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I have this problem: A photovoltaic system with Power one Aurora 12.5 inverter divided into two sections: one with 36 inverter, one second with 26 inverter. The inverters of each section are connected by a RS485 daisy chain cable.
I have recently installed a data logger that acquires the data of the first section (36 inverters) and everything is fine. Now I have to connect the second section (26 inverters) but it is impossible to pass a cable to complete the chain (the data logger accepts up to 64 inverters).
Studying radiomodems it seems to me that it is possible to replace the wired line with a radio link. If I have not misunderstood I should:
- Connect the RS485 line of the second section to the radiomodem.
- On the other side, near the data logger, mount the second radiomodem from which to take the RS485 line to be physically connected to the data logger itself.Which radiomodem would you recommend to me?
Can the ZigBee fit?Let's say I don't need exceptional speeds, as I just have to download numerical data from the inverters.
I would say that you have centered the application, given the reduced distance 400 meters as the crow flies, a pair of ZigBee radiomodems can be for you. I remind you that given the high frequency it is important that the two radiomodems are in optical view, no obstacles between the two within the Fresnel zone.
The application is very simple and a couple of ATC-3200 can do for you. The radiomodems are already equipped with both the RS232 and RS485 interface and have a limited cost.
I raise two doubts.
The RS485 standard can theoretically support up to 32 devices connected on the bus (with modern 485 nodes you can easily reach 128 nodes and with some particular 485 nodes and for this expensive you can reach up to 256 nodes) (See post). It is necessary to verify that the Power One inverters have this type of high impedance driver, otherwise the radiomodem connected with the data logger would have to drive 36 + 1 (Data logger) nodes, and there could be impedance problems.
On very large networks, we usually recommend splitting the network with converters optical fiber, to prevent extra voltages (e.g. lightning strikes) from causing faults on the entire system.
In the meantime, thanks for the information. Let's see the doubt about the impedance. As a data logger I am using the Power One EVO model. It has two RS485 ports, each can address up to 64 inverters.
The first one I use for section 1 (the first 36 inverters). I plan to use the second to address the remaining 26 inverters. I don't know how the two ports inside the data logger are connected; I hope they are decoupled, so as not to load all the impedances of the nodes on one line.
The radiomodem on the data logger side should therefore only see the 26 inverters + the impedance of the data logger. We hope well.
In your opinion, is the omnidirectional antenna provided enough or better to use a directional one?If the data logger has two ports, they are definitely decoupled, so no impedance problem, the radiomodem connected to the inverters will see 26 inverters, the radiomodem connected to the data logger will see only the data logger.
As for the antenna, if you position the radiomodem with its antenna at the top, maybe putting it in a watertight plastic box, you shouldn't have problems covering 400 meters. Of course a directive antenna would greatly increase the distance, but the cost of the antenna and cable exceed the cost of the radiomodem and honestly in your case I would try only with the supplied antenna.
I suggest you do transmission tests, using a radiomodem as a repeater (Connect the Rx with the Tx), the other radiomodem connected to the RS232 port of a PC, where with a terminal emulation program (Example Hyperterminal), you send characters and wait for the response echo.
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