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Inverters and stop switches

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Michael Briggs09/11/2019 00:41:48
166 forum posts
9 photos

SOD with due respect, I haven't spotted that VFD's are not all equal, I have worked with them for the last 40 years.

Regards, Michael

Brian H09/11/2019 07:15:59
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1272 forum posts
98 photos

I decided not to fit the stop button that I have, it's easier that way.

Brian

SillyOldDuffer09/11/2019 08:29:15
4790 forum posts
1011 photos
Posted by Michael Briggs on 09/11/2019 00:41:48:

SOD with due respect, I haven't spotted that VFD's are not all equal, I have worked with them for the last 40 years.

Regards, Michael

Michael, the comment I'm picking up on is:

'A switch between a VFD and the motor does not risk damaging the drive provided that it is only opened or closed when the drive is at standstill though there are exceptions.'

Given that most readers of this forum buy VFD's from the "though there are exceptions" group, I thought it worth highlighting the value of reading the manual to anyone thinking of switching VFD outputs!

I'd have been happy if you'd shifted the emphasis to suit an audience buying small VFDs: 'Though there are exceptions a switch between a VFD and the motor risks damaging the drive .'

Dave

not done it yet09/11/2019 09:15:38
3494 forum posts
15 photos
Posted by Michael Briggs on 09/11/2019 00:41:48:

SOD with due respect, I haven't spotted that VFD's are not all equal, I have worked with them for the last 40 years.

Regards, Michael

Well, you should have now! Things have changed a lot in 40 years!

That said, I for one will not be going plug and play - ever. I’m not prepared to pay perhaps ten or twenty times the cost (of a cheap chinese inverter) for that luxury.

The sentence of text in the ad makes that clear: This type of Plug and Play system when correctly sized can be used to power a whole workshop via a ring main,

There may be some on the forum that this could apply to, but I doubt there are many - and likely none would even consider this option as a practical proposition at this time. Another 40 years and things might have changed again.smiley

For a start all the programming opportunities and protection, afforded by discrete VFDs, is non-existant. That would not be acceptable to me.

Most certainly any failure to follow the inverter manufacturer’s instruction (just looking at the wiring diagram is enough) would void any warranty in this respect. This is the first time (within the last year?) I have seen this type of system on the market, btw.

But the fact remains. They are available.

Michael Briggs09/11/2019 09:51:56
166 forum posts
9 photos

Hello Dave, by "the exceptions" I meant that there are VFDs that are capable of having the load switched while the drive is running, large and small.

The point I would like to make clear to the forum is that the type of VFDs we generally have in our workshops when at rest and powered are unlikely to start due to failure of internal control circuit but are not safe. I recommend that when you are setting up a job on the faceplate for example, you isolate the power. I don't isolate for everything, that is my choice.

Michael

old mart09/11/2019 22:04:37
731 forum posts
69 photos

It seems patently obvious to me that disconnecting the motor from the VFD when the motor is not running will not harm the VFD. There is no current flowing between them at the time.

As for the pastry mixer, it seems the switching between the VFD and the motor is only used when the motor has already been stopped by the VFD and is nothing to do with emergency stopping, but only an extra means of isolating the mixer.

 My use of latching emergency switches works quite well as when the stop circuit is broken, the start switch is inoperative. If I was changing the tooling and someone pressed the start switch, nothing would happen.

 

Edited By old mart on 09/11/2019 22:10:09

XD 35110/11/2019 05:11:26
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1358 forum posts
113 photos

I think the important thing to remember is that we are talking about a domestic installation and not an industrial one !

Brian,

For the simplest installation all you need is :

A latching stop switch for an emergency stop - IMHO all machines should have one of these, whether it is cutting off the mains power or telling an inverter to stop is irrelevent as long as the machine has one that works .

A momentary pushbutton switch for a start switch and the same for a stop switch , you can use a toggle switch for forward / reverse switching as it only changes which terminal the start switch is connected to ( you will have start fwd and start rev on the inverter ) the stop is connected to reset and you can usually configure e stop in the programme to use a terminal suit your needs .

My mini lathe is running a 3 ph motor and inverter ( see my photo library ) and the only other thing i have is a mains power switch mounted next to the lathe head to turn it all on and if i was pedantic enough i might even turn that off while i fiddle around mounting something on the faceplate ! . What is the make and model of your inverter Brian ? Maybe i can download a copy and try to make some sense of it for you .

Back to the discussion -

In all seriousness once the E-stop is active no input signal of any kind should turn the inverter output on - it is in the programming ! , even if the IGBT'S failed and went short they would only supply DC and fry the motor coils .

If you have an inverter that is activating randomly you have issues with shielding and / or transient voltages .

Mark Rand10/11/2019 16:36:07
789 forum posts

I guess that I shouldn't rattle on yet again about my VFD that feeds the entire shed, with three machines and a combined 6 three phase motors all direct on line started from it then... laugh

old mart10/11/2019 16:59:51
731 forum posts
69 photos

I have also asked Brian for the details of his inverter, with no success.

Mark, do you run more than one machine at once, and if so, how many?

