Meddings MF4 drill electrics

Now I have my MF4 I need to convert it to single phase. I thought I would start a thread on this just in case it interests anyone, or of course if anyone has comments/suggestions on what I am doing!

I suspect progress will be in fits and starts but I'll do my best to update here as as I go.

So, first step was to see what I have got to work with and document the existing setup just in case I want to return it to 3 phase.

So it looks like the stop start switches are orginal, as is the contactor but the reversing switch and e-stop look to be add ons. Oddly, the reversing switch appeared to be linked out, not sure why!

Also an interesting arrangement of square of polycarbonate behind the reversing switch, held on with a small stud but no nut.....

Anyway, that lot was all stripped off, leaving just the ally bracket at the back which I am thinking of using to mount the inverter.

Next step was to get an inverter. I do have a spare but it is 1.5kW and pretty bulky. Plus it doesn't have a display/keyboard and I have yet to work out how to configure it via RS485. So for this one I decided to buy new.

Given that, first job was to decide what size. The motor plate says 3A FLA at 240V 3 phase and I will be using this inverter only for the drill so can use soft start. Given that, and the fact it will not start under load I think (hope! ) I am safe using a 3A+ inverter.

A quick trawl of the internet found a Yaskawa J1000 (0.75kw/0.4kW) that appears to fit the bill at a reasonable price. The two ratings are because it has two modes: Normal duty where it is rated at 3.5A and 120% overload for 60 seconds and heavy duty where it is rated at 3A but 150% overload for 60 seconds. Doing the sums shows that normal duty is good for 4.2A for 60 seconds but heavy duty is 4.5A for 60 seconds. I'll probably use heavy duty although I doubt it will matter much in practice.

Less than 24 hours from ordering (from www.inverters-uk.co.uk) this turned up......

The silver box in the middle is an emc filter. Previously (on my boxford) I have got away without using one of these but you really should and it can cause real problems with other equipment if you don't so this time I ordered one. It was a bit of a shock to find it has a bigger footprint than the inverter but that isn't really a problem

Edited By Toby on 12/01/2017 16:53:08

Edited By Toby on 12/01/2017 17:11:14

What does a emc filter do in practice?

And what problems will the lack of it do to other equipment?

Next thing to do is decide how to wire it. Obviously the 1st thing to do is swap the motor over to delta configuration but it is snowing outside so I don't fancy going out the garage

In lieu of that, I have looked at how the inverter control can be connected. Looks like 3 wire mode is best which gives me the following:

I can use the existing stop and start switches but have yet to decide whether to fit the reverse switch and speed control pot. If I do I suspect I will put them at the back with the inverter so my general wiring will be 240V in to the filter/inverter on the back of the drill, 3 phase out to the motor and control cable forward to the existing start/stop switch box.

What I haven't decided yet is what to do about an e-stop. The inverter will deal with the NVR but it would be nice to have a more prominent stop button so I am wondering about something as a kick switch. The question being where to wire it in.

I have two obvious options:

1) as a hard stop input to the inverter. This will have the advantage that it can use braking and so potentially stop the drill quicker. The disadvantage being the (theoretical) chance a control software crash in the inverter means the e-stop is ignored. Not sure what the chance of that is though and, as a last resort, I can always turn it all off at the mains.

2) Fit the e-stop before in the mains in to the inverter. This has the advantage of not relying on the inverter plus can be used to turn the isolator off. The downside being that the drill will freewheel when stopped.

Anyone got any comments on this?

Toby

It creates essentially a barrier directly between the power source and equipment, the power lines which are supposedly vulnerable to electronic noise.

On our end of the spectrum, i.e home workshop use, where you're equipment is close to the power source, it wouldn't produce any noticeable difference to not have one on a typical inverter.

However, if you were using it in a big factory where the power line "might" run many many metres(or in an area with a lot of other electronic equipment), you would probably find you would have difficulty holding a particular frequency on finer levels, the fluctuations; a result of the length of the line acting as a conductor for potential interference in the variable power supply that a wall socket gives.

A reactor is different, where they are designed to stabilize and homogenize the frequency of the power from the wall socket.

Michael W

Edited By Michael-w on 12/01/2017 17:51:19

It stop (or reduces) electrical noise going into or out from the inverter. If this noise is bad it could affect the operation of other bits of equipment, particularly if they are electronic.

An inverter chops up the rectified mains to create the 3 phases. Given this it is a prime candidate for chucking this electrical noise back into the supply.

A mate of mine was telling me last night that when he fitted an inverter (I think a fairly hefty one to his bridgeport??) it completely screwed up his fancy fridge (one of those that does ice on demand etc) until he fitted a filter on it.

Hi Toby,

The one thing you must be careful with on a hard stop is that when a motor is running at full speed and the input suddenly is halted. The inertia of the rotor continues to spin, potentially sending a backward current to the inverter, to mitigate the effects of this, a braking resistor is often used.

A good point.

