which can be turned using a screwdriver (Figs. 1 and 2). The numbers from 2 to 9 are available, as are the letters from A to F, that is, 14 different values. The NetID "0" is used to turn off the Bluetooth functionality, with the 1 (factory setting) the inverter establishes a maximum of two data connections to computers with the Sunny Explorer software. The query devices (e.g., Sunny Beam with Bluetooth, computer with Sunny Explorer or the forthcoming Sunny WebBox with Bluetooth) are not set manually, but rather, they adopt the NetID of the inverters within range. If available, the different NetIDs from which to choose are listed. Since you should disconnect the inverters completely (on the DC and AC sides) after a change of NetID and must restart them afterwards, you should check for the presence of other Bluetooth networks before commissioning. To do this, use one of the query devices mentioned above.

Abb. 2: ...und am Bluetooth Piggy-Back (z. B. für Sunny Mini Central Wechselrichter)

2. Sunny Beam: which rechargeable battery should I use?

The mobile Sunny Beam yield display is also forward-looking when it comes to energy supply: by means of the solar cells the integrated accumulators are always charged when there is light available – that is, the Sunny Beam is independent from the power outlet. Should there be a need for a change of accumulators, however, you must take into account the different types of accumulator. In standard Sunny Beams, RAM-cells are used. The Sunny Beam equipped with Bluetooth, on the other hand, uses state-of-the-art NiMH accumulators of the "LSD" type, with a similarly reduced self-discharge. One must not confuse these two, because they have different cell voltages and also because they are charged differently. Both have the form of AA cells (mignon).

3. Sunny WebBox: sending data via mobile cellular wireless

Abb. 3: Die Antenne grundsätzlich einschrauben: Sunny WebBox mit GSM-Modul

When you use the Sunny WebBox with GSM module, you can transmit the plant data independently from a classic telephone or data line. You only need a GSM cellular network with a strong enough signal where the Sunny WebBox is located. For a successful configuration, two things must be observed, however: upon commissioning the GSM module you must always use as a dialing number for the data connection the "99***1#", mentioned in the manual (this is valid for all service providers). The asterisks are not variables representing random numbers, they are necessary command symbols. Please also note that the antenna included is always screwed on, – even when you are not intending to use the GSM module (Fig. 3). Otherwise it could happen that the Sunny WebBox does not start, or that the network connection is interrupted at irregular intervals.

4. RS485: how does the flexible data network work?

A field bus (e.g., RS 485) is a system for the data exchange among several devices via a common line. Unlike the computer network in your office or the 230-volt (or 120-volt) cabling in households, the assignment and connection of the devices in many field buses is not done in just any way. In case of the RS485 field bus, the individual participants are connected one after the next on one single cable going through – like pearls on a thread. Branches are not allowed here, nor are rings or star-formed structures (Fig. 4). Nevertheless, the bus system offers a few advantages. The order of the participants has no effect: if you install several inverters and one Sunny WebBox, it makes no difference if the Sunny WebBox is at the end of the cable or between two inverters. In addition, bus participants can be added or deleted at any place.

Abb. 4: Der RS485-Bus wird in Linientopologie aufgebaut

Important detail: the termination resistor

You must make sure that the bus cable is terminated on both ends with termination resistors. In the case of Sunny Mini Central inverters, older Sunny Boy series and the Sunny WebBox, the termination resistor on each device can be enabled or disabeld: using jumpers, small plugged bridges which are connected at corresponding poles on the circuit board and which function as switches. In the case of inverters, the termination resistor is disconnected at the factory (no jumper) whereas it is connected at the factory in the case of the Sunny WebBox. In case of inverters of the new generation (e.g., Sunny Boy 5000 TL or Sunny Tripower) and of the Sunny SensorBox, a real termination resistor is connected between the terminals D+ and D– of the output side, which you have to remove, if required (Fig. 5).

Abb. 5: Klein, aber wichtig: RS485-Abschlusswiderstand in einer Sunny SensorBox

With these indications and practical tips you can use the SMA solutions for plant monitoring even better and apply them to multiple task. The second part of the series will deal especially with the configuration of the Sunny WebBox – including the network configuration.

Further Information

Do you have questions? Then you can contact our Service department by phone (+49 561 9522-1499) or via email (Serviceline@SMA.de).

In the following documents, which can be obtained in the download area (Service > Downloads), you can find detailed information on the topics visited: