HY VFD DCM connection

[Neale]

I'm currently replacing the motion controller in my router with a UC300ETH+UCBB board. Previous motion controller had an on-board relay for the VFD control which used a n/o contact to connect "For" to "DCM". DCM is the common ground for the digital inputs on the VFD. However, the UC300/UCBB combination does not have a relay. The UCBB digital outputs use a MOSFET to short the output to board ground, which is fine for things like the stepper drivers. I don't really want to have to install a separate relay board, so wonder if I can connect DCM to the UCBB ground and "For" on the VFD to a UCBB digital output. The main issue here is whether it is safe to connect VFD DCM to ground in the control box.

The HYmanual I have is no help on this one!

Anyone have experience of switching an HY VFD like this? I'm sure that there are plenty of UC300/HY VFD systems out there...

Thanks in advance,

[Doddy]

31021

That's from the manual. The UCBB should be more than able to drive the inputs to the VFD. Connecting the DCM to the main controller ground (/UCBB ground input) is perhaps something to be avoided if possible, but it's not the end of the world to connect them (arguably, less noise immunity). If there is a problem then you know you have a solution that is to provide true galvanic isolation with a relay. It might be worth examining your system - you *might* find you have a lightly coupled 0v reference in any case through any EMI capacitors in any SMPS you have, negating any advantage and the connecting of 0V to DCM may actually be beneficial.

Exec summary: It'll work, go into this with eyes open for noise immunity.

[Neale]

Thanks for the comments. My main concern was about the isolation of DCM inside the VFD but overnight it occurred to me that if I just check volts between FOR and DCM (expecting 12-24v or so), then both to control box ground, I can get some idea whether or not they are isolated. And if all else fails, I stick a relay in there. I've just found that I need to get a 16-pin IDC connector to pick up the analogue output on the UC300 as they don't provide that as part of the kit so things are going to be a little delayed anyway.

I have a copy of the manual - it's good that they show a circuit diagram of the board's interfaces. Gives a bit more insight into what's going on under the covers!

[dazp1976]

Thanks for the comments. My main concern was about the isolation of DCM inside the VFD but overnight it occurred to me that if I just check volts between FOR and DCM (expecting 12-24v or so), then both to control box ground, I can get some idea whether or not they are isolated. And if all else fails, I stick a relay in there. I've just found that I need to get a 16-pin IDC connector to pick up the analogue output on the UC300 as they don't provide that as part of the kit so things are going to be a little delayed anyway.

I have a copy of the manual - it's good that they show a circuit diagram of the board's interfaces. Gives a bit more insight into what's going on under the covers!

You can use Dupont 2.54mm wires/ connectors directly on the UC300eth IDC pins.
VFD FOR - DCM is just a ground sinking line.
External relay (or opto module) is needed to control it, COM/NC to make or break that single line (on/off).

See my posts of this cncdrive thread:
http://www.forum.cncdrive.com/viewtopic.php?f=22&t=3780&start=30

There are some wiring diagrams on page3 and images on page4

Diagram here too:
http://www.forum.cncdrive.com/viewtopic.php?f=19&t=3829

Shows connecting relay via Bob and also dupont uc300 direct.
Has AO1 wires too.

(your vfd may differ slightly)

[EddyCurrent]

I would definitely use an interposing relay.

[dazp1976]

I would definitely use an interposing relay.

You need to. Or any other kind of 'switch'.
You can't directly connect a breakout board / controller output to vfd FWD / DCOM.
It simply does not work (or will break them) .

Put a single wire link between fwd an dcom and fwd will come on. Break that link and it will go off.
Use the relay to control the make or break link.

[Doddy]

You need to. Or any other kind of 'switch'.
You can't directly connect a breakout board / controller output to vfd FWD / DCOM.
It simply does not work (or will break them) .


Why?

[Neale]

I was wondering the same thing! At the heart of my original question was, "is the digital input section of the HY VFD floating WRT ground?" My quick measurements suggest that it is - 24V between FOR and DCM (to be expected), but a few tenths of a volt between either connection and ground. Measurement with a DMM, so high impedance and that doesn't sound unreasonable. When I look at how I wired the analogue speed signal to the VFD, I see that ACM (analogue "ground") was connected to the control box ground as that was how the analogue output from the motion controller was referenced so floating digital input doesn't seem silly.

