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Messages - gxmpersonal@gmail.com

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Technical support / Nano10 MCU chip temperature

« on: February 27, 2022, 12:09:48 PM »

Now that I have gotten my Nano10 up and running, it has been powered for a week straight and working great. I noticed the main chip seems very hot.

I have not measured the exact temp yet, but I can't keep my finger on the chip, I would estimate it must be at least 130F. Is this normal? What is the safe operating temp?

I had a few copper ram heat sinks, so I put one on the MCU chip. The sticker did not come off easily, so I left most of it on. I know it is not the best thermal interface, but with copper heat sink is getting very hot, so it is pulling heat out of the chip. I think it dropped the temp a fair bit, but it is still over 110F. I will try and get a real temp measurement soon. I have it inside of a plastic enclosure, of about 50 cubic inches. The air inside does not seem warm when I open the lid, and I left the box open for a while, and it did not seem to lower the chip temp. Should I add vent holes and/or a fan to move air past the board?

Technical support / Re: Nano10 RS-485 Modbus termination

« on: February 26, 2022, 01:09:49 PM »

Thanks for the input. I had worked with RS-485 quite a bit in the past, but this was my first time setting up a new link in a few years. I never had a problem like this before. Most of the gear I used in the past had chassis ground referenced ports and with just a simple termination resistor at each end, we never had data issues on the buss. I am sure the issue is with the power meters and not the Nano10. Maybe they suffer from some offset, noise, or other issue, I can't be sure without digging into the circuit, but I can be sure that having the data lines fail safe biased cured my problem. Now that I am getting every data request, I am not going to dig deeper into them. They are cheap, and if this project works out well, we may upgrade to better components.

This time, I spent about 3 days messing around with the two power meters and the Nano10 trying to get reliable data. The part that made this hard to diagnose, was that when I would try to monitor the buss, it would start to work. The Nano10 port never seemed to have a problem, but the power meters just were either not seeing the requests, or the request was invalid due to a data reception error. When I first connected the buss tot he PC to monitor it, I was using the cheap RS-485 adapter that came with the power meters. This USB to RS-485 device supplied a mild bias, with just a pull down on the D- lead. It only has two terminals for the buss, and no signal ground lead. It worked ok when connected to just one power meter, but was not completely reliable with the 2 connected. The U-485 adapter that I purchased with my Nano10 made the buss completely reliable as soon as it was connected to the UBS port. Looking at my scope, I it appears to be providing bias to both data lines. Even with only the D+ and D- connected, it was instantly rock solid.

The power meters do have isolated ports. There is a tiny switching power supply to power the 485 interface chip and a pair of optocouplers to get the data from the logic to and from the interface chip. I did not measure any leakage current from the line measuring side to the interface side. I agree, the isolated port was part of the problem, but it was not the only problem. I did try tying the negative power supply of the Nano to the signal ground of the isolated port, but that did not cure the situation. Termination only across the two signal wires also did not help, but once the buss was biased, the data became rock solid.

The power meters even have the interface 0v signal ground and 5 volt available on the terminal block with the data D+ and D- data pins. That made it very easy to just add the resistors there on the unit at the end of the data buss. In normal operation, my data buss is only 6 feet. At 9,600 bps, I did not expect any issues with data. The two power meters are in a common box, with just a few inches of wire between them. The CT's to measure the current are remoted to the breaker panel. I did not want to place the electronics in the breaker panel and run the data in there. I only have the signal ground connected at one of the power meters, the other one only has the 2 data wires connected, at this time, and it is responding to every query and no data errors. I thought I might need to tie the signal grounds, but it has not shown to be an issue at all.

Technical support / Nano10 RS-485 Modbus termination

« on: February 22, 2022, 12:19:47 PM »

I am working on an energy monitor project where a Nano10 is monitoring solar production and energy usage.

Most of the data and control is coming from ModBusTCP talking to a Schneider inverter. But we also need to know the power being used by loads back in the main panel. So we added a pair of ModBusRTU power monitor boxes. I tested them with their supplied app from a PC and they were reading the power and accurate to my measurements. So I wired them into the RS-485 port on the Nano10 PLC. I was not getting any replies from either power monitor. I even tried them one at a time with no luck.

When I connected a fairly long line to get the RS-485 data into my PC, I saw that the app was using function 04, so I modified the code to use 04 with the SETSYSTEM command, and also added SETPROTOCOL to lock it to ModBus mode. And it worked. Everything seemed perfect.

I disconnected my monitoring cable and worked on the code for a bit and after a while, I saw the data return from the power monitors quit again. I am only running 9600 bps over 6 feet of wire, and I have 150 ohm terminating resistors at both ends. When I connected the monitoring cable back up, it started to work again.

I think the power monitors are either very picky, or they may even have a slight offset. Any noise on the RS-485 buss must be causing framing errors. The U-485 adapter I am using for monitoring at the PC appears to be adding bias resistors to the line. So when that is connected and powered in the USB port, it all works. I am adding bias resistors in my system now. I probably would have caught this a lot sooner if it had quit as soon as I disconnected the monitoring cable, but it didn't, it stayed working for over an hour for sure.

I did quite a bit of looking online and even in here to find anything about unreliable ModBus RTU connections, and I finally found a TI article talking about biasing the network to ensure a stable state when the bus is not being driven. I hope this post can help others from having the issue I had.