Inverter problem?

I was happily making chips on my Boxford VM30 yesterday, took a short break, came back and the mill would no longer run.

The machine has worked happily with the inverter (Nordac Compact) for about 12 years so this has come as an unwelcome surprise.

The inverter is electrically live and the parameters are accessible from the simple buttons on the panel. The parameters are unchanged from when it was running OK.

Now when I switch on, the inverter panel displays 036.8 (no "F" so not a fault code?) and the 8 flickers on and off.

I am electronically a dimwit.

Can anyone offer advice?

Just in case you dont have the manual...

https://www.nord.com/cms/media/documents/bw/BU330X_GB_1096.pdf

Having had a quick flick through it, I cant see anything that relates to the characters being displayed...

Thank you John.

My inverter seems to be an earlier variant. There are only 3 buttons on the panel,  P, + and -.

I have the manual and can work through the parameters but that's about my limit.

The motor is 3 phase and a large capacitor is included in the wiring.

Edited By charadam on 16/06/2016 18:26:44

Are you using the controls on the inverter for run stop or a pendant. May be a broken connection between pendant and inverter if the latter. If you are using a pendant try changing the parameter P007 to change to panel control and see if it then fires up (you may also have to alter P121 - 124)

Edited By Graeme W on 16/06/2016 18:31:43

Graeme, the inverter gets switched on at the 13A wall socket, then the motor is switched on using the original Boxford switch on the machine panel.

Not clear why there would be a capacitor in wiring for a 3-phase motor, but if it has worked for 12 years....

If switch on machine panel is after inverter, that is asking for problems - never break connection between inverter and motor, risks blowing output stage of inverter.

Oops! The capacitor is in circuit with the coolant pump.

Sorry for the red herring.

Do you let the inverter run up to 50Hz before switching the motor on?

If so odds are you are overstressing the electronics to some degree due to the large surge current when the motor starts. Hopefully its just one of the input capacitors or diodes gone which should be fairly simple for an electronics guru to sort on a relatively old design like that. If its an output device fixing may be harder and there may be deeper damage. Repair may not be economic.

Although this sort of "plug and play" operation is possible using a correctly (over)rated inverter normal use with an inverter fairly closely matched to the motor power assumes that the inverter does both switching and speed control duties. The motor run up to speed from zero and run down to stop is controlled by the inverter circuitry to avoid potentially damaging surge currents. Plug and play using the machines own switchgear with the inverter acting as a 1 box substitute for mains three phase needs an inverter whose rated capacity is at least twice the power of the largest individual motor to be run with a high overload capability probably at least 200% overload for 60 seconds. Still hard on the electronics although smoothing incutors on the output helps. Looking at the manual John linked to your inverter has a decent overload capability of 150% for 60 seconds so its a pretty tough device but I'd expect the hard starts and current surges to wear it down eventually.

Clive.

It not clear from the above statement whether the Boxford switch is actually switching the motor wiring or whether it has been wired to the inverter controls input (for remote pendants etc).

Without knowing how the inverter is wired I think we can only make guesses as to the cause of the fault.

Maybe someone with some relevant knowledge is local to you and could help, I certainly would but have no idea what country or where you are.

Ian P

Graeme,

Thank you - I think I understand.

Are you saying I should have been setting the motor switch "on" before firing up the inverter?

Absolutely.....

Manufacturers usually provide a connection drawing on how to hook up an inverter...and all the time I've been repairing/selling them, I've never come across one where it shows an indirect connection...

All switching is done on the input side of the inverter....

The consensus is that I have fried the inverter over time by incorrect starting technique.

A new item has been ordered.

May I thank all who offered help and advice, with special thanks to John Rudd who advised off-forum.

Onward and upward - but select the motor "on" first!

Charles

It seems unlikely to me that what you have done for 12 years should suddenly cause the inverter to fry, although it certainly is possible. Switching the machine OFF  on the downstream side when the inverter is running is what the handbook for my inverter warns against. Of course you may be doing this...

Perhaps more likely is that the big electrolytic capacitors have gradually reached the end of their life and need to be replaced - this may be what your message is telling you. My inverter keeps track of usage hours and can be set to warn when the capacitors need replacing.

Neil

Edited By Neil Wyatt on 17/06/2016 14:55:52

Neil,

Aye, there's the rub!

Of course I switched off wrongly as well.

I am, at least, consistent.

Charles

Just smile and accept the Kama.

If you have had it 12 years chances are it's 15 to 18 year old inverter technology, possibly longer ? which puts it at about coming out of the Jurassic period, possible a few decades in front of a Myford.

If I understand the wiring scheme you have been using with this mill and inverter for years (switching motor on and off instantly) then you have been missing out on many of the basic advantages of a VFD system. Like the ability to adjust the acceleration and deceleration rates of the drive and vary the speed (right down to zero) plus lots of other features etc.

Presumably your replacement VFD will be a more modern model which will come with a manual so fitting it should be straighforward.

Ian P

Ian,

The mill used its original controls so I had mechanical control of speed and never considered using the electronics in their place.

The inverter was inconveniently remote mounted so using functions was not ergonomic (translate: big lad, small workshop, too many belly bruises from corner of table).

The new inverter will be mounted on the belt guard so will be convenient to use.

But I will probably continue to use the mechanical controls for speed.

Charles

Edited By charadam on 18/06/2016 00:00:33

When you alter the wiring so that the motor on/off is done on the signal input side of the VFD (you can wire the existing switch to do that) then the very nature of the VFD will give the acceleration ramps.

To get the same 'feel' as your existing setup you could reduce the ramps to zero but there is no much point, far better to have say, a half second ramp, apart from putting less shock loads on the drive line it makes the machine feel smoother.

Certainly if have got used to the machine over such a long period I would not want you to have to re-learn anything so stick with the mechanical speed control. I am not conversant with your mill but one thing I find useful on mine is the VFDs ability to rotate the spindle at dial indicator sweep speeds (20-30 RPM) as its the speed I use when using my edge finder. At such low speeds the torque is laughable but as the motor is doing no work as such it would never even get warm.

Ian P

I hope this isn't going to confuse everything (comparing apples, pears, and oranges). I have two transwave inverters (one static and one rotary). The lathe and milling machne are plugged into them. What's the recommended sequence for starting and stopping them?

If your static converter also steps up to 440 3 phase, then you switch the motor of by turning the converter off. Else a, the start caps won't be switched in and, b the back EMF from the transformer will blow up your capacitors (guess how I know?)

Frank