E-stops with inverter drive?

I'm just rewiring the control board for my CVA lathe, with an inverter
motor drive.
The lathe had an estop button which shut off all power. I'm concerned
about shutting off the inverter drive supply whilst under load, and
I'm planning to use the estop to issue a stop command to the drive,
which will include some dc braking. There is an 'off' button for the
main inverter supply right next to the estop, but it's not the one you
would hit in a hurry.
Is this a sensible approach? It should, I think, stop the spindle
quicker than if I just cut the power, and is unlikely to harm the
drive.
I could arrange for the estop button to shut off power and 'stop' the
drive, this would presumably provide a little braking but what would
it potentially do to the drive?
Is there a conventional wisdom on such things?
Thanks
Tim
Dutton Dry-Dock
Traditional & Modern canal craft repairs
Vintage diesel engine service
Reply to
Tim Leech
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Tim, I'd go with what you want to do use the estop as a stop button. Your true e-stop will still be there at the side of it. . -- Regards,
John Stevenson Nottingham, England.
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Reply to
John Stevenson
I know that my VFD is probably a different type, a Mitsubishi. But to aid my emergency stop to work I had to fit an external resister of some 200 watts at low value to provide power dump and braking for the motor. I certainly stops a lot faster then hitting the normal stop switch.
It will never be as fast as the 3 phase mains wiring and control box it originally had that would stop the motor dead by reversing a two phases with aid of a rocker switch on the motor shaft, that was really brutal.
I think the fastest I can achieve is 1.5 secs to a rapid stop any faster and it trips the drive out completly. But it does ok with a 3 HP motor and chuck spinning around 1800 rpm.
adrian
Reply to
Adrian Hodgson
Thanks John & Adrian. I'll stick to plan A.
It's a Siemens Micromaster, it has DC braking built-in, with provision for a braking resistor if needed. I haven't tried pushing the braking limits yet, it 's quite effective at about 25% of potential braking. So far as I can see, although there's a separate digital 'off' input with braking included it seems to use the same percentage as is set for the main 'off' command. It would have been handy if this could be set to a higher %, & use this input for the e-stop.
I've just come away from the job to rest my brain. All the original lathe wiring disappears into flex conduits which wander round the various cavities in the cast machine base, they're all nicely numbered at each end. I'd innocently assumed that they would be labelled the same at each end, so hooking them up into the new system would be dead easy. WRONG :-(( I've now got to identify them all over again, there's the same numbering used for *different* wires in other places, I can't see any logic to it at all. It's quite surprising how many wires were needed for a simple manual lathe, & I'm having to add a few. Time for a cup of tea!
Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
Tim Leech
Tim, The wiring numbers maybe consecutive i.e. 13 on one end 14 on other. The motor drive units fitted to my companies automated machinery, 3 axis robot loaded washing machines are wired such that when the EM is pressed all power to the motor is cut and a mechanical brake is released stopping everything dead in its tracks.
Martin P
Reply to
campingstoveman
Martin
Nothing so simple. I've cracked it now, it wasn't too hard after a break and with the aid of a very sketchy diagram in the manual which bears just a little relationship to reality
Wires which are labelled 'A1, A2, A3, A4' at one end are labelled '5,6,7,8' at the other. Then next to the '5,6,7,8' were '1A....'etc. Except that the numbers were put on the wrong way round, to give A1.. again!!
The panel, complete with inverter, is all wired up now ready to refit to the cabinet once I've made some new standoffs for it.
I don't think there's a need for extreme braking, I'll experiment with different levels of DC braking from the inverter once it's all up & running.
Cheers Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
Tim Leech
I've got a second lathe very similar to the one I'm converting. This second lathe has a braked motor, but also seems to employ some magic to stop the spindle quickly if you move the control lever quickly. Whereas the current lathe had three contactors - one each for forward, reverse and coolant - the other has *seven*. I can appreciate the brake will need one, just conceivably one for each direction, but that still only makes five. Can anyone offer any insight as to what's going on there?
Thanks
Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
Tim Leech
Not sure what contactor arrangement you have but my Denford synchro 280 has six! relays and two contactors associated with its braking facility.
It uses DC injection braking and the control logic seems to be as follows.
No 4 enables motor power ON if brake supply is OFF
No 3 Prevents power ON until a time delay after DC OFF
No 2 enables DC brake after a 0.1 sec delay
No 1 DC brake ON
No A reed relay - 2 sec delay DC brake timer
No B reed relay - 0.1 sec DC brake delay timer
One of the relays developed an intermittent coil open circuit - it took ages to sort out what was happening! Good luck.
Jim
Reply to
pentagrid
Thanks. I might need the luck if it goes wrong It doesn't sound as though it's really similar, though it's interesting to learn of different arrangements. I *think* what the extra relays are doing is 'plugging' the motor, swapping two of the phases briefly to provide extra braking. There's no DC source that I can see. The designers must have been keen for it to stop quickly, giving it 'dual circuit braking'!
I've got the 'converted' lathe up & running now, just a little bit of tidying to do and sort out the coolant pump. This is dual voltage, labelled as .09kW (about 1/8 hp). The only reference I can find suggests that to run it from a single phase with a permanent capacitor for the third needs about 35 mfd/hp, or about 4mfd in this case. Anyone with practical experience know if this figure is about right, and how successful it's likely to be?
Cheers Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
Tim Leech
For fractional horsepower suds pumps I've always got away with the ~7mfd caps found in old fluorescent light fittings.
Just have to measure the voltage on the 3rd leg to ensure it's around line voltage.
Wayne...
Reply to
Wayne Weedon
Thanks Wayne & Jim. I'll see what I can find to play about with, smallest so far is 16mfd.
Cheers Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
Tim Leech
Snip
Schaublin 13 suds pump, delta connected.
16uf start, 6uf run.
The start capacitor is essential with neat cutting oil. You might get away without it with thin suds.
Jim
Reply to
pentagrid

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