Convertors v Inverters

[Robert Atkinson 2Participant @robertatkinson2]

I’d argue the claim “It does have the great advantage that it’s possible to buy 3 phase machinery and just plug it in.” This is not correct for all rotary converters and loads. In particular control circuits connected to one phase and neutral can have problems. Addiionally the phase voltages and currents may not be balanced. Some motors may not like this and it can cause torque ripple.
It’s not clear to me if a typical rotary (or static) converter would meet electrical safety standards or pass a safety test on the output. In particular the neutral, if provided, is not at ground potential as would be expected in a normal installation.

Robert.

[Mark RandParticipant @markrand96270]

There’s a fair amount of irrelevant information in this thread and some downright bollocks.

The Dives direct unit will happily replace a rotary converter and will be plug and play. They actually use good brand inverters, modify them to add a voltage doubler circuit and configure them for fixed frequency use. I’ve had a 7hp one for a number of years and if supplies the 6 three phase machines in my shed quite happily. It’ll whistle a bit, but will be quieter than a rotary.

One could build an equivalent for a bit less money, but one wouldn’t get any support or warranty if one did.

[larry phelan 1Participant @larryphelan1]

Delighted to hear that Dave, and like you, I,m not really interested in variable speeds since the machines own speeds are good enough for my needs.

I find that these “Smart” meters are not quite as easy to read as the old disc type [a sign of old age ?? ] With that type, you could see the disc whizzing around, the new type just changes things on the sly !  Apart from all that, the cost of electricity has gone through the roof here, which was what  brought about my interest in inverters.

Might just forget about them for now.

Thanks very much for your reply and enjoy your new shop when you get it going.

[Mark Rand]

On Mark Rand Said:

There’s a fair amount of irrelevant information in this thread and some downright bollocks.

The Dives direct unit will happily replace a rotary converter and will be plug and play. They actually use good brand inverters, modify them to add a voltage doubler circuit and configure them for fixed frequency use. I’ve had a 7hp one for a number of years and if supplies the 6 three phase machines in my shed quite happily. It’ll whistle a bit, but will be quieter than a rotary.

One could build an equivalent for a bit less money, but one wouldn’t get any support or warranty if one did.

The statement “The Dives direct unit will happily replace a rotary converter and will be plug and play. ” is a bit vague. What unit exactly? I can’t find any “plug and Play” converter on the Drives Direct sales listings on ebay. As an aside I think it is very poor that their website points you to ebay for information and then tells you to call them to buy off ebay at a lower cost…
This uniit for example:
https://www.ebay.co.uk/itm/154157585432
Isn’t exactly cheap and certainly isn’t plug and play. The fact that they say to use a unit of 3 times the nominal rating is a big red flag to me. They also say that you may also need a sinewave filter and if if your machine needs a neutral a neutral “generator” as well as the filter.
I’m pretty certain none of the units listed on ebay would conform to UKCA / CE / Electrical safety requirements as supplied.

Any chance of some more information on the unit you have and some photos of it installed?

Robert.

[larry phelan 1Participant @larryphelan1]

I seem to have stired up quite a stew!

Never thought there was so much to know about those things.

I now have the Headstaggers.

[larry phelan 1]

On larry phelan 1 Said:

I seem to have stired up quite a stew!

Never thought there was so much to know about those things.

I now have the Headstaggers.

Yes, but people like me facing the same quandry are learning as well.  So thanks  Larry and to all those contibuting.

Martin

[larry phelan 1Participant @larryphelan1]

Yes indeed Martin, my thoughts exactly !

So much to learn/so little time .

[Robert Atkinson 2Participant @robertatkinson2]

Interesting that no one has come back with details of a working Drives Direct converter (one unit driving two or more machines) installation. In particulr it would be useful to know:

exact model / part number of the unit, were any additional items needed, what was the total cost, what machines have been used on it, where any modifications needed to the machines, photos of the installtion.

Robert.

[renardiere7Participant @renardiere7]

Hi Robert, I seem to have overlooked this thread or at least, not been following.

