vfd question

the little screw on cover protects all the low voltage control terminals.

the high voltage connection wire go directly into the oval slots on the base below (one terminal per slot for avoidance of doubt). However, this appears to be a common feature of most VFDs.

Access to the power terminals is also via the screw on cover - you can't get a screwdriver through the cable entry slots to tighten the connector screws. The cable entry slots also appear to be sized such that accidental finger contact with the terminals is unlikely, partciularly so with cables going through the slots.

The point I was trying to make (unsuccesfully it seems) is that the assertion that the power terminals are are not shrouded or adequately protected against accidental contact and are thus a dire health and safety risk does not seem to be correct - the Chinese inverter does not seem to be substantially different to branded European or Japanese products in that respect. I

Other aspects of it's construction. circuitry, interference levels & documentation are all different issues, though !

I could be tempted to try one on the Triac if a branded one doesn't come my way - if I could ascertain that the analogue input was isolated. It would be mounted in a steel enclosure, with shielded cables, an input filter & ferrite rings on the output cables -same installation as a branded one in that regard.

Nigel B.

Without wishing to offend anyone, could someone post in a link to what they consider an equivalent spec VFD but of better quality. Reason being I may go down that route if any of my current motors fail and it would be good to see the difference in costs.

@Neil, I must admit that I am slowly replacing any terminal strip I find at home with wago connectors, it's a hit in term of costs but piece of mind and all that.

Dave / Emgee not let the motor run for very long so far so not sure if there is an overheating problem. Unfortunately I have no wattmeter or any other test equipment. I got my readings from the VFD display panel.

Martin, turning the potentiometer quickly did cause a trip before I slowed the ramp up speed but it seems ok now. I have tested it from the VFD and also from the remote Potentiometer. Could the display inaccuracy you mention be caused by the unit not being shielded?

John

If it is advertised as a one horse power motor (mechanical power, not electrical input) it could well only be ??? efficient, thereby requiring rather more input power than output. Now take into account (possibly) the power factor and quite a deal of difference (than expected) in current reading could be recorded.

As a matter of comment only, that ebay item linked to by mgnbuk does not appear (to me) to indicate it is the inverter in question, so possibly just a ‘red herring’ thrown in?

I enjoy reading all the posts on VFD,s and 3 phase motors etc. Do these produce better quality work than a single phase motor with gearbox or belt/pulleys as they seem a complicated way to rotate a chuck or cutter ?

John,

non conforming display nothing to do with shielding. The best guide is to check motor temperature. If really drawing 5A on 750W motor when you put your hand on it will get 'aargh S***' hot very quickly.

I assume that the display current is measured on the output phase, but I don't know for sure.

I have seen on various setups higher than expected current on the display. For example, I am setting up an 8 pole 370W motor at the moment -

plate indicates 1.3A at 400V 50Hz. display shows 1.9-2.1 A no load at 410v from a 220v in 380v out dual stage VFD (spindle not connected). For an 8 pole fractional motor I would expect about 1 A current draw no load. If I run the motor for an hour or so, it gets warm but not hot - stabilises at about 45-55c (without the fan).

I could be very wrong, but that suggests to me the motor is not really drawing 2A and similar logic may possibly apply in your case but you have to proceed with care.

In other applications I had noticed a similar discrepancy at the pad display relative to plate, but it was not as large as in this instance. I have been awaiting the arrival of a replacement clamp on meter to check phase currents at the motor for comparison, but it has been a long time coming. If I get it any time soon I will update.

In theory a 3-phase motor is smoother than a single phase one as the rotating magnetic field in a 3-phase motor is of constant amplitude whereas in a single phase motor it pulsates. They also provide easy speed changing and useful features such as controlled ramp up and down and quick stopping if a braking resistor is used, They can also be used to jog the spindle which is helpful for tapping or using a die to cut threads. It also depends on how big a PITA belt changing is on a particular machine. That's not an issue for me as all my manual machines are gear driven, except the Bridgeport which is a varispeed belt, so just twiddle the handle.

On the downside at slow speeds the power is reduced as the torque stays constant rather than being multiplied up as with belts or gears.

From a manufacturers viewpoint they allow one to get rid of belts and/or gearboxes which are expensive to provide; an important point when customer purchases are made on the basis of cost rather than performance.

There is an argument that belts and gears can cause vibration that marks the work. Some toolroom lathe manufacturers went to great lengths to isolate the belt/gear speed changing from the spindle itself.

In principle VFDs are pretty straightforward, but you do need a fair degree of knowledge to set one up and to understand the manuals. Whereas belts and gears are dead simple.

Andrew

The quality of the work is down to the quality of the machine operator but all things being equal a 3 phase motor with VFD will makes it easier.

