[Al_The_Man]

BTW, here is something that many have used as a guide and is a set up for disaster and has caused shorted outputs of the BOB etc, causing the relay to stay on.
The PDF shows a 20amp relay to operate a VFD ~20ma input!
But the significant error is there is no BEMF diode fitted across the relay coil.
When a relay such as this opens, there is a very large BEMF which can be in the order of several hundred volts.
The output device is usually either a mosfet or by-polar transistor, the rating of which is generally typically ~60vdc.
This can, and has, resulted in the shorting of the output device causing the relay to stay on.
Al.

[mactec54]

BTW, here is something that many have used as a guide and is a set up for disaster and has caused shorted outputs of the BOB etc, causing the relay to stay on.
The PDF shows a 20amp relay to operate a VFD ~20ma input!
But the significant error is there is no BEMF diode fitted across the relay coil.
When a relay such as this opens, there is a very large BEMF which can be in the order of several hundred volts.
The output device is usually either a mosfet or by-polar transistor, the rating of which is generally typically ~60vdc.
This can, and has, resulted in the shorting of the output device causing the relay to stay on.
Al.

Correct if this was a coil operated Relay, I advise anyone to use solid state Relays, which almost all have the diodes built in so no need to fit another one, it does not matter what size the amp rating of the SSD either, they are only being used as a switch simple ON / OFF to control a VFD Drive FWD control, they come in the same form package size, Just pick a quality SSD like Opto 22 or similar

This can not cause any kind of shorting of the output device if you use a SSD, I have been using them this way for more than 30 years and have never seen one fail, because of a short from switching, have some currently on my own machines which are over 15 years old and are still working as when they where installed

Coil operated Relays are a relic of the past SSD is the only Relay any new builder should be using

[Al_The_Man]

So is this an about face of post #14???

Also many of the Chinese BOB's include a mechanical relay to operate the FWD operation of the VFD.

[mactec54]

So is this an about face of post #14???

Not at all

Also many of the Chinese BOB's include a mechanical relay to operate the FWD operation of the VFD.

Correct and they work fine most are already protected, some are not, but cause no problems, also they are not a relic, like what is used in the Homann design, ( 48v Coil ) so don't cause any VFD Drive connection problems with this type of switching, I have tested most of, even the cheapest $5 Breakout Boards that have built in relays and if they work, don't cause any problem for VFD Drive switching

[Al_The_Man]

Doesn't matter what (mechanical) relay is used, it is imperative to fit the reverse diode when fed from a solid state device.
Even if not, due to noise imposed issues.
If the relay is built in to the board, then it should normally have the diode.
I am referring to the likes of G540, that some (unnecessarily) use a external relay as shown on the Homann diagram.

----

[mactec54]

Doesn't matter what (mechanical) relay is used, it is imperative to fit the reverse diode when fed from a solid state device.
Even if not, due to noise imposed issues.
If the relay is built in to the board, then it should normally have the diode.
I am referring to the likes of G540, that some (unnecessarily) use a external relay as shown on the Homann diagram.

----

Most Solid state SSRs already have that protection so a diode is not needed, and if you wire correctly you don't have a noise problem which I have proven many times

The Homann Design is just one of many that have used a similar wiring diagram to use Relays, any one that uses a Relay with the G540 has experienced false starts which have happened with many G540 installs but not everyone is using a G540 there are a lot more that just use a regular Breakout Board and stepper Drives

[Al_The_Man]

There seems to be some confusion as to the Description Relay, RELAY, although a little vague, is commonly used among electrical/electronic personnel to mean a mechanical coil operated device when referred to this way..
If a solid state version is referred to, the term SSR or Opto relay should be used..
Essentially the interface I suggested is the same technology used in a SSR/Opto, just it does not have galvanic isolation.
Which in practically all situation is no problem due to isolated supplies used.
Just simply enter 'Relay' into Google and see what comes up.

[mactec54]

There seems to be some confusion as to the Description Relay, RELAY, although a little vague, is commonly used among electrical/electronic personnel to mean a mechanical coil operated device when referred to this way..
If a solid state version is referred to, the term SSR or Opto relay should be used..
Essentially the interface I suggested is the same technology used in a SSR/Opto, just it does not have galvanic isolation.
Which in practically all situation is no problem due to isolated supplies used.
Just simply enter 'Relay' into Google and see what comes up.

Every Manufacture calls a SSR a Solid State Relay, galvanic isolation Great word, and what most systems lack hence the need for a Relay of some kind you choose what you want to call it, or use to do the job

[Al_The_Man]

Yes, SSR IS a Solid State Relay.

I was referring to the word 'Relay' in the accepted general sense, when used on its own with no other reference, where it is universally acknowledged to mean the electro-mecanical kind.!

[mactec54]

Yes, SSR IS a Solid State Relay.

I was referring to the word 'Relay' in the accepted general sense, when used on its own with no other reference, where it is universally acknowledged to mean the electro-mecanical kind.!

Hey Al this is a mostly hobby forum and adding Tec terms is not needed, when someone writes Relay they then will know what that is, and can choose what type they want to use, or can ask if you want to get technical so no one can under stand that is fine by me, you must remember that most don't know the basic's of any type of electrical installation, but they get by with simple instructions

[ian8555]

I am massively confused by all this discussion. I thought Huagang vfd's can be controlled only by a 0-10v output, just one. 0v is off, 10v is full speed. No forward signal needed.

[joeavaerage]

Hi,

I thought Huagang vfd's can be controlled only by a 0-10v output, just one. 0v is off, 10v is full speed. No forward signal needed.

Mostly. The speed control is, as you say, 0V-10V, but you also require a set of relay contacts to turn it on.

Another means of controlling a VFD is by Modbus. Unfortunately early Huanyang VFDs had a non-standard Modbus protocol implementation. Some enterprising souls had made a plugin
that converted the standard Modbus to the Huanyang version....but it was a bit hit an miss. In recent years all Huanyang VFDs have a genuine Modbus compliant protocol.......so you can control the VFD
by either method (conventional:0-10V plus relay contacts OR Modbus).

Craig

[Al_The_Man]

I am massively confused by all this discussion. I thought Huagang vfd's can be controlled only by a 0-10v output, just one. 0v is off, 10v is full speed. No forward signal needed.

See the pic in the OP of the terminals, FWD & REV.