Harrison M300 electrics

[Welderpaul]

Here we go again

The electrics are a right mess on this lathe. The lathe is a 3 phase version, and currently run from a VFD which has been 'butchered in'.

Firstly i'm trying to establish a list of items that need connecting. I've got these as, in no particular order:

Emergency stop to front of change wheels enclosure (fitted and wired to VFD)
Indicator light to front of change wheels enclosure (missing)
Pair of limit switches either side of cam on spindle control lever (fitted but not wired)
Limit switch on footbrake (fitted but not wired)
Suds pump (fitted/wired but not connected in electrical panel)
Lathe motor (fitted and wired direct to VFD)
Limit switch to change wheel cover (missing)
Chuck guard limit switch???? (missing if there ever was one?)

Have I missed anything off the list that should be present on the machine when original?

 

[Seadog]

For simplicity you can connect all of the switches in series. As to what's missing, that I can't help you with, I'm afraid.

Suds pump, see if it can be wired for Delta, most I think you can. Then rig it with a capacitor to run from single phase 240V.

 

[Welderpaul]

Found this - wish i understood what it all meant.

 

[Agroshield]

Emergency stop to front of change wheels enclosure (fitted and wired to VFD)
Indicator light to front of change wheels enclosure (missing)
Pair of limit switches either side of cam on spindle control lever (fitted but not wired)
Limit switch on footbrake (fitted but not wired)
Suds pump (fitted/wired but not connected in electrical panel)
Lathe motor (fitted and wired direct to VFD)
Limit switch to change wheel cover (missing)
Chuck guard limit switch???? (missing if there ever was one?)

Have I missed anything off the list that should be present on the machine when original?

Buttock-pucker-operated E-stop?

I think you have everything there. Certainly, everything you list (other than chuck guard) is also listed on the diagram you posted and there is nothing on his diagram that is not on your list.

He has a delay relay on the suds pump for switching the capacitors, which is really just icing on the cake.

He seems to be switching the main supply to the VFD through the contactor. This, I think, is wrong and bad.

 

[Seadog]

He seems to be switching the main supply to the VFD through the contactor. This, I think, is wrong and bad.

Normally you wouldn't do this since you remove any control the the VFD exercises over run down. But it seems that the M300 has a brake, so that is probably why. I think I saw a comment to that effect somewhere.

 

[mtt.tr]

.

He seems to be switching the main supply to the VFD through the contactor. This, I think, is wrong and bad.

In an emergency its best to not rely on the vfd but the contactor.

 

[Welderpaul]

Normally you wouldn't do this since you remove any control the the VFD exercises over run down. But it seems that the M300 has a brake, so that is probably why. I think I saw a comment to that effect somewhere.

Yes the M300 has a mechanical brake

 

[Agroshield]

Normally you wouldn't do this since you remove any control the the VFD exercises over run down.

I was under the impression that killing power to the VFD while its output is live was quite bad for the device, so should be avoided if at all possible. If there is a power cut, you cannot do a lot about it, but other than that, it should always be allowed to control the system.

Wired as the diagram, it relies on user-discipline never to hit the e-stop unless it is really an emergency to prevent any VFD damage. Also, if you open the gear cover while the machine is running, it will kill the input to the VFD. In any properly-designed system, accidental triggering of the safety features should not have expensive consequences.

To me, if either of these situations does happen, the VFD should slam on its own brakes as fast as possible. In a real emergency you might not be able to get to the footbrake, especially if you are poking your fingers in the geared end, away from the brake pedal.

In a normal stop, the VFD can coast to allow the footbrake to be used but I think the argument about the VFD brake fighting the footbrake is not necessarily a foregone conclusion and needs more thought. On a practical note, the VFD braking would allow one less limb to be used when threading up to a shoulder.

You would also have to read the VFD manual to see what it does when its input power is killed. My guess is the motor goes into free-spin but the manual has the last word.

 

[mtt.tr]

I was under the impression that killing power to the VFD while its output is live was quite bad for the device, so should be avoided if at all possible. If there is a power cut, you cannot do a lot about it, but other than that, it should always be allowed to control the system.

Wired as the diagram, it relies on user-discipline never to hit the e-stop unless it is really an emergency to prevent any VFD damage. Also, if you open the gear cover while the machine is running, it will kill the input to the VFD. In any properly-designed system, accidental triggering of the safety features should not have expensive consequences.

To me, if either of these situations does happen, the VFD should slam on its own brakes as fast as possible. In a real emergency you might not be able to get to the footbrake, especially if you are poking your fingers in the geared end, away from the brake pedal.