Sorry, I was probably incorrect in calling it a hard stop. I think the inverter allows you to configure different deceleration times. So for for a normal stop I could program this to something relatively slow (eg a few seconds) to make it easy on the motor but for the e-stop input I could program it to be something much faster.

The inverter has two braking methods - an external resistor and DC injection. From what I gather the DC injection can be hard on the motor (it effectively dumps the energy back into the motor rather than a resistor) and isn't so good if the load has a lot of inertia but it is probably ok on a drill for emergency use?

Any thoughts on this?

I wouldn't disconnect the input to the VFD when it's running as a means of e-stopping the drill. It should survive in the same way that a power cut when running shouldn't cause damage. But it's not going to stop quickly. These VFDs are going to be very well designed and pretty well flawless in operation. If you are bothered about bringing the spindle to a rapid stop, you could just fork out on the recommended braking resistor. Having said that, DC injection isn't going to stress the motor unduly, as the moment of inertia on a drill is dominated by the motor itself. Induction motors are pretty simple and robust.

It's a bit late now although hardly relevant when you are talking about a pillar drill but the vector control sister of the J1000 (called the V1000) has a hardware inhibit input called "safe disable" which is intended for use where it used in more safety critical applications. The idea is that you could use this to provide a more failsafe inhibit. It's to ensure you can shut down in the unlikely event that the control software has a wobbly.

EMC filters work 2 ways - to prevent electrical noise from the VFD interfering with adjacent equipment (either by conduction or radio transmission) and to prevent the VFD from being upset by conducted noise on the AC lines. All the safety regulations specify limits. In UK / EU it's covered by the CE mark (EN55014 etc).

Murray

EMC stands for "Electromagnetic Compatibility" and you can read all about it here.

Not having an EMC filter means that any electrical muck produced by an equipment will flow back out into the mains cabling, potentially causing interference or the malfunction of other nearby electrical equipment. . 'Nearby' is a relative term as interference can be radiated and easily travel several miles.

Although invisible, electromagnetic muck is a potent nuisance and a serious problem. Like farting in a lift, it's bad manners. There are also legal issues. That you personally cannot detect an EMC problem in your home means very little: it's the effect across the neighbourhood that matters.

An EMC filter also has a benefit in that it stops muck emitted by someone else from entering your equipment. Is this likely? Yes. A local radio transmitter, say in a passing ambulance, could easily scramble the brains of an unprotected VFD. It's why using mobile phones is discouraged in Hospitals, Aircraft and Petrol Stations.

Dave

In the factory I worked in an estop for a drive was always effected by a pair of monitored contactors, this always prompted the debate that the drive could control the load to a stop quicker than just cutting power. However a controlled stop can only be effected by a drive in working order so to cover all possibilities the contactors with redundancy and monitoring were used. This is a bit over the top in a home workshop and a risk assessment would probably come up with a different category of safety required and what we normally do will be sufficient. In my own workshop I work in a way that would have me marched off the site if it were industry, I hope that I am aware of the risks and as I am the only one at risk the precautions I take work for me. Large industrial drills that I had dealing with used DC injection and an antenna limit switch alongside the drill to protect the operator. The speed of the stop was savage but if you were tangled up in a 8ft radial drill you might be glad of a near instant stop but not sure the drivetrain enjoyed it. I like the way you're going with this Toby I must get on and upgrade my MF4 to an NVR and put a more useful estop on it. There is always a little voice that tells me this could be safer when I use it and now you have shamed me to take action.

Mike

Worth mentioning perhaps that VFD EMC filters often have a high earth leakage current, which can cause domestic RCD-protected circuits to trip. See many long discussions elsewhere on this forum!

Also, many inverters now have EMC filters built in so no need for a separate unit.

Edited By Bikepete on 12/01/2017 18:55:35

Thanks Murray, that confirms what I was thinking, using the inverter for the e-stop being the way to go. I have to admit I didn't look at the capability of the V1000 as the J1000 appeared to do what I wanted. Also the V1000 has the disadvantage of costing 80% more

Toby

Interesting stuff Mike, Like you said, at work you need to do everything by the book, in my garage I can do what I like as long as I am convinced it is right

I am hoping this one doesn't have RCD problems, if not I might have to build one myself. I am no expert in power circuits but I work with someone who has designed plenty of power supplies - ironically we are currently designing a bespoke VFD together, he is doing the electronics, me the software, not for induction motors though. Or I have the wherewithal to play with the supply RCD if necessary....

The other inverter I have (mitsubishi E500 iirc) has a separate filter but it fits in a recess in the heatsink so gives the appearance of being built in. Quite a nice solution as it does not take up any more space but can also be removed (or changed) if necessary.

Absolutely Toby, I do the same, in my garage it's my game and my rules, I have a few dodgy setups but I know they are dodgy and no one else plays in my workshop, neither of my sons is the slightest bit interested in my activities which as far as motorcycling goes I am in two minds, on one hand I have had a huge amount of enjoyment but on the other too many people are killed and injured so maybe it's for the best.

