Thread: VFD Circuit Diagram Question

A couple of comments. Firstly, Dean, the circuit you ended up with in post #1 is exacltly what's in the Huanyang user manual on page 37. That's the startting point to understand what's going on. The stop button doen't issue a stop command, it 'resets' or cancels the Forward or Reverse commands (if I understand it correctly). Adding the jog buttons was my challenge. It seems too easy in retrospect but had me floundering for a while.
I still haven't found (if there is) a difference between 'Stop' and 'E-Stop'. ...
Secondly, I'm in the middle of (tonight in fact - the parts arrived in the mail today) adding the missing brake circuit components to one of my Hunyang 3kW VFDs. I really want to know what's possible with the right external braking resistor and settings. I'll report when I have something to report - success or failure.
However, I have run a 0.3kW motor on the bench with a 3.0kW VFD and set the decel time to 0.1 sec. It stopped DEAD from full flight! In fact it nearly threw itself of the bench so violently that I discovered that the colour of Adrenaline is actually brown....

So at least it SHOULD be possible to have a functional electric e-stop rather than a mechanical brake. I really want that because my lathe has no brake and it would be difficult to fit. I also want to implement 'final' limit switches that actually stop the lathe if all goes to $h1t - not switch it off and let it coast to a stop....

We'll see.

Originally Posted by jhovel

..................Secondly, I'm in the middle of (tonight in fact - the parts arrived in the mail today) adding the missing brake circuit components to one of my Hunyang 3kW VFDs. I really want to know what's possible with the right external braking resistor and settings. I'll report when I have something to report - success or failure..............

Smaller VFD use "dynamic braking". Dynamic braking uses a resistor to convert braking energy into heat. The motor acts as a generator when the frequency output from the VFD is lower than the corresponding motor rpm. The motor is braking whenever the frequency generated by the VFD reduces quicker than the motor (and its attached inertia like gears, spindle, chuck and workpiece in a lathe) can coast to a lower speed. Without a braking circuit, the VFD would have to "trip" (= switch itself off) to avoid the bus voltage rising too high.

Most VFD's come standard with an inbuilt "brake chopper" circuit and an inbuilt small brake resistor. The brake chopper transistor connects the brake resistor across the DC bus of the VFD. The chopper limits and modulates the braking current from the motor, and at the same time prevents current from the VFD input to reach the resistor. The maximum braking current is limited by the current rating of the brake chopper transistor and the brake resistor. The maximum braking energy is limited by the power rating of the braking resistor. Such VFD often have two terminals for an optional, much larger external brake resistor. The larger brake resistor does not allow for a larger braking current (or braking action) because it uses the same chopper transistor, but rather for a longer braking duration or and shorter intervals between brakings (as extreme example think of the huge inertia in a conveyor belt for a rock crusher). One needs to tell the VFD that an external braking resistor has been attached, so the brain can tell the chopper circuit that a longer braking time and/or shorter braking repetition interval is now possible.

Some other VFD do not come standard with any inbuilt brake chopper circuit and brake resistor. To provide any dynamic braking, they need first to be fitted with an optional external brake chopper/resistor unit. Unlike a simple braking resistors with two wires, such units must connect to the VFD with a special multicore cable. And unlike a simple braking resistor, that can be mixed to any brand/model VFD as long as resistance and power rating match, such external brake chopper is always proprietary to the VFD brand and model used and hence more expensive. On the up side, it may be possible to choose a larger size of the chopper circuit to increase braking capacity.

Finally there is DC injection braking. This is usually provided in addition to Dynamic or regenerative braking. It is only applied shortly before the motor comes to standstill. It essentially prevents the motor to rotate freely once stopped. It is not suitable to decellerate the motor, because the braking energy is dissipated within the motor, and the motor would quickly overheat.

Larger VFD sometime use "regenerative braking" instead of "dynamic braking", whereby the energy from the motor is returned to the AC mains line through a separate inverter, dedicated to only this task.

Originally Posted by cba_melbourne

Dean, this is your personal lathe and workshop is it? You have no employees using it, no plans to put on employess in future? You have full access control to your workshop, no kids to play around it? Then I would think you can do as you like. As long as you keep the electricals safe from starting a house fire. You can choose for yourself what degree of safety interlocking you want to put up with.

In this situation, I personally would consider to remove interlock switches on gear covers and electrical box. And certainly that most annoying of all safety switches on the splash guard - there are lots of routine tasks that are not compatible with it.
I would feel perfectly safe regarding the brake pedal as my only emergency stop (with a safety switch on the pedal of course, to prevemt the motor fighting with the brake). For me, no need for additional e-stops. I am old enough to look after myself. What I would never do without, is a plug that I can pull out of the wall socket, to positively and unmistakeably visibly from far away cut all power to the machine. Before and whilst doing any work on the electricals, I want to see that plug on the floor.

