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Author Topic: Modbus control of Nowforever VFD troubles with usb interface  (Read 5045 times)

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Modbus control of Nowforever VFD troubles with usb interface
« on: August 06, 2016, 07:26:13 PM »
I've connected my nowforever vfd with a USB->RS485 interface and I can write to it to change frequency (2301, 901HEX) but I get a error response. This is using modbus master poll software. In mach3 I can't get it working at all. It does however seem to be a problem with the response from the slave not returning properly.

I have programmed a PLC to set the frequency and read out a few parameters and that works flawless so it's some kind of issue with the computer/settings/interface I guess.

I don't know how to upload pictures to this forum but I hope I don't break any rules by posting a link to another forum where I have uploaded photos/logs/screenshot that explains the problem more in detail.

http://www.cnczone.com/forums/chinese-machines/275124-cnc-cad-software-forum-post1921498.html#post1921498
Re: Modbus control of Nowforever VFD troubles with usb interface
« Reply #1 on: August 06, 2016, 07:37:58 PM »
I'll reply to myself. I realized when looking through pictures that the  VFD and the PLC was grounded common and that I used only two wires for RS485 skipping ground wire. With the computer prolly not grounded that good since the PSU isn't grounded I guess it must have been some potential difference. Grounded the RS485 interface and communication was working.
Re: Modbus control of Nowforever VFD troubles with usb interface
« Reply #2 on: August 06, 2016, 07:56:17 PM »
Don't you wish all problems were this easy to solve????
Mike
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
Re: Modbus control of Nowforever VFD troubles with usb interface
« Reply #3 on: August 06, 2016, 08:38:45 PM »
So true :) Guess I ask to fast on a forum but sometimes you work so long with a thing that you get stuck looking at the wrong things/over complicating the problem. This was kinda the same thing. I've been working on it more or less the last 12hours not getting much progress. When I started going through pictures and making posts it got me looking at it from another perspective and it gave me a idea :)