Replacement inverter advise

Sorry I made a typo. KW instead of kW is not a typo, it is a common error i expression of units. Not as bad as M instead of m and vice versa though
On the point of setting up the VFD to suit the motor, that is fine if can do it given the quality of the manuals. And if you do, yes the electronics will be lightly stressed but if you buy a decent VFD you don't have to de-rate it to 20%. The is also the point that you will only be using 20% of the dynamic range of the control system. For example if it uses 10 bit conversion there is a total of 1024 levels over the full range. Limiting it 20% will only use the 256 streps. the 8 least significant bits, down in the noise. Thiss reduces the performance. Using a drive with adequately rated components preserves the dynamic range. If you are using a bigger VFD to rive multiple mtors then you loos the benefit of overlod protection.

Robert G8RPI.

Edited By Robert Atkinson 2 on 26/12/2019 21:03:47

A mistake is a mistake ,we both hit the wrong keys.

Regarding the VFD ,surely the control circuits are more or less the same on low power inverters.The output power will be governed by the size of the insulated gate bipolar transistors and overload settings etc .I can’t see how it affects the pulse width modulation frequency or the microcontroller.

Maurice

Quite so, but that's not what Robert was saying. If one has a VFD capable of x watts output but one is only running at a maximum of x/2 power then the effective resolution of the signals such as output current is reduced by half. In practise that may not matter, but an axiom of signal processing is to start with the biggest signal, and best S/N ratio, one can.

It will also depend upon how the signals are processed. Any cheap processor based on mid-range ARM cores will have floating point hardware and probably sigma-delta ADCs. So loss of a bit or two isn't critical. But really cheap VFDs couldl use really cheap microcontrollers without floating point, at which point loss of resolution can be more important for algorithm stability.

I doubt that VFDs use discrete IGBTs, or MOSFETs, these days. Way too expensive to assemble. They will use 3-phase H-bridge modules with dies mounted directly on a substrate. You get better heat flow from die to heatsink that way too.

Fundamentally I agree with Clive. for any properly designed VFD there is no point in using a rating of twice the motor power. Simply use the next power rating up from the motor power.

Andrew

Thanks for all the good information here. The Chinese units are very tempting, but on balance I've decided to go for a branded unit. I chatted to the sales engineer at Inverter Drives Supermarket and they recommended a Schneider ATV12 unit which has known EMC filtering and hopefully better reliability given it costed over 2 times as much.

The documentation installing the unit is also really easy to understand.

If anyone is interested I could post a thread in the installation.

Now whilst this new inverter will get me going again, I'm tempted to turn my attention to my Mitsubishi inverter. If I posted a question about repairing it as a spare/ backup is there anyone here who is likely to know about servicing it? From what I've read it might need replacement capacitors to bring it back to life.

Lot of talk here about Chinese VFD's and the likely use of low cost components that may prove to have a short life.

Is this all assumption because of a much lower cost or has anyone dismantled and checked component suitability in the imported units ?

Certainly not a lot of failures reported on this forum in the last few years, plenty of reports ref poor programming information but most have got things sorted.

Emgee

Another reason for my buying a Schneider ATV 12 was the wattage lost to heat at maximum output. The unit is 0.75 kW and runs a 1 hp motor. The waste heat is equivalent to 44 watts which is as good, or better than the competition, the efficiency, hopefully, being the result of design and quality components.

Give NewtonTesla a call, regarding repair of your Mitsubishi inverter.

This link takes you to one of their information pages :- **LINK**

It's a tricky one. First, any modern up-to-date maker of electronic components is likely to be using exactly the same machinery and materials as everyone else. It may be difficult for patriotic Brits and Americans to accept, but Chinese manufacturing can and does perform in the international first division. As does India, Brazil, Mexico, and any other country where it's convenient for investors to set up a factory.

But not everyone is up-to-date. Factories using obsolescent equipment to knock out second class goods (as the British Car Industry did in the 1970s), and new old stock, seconds, and forgeries are all possible. While it's not difficult for an assembler to source decent components and pay for competent designs, its also easy for less respectable types to make a quick buck by knocking out rubbish!