This whole argument changes completely, as soon as you share your workshop with someone else.

If I ever made the decision to employ another person to operate my machinery I would have to make major changes first. It is a hobby lathe. I place a great importance on our privacy. I do not want people having access to my home and workshop for that reason. We live a long way from the nearest neighbors. We cherish that privacy. The splash guard came off very soon after I got the lathe. Maybe I will put it back on some day, but it won't have an interlock on it. Like you, I believe I am old enough to look after myself.

I do understand what you are saying. Even if a friend was to use my lathe I would not expect them to access anything without my knowledge. Your comments regarding the plug that can be removed from a wall socket is an interesting one. At the moment it is all connected temporarily via a standard GPO. When working on it, I made sure I removed the plug from the socket. The second time I said to myself that I have switched off the main switch on the lathe, but I still removed the socket from the GPO. That is a good point. I guess I should look for a 32A plug and socket.

Dean

Thanks CBA for the detailed explanation. It will help members understand what to ask for or look for.
It provided good background to explain what I'm doing.

So to follow on, the issue gets a little more clouded with our ubiquitous Huanyang VFDs.
The manuals describe in much detail how the dynamic braking is implemented and how it works and what size braking resistor is used for the different models and which terminal to connect them to.
Just as others have found out, I connected a suitable braking resistor to the terminals and nothing changed, nor did the braking resister get even warm.... So again like others before me, I opened my VFDs up to find that in one the braking resistor terminal wasn't connected to anything and in all three that the chopper IGBT nor its optocoupler nor the diode to send the braking power to the chopper was even installed. The circuit board however has all the connections and silk screens for the parts.
Since they are all cheap parts, I ordered them and they duly arrived. I've now installed them in one of the VFDs. I haven't reassembled it to test anything yet, but will over the weekend.
In the meantime, I've also contacted two of the Huanyang manufacturers in China (Hyuria and Fullwell) and had a Hong Kong distributor (I knew from the CNCzone forum) contact a third.
Hyuria got back to me and said that these components were only ever installed if the customer asked for them as the were 'optional' (be nice if the manual said so, right?). I then asked if the coding of the processor for dynamic braking was in all delivery options - and have predictably not heard back since. Fullwell didn't even acknowledge my message. The third manufacturer reported back to the Hong Kong guy that 'it was not possible for end users to fit the parts as it was a very complex operation and required complicated testing equipment and procedures and that I should order a new one with the optional braking circuit - I guess also predictable....

So we will see!
Fitting the parts is no more complicated than any soldering of components by the way. I can't think what testing might be involved since they don't seem to be testing anything - not even for QA - in any case

In the process, I also discovered that only one out of three of my Huanyang VFDs has a thermoswitch fitted - yet all have the connectors for it....
The manual indicates that overheating of the VFD will trigger an alarm - nice - that means the other two out of three won't! Interesting... I've just ordered five thermo switches (that's how many come in a packet for AU$ 6.71) to fit to the other two. I'll pass the remaining three on to other forum members who want them.
The connector pad(s) for them is labelled CN3 and is right next to the earth terminal on the lower main power PCB.
It is visible with the terminal cover off - if anyone wants to check if their VFD has that switch installed.

Thanks for that information CBA and Joe. Very useful. I will check my vsd for the thermo switch.

Dean

Time for another thread Joe? I know there will be a lot of questions. I know I have a bunch.

Stuart

Originally Posted by jhovel

Fitting the parts is no more complicated than any soldering of components by the way. I can't think what testing might be involved since they don't seem to be testing anything - not even for QA - in any case

In the process, I also discovered that only one out of three of my Huanyang VFDs has a thermoswitch fitted - yet all have the connectors for it....
The manual indicates that overheating of the VFD will trigger an alarm - nice - that means the other two out of three won't! Interesting... I've just ordered five thermo switches (that's how many come in a packet for AU$ 6.71) to fit to the other two. I'll pass the remaining three on to other forum members who want them.
The connector pad(s) for them is labelled CN3 and is right next to the earth terminal on the lower main power PCB.
It is visible with the terminal cover off - if anyone wants to check if their VFD has that switch installed.

Nice bit of detective work there Joe! it will be interesting to see how much effect the braking resistor has.

Ray

Joe.

What does this thermoswitch look like?

Is this the location you are referring to?

VFD Thermoswitch Location.jpg

I can't see a CN3 label.

Dean

Originally Posted by Oldneweng

Joe.

What does this thermoswitch look like?

Is this the location you are referring to?

VFD Thermoswitch Location.jpg

I can't see a CN3 label.

