Constant current source with MODBUS - Page 1
Forum section: electronics / beginners

author: anvoice
author_rank: Frequent Contributor
timestamp: May 21, 2020, 09:06:56 pm
content: Hi, I bought two 50A constant current modules (CNC PSUs that I'm using or a different purpose) from ebay. There was a more expensive option with MODBUS, which if I understand correctly is a special communication protocol to connect it to a computer, but I didn't opt for that. Now the seller is telling me he will send me one with and one without MODBUS, possibly due to a stock issue. Does anyone have experience with these CNC power supplies with MODBUS? Does MODBUS imply I will not be able to control the module without a computer, or is it simply an added convenience? I'm fine with the latter, but if computer control is the only option I'd rather not get the MODBUS version.

author: wizard69
author_rank: Super Contributor
timestamp: May 21, 2020, 09:22:14 pm
content: Quote from: anvoice on May 21, 2020, 09:06:56 pmHow would we know? You mention nothing about the supplier, the model or anything else.As for Modbus, it is a communications protocol developed by Modicon (no longer exists) for communication with PLC's and similar hardware. It is actually fairly simple and there is an organization that now supports it as a standard.As for your power supplies we have no way of knowing what and how! I can imagine the supplies supporting a human interface along with Modbus but that isn't a given.

author: anvoice
author_rank: Frequent Contributor
timestamp: May 21, 2020, 09:28:08 pm
content: Quote from: wizard69 on May 21, 2020, 09:22:14 pmIt is this module:https://www.ebay.com/itm/273810462533?ViewItem=&item=273810462533Their description is rather poor with flaky english, they only show one version of the module, and their description of the parts of the board is in Chinese. I just assumed that someone might know whether MODBUS complements manual controls, or just replaces them.

author: senso
author_rank: Frequent Contributor
timestamp: May 21, 2020, 10:06:22 pm
content: There are lots of modbus programs to use on windows/linux/mac, and its just RS485, so lots of cheap USB to RS-485 adapters available as well on ebay, but you need a register map to be able to use it, might even be handy in the future.

author: anvoice
author_rank: Frequent Contributor
timestamp: May 21, 2020, 10:38:47 pm
content: Quote from: senso on May 21, 2020, 10:06:22 pmRight, just wondering whether I will be able to control it wuithout a computer if it does have the MODBUS option. I also don't know whether they have documentation for it, i.e. the register map.

author: wizard69
author_rank: Super Contributor
timestamp: May 21, 2020, 10:46:24 pm
content: Quote from: anvoice on May 21, 2020, 09:28:08 pmHonestly if they can't supply documentation I'd look elsewhere. I mean solid readable documentation. Otherwise you may end up struggling even with the manual one.QuoteWell looking at the little control box I can assume that the unit supports manual control and Modbus. But I could be completely wrong.As Senso indicated there is support for Modbus protocol almost everywhere. I would not dismiss a unit because it supports Modbus, in fact it is probably a good idea to have some sort of communications port on the device. With a good library Modbus is pretty simple as you just read and write registers. Of course you need to know which registers to talk to and this is where you need a decent manual.One other thing; As Senso indicated Modbus is generally RS485, however it can also be done over RS232. Of course if you use the unit manually it doesn't matter.

author: anvoice
author_rank: Frequent Contributor
timestamp: May 21, 2020, 11:44:34 pm
content: Then I will ask the seller if he has either a register map or control software in english. Otherwise it will not be usable, at least for computer control. Thank you for the input!

author: anvoice
author_rank: Frequent Contributor
timestamp: May 22, 2020, 05:50:34 am
content: Turns out it was the seller's way of saying they have 2 products, but what they are sending me will not have MODBUS.Is there any compelling reason to go for MODBUS? I could still cancel the order and pay them extra for this feature, but I don't see myself using it from what I know about it now.

author: ebclr
author_rank: Super Contributor
timestamp: May 22, 2020, 09:55:52 am
content: "Constant voltage constant current, optional MODBUS communication!"Apparently, modplus is a "plus" , Just make sure if they will come with the control panel, Perhaps the Modbus one is only controllable by serial modbus, but I don't think that is the case

author: anvoice
author_rank: Frequent Contributor
timestamp: May 22, 2020, 10:04:20 pm
content: Quote from: ebclr on May 22, 2020, 09:55:52 amCiting their listing,"Package Included:1 x 50A DC step-down power supply module constant voltage constant current LCD"So if there is no LCD, whether as a separate control panel or on the module, I believe that will qualify as not as described.