Mike

Edited By Mike Poole on 12/01/2017 19:33:03

Similarly I'm the only user of my stuff, but I always have in mind that if run over by a bus, all my tools would be disposed of and go on to who knows who. Or I might want to sell them on so as to upgrade or downsize. So I try to label any custom controls clearly and make things reasonably 'as you would expect'. Another nice courtesy to the next user is to print out a circuit diagram of anything you have made or modified, and pop a copy into the control cabinet (secured where it can't be a fire risk) for the next user to find when they open it up...

The 10A Schaffner EMC filter that I assume you have there appears to have 220nF Y caps and generates ~10mA of earth leakage current (= 230V / 220nF @ 50Hz). Unless you have several of these connected simultaneously, it's unlikely you'll have a problem withthe standard 30mA RCD.

If you get RCD trips, there are solutions such as using an individual RCBO for this circuit. Changing the main RCD is not really approved and daisy chaining them isn't ideal either.

Thanks Muzzer, that is indeed the filter I have. Where did you get the Y cap info? I was thinking about taking mine apart but it is rivetted. Anyway, you just saved me the hassle

If I have problems (looks unlikely) then I can change the protection device - it is currently planned to be on the garage power circuit (which is an RCBO) but I have spare ways in the garage CU (and spare RCBOs) so could move it to its own circuit if necessary.

Don't worry, having worked as an electrician I have seen the hassle caused by people who don't understand RCB discrimination

Going on my Mitsubishi inverter the emc mains filter is optional and only fitted if required. It has a built in emc filter. Lots do have now. They also show the fitting of an AC reactor in the mains line if needed. A lot of this is woolly because there are variables outside of their control In other words if the unit does cause interference fit a filter and maybe also a reactor.

They show a magnetic contactor in the supply and point out that this shouldn't be used to start and stop it. It can be done but it will shorten the life of the unit. They also show a current trip pointing out that allowances have to be made for in rush current . Effectively some large very high quality capacitors are being connected to the supply when it's powered up.

Later they give some numbers if the mains to the inverted is disconnected via an emergency stop to the contactor. Life 500,000 cycles dropping to 25 times if used for an emergency stop. (AC-1 rated contactor.) They then go on to mentioning what rating of contactor should be used on the motor side if that is used for an emergency stop. They also discourage doing this. AC-3 rating for any contactor there.

Most of the em noise from these units come from the drive to the motor. They stress single point earthing and shielded cable. Plus earthing of the motor and inverter. Optionally filters can be installed in this line as well. A simple one or one I wish I could get my hands on, a sine filter. (1hp if anyone wants to give me one.) These may be needed I assume on long feeds to the motor.

The earth current flow may have an influence on the rating of any earth leakage trip that is fitted.

They give minimum motor cable sizes based on a max drop of 2% over 20m.

Then comes sensible routing of the control cables. In other word keeping them away from the others. >= 10cm. They show shielded cable being used to the speed pot or current drive and also on the analogue speed output. Not on the rest though as all leads go to the inverter and represent 24v being pulled down with a current of 100ma max. I ran mine in a shielded cable.

Single point earthing in my case was provided by a slab of aluminium by the connection block so was pretty easy. No need to try and take all to a single bolt etc.

Most modern up to date inverters have a self tune facility buried in the menu and also motor modelling to help prevent over heating. Random switching too in some cases. That reduces noise.

They also mention that higher switching frequencies increase noise but tend to make the drive quieter. Really here they must mean noise power levels as I would assume that the switching waveform has the same rise times what ever frequency it is running at but I suppose they could play with that but doubt if they would,

I did wonder but on my Meddings I changed the motor to a 240v. The main reason I changed drill was to get one with a back gear as on a few occasions I have wanted a lot more grunt at lower speeds. If I had gone the other way I would have wanted a more powerful motor - just as many do when they change lathes over to inverter drive from 240v.

John

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I haven't fitted a contactor on mine by the way. I rely on the inverter and a switch. Mit list it as they do because this is often how things are wired, machine tools and conveyors etc. Metal boxed multipole isolator some where. A no volts switch, a contactor and a panic button plus any safety cut outs. People do wire the panic button to the inverter rather than breaking the supply and I understand some inverters say don't stop the machine by disconnecting the supply. I've not seen one though. The panic button wiring will vary according to the inverter. It need to stop the drive and prevent the start button from working. . Mit do a separate safety module but I haven't looked at the data so no idea what that actually does. Might be for something else.

What they effectively say is us a magnetic contactor to power the inverter, include a panic button and no volts type on off switching to the drive to that but start and stop the drive using it's controls. ie

What that means effectively is the usual no volts release switch and that it can be de activated by the panic button. They add a magnetic contactor because the inverter currents can be much larger than what these switches can handle. A NVR switch contains a contactor of sorts so the panic button can simply break the supply to that.

The current inrush when powered up will be there on all makes because of the capacitors in them.

If it sounds complicated I've heard unwiring even a simple Boxford that has been wired to the book can be a bit confusing. Most drop the lot.

John

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