Leeson Speedmaster SM Plus Series Sub-Micro Inverter

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I've been asked to troubleshoot an issue with a motor controller built around a Leeson Speedmaster SM Plus Series Sub-Micro Inverter.

 

I realise that this should perhaps be in Off Topic instead of General Electronics, but as Off Topic can only be viewed by members (and therefore no Off Topic threads are scraped by Google et al) it would be better here for the benefit of others in the future.

 

Is there anyone here who has experience with this or a similar VFD?

 

The issue is that occasionally, the unit either:

  • fails to drive the attached motor upon command, or
  • begins to drive the motor upon command, but then ceases after a random interval ranging from a few seconds to a few dozen seconds.

 

The drive is operating with speed control via an external voltage, provided by a potentiometer.

 

When these failures occur, the code 'UF' is show on the display.  The fault seems to clear when a stop command is issued, after an interval of several seconds.

 

I've read the relevant parts of the manual and quick start guide, and I'm left with the impression that the associated 'START FAULT' tied to the 'UF' display code should not occur while the drive is in operation, but only when power is applied to the unit.

 

A review of the most recent fault codes using Parameter 50 (fault history) does >>not<< show UF among the recent codes.  However, I expect this is normal...?  The codes which >>are<< listed are 'LF', for 'Low DC Bus Voltage Fault', and F9, which suggests 'Internal Faults: The control board has sensed a problem - consult factory.'

 

I've sent an email to the local distributor, and they've forwarded it on to their 'tech team', but I don't expect an answer soon.

 

This is of a somewhat time sensitive nature, as the drive/motor is used to operate a revolve in a stage production which is opening very soon... actually, 30 minutes ago... so they're swinging without a net at the moment!

 

 

Any ideas?

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

Last Edited: Fri. Mar 16, 2018 - 12:32 AM
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... you are associated with a stage production of swingers? (it is Friday)

 

Ross McKenzie ValuSoft Melbourne Australia

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Have you checked the ususal suspects?

loose wiring, broken or worn potentometer, etc.

 

Small VFD's start at about USD100 nowadays. Hardly worth the time to troubleshoot, especially in an industrial setting or if there is any doubt about continuous reliability.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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... you are associated with a stage production of swingers? (it is Friday)

Nope.  Gershwin's Of Thee I Sing.  Openned tonight.  Dunno how it went, I was called in just to look at the revolve controller this afternoon.  Long story.

 

Have you checked the ususal suspects?

loose wiring, broken or worn potentometer, etc.

Yup.  Not any of those.

 

The whole unit (which contains the VFD) is itself part of a somewhat sketchy rental package.  The theatre came into possession of this >>enormous<< stage revolve (which half-fills a 53' truck) some years ago, but it didn't come with the motor unit.  For several years the revolve was turned by hand by stage crew.  I was one of them.  Then they started using a rental unit which was custom made, commissioned by another outfit to keep in their rental inventory, they had a lot of entertainment clients which used these kinds of things.  Then they were bought by a metal supply shop, who have kept the kit mostly for in-house use (it occasionally runs their bender, or something).  That shop is still happy to rent it out to the theatre occasionally, but they have no idea, and couldn't care less.

 

It has worked just fine for many years, many shows, many rentals.  Started acting up this week.

 

My best guess is that either the drive is in fact failing, but I think more likely is that the 'custom' controller assembly was poorly designed.  The VFD is of course just a small brick about 8"x6"x4", but it is mounted in a 19"x19"x12" electrical box along with a number of relays, disconnects, contactors, switches and other controls to select speed, direction, and control locale (panel or remote), provide safety interlocks, etc.  The cable routing internally seems reasonable enough, but the feed cable, motor cable, and foot pedal cable (that's the pot) don't appear to be shielded.  The manual is quite clear (and it's obvious anyway) that the control wiring must be run in separate conduits from either the mains input or the motor output wiring conduits to avoid the disruptive influence of noise on those cables.  No conduits, as this is a portable unit, and as I say apparently unshielded cables.  When I arrived at the theatre, the operator's station was a bit of a mess cable wise, with the motor output wiring snaking in and around a lot of other wiring (camera, monitor, clearcomm, other LX, etc), including the foot pedal cable.

 

I was able to get the 'UF' fault code to appear about a half dozen times over the course of my visit, but after I relaid all of the cabling in a tidy fashion (keeping each of the three motor unit cables clear of each other, and of all the other cabling present), I was unable to force a fault.  That is by no means definitive.  A sneaky, faulty connection somewhere, which I may have missed, and which might have been massaged in just the right way by relaying cables, could easily explain the disappearance of the symptoms.  Either way I'm hoping they make it through the week's run.  Only 4 performances.  It's an opera at the school of music.

