vfd question

[Clive Brown 1Participant @clivebrown1]

I'm surprised that a Boxford seems to take 5 amps. unless under fairly heavy load at highish speed, which I assume is not the case for these trials. Is it certain that the motor is good?

I have one of these VFDs, but not on my Boxford, and it seems good value so far.

[not done it yetParticipant @notdoneityet]

Beware of increasing deceleration from zero with a screwed chuck.

[john barnes 4Participant @johnbarnes4]

Hi Clive, the motor and the VFD are both new.

[Martin of WickParticipant @martinofwick]

I suppose it depends on motor power?

As stated, the display current doesn't always reflect true motor current draw in my experience. If the OP has a clamp on meter, it is best to confirm real current. I have found that P67 and P73 to P75 seem to impact offset and span on the display pad – but I haven't been able to work out how to apply them, or whether they do more than impact the displayed V A, so have been inclined to leave at factory setting.

Even so, the VFD interlocks reflect what is shown on the key/display pad, so if the overcurrent trip is set at 6 amp, then when the display shows 6 amp, it will fault. I take from that if the real draw was say 2.5A at an indicated 5A then cutting out would occur at a true draw of just over 3A. Difficult to be sure, but have not had a problem with overheating motor so far….

[john barnes 4Participant @johnbarnes4]

I have just had another go with the VFD. with some success. I increased the main current overload P78 to 7000 and it ran up to 75hz before it tripped. I have set the minimum working frequency to 15hz and the maximum to 65hz. Still not perfect I know but I think it will do for me. I always intended to keep using the pulleys anyway to keep the motor running near the 50hz mark. I have not tried it under load yet I just hope it doesn't trip. A big thank you to the forum members for their assistance I hope I can do the same for someone else one day.

[Martin of WickParticipant @martinofwick]

John,

Bear in mind that while a VFD is very useful, it is no substitute for speed reduction via belt ratios, gearbox etc.

I wouldn't recommend that you regularly use your VFD at above 60 Hz, as torque will decline significantly at frequencies above design – so ok to go 65 Hz for a short burst of small diameter work or polishing but not for an extended bout of turning, because just you cant be bothered to change the ratios and run the motor at closer to design frequency.

Similarly, if you run the VFD at 20 Hz output, remember effective power at the motor is 2/5 of design and at 15 Hz it is 1/4 (approx.). Induction motors are pretty robust, but extended high torque use at low powers should be minimised.

Just because you can, doesn't mean you should!

Don't know what spec your motor is, but assuming 1kW should show approx 4.5 to 5 A setting the trip to 7A is 40% higher than design and will warm your motor somewhat if you operate at that current, might be OK for the odd peak but not for general operation. I would set a good deep cut on the auto and observe the indicated current and draw your own conclusion.

Secondly, if it is a 1.5 kW inverter, what is 220×7 ? If those are true V I, you would be running your inverter quite hard. I always treat Chinese specs as being at maximum output prior to magic smoke release, not an indication of continuous duty.

 

Edited By Martin of Wick on 21/03/2020 15:04:24

Edited By Martin of Wick on 21/03/2020 15:27:43

[Robert Atkinson 2Participant @robertatkinson2]

I would note that regardless of being "Commercial" or not, most of these cheap far eastern VFDs do not meet accepted safety and quality standards. Additionally tthe internal components may be sub-standard or under-rated. This is why many sources (including at least one UK reseller) recommend buying a larger unit than should be needed.
Even quallity units need to be mounted in a proper enclosure and most also require a EMI filter on the mains unless te VFD specifically states it has one internally. A good filter can cost more than the VFD.

Robert G8RPI.

[Martin of WickParticipant @martinofwick]

Posted by Robert Atkinson 2 on 21/03/2020 16:12:26:

I would note that regardless of being "Commercial" or not, most of these cheap far eastern VFDs do not meet accepted safety and quality standards. Additionally tthe internal components may be sub-standard or under-rated. This is why many sources (including at least one UK reseller) recommend buying a larger unit than should be needed.
Even quallity units need to be mounted in a proper enclosure and most also require a EMI filter on the mains unless te VFD specifically states it has one internally. A good filter can cost more than the VFD.