In a normal stop, the VFD can coast to allow the footbrake to be used but I think the argument about the VFD brake fighting the footbrake is not necessarily a foregone conclusion and needs more thought. On a practical note, the VFD braking would allow one less limb to be used when threading up to a shoulder.

You would also have to read the VFD manual to see what it does when its input power is killed. My guess is the motor goes into free-spin but the manual has the last word.

This isn't for a functional switching its only for emergencies, everything else should be done through the vfd

 

[Welderpaul]

There's a note on the circuit drawing:

Since version 3 of this design 110V control has been changed to 24v. The footswitch will now operate with any type of VFD and does not use the E-stop function. The VFD must only use COASTING stop, otherwise the footbrake will fight the VFD deceleration

 

[Kram]

Cutting power to the vfd should be fine, what model is it? Just do not have anything between the vfd and motor! Cutting the motor will kill the output stage.

Invertek told me the best way to e-stop on mine is to cut the mains input, with the drive set to fast stop on input loss. It stops instantly then takes 30 seconds or more for the drive to lose power. It will not restart when power is restored.

 

[Agroshield]

Invertek told me the best way to e-stop on mine is to cut the mains input, with the drive set to fast stop on input loss.

And the bit you were told, and that is highlighted, is the crux of the matter. Without that crucial step, the only way the inertia of the 10kg workpiece spinning at 800rpm will be dissipated is by ripping off your arm.

Not only do you have to consider the physical switches but also to program the VFD correctly. The two are hand in glove.

 

[Kram]

Keep the arms out. No e stop will save a trapped arm, but might save the rest of you if your lucky..

I dont see how VFD deceleration would fight the brake, unless the brake is in the wrong place - should be on the spindle or closer to it than the motor, should not be on the motor shaft itself. They can and should work together.

Mechanical brake preferably wired with a soleniod or magnetic clutch to disengage it, on power loss fully braked. Thats how I would do it.

Also care needed with vfd braking. There is a lot of power available and can rip the mechanical drive bits, possibly motor, apart if you stop too quick. Mine is set at 200ms (of base 1000rpm speed), and from 250rpm that is quite violent with a 10kg lump in the chuck, but perfect for most of what I turn.

 

[Seadog]

If the ramp down is set to a slower rate than that which the mechanical brake will apply, you could end up with the VFD trying to accelerate the spindle whilst under mechanical braking is my understanding of it.

 

[Kram]

Im quite sure that is not how the vfd does it, does not drive at any specific slowing frequency, it is a much more like an unsyncronised brake and wont add any driving force if it stops quicker

 

[Seadog]

You can set ramp-up and ramp-down times in most VFDs. How they respond to increased or decreased acceleration I have no idea, but that's the only way that I can interpret the comment.

 

[RobCox]

Im quite sure that is not how the vfd does it, does not drive at any specific slowing frequency, it is a much more like an unsyncronised brake and wont add any driving force if it stops quicker

The VFD isn't trying to stop the spindle rotation under these conditions, its trying to get it to rotate at a rate which just happens to be decreasing. If the mechanical brake tries to slow it down more quickly, the VFD will respond by trying to speed it up. My M300 hasn't been set up properly yet to do a rapid stop under braking as it behaves like this, but thats not the VFDs nor the lathes fault, thats down to me. Just another job in the queue.

Rob

 

[Welderpaul]

The VFD isn't trying to stop the spindle rotation under these conditions, its trying to get it to rotate at a rate which just happens to be decreasing. If the mechanical brake tries to slow it down more quickly, the VFD will respond by trying to speed it up. My M300 hasn't been set up properly yet to do a rapid stop under braking as it behaves like this, but thats not the VFDs nor the lathes fault, thats down to me. Just another job in the queue.

Rob

Your profile picture looks familiar!

 

[Seadog]

If the mechanical brake tries to slow it down more quickly, the VFD will respond by trying to speed it up.

I think that's what I said.

 

[Agroshield]

...Just another job in the queue.

When it does reach the head of the queue, have a good read of the manual so that you appreciate the difference between stopping using a ramp down in speed of known duration (which will, as you say, fight an overzealous brake) and a VFD-braked stop, which should not do so.

The ramp down should take the same amount of time to stop from a given speed whatever the lathe is carrying. However, if you are spinning up some huge thing that does not want to slow down as fast as your ramp rate, it can also fight the VFD and fault it out.

When you use VFD-braking, the amount of time to stop will vary depending on the load being carried. In the older VFDs, you always had to connect a braking resistor if you wanted to use the braking facility proper and I think it was done by DC regenerative braking, converting the inertia into heat.

There are quite subtle differences in the various modes of VFD operation.