I'll be testing this anyway, once I've resolved the little issue of why my stepper drivers don't seem to be responding to the pulse output from the UC300. Probably forgotten a wire somewhere...

[dazp1976]

Why?


It's been done on another forum a while back.
Directly connected it and broke the axbb-e. Had to replace it.
May have done it wrong in first place.
Relay is the way to go.
24v coil spst.
24v module type.
24v ssr.

Think of vfd like sticking a jumper between for and dcom.
In = on, removed = off. Simples.

[Doddy]

Final comment from me then I'm going back under the rock for 6 months. The control inputs to the HY VFD are fed each though onto-isolators on the control board internal to the VFD. You already have galvanic isolation... until the point that Neale asked about - providing a common 0v line between the VFD DCM and the UCBB 0v. I've not stripped my HY down for a few years, but there's descriptions on the net of all internal supplies (including the 24V sensor input bias supply, and presumably the logic supplies) from a single transformer (presumably independent secondaries) - so that helps to explain the isolated nature of the supplies that Neale has observed. Yes, you have to expect that you will be presented 24V (minus any Vf on the opto-isolator LEDs) and that could destroy any control board directly coupled to the VFD UNLESS that control board is designed with an open collector/open drain output current sink, as is the case with the UCBB - see first reply - or for the isolated outputs from the AXBB-E. Both of these controllers are intelligently designed around the intent to drive such 24V signalling control systems 9such as the VFD).

Anyway, I'm off.

[JAZZCNC]

You need to. Or any other kind of 'switch'.
You can't directly connect a breakout board / controller output to vfd FWD / DCOM.
It simply does not work (or will break them) .

My favorite Quote that you maybe should think about.?

"Better to remain silent and be thought a fool, than to open one's mouth and remove all doubt.!"

[Neale]

I most definitely don't want to upset anyone, and I appreciate the difficulty of dealing with questions on the forum when you don't know the background of the person asking. In particular, very few participants here understand the first thing about electrickery and questions tend to be of the general form, "Where do I stick the red wire?" However, in my case with a degree in electronic engineering, many years playing with building amateur radio kit, and having built a couple of CNC routers and done a brain transplant on them more than once, I had looked at the UCBB output circuitry (usefully given in its manual, although the AXBB manual didn't seem to do the same thing) and noted the output MOSFET 2A/50V rating. I was really just looking at whether someone had internal (literally) info on the HY VFD ground isolation. I would have been reassured to hear something that backed up the checks I was going to do anyway (and which suggest that there is ground isolation on the DCM and digital input pins). I'm one of those people who find it difficult to accept a "do it this way, don't do it that way" without a technical explanation. Even if many people asking questions here do want exactly a "tell me how to do it, don't bother explaining!" approach!

If I were doing this job from scratch, I would have designed in a relay (for belt and braces rather than necessity) and allowed space for it in the control box. However, as this is a brain transplant job, adding a relay as well as having two boards to replace the one original would be a bit of a fiddle that I would rather avoid. I'm using the UCBB rather than AXBB because I want to retain the 24V signalling in the control box rather than go to 5V.

Jazz - out of curiosity, I'm assuming that you have used the UC300/HY VFD combination, so how would you normally switch the HY digital inputs? Depends on BOB used, maybe?

Oh, and if you want a laugh at my expense - after installing the UC300/UCBB and wiring it all together, installing the latest version of UCCNC (and even noting a minor bug in the diagnostic screen display) and configuring it, I can't get the steppers to move... I've probably forgotten a ground wire somewhere or something stupid like that. There's nothing like confessing to a problem like this to make the answer leap out at you, so I'm off to the workshop with my oscilloscope to find this week's stupidity!

[dazp1976]

My favorite Quote that you maybe should think about.?

"Better to remain silent and be thought a fool, than to open one's mouth and remove all doubt.!"