 

For some years now the TD has been on the lookout for a complete system they could purchase, rather than be at the mercy of a rental unit which might vanish in the future, and which today has zero support.  While the VFD itself is not terribly expensive, the motor and the greater control system of which the VFD would be a part is quite prohibitively expensive.  The companies which manufacture entertainment equipment of this type don't really care about a relative small fry like this theatre.  He's looking at $20K or more, and that's when they can even get a sales rep to bother to return a phone call.

 

 

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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joeymorin wrote:

... you are associated with a stage production of swingers? (it is Friday)

Nope.  Gershwin's Of Thee I Sing

 

 

I will let the US politics slide this time... cheeky

Ross McKenzie ValuSoft Melbourne Australia

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It seems the inverter must be restarting ang getting upset that the run input is active.
Ifcthe wiring between the inverter and the motor is not shielded, then funky stuff may happen - pwm at significant energy radiates and wants to couple into everything.i designed a large display board rotator many years ago (used a mega103!) and the electrical guys would be puzzled when it would operate strangely. Did you use proper shielded cable? I’d ask. The response would be no or ‘we used steel wire armoured!”. It was only a 1hp motor. The scope would pick up a decent signal at 10 paces.
Also note the capacitors only have a finite life, so if the inverter is many years old, it might be time for a new one.

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Keeping power cables away from signal cabling is indeed a very important rule.

I once had a  situation where somebody did not want to go through the hassle and threw a signal cable in the power conduit, because it only had some 24V signal light bulbs on the end.

the conduits were over 50m long and making a separate conduit for that is ... quite some work.

The 24V lights were constantly flickering like carnaval and often had to be replaced because they blew like shorted fuses.

I believe some of them even exploded.

I believe it was eventually solved with heavy filtering and TVS diodes.

 

So I'm not surprised your symptoms go away if you separate the signal from the power cables.

As a quick alternative you could route the important parts of the signal cables through some metal pipes / tubes.

 

On old ciruits you might have oxidized wire ends, which make bad contact even when the screws seem snug.

Part of new installations is to make sure all screws are tight enough to deform the copper conductors.

This forms an airtight contact area where the copper will not oxidize.

But if oxidization has set in, tightening the screws more does not help, it only hides the problem.

Damaged screw heads may indicate tinkering from unqualified personell.

 

With badly routed cables you might have stress on the PCB and cracked solder joints.

 

VFD's only tend to get smaller and cheaper. Just replacing the VFD and not the motor, cabling or other sub assemblies is pretty trivial.

New VFD's have to be set up properly. There are a bunch of different parameters such as Max current, limits of overload protaction (time constants) Voltage to frequency ratio and more.

Having to browse through 100+ different parameters is common, but usually only a handfull of them are important.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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It seems the inverter must be restarting ang getting upset that the run input is active.

First thing I thought of when I saw what 'UF' signified, however the unit shows the 'parameter version number' on the display on power-up, which is not shown when the symptoms occur, so it isn't a full restart.  It's unclear whether the version number would be displayed during a 'UF' power-up condition, though, so this is still a possibility.  Certainly if EMI is at work then all bets are off.

 

Also note the capacitors only have a finite life, so if the inverter is many years old, it might be time for a new one.

Yup, and the manual speaks of this, and of how to 'reform' the caps after a long period of non-use or storage.  I don't believe that's the issue though.  There appears to be no correlation between motor load and the symptoms.

 

There's also a diagnostic mode which allow monitoring the DC bus voltage.  It does not waver at all under any loading conditions.

 

So I'm not surprised your symptoms go away if you separate the signal from the power cables.

I'm not convinced that the cable tidying I performed 'solved' anything, or if it did that it was EMI and not a fussy connection at work, but it was the only 'solution' I could provide in the time allowed.  I haven't heard from them yet how last night's performance went, whether the unit malfunctioned or not.

 

VFD's only tend to get smaller and cheaper. Just replacing the VFD and not the motor, cabling or other sub assemblies is pretty trivial.

As this is a rental unit, that's not really in the cards.

 

New VFD's have to be set up properly. There are a bunch of different parameters such as Max current, limits of overload protaction (time constants) Voltage to frequency ratio and more.

The parameters on this unit are protected by a password, and it's not the factory default password mentioned in the manual.  I guarantee the shop which owns it has no idea.  I doubt they've ever even opened up the box to see that it contained a VFD at all, or what the letters V F D mean.  While it's only a 3-digit password, the entry sequence is tedious, and trying them all would take a significant amount of time.  Once in, I could gather the parameters for programming into a new unit, but as mentioned above "this is a rental unit, that's not really in the cards."

 

 

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]