Robert G8RPI.

To be meaningful you would have to define who's safety standard and what quality requirements. If you are in the market for a £60 VFD you would be inclined to assume it was built down to a price in terms of component spec. and had limited functional software. If your 'standard's are high, then better units are always available.

My safety requirements are you don't get electrocuted while setting the parameters and as long as it runs more or less as expected for a few years, my quality requirement has been met. I will put up with all the other shortcomings.

No point ranting and raving about iniquities of Chinese hobby equipment, real or imagined. It is what it is. Ya pays yer money and takes yer choice.

[john barnes 4Participant @johnbarnes4]

I tried the VFD again and it tripped at 60hz. I ran it with the gear train disengaged and no load applied. It works at 50hz but any higher and it trips. I now think it may be the motor drawing too much current.

[SteviegtrParticipant @steviegtr]

There must be a setting somewhere in there that you are missing out on.

Assume the motor & VFD are not faulty.

Is there a reset command you can use to start over.

Write every thing you do down on paper. Only alter one parameter at a time & log.

The reason I say assume the parts not being faulty is so you will not just give up & become negative.

As I say start again. Do the Sherlock thing on it.

If at the end you are no nearer then get the gear checked out.

The motor if faulty will have a different impedance reading on the 3 windings if it is faulty. Or a tight bearing.

Steve.

[Anonymous]

Seems a bit odd, one would expect the phase currents to go down above the base speed of the motor (probably 50Hz). I'd agree with Steviegtr, reset and start again altering one thing at a time.

Andrew

[Martin of WickParticipant @martinofwick]

John,

can you tell us exactly what the power of the motor is / plated current rating etc. at all voltages etc, or provide a photo of the motor plate and inside of the motor connection box.

Are you using the supplied keypad or a pendant?

Do you have access to a clamp on meter to measure true motor current or at least a regular meter to check motor coils?

In addition, set out your stored parameter values P00 to P26 and P65 to P78

Then we might have a clue as to what parameters need modifying to solve your problem.

Don't implement factory reset at this stage – my experience with this type of inverter is you may well get additional complications depending on the exact type of inverter (they look the same but not always set up the same!).

[Stuart BridgerParticipant @stuartbridger82290]

Posted by Andrew Johnston on 22/03/2020 07:44:02:

Seems a bit odd, one would expect the phase currents to go down above the base speed of the motor (probably 50Hz). I'd agree with Steviegtr, reset and start again altering one thing at a time.

Andrew

Andrew, can you please explain here. I would have thought that higher frequency, meaning higher spindle speed would need more current? Certainly when I converted my Chipmaster, it struggled at higher speeds until it was warmed up. Never as bad a tripping the VFD though.

I don't wan't to distract the main thread. Martin's suggestion above is key to answering this one.

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Martin of Wick on 21/03/2020 16:30:52:

Posted by Robert Atkinson 2 on 21/03/2020 16:12:26:

I would note that regardless of being "Commercial" or not, most of these cheap far eastern VFDs do not meet accepted safety and quality standards. Additionally tthe internal components may be sub-standard or under-rated. This is why many sources (including at least one UK reseller) recommend buying a larger unit than should be needed.
Even quallity units need to be mounted in a proper enclosure and most also require a EMI filter on the mains unless te VFD specifically states it has one internally. A good filter can cost more than the VFD.

Robert G8RPI.

To be meaningful you would have to define who's safety standard and what quality requirements. If you are in the market for a £60 VFD you would be inclined to assume it was built down to a price in terms of component spec. and had limited functional software. If your 'standard's are high, then better units are always available.

My safety requirements are you don't get electrocuted while setting the parameters and as long as it runs more or less as expected for a few years, my quality requirement has been met. I will put up with all the other shortcomings.

No point ranting and raving about iniquities of Chinese hobby equipment, real or imagined. It is what it is. Ya pays yer money and takes yer choice.

Actully you can't just "pays yer money and takes yer choice" there are legal requirements that everyone, even hobbists at home, are required to meet.