Hey. I'm only going on what someone else did and broke their axbb-e.
The bbe is basically the 300eth and a smaller ucbb.
So :tongue:



Edit: although 1 side of it is non-isoltated. Could that be why.

[EddyCurrent]

The reason I would use a relay is because when I worked in industry that was the standard method for a reason and I liked it, same thing with PLC's
It was found that if a fault developed it was cheaper, easier, quicker, to replace a small plugin relay than a VFD, PLC, or the device controlling it.
Galvanic isolation with a set of "volt free" contacts would always be my solution, there can be some undesirable and unforseen results by connecting supposed "earths" together.

[dazp1976]

The reason I would use a relay is because when I worked in industry that was the standard method for a reason and I liked it, same thing with PLC's
It was found that if a fault developed it was cheaper, easier, quicker, to replace a small plugin relay than a VFD, PLC, or the device controlling it.
Galvanic isolation with a set of "volt free" contacts would always be my solution, there can be some undesirable and unforseen results by connecting supposed "earths" together.

I'm not that "fool"ish then, yes?.
I tend to use optocoupler modules instead of relays for switching DC components lately.
Can get them for peanuts.

[Neale]

Certainly in an industrial environment, the situation is different. For one thing, you are not necessarily in control of where things are used and given that there might be a mix of three-phase supplies plus single-phase supplies coming from different phases, "ground" potentials all over the place, then relying on a connection between grounds on two bits of kit might not be a good idea. After all, it's one reason why ethernet is galvanically isolated. There is also the "make it idiot-proof" requirement. In my case, all my kit is being fed off a single 13A multiway extension off a single 13A socket, and I am the only idiot allowed to use the kit! After all, similar reasoning says that I haven't fitted door-open trips on my control box where that would be entirely unacceptable in industry. A relay is definitely the proper way to go, but I've run out of mounting space and I don't have one to hand. In addition, the UCBB outputs are each opto-isolated on the board and feed distinct mosfet output devices rated well above my requirements, so while a fault might take out one channel, I have spares. And a VFD fault major enough to cause such a failure is likely to be a major VFD failure anyway.

For those who might be wondering, the digital inputs on the HY VFD are sufficiently isolated that a direct connection to the UCBB works fine. I have had the thing running this evening. Just like the analogue output from the UC300ETH which connects to the VFD analogue in and ACM pins. I mentioned above that I was going to need a 16-pin IDC connector to pick up the analogue signal but as I finished typing that entry, I suddenly realised that the 2.5mm pin spacing, etc, matched that used on PC motherboards for USB connections, etc, and I was able to find a surplus connector that I could use. I think that this is the equivalent of the connectors that someone else (forgive me for forgetting who at this point) mentioned - thanks for reinforcing my own thoughts!

But I have to confess that I did shoot myself in the foot with the UCBB - stepper driver connections. I was replacing a motion controller with differential outputs, but for convenience wanted to reuse the UTP cables between the two devices. I used the "solid" colours for the signals and just trimmed back the "stripe" connections, and made up a set of jumper cables to provide +5V to the drivers. Bit of a shame that without thinking, I "assumed" that the solid colours connected to the -ve side of the stepper driver inputs so having removed the "stripe" connections I replaced them with the +5V feed. I really should have looked at the markings on the drivers as I had the polarities reversed and it took me most of the evening to realise it. I knew it was something silly that I had done, but didn't imagine just how silly...

You are allowed to fall off chairs laughing :stupid:

[JAZZCNC]

Hey. I'm only going on what someone else did and broke their axbb-e.
The bbe is basically the 300eth and a smaller ucbb.
So :tongue:

Exactly why you should remain silent or at least think before telling people that something can't be done like you are an authority on it when really you have no clue or experience yourself other than something you read.!

The fact it's not the best idea has nothing to do with anything, it can be done and that's what was basically being asked but luckily Neale is no duck egg so knows better but if this had been a new user then your post could have sent them off in directions they didn't need to go. If you or anyone is not 100% on electrical matters they should either state this when dishing out advice or keep quiet.