I bought a Drives Direct VFD in 2015. I needed a 240 to 415v set up and was offered what they claimed was a plug and play system, this would appear to be what Mark Rand has installed. See a few posts back.

At the time it was too costly for me (around £1800 I think ) and I purchased a smaller unit capable of 3hp output.  For my lathe and mill I did take the time to integrate the machines switch gear with the VFD supply and this has worked faultlessly over 10 years in a professional workshop setting. As more machines were added to the workshop the same VFD was used to supply them, all of these directly wired to the motor and controlled by a pendant.

So currently I have a lathe, mill, surface grinder, drill press, tool and cutter grinder, and jigsaw all supplied by the same unit. A second lathe is about to be added.

I know that this is not the plug and play set up you refer to but I mention all this to show that one unit can deal with a wide range of different motor sizes without any fuss and no hint of any fault over the last 10years.

I’ve got no reason to doubt that the larger output unit Drives Direct offer could indeed be used as a plug and play supply.

[Martin Johnson 1Participant @martinjohnson1]

The link you gave, Robert, seems to be such a beast.  If I understand the listing correctly, it has to be well oversized to cope with starting inrush current – no great surprise there.  So a more economic and elegant solution is one drive per motor with no intermediate switching so that the soft start capability of the inverter can be used.

While I am here, can anyone provide a dunce’s guide to selecting what filters are needed for an inverter installation?  Also can the inverter be trusted with motor overload protection in lieu of thermal trips?

Martin

[Julie AnnParticipant @julieann]

No filters are needed on the output of an inverter. It is usual to fit a common-mode/differential-mode filter on the mains input. This filter is primarily to prevent noise from the inverter entering the mains, and to filter harmonic currents due to front end rectifier in the inverter. These filters are available off the shelf, in a shielded metal case, from any good electrical/electronics distributor. No point in rolling ones own. Chose one based on maximum current draw from the mains.

The output current protection in the inverter will be faster and more accurate than any sort of thermal overload will ever be.

Julie

[old martParticipant @oldmart]

I chose an inverter with C2 emc filters built in simply because the museum is not a domestic situation and I was afraid of causing interference. Filters have a small current drain to earth and I was also worried about the 10 mA RCD’s at the museum tripping, but the problem did not arise, whereas domestic RCD’s are normally 40 mA.

The price of two individual industrial VFD’s of 1.5Kw, which would run from a domestic socket, and full remote switchgear plus two new motors (assuming the existing ones don’t have the common star to delta connections already) would be less than 1/3 of the Drives direct one on ebay.

[Martin Johnson 1]

On Martin Johnson 1 Said:

The link you gave, Robert, seems to be such a beast.  If I understand the listing correctly, it has to be well oversized to cope with starting inrush current – no great surprise there.  So a more economic and elegant solution is one drive per motor with no intermediate switching so that the soft start capability of the inverter can be used.

While I am here, can anyone provide a dunce’s guide to selecting what filters are needed for an inverter installation?  Also can the inverter be trusted with motor overload protection in lieu of thermal trips?

Martin

As Julie has mentioned you only need a filter on the input for EMC. A good manufacturer will include guidance in their documentation. Some models have built in filters. These are normally for the higher industrial limits but better than nothing.

A VFD should not need to be oversized. They certainly don’t need it for inrush current current as the electronics provides a soft start. I’ve seen installations where a VFD was used purely to provide a soft start function and reduce inrush. I think the reason Drives Direct say to use a bigger VFD is so that you can switch a load onto a running inverter rather than letting the VFD start it up softly. Soft stary reduces stresses on the mechanical parts f a machine as well as the electrical system.

Again as mentioned by Julie, A properly sized and set up VFD provides better protection of the motor than a external trip. Most will support a temperature sensor built into the motor providing thermal protection as well as over current. The Drives Direct converter “solution” does of course remove this protection as the VFD and settings are over-rated. This needs external motor protection at extra cost. Ideally there should be no components between the output of the VFD and the motor. Drives Direct mention output filters but these are to provide a more sinewave like output by integrating the PWM pulses.

Robert.