Complication is irrelevant, looking inside a mechanical watch or clock one could say it was a complicate device compared with a digital version (tiny bit of silicon and a few other bits.

Ian P

Thank you for your replies.

As a matter of comment only, that ebay item linked to by mgnbuk does not appear (to me) to indicate it is the inverter in question, so possibly just a ‘red herring’ thrown in?

Not sure what you mean by this ? The link is to an XSY AT1 inverter,as originally referenced by the OP

Still can't see the terribly dangerous, exposed, not protected by a screw secured cover terminals that generated your original comments NDIY ? Could you post the links to your source that suggest that this is not the device in question to clarify please ?

Nigel B.

mgn

The XSY's that have passed through my hands all look like that (but in varying colours and plus or minus a fan or pop out keypad).

No, it’s not. The OP has already stated he acknowledges the non-screwed cover. Perhaps you did not see the VFD at the top of the search and/or copied an entirely different VFD from further down the page? Please show the manufacturer and model number of this pic - I don’t think it is the unit under consideration at all. I could see no positive identification marks on it and, as such, is likely just another chinese clone popped into the thread (as a red herring?).

I suspect 'AT1' is a family of similar devices, not a specific unit made identically by only one maker. What's true of one example may be wrong for all the others. Perhaps everybody is right!

NDIY's first post mentions a VFD he saw on YouTube. Can NDIY provide a link so we can all look at the guilty example.

I don't think VFDs are consumer items meant to be wired up and used out in the open. Rather, they're expected to be installed in a well-ventilated electrically safe box, protected from flying coolant, swarf, and people. The VFD in my lathe is as safe as the contactor. Both protect against accidental electrocution, but neither is screw-driver, idiot, or water-proof. Wired competently inside a protective box, both are safe.

I've not seen a VFD more dangerous than a British Made 405 line TV set. Full of high-voltages provided by a transformer-less mains power supply, no earth, and a loosely attached cardboard back full of holes. Cooling slots had to be small enough too prevent a little finger getting inside, but the main safety feature was positioning the set to make the back inaccessible, and only using the official controls. No way was it safe to touch the chassis, even when the set was unplugged. And it was connected to an aerial on the highest point of the house, the chimney, which put a partly ionised column of conductive air a few hundred feet closer to passing thunderstorms. Ah, the good old days...

Dave

Edited By SillyOldDuffer on 23/03/2020 11:30:35

Dave,

...and your mum used to put a vase of flowers on the TV and top it up with water.
I still remember the incident from when I was a child, all was Ok until she switched it on to see if it was still working.

Please show the manufacturer and model number of this pic - I don’t think it is the unit under consideration at all.

I realise that the picture isn't the largest, but even with my less-than-perfect eysight I can read "XSY-AT1" on the rating plate. It appears to be a product of the Xin Shuang Yuan Co.Ltd (also on the rating plate) who appear not to have an easily findable website.

Maybe my version of Google is different to yours (not being funny here - I get different results from my home computer & work computer for the same search term), but searching for XSY- AT1 only gets me these units. There are also AT3 (380V 3 phase input) & AT4 (220V input 380V output) devices. Looking around I can see that there are some Chinese vfds with more exposed terminals, but non of these have been marked XSY-AT1. It would be helpful to have a link to the units you have seen.

Nigel B.

You are right. It is there. But try looking on you tube. It is very apparent that these units were available with a non-fixed cover. The first hit on epay showed a smaller unit clearly (or unclearly) with a flip-up cover.

The first hit on epay showed a smaller unit clearly (or unclearly) with a flip-up cover.

But still with a cover. Covers do not appear to be compulsory :

Currently available UK manufactured chassis mount DC drive. Bit easier to access the mains terminals than on a compact VFD with a flip-up cover, but still available for sale.

Nigel B.

That is clearly a "component" meant to be incoroporated into a final "product" by a competent entity that ensures it's safeand compliant. Most VFDs fall in the same category it's just not so obvious from looking at them that you need to put them in a box with an isolator, fuse, filter etc.

Robert G8RPI.

That is clearly a "component" meant to be incoroporated into a final "product" by a competent entity that ensures it's safeand compliant. Most VFDs fall in the same category it's just not so obvious from looking at them that you need to put them in a box with an isolator, fuse, filter etc.

Which is the point I was labouring to try & make, Robert.

In some ways, the type of terminal cover NDIY prefers seems to me to be less safe overall, as it leads untrained users to make the wrong decisions about mounting these (at best) IP20 components - screwing them to walls behind the machine being the all too regular dubious choice. More visible terminals might make some reconsider this approach, though I accept that some might just go ahead anyway regardless of the consequences.

Nigel B.