Brian H10/11/2019 18:26:22
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1272 forum posts
98 photos

Old Mart, I posted pictures of the manual for my inverter on page 1 of this post and have just found the makers (or suppliers) name, it is;

Xin Shuang Yuan Co Ltd. Model No AT 1-150X

This was chosen because the control panel is removable and has a 5 foot extension lead so that it can be positioned where it is easily accessible. meaning that an emergency stop button is not so urgent (though I shall fit one eventually.)

It was the simplest thing to wire up with the 2 connections plus earth for mains input and the 3 connections plus earth for output being clearly marked on the main unit as well as being easily identifiable in the operating instructions

The mill has now been run several times to bed in the new motor bearings and the repacked spindle bearings, as well as finding out how the mill gearbox etc works.

Brian

Mark Rand10/11/2019 18:54:28
789 forum posts
Posted by old mart on 10/11/2019 16:59:51:

Mark, do you run more than one machine at once, and if so, how many?

Lathe or mill with the surface grinder chugging away in the background is not uncommon. All three at once has only happened once due to the limited number of times I've had work pieces that could be left alone with a long cut on the mill for any length of time while also using the other machines.

old mart10/11/2019 20:10:30
731 forum posts
69 photos

Sorry, no luck in finding info on the VFD.

XD 35110/11/2019 22:41:03
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1358 forum posts
113 photos

I think this manual is the same as Brians .

https://en.ppt-online.org/448529

The parameters you need to change are pretty straightforward:

P10 and P11 set the control input source - if you want to mount a controller box on the machine you set these to external.

P50-P55 set what the X1-X6 terminals do .

You shouldn’t have to change any other settings .

AJAX11/11/2019 06:34:32
18 forum posts
5 photos

Are you sure those crimp connectors have been terminated with the correct amount of force? Did you use a ratchet crimping tool (should work correctly), a pair of pliers, or those cheap crimping pliers with no ratchet action? I wouldn't want to risk any terminations being made incorrectly.

Brian

Robert Atkinson 211/11/2019 07:37:12
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385 forum posts
21 photos

Those who say they cannot see how disconnecting a running motor will damage a VFD do not understand high power electronics. When the current though a coil (inductor) changes there is a voltage developed that is proportional to the rate of change. For disconnecting a motor, that large motor inductance can cause enough voltage to case arcing at the disconnect contacts (and possibly feed back into the drive causing issues) but more importantly for drive damage the inductance of wiring and even transistor internal connections on the drive side can cause voltage spikes high enough to cause damage. Yes you can design to account for these but don't bet on a cheap no name inverter having such protection. This does not mean every drive will fail the first time you disconnect it the magnitude of the spike and ability to cause damage depends on (among other things) the mains voltage, load, speed, temperature and most importantly the exact timing of the disconnect in relation to the load current.

I note that the drives direct advert that was linked to says they are "special" in respect of switching loads and also that they need to be rated at FiIVE to EIGHT TIMES the actual load. So for a 1hp motor you need 5 to 8 HP inverter with presumably a suitable input supply. Most electronics will take mose abuse if you only run them at 20% of their design rating.

Robert G8RPI.

Brian H11/11/2019 08:32:46
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1272 forum posts
98 photos

Ajax, the wires and crimp connections are the same ones that were removed to change from star to delta and, judging by the green paint on the outside of the cable, were the ones it left the factory with.

Brian

jimmy b11/11/2019 08:42:28
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524 forum posts
29 photos

As I don't fully understand VFD's I'm just enjoying the "new" lathe mine has given me!

I have just installed the remote pendant and made a mechanical "interlock" cover for the switch, that covers the srtart button unless the chuck guard is down (to prevent accidental starting).

Jim

old mart11/11/2019 17:42:09
731 forum posts
69 photos

I looked up the instructions that XD351 posted, and they look right. Unfortunately all my attempts to save them to favourites has failed. They are the usual poor quality expected from VFD manufacturers who expect only electrical engineers to read them. The only external device I could make out on the circuit diagram is a potentiometer.

My advice to anyone thinking of getting a VFD is to look at the Inverter Drive Supermarket site, and select one which has their own quick start guide and avoid all this trouble.

Brian H11/11/2019 17:57:54
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1272 forum posts
98 photos

XD 351

Many thanks for all your trouble, I have carefully filed away your suggestion for use at a later date and yes, those instructions are identical to the ones that came with the unit.

I have been running the motor and mill at low speeds to bed in the new bearings and also to distribute the grease in the re-packed bearings. The mill is quieter that the VFD unit!

Brian

Ian P11/11/2019 19:21:35
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2224 forum posts
90 photos
Posted by Brian H on 11/11/2019 17:57:54:

XD 351

Many thanks for all your trouble, I have carefully filed away your suggestion for use at a later date and yes, those instructions are identical to the ones that came with the unit.

I have been running the motor and mill at low speeds to bed in the new bearings and also to distribute the grease in the re-packed bearings. The mill is quieter that the VFD unit!

Brian

Is it fan noise you can hear from the VFD?

Ian P

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