[Wade BeattyParticipant @wadebeatty78296]

The unit that Robert had a link to https://www.ebay.co.uk/itm/154157585432 is the drives direct item I have had for 7 years with no issues

[Robert Atkinson 2Participant @robertatkinson2]

Thanks for that Wade,
Can you answer my other questions please?

Were any additional items needed?

What was the total cost?

What machines have been used on it?

Were any modifications needed to the machines?

Do you have any photos of the installation?

Robert.

[Wade BeattyParticipant @wadebeatty78296]

Robert,

No additional items needed.

The cost was included with the Omnimill I purchased from a friend, a real deal, so for me there was no cost.

I use it on my Omnimill (3hp horizontal and 1hp vertical) and my Boley 6LZ 2.4hp

There were no modifications on the machines, however the 240V output electrical outlets for light, dro, coolant knocked the lights out when anything was plugged into the 6LZ. The controls for the machine are all 24V so the control circuits are fine but the auxiliary 240V does not play well with the Drives Direct unit. A power strip for the auxiliary items (DRO and Light) was sufficient.

The machines are never run simultaneously, to make sure one must be unplugged prior to plugging in the other. Kind of a pain but i am not running between machines at any great speed.

I will send photos later

Wade

[Robert Atkinson 2Participant @robertatkinson2]

Thanks for that Wade. Not quite “plug and Play but about what I expected. The unit on Ebay looks like their DSA series but the manual on their website https://www.drivesdirect.co.uk/Downloads/DSA%20Series%20Manual.pdf
Does not match the reported performance. In particular the 5HP unit is listed as 3 phase input and the 230V input models are not a step-up to 415V.
The manual also says they need an input filter even to meet industrial EMC levels never mind domestic.
I think Drives Direct are overselling somewhat.

Robert.

[Wade BeattyParticipant @wadebeatty78296]

The manual is awful, complete crap. The DD unit I have was not set up with filters when I first saw it in Scotland and I set it up the same way when I had the mill in Norway. It has only been since joining this forum that I have seen that filters are recommended.

I have searched for filters but got lost in details, since it works so well, I have not gone further. Everytime this comes up I promise myself that this time I am going to get filters….

 

W

[FulmenParticipant @fulmen]

As long as you don’t have any problems I wouldn’t worry too much about it. It’s a much bigger deal in industrial setups due to the sheer amount of electronics of varying age and quality it could interfere with. I’ve been running a “naked” Lenze VFD for years and years without any problems.

[Fulmen]

On Fulmen Said:

As long as you don’t have any problems I wouldn’t worry too much about it. It’s a much bigger deal in industrial setups due to the sheer amount of electronics of varying age and quality it could interfere with. I’ve been running a “naked” Lenze VFD for years and years without any problems.

What about others? Your system could be causing problems for other people who may not realise their poor internet, radio reception or intermittent problems are being caused by non-compliant systems. If you buy a component, which is what a VFD is, you are responsible for ensuring it is compliant with the EMC and safety regulations.

There is also a risk that noise from one machine could cause unexpected operation of another. This can be very dangerous and it’s too late when it happens.

Robert.

 

[FulmenParticipant @fulmen]

Fair enough. But what are the chances of others having issues if I’m not? As I understand it the biggest issue isn’t noise on the mains but on nearby signal cables. So chances are it will be confined to my house.

Sure, some neighbor could have something that is especially sensitive, but at some point surely that must become at least partly their problem? I’m not running dodgy import electronics, and it’s not like every other VFD in the country is set up with filters.

[Fulmen]

On Fulmen Said:

Fair enough. But what are the chances of others having issues if I’m not? As I understand it the biggest issue isn’t noise on the mains but on nearby signal cables. So chances are it will be confined to my house.

Sure, some neighbor could have something that is especially sensitive, but at some point surely that must become at least partly their problem? I’m not running dodgy import electronics, and it’s not like every other VFD in the country is set up with filters.

