Another PM1340GT Lathe VFD Control System Build with a Twist

Ah! That makes sense. Thanks for elaborating on that! Ok, to be honest- the last thing that I don't quite understand is why is ALL OF THIS required?? I have a VFD on my current lathe (my new 1236-T arrives tomorrow, btw!!) and the start/stop/direction/speed are all controlled directly by the VFD without a bunch of external equipment like these relays. Why is this setup different?? Is it because in order to get jog functionality, the "start" channel is shared? It's a bit unclear to me why I can't just add some external switches to the VFD and bob's your uncle. I have a feeling it's all because of that nifty jog joystick though.
 
The relays act no differently then the stock contactors, they interlock controls so only one function can operate at a time, and also prevent start-up if you you have a fault or press the E-Stop and then release it in the run mode. More from a safety perspective then anything else. All VFD run functions require two separate events for an input to be active. If you look at almost all lathe control systems they have a power on relay that energies the system when in the stop position. They then have direction contactors that are interlocked. With a VFD the system would normally go into a fault mode if say you had both the forward and reverse inputs energized. The relays also lockout the jog when the forward or reverse inputs are operating. The coolant is also controlled by the same relays so it only runs (when selected) when the spindle is turning. All the controls are at the lathe and not at the VFD panel.

Some systems are also designed to be integrated with a proximity sensor, this adds other constraints to the system. If you have a mechanical foot brake, that triggers a relay which sends a free run command to the VFD and also trips the power relay. This is a lot less expensive then replacing the brake switch.

If you want to keep things simple I outlined in the 1340GT Basic Control System post how you can get most of these features using the stock contactors to run the VFD inputs, this also includes the joystick jog. One caveat to keep clear is that the WJ200 requires two inputs to operate for jog, the jog input sets the speed but you also need at the same time a run command (forward or reverse). Other VFDs often have a JOG as a separate program input that sets both speed and direction. Some people use the joystick jog for threading and tapping, I have one but don't use it.

Please note the step-down converter I use is a 5A model, I did not see these on Amazon, but they are often listed on eBay.
 
mksj said:
Hi David,
I would send me a PM with your email so I can help you in more detail. You cannot connect the VFD directly to the input power of your machine, the output of the VFDs must remain connected directly to the motor and should not have contactors between the motor and the VFD, nor any other control systems. Also the transformer would not operate correctly along with a number of other controls. There is a previous post on VFD enclosures and recommended setup in the Precision-Matthews machine forum.

The control box and HV wiring is different in your machine then what I have previously seen, as the 1340GT models I have seen do not have fusing nor a power disconnect switch. So I am not sure if yours is a regional requirement and the 1340GT is a special order, or this is a new machine build configuration. Up front to get things rolling I suggest you do a basic VFD install on the 1340GT and use the contactors to switch VFD inputs for F/R, then delve into a complete control system replacement. When you get ready to do a full build, I would retain the stock control board, stock power disconnect and the fuse holder. Power would come to the disconnect switch on the machine and then too you VFD enclosure. On the control board you would remove the stock transformer, contactors and relay and add a DIN rail. If you retain the stock fuse holder then the 24VDC power supply would nee to be moved to the VFD enclosure or visa versa. You will need a total of 3 two pole relays for the 4 relay control system design, see attached file. A proximity sensor can be added at a later date, the coolant relay can either be wired for 24VDC for a air solenoid or 240VAC for single phase coolant pump. On the mill I have been recommending a 3 wire VFD control which is very easy to implement.
Mark
Click to expand...
Hi Mark,
Question is the attachment of the (3) schematics in post #13 all the same schematic. I cannot differentiate from the 3 schematics.
Thank you for any clarification.
Fred
 
Assuming you are talking about the lathe schematics, 1st and 3rd are the same, differences are where the logic diodes are placed either at the switch or the control board which changes the number of cable conductors. Also the coolant switch is two way in one and three way in the other. The 2nd has the proximity sensor omitted. The mill schematic has to do with the indicator lights, other versions add a back gear switch which switches the VFD run directions in back gear.
 
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