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Topics - 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?

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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.

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