Spot the connection

John, the input side filters are a good idea according to the drive manufacturers but they did nothing for the output noise I had problems with. The main advantage as I understand it is preventing problems with other items connected to the same ring main, perhaps Murray can expand?

Murray, "filter out noise on the inputs" - guilty as charged! Problem I always seem to have is feedback loops that require psychic ability. Its also hard a lot of the time to be able to change the circumstances so you have to go the filter route rather than fixing the problem at source but then I guess you know that already.

To explain about psychic feedback, I am talking about dynamic control (mostly speed control in response to some process variable) which involves trying to maintain a steady state in the process. Often, responding to a change is too slow and you have to try and anticipate how much change is needed before it happens - an operator can judge and anticipate but electronics (PLC or industrial PC's) are not so clever - yet!

In my case, the process would best be controlled by responding to the magnitude of a specific frequency out of a "spectrum analysis" output but that wont work so we have another work around that seems to work for the job.

(For Murray and anyone else daft enough to be interested; I actually tried to use an FFT implementation on an Arduino using "n" buckets and using the first as the PV for speed control but it generates a signal that is always lagging "n" number of machine cycles. I ended up programming the PLC to perform a rolling average of the output and look for a change greater than a preset magnitude to indicate the degree of speed change to make and just accept a severely damped response)

Mark

Mark

Still waiting for the Huanwang VFD to arrive, and in the meantime I'm sorting out the original wiring. A couple of questions spring to mind:

1. The DOL starter on the lathe is an MEM ads7, probably a replacement as it is mounted in its own enclosure and there are signs that the original starter was a panel mounted one. In any case it obviously has a 415v coil and a 3.7-5.6A overload so is not going to be a lot of use to me. Do I need a new DOL starter wired into the supply to the VFD, or is there sufficient overload and no-volt protection provided by the VFD itself?

2. The original (rotary) switches on the lathe (a main on/off, a FWD/OFF/REV and an ON/OFF for the coolant pump are all good quality and positioned in sensible places. They are what I would call latching, as opposed to momentary, and I'm hoping that they are suitable to connect to the VFD as remote controls.Can someone confirm? I think the answer is yes from what Mark C has written in his post at the top of page 2 but I'd sooner ask another dumb question than risk damaging the VFD.

ps I have downloaded the manual and am slowly ploughing my way through it, but as everyone has said in previous posts on this topic, the writing takes a bit of getting used to!

Any switch should be OK, but whether its momentary or latching means different programming required.

A down side of big switches carrying tiny control currents is they are prone to poor contact, compared to small signal switches, which can interfere with operation.

Neil

Steve, As far as I can tell there are no such thing a stupid questions, just stupid people who live in ignorance rather than ask the question!

Bearing in mind that it is my private workshop, I do not use any switching in front of the drive (mains side) other than the main isolator switch. I do have an e stop wired in (no volt release) on the input control wiring/switching. If you are bothered you can use an interlocking switch for this but the inverter does this function if you set the input logic up properly. In reality, if you want a true e stop function you would need a relay in front of the motor as the inverter will continue to run while it still has DC bus voltage to do so and this takes a few seconds to drop off as the charge dissipates from the capacitors. As a point of caution, an e stop disconnection will cause the motor to coast to stop but it might also require you to buy a new inverter if the output throws the towel in as a result of the (suddenly) open circuit output.

I will take a note of the settings on my inverter (same as the one you have ordered - all but the size at least) and post them for you. I will bear in mind that your switching will be latching rather than momentary.

Mark

Neil,

You are correct of course, the answer is to give them the occasional squirt with contact cleaner/lube. I had one of my other inverters swapped over thinking there was a problem only to find that the rotary switch was playing up! I think there might be a saying about hasty action?

Mark

The e-stop input on VFDs is usually a simple hardware override that inhibits the switching devices. That's in case the software or the control inputs have a wobbly. Generally you don't plan to cater for 2 faults happening together, an approach that is taken in industrial, automotive and other environments - look up IEC 61508 or ISO 26262 if you need to get to sleep.

As you say, some (many) VFDs will get upset if you disconnect the motor from the output when it is getting busy with the motor. It won't come to rest any quicker and you are probably better off using the regen / braking resistor / DC current injection functions to stop it quickly.

Industrial sensorless VFDs aren't really designed for closed loop speed control. No idea what frequency response you will find if you characterise yours but as you know conventionally you would use a servo drive which will generally contain a tunable PID controller and is designed for that application.

Murray

My HY inverter on my Chester Eagle mill, comes to an almost immediate stop when the primary supply is removed...,Not sure if thats the dc bus decaying fast or something else....

Edited By John Rudd on 08/10/2015 20:39:37

Murray,

Deciphering the Chinglish took me long enough (and that was given I am reasonably conversant with the more mainstream makes, so I had an idea of what I was looking for). trying to find out if there was a suitable hardware e stop function was not top of my priority list by then! As for meeting IEC directives, they couldn't manage a working implementation of ASI bus, I don't know how that bodes for safety items but I think I can guess. Having said all that, the drives work OK and at bthe price and given the job - that was all I wanted.

As an aside, many older machines found in our caves have screw fitting spindles (thinking lathes here) and sudden stops can be problematic with these.

On a more technical note, the drives on my recent machines (production jobs) require tight speed control (and good response) as the feedback loop is very damped (can't do much about it). I am getting very good results using sensor-less vector drives with them and they do have good(read flexible) PID routines but I am not using the drive PID's relying instead on my own routines tuned to the process and implemented in the PLc. My experience of drives has been the increasing replacement of servo drives by vector drive AC motor combinations probably due to their rugged/robust and economic offerings.

John, I have never had occasion to shut one of my drives down in that way so I don't know how long they will run on when driving a load but they take ages to die when you pull the plug at the end of the day!