Second, technical improvements aren't always used to improve reliability. Older electronic components (and machines) tend to be sturdily built - oversized, over-engineered, and over-priced. Replaced 1 for 1, the best newer technology always outperforms older. Unfortunately, stuff isn't replaced one for one in the products we buy. Instead, reliability is often exchanged for miniaturisation, running at a higher-temperature, and reduced manufacturing cost. Planned obsolescence is more common than not.

Generally, it can be assumed that sellers of reliable cost-effective gear will survive, whilst over-priced sellers of reliable gear go to the wall as does anyone making gear that is cheap and nasty. It's actually hard to make a living out of tat - too much hassle for low profits!

Twenty years ago it was fairly safe to assume Chinese electronics would be inferior. Absolutely not so today. Once a modern factory has paid off the initial set-up costs, it's remarkable how cheaply it's possible to churn out good products. This is what we are seeing today - the benefits of mass-production coupled with inexpensive labour selling into a global market. But it's NOT safe to assume that everything made in China is wonderful - it's not!

The current generation of budget VFDs bought from a reliable vendor are likely to be competent performers. Not the best available, but good enough to run a home machine without costing a fortune. Imperfections, yes - Robert's comments about missing EMC are all too valid!

I've not dismantled a cheap VFD. Forty years ago I took Japanese electronics apart and found glaring quality issues, today I'd be amazed to find anything wrong. Fifteen years ago, Chinese electronics was often dubious: now the bulk of the world's consumer electronics are Chinese and of good quality. If you want to believe China makes nothing but rubbish, pound shops are your oyster. Otherwise, buy something expensive and prepare for a shock...

What's interesting is who will become the next centre of manufacturing. At the moment China is doing well, but it may be a bubble. Could be we see manufacturing shift somewhere else fairly quickly as the world moves on. Africa and South America are both candidates whilst transport is cheap, but high-fuel costs would shift the advantage back to local manufacture of long-lasting goods again.

Meanwhile, I'd be prepared to try an inexpensive VFD should I ever need one!

Dave

I have a Schneider ATV12 unit on a small mill. When first fitted it was unuseable as it tripped the workshop RCD when switched on, and an unprotected circuit wasn't practicable.However, the manual, linked to above, does note that this may be a problem as the built-in EMC filter capacitors allow a leakage current path, (p28). The solution is to remove what's referred to as an IT jumper in the unit. I've done this and all is now well.

The Teco VFD on my Boxford also has an EMC isolating jumper, but it's never tripped the RCD. Likewise my recent Ebay purchase has behaved, but I suspect that this is because it doesn't have a filter to cause problems.

Out of idle curiosity I looked up the quoted losses for the VFD I bought to drive the motor on my Pultra lathe. The unit is by Yaskawa and is single phase in, 3-phase 200V out rated at 0.75kW in normal mode. The table gives a heatsink loss of 14.6W and an interior loss of 14.4W. The table quotes a total of 29.1W. That's a shade under 4%, which is pretty good.

Note to SoD: There are many companies in the far East that churn out commodity components in high volume and low price as they haven't had to do the development R&D. They're not companies that sell through distribution. I've been told to shove off because they weren't interested in volumes of 100k per year for a custom transformer, minimum was 100k/month.

Andrew

I've not looked at inside a cheap VFD (the photos are often enough to identify CE non-compliance), but have looked at lots of cheap power supplies. Most of these have lacked EMC components, had unqualified fuses (if any) and worst of all had poor basic electrical safety, for example unsuported solder joints on mains connections, weak cases, inadequate spacing / insulation between mains and low voltage. They "work" but are one failure away from electrocuting someone. VFDs may not have the direct, un-earthed connection to the user of a power supply but can still be dangerous. The Schneider ATV12 looks like a good unit. It might be twice as much, but the difference is less than the cost of filling your car, is it really worth it? I would not entertain a cheap unbranded far eastern VFD personally.

Robert G8RPI.