Assuming you are in the UK or EU, your equipment must by law comply with the relevent emissions limits. Again I assume you are on a domestic supply (one or more domestic properties on the same same power line as the equipment) the equipment must meet the lower domestic limits. It’s unlikely that a VFD, even with built in filter, will comply “out of the box” even if a “good” make. They are desigined for industrial use. IF your VFD interfers with some neighbours equipment (which is compliant) you are liable. It is not their problem it is yours and you could be prosecuted. Note that the industrial susceptibility limits are also higher so you may not see effects on that.
What if your equipment is radiating on an aviation frequency? Not aproblem if you are not near an airport but playing devils advocate,  Your neighbour has  heart attack and the airmbulance is called. No problen on approt when they call for clearance to take off thay can’t hear air traffic control due to the combination of weak signal on the ground and your interference. Not very likely? Probably not, but there have beeen much more unlikey instances of real interefence. For example:
https://www.ofcom.org.uk/spectrum/interference/interference-issue

You must make your own risk assesment. I’m not the EMC police, just making people aware of the issues and their responsibilities. Unfortunatly most purchasers assume if they can buy it it must be OK and many sellers either don’t know, don’t care or even worse, know that it’s the installers responsibilitiy not theirs and don’t care.
This is not always the case. There are a growing number of commercial equipment, electronic component and chemical suppliers who have decided that they might be responsible or / and don’t want to ave to comply with consumer laws  and have imposed a ban on selling to individuals. The best know example is Keysight (formerly Agilent / Hewlett Packard). This makes it hard for responsible hobbyists. Raspberry Pi is an interesting example. Their trms and coditions say all sales are business to business but they have a retail store in a shopping arcde in Cambridge. See clause 2 of https://www.raspberrypi.com/terms-conditions-sale/ Note that the store webpage links to the same terms and conditions. However their website is only for domestic and personal use see 6.1 of https://www.raspberrypi.com/terms-and-conditions/
They are obviously adverse to liability…..

Robert.

[DC31k]

On DC31k Said:

As is usual here, due to not reading properly the initial post in the thread, there are some misleading answers.

The OP states he wants to replace a rotary convertor and is considering the Drives Direct offering for this purpose.

It is unstated, but obvious with a moment’s thought that the input to the converter is 230v single phase and the output of the rotary is 415v three phase. The suggested Drives Direct replacement matches this.

That means the ‘Inverter Drive Supermarket’ and ‘look on eBay’ suggestions are poorly made as neither will provide an input/output voltage/phase combination that matches the OP’s current set up.

Not mentioning this explicitly is doing the OP a massive injustice. Yes, a 230v three phase output VFD likely can be made to work, but remaining silent on the work involved in doing so is bad form.

Unless I’m misunderstanding your post,  this is incorrect.  You can get VFDs that will take in 230V single phase and output 380V three phase.

I have one (albeit a cheapy Chinese one, but since it powers a tool grinder expecting 400V, and it cost £60, I don’t expect it to explode into a big ball if flame, and if it does fail, it’s paid it’s way).

Whether that 35V difference will make a big difference to the OP’s use case is something I am not qualified to comment on.

[David AmbroseParticipant @davidambrose86182]

R/S are showing over 2000 Keysight items for sale.

[southernchap]

On southernchap Said:

……You can get VFDs that will take in 230V single phase and output 380V three phase.

The DC voltage (DC link) from a rectified 3-phase supply is significantly higher than that from a single phase supply, and varies according to the rectifier arrangement. Since the DC output from rectified single phase is lower a 415V 3-phase output cannot be generated from the DC link, hence the usual 230VAC 3-phase output. The way round this is to boost the DC link voltage. The ‘proper’ way to do this would be to use a boost converter after the rectifier.

Most cheap inverters do not include power factor correction (PFC) at the front end, relying instead on external filtering to prevent harmonic current distortion being fed back into the grid. A PFC is essentially a boost converter, so could also be used to increase the DC output voltage as well as constaining the input current to be sinusoidal.

However, a boost/PFC converter is relatively expensive. In a cheap VFD a simple voltage doubler rectifier will be used in place of the standard bridge rectifier. This creates a higher DC link voltage thus enabling a higher 3-phase voltaqge output. However, even with voltage doubling the DC link is not quite high enough to generate a 415VAC 3-phase output. Hence the specification of 380VAC 3-phase.

Julie

 

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