Mark

Interestingly, my inverter monitors the health of the bus capacitors and tells you when they need replacing (hopefully in many year's time at hobby duty cycles).

Neil

I have three inverters all of different make. I have wired each of them via a 20 amp relay to give No volt release. Each station has a large red e stop button together with a local stop, start, reverse and jog buttons. The control wires are screened ex computer cables and fortunately I don't have a interference problem. I have used Sy screened cable from the inverter to the motor and all three inverters are now mounted in ventilated steel boxes, trying to stop interference escaping. When I set things up I walked around the workshop with a radio seeking out any leakage. I wouldn't consider interrupting the inverter output in anyway the energy has to go somewhere and why should anyone need to disconnect the motor from the inverter output, am I missing some thing? . Anyway that is my experience with inverters and I'm pretty pleased with the inventers. John

John, SY is not really a "screened" cable. You need CY which is classed as a screened cable rather than the steel braid used in SY which is armour rather than screen.

Mark

I've just realised this thread should probably be moved to the Astronomy topic...

Neil

Neil,

That would confuse matters and Steve is unlikely to get any help from me setting his inverter up as I would only look at a post under that heading if it is either very popular or of some intriguing subject.

However, I might be missing the point of the comment completely, or is it a Bill moment?

Mark

Sorry Mark,.

Though many people seem to enjoy astronomy as an adjunct to model engineering, there are a few people who feel that if it is to be discussed it should be shrouded like a victorian table leg.

This morning I twigged that this thread was subtitled "Help needed to locate the star point", and I desperately wanted to get some levity back into the issue... hence the attempt at humour...

Neil

I think there is a difference between thread drift and legitimate thread development. In this case, I have (I very much hope!) sorted out the star point and have now re-installed the motor and in the middle of removing the old wiring and working out how to use as much of the existing control gear as I can. All related to the installation of the VFD (which has now been stuck 6 miles away at a parcel depot in Gatwick for the last 36 hours thanks to Yodel).

Anyway, it looks as though the re-wiring is going to be considerably simpler than it was - particularly enabling the fwd/rev switch - compared to the previous 3phase setup. I'm slowly starting to understand what Mark meant by 2-wire control I think!

The advice has been invaluable so far, thanks to everyone, but I'm sure there are more questions to come.

Neil,

As a sad social outcast (mechanical engineer) the link was slightly to obtuse for me without you pointing it out, but now I see your point (he types with a smile)

Steve,

Yes, wiring an inverter is much easier - nothing like the amount of wiring or requirements of a 3 phase installation and much easier to add controls etc at a later date. It mostly needs almost no current (apart from the supply to and from the inverter) so you can almost make money cashing the scrap copper in (you might need to do more than one mind).

Mark

To Mark ,I got it wrong it is CY cable which I used, its a long time ago since I did the wiring and got mixed up. Its all very good reading here and it is also good that people are prepared to share their knowledge and experiences. John

John, I agree, you might not always get the "book" solution but often people will talk from their own experience which is often far more valuable than the theory.

As a point of interest (and I thought I typed this already but can't find it, perhaps a senior moment), did you ground both ends of the screen on the output cable? Normal practice is to ground just one end but that is to keep interference out, you want to keep it in so both ends need doing.

Mark

Partial success, thanks to all the help. I've removed all the original wiring from the lathe as it is all redundant, but I will be keeping the switchgear and using it to control the vfd in due course. I decided to get a new dol starter as the original had the wrong coil and overload for the 240v supply. I already had a convenient 16A outlet wired as a radial circuit with a 16A mcb.

I really struggled with the manual - it omits basic information, has no logical order to it and assumes that you've set up dozens of the things already, but I found a few useful forum threads on a cnc website explaining which parameters are important and what the settings are for this type of induction motor. Happily, my star to delta conversion seems to be ok and the motor spins happily at 2900 rpm. More wiring to do after I install the motor, and then I'll sort out the control switching.

Steve, sorry it took so long but here are the settings I used:

1. PD 001 = 1
2. PD 002 = 2
3. PD003 = 50Hz
4. PD004 = 50Hz (MOTOR FREQUENCY FROM MOTOR PLATE)
5. PD005 = 50Hz
6. PD014 = 4 SECONDS (START ACCELERATION TIME TO SET SPEED)
7. PD015 = DECELERATION TIME IN SECONDS (not required if coast to stop set)
8. PD023 = 1 (ENABLE REVERSE ROTATION)
9. PD026 = 1 (COAST TO STOP, UNCONTROLED DECELERATION)
10. PD044 = 2 (RUN FORWARD)
11. PD045 = 5 (CHANGE DIRECTION FORWARD/REVERSE)
12. PD046 = 4 (STOP)
13. PD141 = VOLTAGE FROM MOTOR PLATE IN DELTA (PROBABLY 240/250 VOLTS)
14. PD142 = AMPS FROM MOTOR PLATE IN DELTA (THE BIGGER VALUE)
15. PD143 = MOTOR POLES ( IF IN DOUBT, SEE BELOW)
16. PD144 = MOTOR RATED SPEED RPM FROM MOTOR PLATE

Motor pole count = 6000/(motor rpm x 1.0526)

EG. For 50Hz motors, 2850 rpm = 2 pole, 1425 rpm = 4 pole, 950rpm = 6 pole & 700rpm = 8 pole

This is the switch wiring I have and remember that the speed pot needs its own ground separate from the digital input ground (in other words you need 7 wires). The settings I used give a 10 volt signal on the speed pot (10k ohm) but you can change it to 5 volt or current sensing with PD070 and you can set/change a filtering function on the analogue input with PD071 (factory setting is 20).

How does it compare with your settings?

Mark