Yes I know there is virtually no enforcement and most people don't bother. I didn't want to go down that rabbit hole which is why I didn't mention specific standards. But you raised so here it is.
To be legally used the installed VFD must as a minimum meet the Low Voltage Directive, the EMC Directive and depending on the application the Machinery Directive. This provides CE compliance. You also need to meeet the wiring regulations for the mains connection. Some VFDs are CE marked which is interesting as they could be considered components which don't need marking, but even in this case it does not mean that the installation is compliant.
These is not just a legal requiements the are good reasons fr them The matter of EMC (interference) is particuarly important and this does not just affect you, it can spread beyond your property and affect others including, possibly, safety of life systems or services.
Yes, extremely improbable that it happens, but if it does you could b prosecuted. Somewhat more probable is that a poor installation causes a a fire or injury and you end up on the wrong side of an insurance dispute. Even if you have not fully complied with the law, following good practice and using qualitity parts will considerably reduce the chance of being there and give you some defence.
I'm all for people doing this stuff for themselves, but lets support them to do it properly, not give advice that safety and quality don't matter.

Robert G8RPI.

[Alan Waddington 2Participant @alanwaddington2]

Why do these threads always descend into Health and Safety lectures.

I think the majority of people who have homeworkshops employ a decent amount of common sense, practical ability and a healthy respect for things that try to kill you.

Pretty sure by todays commercial standards many of our workshops, mine included would probably be deemed highly unsafe and fall short of many ‘Regulations’

But strangely enough in 40 years of using it, iv’e managed to retain all my digits, still have both eyes and despite wiring everything up myself, including all manner of 3 phase workarounds over the years, never had so much as a tickle from the electrickery.

[Anonymous]

Posted by Stuart Bridger on 22/03/2020 08:55:56:

Andrew, can you please explain……………..

In an induction motor the poles create a rotating magnetic field. This rotating field induces a current in the rotor than in turn produces a magnetic field in the rotor that tries to catch up with the rotating field from the poles. But the rotating magnetic field in the rotor also induces a current (and voltage) in the pole windings. This induced voltage (back emf) in the poles opposes the applied voltage, reducing the current. The rotor never quite catches up with the rotating magnetic field from the poles. The rotor moves at a speed where the back emf and the torqure required (basically set by phase current) balance. The difference in speed is called the slip and it increases as the required torque increases. As the rotor slows the generated back emf falls slightly allowing more current to flow in the poles.

Let's take a standard motor designed to run at rated voltage and power at 50Hz. As the load increases and the torque required goes up the current in the poles increases as the rotor slows slightly. The motor will be designed so that at rated voltage and full torque, at 50Hz, the rated current flows in the poles. This current is driven by the difference between the applied rated voltage and the back emf. The speed at 50Hz is the base speed.

As we increase frequency the rotor turns more quickly and generates a larger back emf that opposes the applied voltage. But we're already at rated voltage, so the difference voltage driving the current through the poles cannot be increased. Instead the current (and hence torque) falls as the greater back emf opposes a fixed voltage. But of course the speed has increased, so although the current (and torque) falls above base speed the power remains constant, at least to a first approximation.

This is in contrast to frequencies below base speed where it is normal to keep the current (and torque) constant and the power decreases in proportion to the speed.

Andrew

[Martin of WickParticipant @martinofwick]

Well, Robert is right in his way. you have to be aware of all the various risks, assess them correctly and mitigate them in the appropriate manner.

But that is different from baldly stating that ' most' low cost VFD are substandard or inherently more unsafe than other similar products. If I saw a reliable body of factual evidence to support such statements, I would probably avoid using them.

Regarding the rating of Chinese equipment – I think it is just a cultural thing. British/European equipment is or used to be, rated conservatively and for continuous duty. It appears to me that the Chinese seem to rate their equipment at the maximum capacity. So if for example I need a PSU to deliver max 1000VA, I make dammed sure to get the one rated at 1500VA! It avoids disappointment.