Dean

Dean, I have no idea about these Chinese Huangyang. But I have not yet come across thermoswithes in VFD's, at least not in a very long time (they were common on heatsinks 20 years ago).

Modern VFD's do normally use one or more temperature sensors. This allows the processor to decide on automatic derating of the VFD as a function of ambient temperature and IGBT module temperature. If too warm, the VFD will as a first measure turn on the inbuilt fan (if this is not set by software to always run when the start button is pressed). If still too warm, the VFD will as second measure reduce in steps the PWM chopper frequency. This will increase audible noise, but keep output power intact. The lower the chopper frequency, the higher the chopper efficiency, the less the switching losses causing heat buildup. If still too warm, the VFD will as a third measure reduce the output power to the motor, if necessary down to zero (but typically some 10 to 15% reduction in output power for each 10C increase in ambient temperature).


EDIT: I just had a good look at your picture. These DC-bus capacitors at the back are only rated for 85C (85 degrees C)? That is not best practice. Normally VFD's would use at least 105C or better 125C capacitors for the DC bus. The DC bus capacitors are the most frequent failure reason for VFD's, that is why only the very best quality capacitors are used for this.

I finally finished my retro-fit of the braking circuitry in one of my Huanyang VFDs. It works!
I described it a little more and took a little video to show the results in the Hunanyang thread:
http://www.woodworkforums.com/showth...09#post1775209

With regard to the thermo switch I discovered in my test VFD, here is a photo of the power PCB of my second one (the test one is now back in the shed and difficult to photograph in its enclosure - sorry).
The switch is mounted below this PCB under a screw holding the capacitor PCB to the heatsink. It is a TO220 case with a heat sink tab.
See http://www.ebay.com.au/itm/351029054518
thermo switch.jpg thermo switch TO220.jpg

To CBA: I'm sure there are MUCH better ways of implementing VFDs than Huanyang's! They just happen to be the common CHEAP alternative. Many of us use them knowing full well that they are certainly not cutting edge or a lifetime investment....

I actually have a Telemecanique 1.5kW one that is at least 25 years old and still works fine. It cost about $5000 when new!!!
I also have a couple of small Siemens Micromaster VFDs and a Eurotherm 650. They are likely to be going when I'm not. These are only 0.3kW and cost around $650 each new now.....
So its horses for courses....

As it happens, a couple of days ago I also got another Chinese one in the mail - even cheaper its a 0.75kW Heng Tai HT1000B like this one:
http://www.aliexpress.com/item/HongT...585922918.html
But I only paid $50 posted! It is apparently used in huge numbers in China, but there is no English language manual for it at all. I got hold of some of the pages of the Chinese manual and spent an enjoyable hour or so at the local University, getting a random group of Chinese students translating them for me . That was much harder than expected, because they had never heard words like 'Jog frequency' or 'DC braking current' in their own laguage either! We got there, but I'm still missing a lot of parameter information.
I'll keep on with my detetective work....

Anyway, today I connected it (not that much to loose if it all went to $h1t) and it worked straight off. I can't set up the display yet, no the maximum frequency nor many other parameters, but it does work.
I only had a 1.5kW 4-pole motor handy to test it with today. This VFD model has no fan but didn't get warm at all. Of course that might be different with a 0.75kW motor on full load. One day I may get to find out. I want to use it for my cylindrical grinder which probably will never run at full load anyway.
Here is a short video of it in operation:
http://youtu.be/AHfy-VbTpOQ

Good stuff, Joe.. I reckon this deserves it's own thread. Huanyang VFD Mods and Improvements.

In the video of the HT drive, what you are thinking is bearing noise, might just be electrical spikes getting into the microphone pre-amp..

Ray

Well, one of my many requests to various agents in China for a Heng Tai manual has paid off tonight!
I just received an e-mail from someone in China I have never heard of - so word has got around (or the State IS actually monitoring international e-mail there....).
Anyway, it is VERY helpful. It also came in MS Word format!!!!! So now I can edit it to make it readable (and get the few Chinese characters still there - and then of course make it available to whoever in the English speaking world might want it
I'm not sure yet if it is the complete manual or what's missing, because its only 16 pages lonmg, but it is described in the manual as a 'Simple VFD'...
As I was looking around the 'net, I also happend to notice that it is available without a case, just with a cable connected control panel - and even without that! And then a lot cheaper still....
Looks to me like a good option for building it right into a smaller machine tool! Maybe that's what it is actually for?

Thanks Joe Going to need a list of your parameter settings.

Those even cheaper VSD's should be very handy for my jig grinder, for $50 its not worth the effort of making two motors run from one VSD.

Stuart

With regard to one of the much earlier posts here:
I just posted here http://www.woodworkforums.com/showth...62#post1775262
about a relatively cheap option of a remote Huanyang panel with mounting box and 5m of cable....