But I have to confess that I did shoot myself in the foot with the UCBB - stepper driver connections. I was replacing a motion controller with differential outputs, but for convenience wanted to reuse the UTP cables between the two devices. I used the "solid" colours for the signals and just trimmed back the "stripe" connections, and made up a set of jumper cables to provide +5V to the drivers. Bit of a shame that without thinking, I "assumed" that the solid colours connected to the -ve side of the stepper driver inputs so having removed the "stripe" connections I replaced them with the +5V feed. I really should have looked at the markings on the drivers as I had the polarities reversed and it took me most of the evening to realise it. I knew it was something silly that I had done, but didn't imagine just how silly...

You are allowed to fall off chairs laughing :stupid:

I've done far stupider and costly cocks so don't go into hiding over it, your not the first and won't be the last to do it.


Jazz - out of curiosity, I'm assuming that you have used the UC300/HY VFD combination, so how would you normally switch the HY digital inputs? Depends on BOB used, maybe?:

Sorry, Neale, I missed this.!
I always control a relay Neale for a number of reasons, isolation being one but I can also control several things at the same time the spindle turns on ie water pump etc.

[dazp1976]

The fact it's not the best idea.

Question. Talking of switching drive directions:
Servo drive. I'm using a small opto module to switch the digital input on/off for cw/ccw - m3/m4.
It's 5v in 24v out direct connected to uc300eth port #5. Works great, however.
What do you think about using the cw/ccw inhibit along with it as an extra measure?. (more just because it can maybe).
So:
ccw=on - cw=inhibit. M3.
cw=on - ccw=inhibit. M4.
I'd use the opto module as a series connection to 2 outputs M3+CWL, M4+CCWL.

Worth bothering or not?.
Thnx.

[JAZZCNC]

Question. Talking of switching drive directions:
Servo drive. I'm using a small opto module to switch the digital input on/off for cw/ccw - m3/m4.
It's 5v in 24v out direct connected to uc300eth port #5. Works great, however.
What do you think about using the cw/ccw inhibit along with it as an extra measure?. (more just because it can maybe).
So:
ccw=on - cw=inhibit. M3.
cw=on - ccw=inhibit. M4.
I'd use the opto module as a series connection to 2 outputs M3+CWL, M4+CCWL.

Worth bothering or not?.
Thnx.

For what purpose.? I see none as it can only spin in one or the other direction never both together so no need. And if the servo is clever enough then it would throw either a fault or inhibit itself if both inputs become active at the same time.

I'm guessing this is for a spindle drive.? In which case, if your hell bent on using the inhibits use them when changing tools either via a switch or on-screen button.!

[dazp1976]

I'm guessing this is for a spindle drive.? In which case, if your hell bent on using the inhibits use them when changing tools either via a switch or on-screen button.!

Yes, spindle.
I didn't think it was worth the bother.
Thought I'd ask the pro anyway.

The tool change idea sounds a good one.
Ta.

[Neale]

I wonder how many of us "home" builders actually do inhibit the spindle during tool change? On my mill, I've configured the M6 macro to go to the tool change position, wait for manual tool change and hit the "change done" button (pop-up menu), then automatically set tool height via the tool-setter. On the router, I skip the tool-setter bit 'cos it doesn't have one. In both cases, I rely on the software/hardware not to spin up the spindle while I'm changing the tool. I'm sure that that is not acceptable in an industrial setting. Is that what everyone else does?

[JAZZCNC]

In both cases, I rely on the software/hardware not to spin up the spindle while I'm changing the tool. I'm sure that that is not acceptable in an industrial setting. Is that what everyone else does?

You'd be surprised just how many industrial machines don't inhibit the spindle, especially routers.

To be fair I think if they did have an inhibit switch very few would use it because they would be forever forgetting to turn it back on again before hitting cycle start and very few would put any checks in the M6 macro to see if the spindle was up to speed before letting the program run again.

One of the things we do is wire our machines so hitting the RESET in the software doesn't drop the drive's power or inhibit them so they stay locked and position doesn't get lost, we then tell people to put the machine into RESET when changing tools this way the OUTPUTS are made safe( well safe as can be without a physical switch).