[not done it yetParticipant @notdoneityet]

The main problem is that is not only the ‘savvy’ that read these forums. Blatantly recommending an unsafe product could lead to a serious situation, should someone blindly follow that advice.

[Alan Waddington 2Participant @alanwaddington2]

Posted by not done it yet on 22/03/2020 12:10:18:

The main problem is that is not only the ‘savvy’ that read these forums. Blatantly recommending an unsafe product could lead to a serious situation, should someone blindly follow that advice.

Not convinced it is an unsafe product, just because the terminal cover can be removed without using a screwdriver, does not make it a death trap, it just doesnt meet this countries regulations.

Think about it, you can take a bulb out in your house and expose live terminals if the switch is on, and most ceiling roses can be unscrewd by hand to expose permanently live terminals.

The world is full of bad advice, doesn’t mean you have to follow it.

[Martin of WickParticipant @martinofwick]

NDY

Nobody here is recommending using an unsafe product or creating an unsafe installations.

I think if you look at most commonly available VFDs, you will see in general they do not have cable anchoring or secondary covers. Does this mean you consider all such VFDs 'unsafe' and not fit for purpose? (better tell inverter supermarkets to withdraw their full range in that case )

Or do you really mean that VFDs in general are relatively high risk devices that need to be installed and used with considerable care. A fact that no one would dispute I would think.

[not done it yetParticipant @notdoneityet]

If you read my post properly, just as it was carefully scripted, you may notice I used the word “potentially”. Perhaps you don’t realise the difference between a risk warning and an out-and-out statement that it will kill you?

Do remember that these devices can be used inside homes and not just workshops.

Yes, all high voltage wiring should have two layers of insulation to protect the user – heard of ‘double insulated’ so don’t need an earth? – mine do and I make sure the leads are anchored securely. My lathe operates from a pendant control and my lathes soon will do, too.

I’ve seen you tube videos where tupperware sandwich boxes have been used for enclosing mains terminals. Not all would recognise the risk and some don’t care about the risk.

I would go so far as to say very few of these devices are idiot-proof. I take all individual cases as they are presented and I refrain from make sweeping statements, such as you are suggesting I do.

Our workshops are potentially dangerous enough, without adding to any extra risk that is obvious, I would respectfully suggest. You clearly do not prescribe to this, I guess?

[Martin of WickParticipant @martinofwick]

Indeed, in that case we are agreed…

…VFDs in general are relatively high risk devices that need to be installed and used with considerable care.

A fact that no one would dispute…

[Ian Skeldon 2Participant @ianskeldon2]

Posted by Martin of Wick on 22/03/2020 15:52:12:

Indeed, in that case we are agreed…

…VFDs in general are relatively high risk devices that need to be installed and used with considerable care.

A fact that no one would dispute…

I think it's also fair to say that some of these devices are not that simple to configure even for the none idiots. It would seem that some come with more useful information on configuring them than others and maybe this is reflected in pricing?

[Anonymous]

I rather doubt that every manufacturer writes their own core control code. It's more likely they beg, borrow or steal it. If the latter then it's quite possible the manufacturer doesn't understand it, so they're not going to be able to explain it to the user.

Andrew

[Martin of WickParticipant @martinofwick]

Ian, you are absolutely correct.

I would go further, these low cost devices are cut down versions of 'proper' VFDs, so hard to know what other compromises have been made. However, I am not aware that they are inherently less safe or inherently less reliable than any other VFD – just more awkward to use.

In short, you don't get what you don't pay for! In addition these devices…

have very limited functionality bar the basics,

have very poor guidance manual or safety advice – barely sufficient to get it going and no parameter explanation

have no back up or warranty

have some rather basic operational oversights

users are entirely on their own and absolutely need to consider all risks.

If these issues are significant to anyone contemplating VFD use or you are rightly wary of electrical installations, then I would say make your purchase from one of the established UK distributors. It will cost a bit more, but you will get good advice on purchase installation and set up assistance.

ps I don't have shares in the XSY company!  but being at the bottom of the food chain have found them to be affordable and useful  and not had any significant issue with one yet.

Edited By Martin of Wick on 22/03/2020 17:01:58

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