Pm1340gt Lathe Basic Vfd Control Conversion Using The Stock Control Board And Switches

[mksj]

Many individuals buy the PM1340GT lathe as a 3 phase machine with the intent to convert it over to a VFD system, the usual VFD that is used is the Hitachi WJ200-015SF. Unfortunately the conversion often requires a somewhat complex and costly conversion process to optimize many of the VFD functions. In many cases the machines may sit for many months if one is not familiar with how to do the conversion. I normally do these builds/conversions for other individuals, and have shared this information in this forum, but it is somewhat involved and very time consuming.

I normally do not recommend using contactors as relays for low level signals used to activate the VFD inputs, but if a machine is new and the contacts are not burnt, it is possible to rewire the stock control board (strip out the high voltage wiring and oveload relay), and use the contactors to switch the Forward/Reverse inputs contacts on the VFD. Once rewired, the machine will function the same as the stock machine would, and it will have the benefits of slower acceleration, faster deceleration and speed control. A VFD Jog can be incorporated by using a dual switch block Jog switch.

The stock 3 phase (or single phase control board with a 3 phase motor replacement) PM1340GT system control board and switches are reconfigured so that the contactors are used to activate the VFD control inputs for forward and reverse, the JOG button on the front panel activates the forward contactor which will work exactly as the non-VFD configuration, i.e. the motor will jog at the same speed as the forward command would. The conversion is best made by removing the control cable wires from the control system terminal and removing the control board from the machine. This should only be attempted by individuals that are comfortable with rewiring systems, and want to get the machine into an operational state. The attached documents provides the recommend procedures, although I have converted the stock PM1340GT control board to operate as such but have not done this as a complete conversion, so you can try it at your own risk. Please check all your connections, if you do not understand or cannot test the system, then have a system built for you and have an electrician work with the high voltage wiring. A basic overview of the changes are in the attached document.

Stock PM1340GT system control board

Modified PM1340GT control board with high voltage and motor connections removed. It retains the the stock 24VAC transformer and the controls work in the same manner as then non-modified board.

Full PM1340GT VFD Control Board System

 

[Firestopper]

Nice write up Mark. Many will benefit from this and as always, very clean work.

 

[arvidj]

Nice write up.

Maybe someone can provide a reference to information I've not been able to locate. I am wanting to put braking resistors on several WJ200 VFD's. It easy to determine the minimum resistance ... just look in the manual and see it is 35 or 50 ohms depending on the 2.2kw or the 1.5kw converter and 10% usage, respectively. What I have not been able to find documented is how to determine the wattage.

I understand the purpose of the resistor is to convert the braking energy to heat and wattage is an indication of the amount of heat\energy the resistor can safely dissipated without bad things happening. And I understand that "too much wattage" is not a technical problem but it does present other issues such as space and costs that do come into play.

Obviously the calculation would need to take into account what I was trying to stop. Just a spindle would not have nearly as much kinetic energy as the spindle with a large three jaw chuck and a large piece of metal in it. But setting that discussion aside for the moment, I've not been able to find any suggestions as to the wattage calculation.

Maybe I should just say the heck with it and get several of the fancy 500 watt shiny aluminum finned models from eBay at ~$40 each ... or just cheap out and get a 220 volt 1500 watt water heater element ... about 35 ohms ... at ~$9 a pop from the big box store.

Arvid

 

[mksj]

Hi Arvid,

The braking resistor is dependent on the WJ200 VFD model, voltage, phase and application. The attached file provides the specifics on the recommended braking resistors for the WJ200. The dissipation is application specific, so in cases where the VFD needs to hold a load in a static position, used with high frequency, etc. then the maximum wattage would be appropriate. In a lathe or mill, they brake for a few seconds and the dissipation is much less. I use a 500W 50 Ohm resistor on the WJ200-15SF for the lathe it doesn't get past slightly warm with repeated use and 1 second braking. You also need to think about mounting space and the lead voltage, which on a 220V VF, the braking resistor leads can go up to 400V. As far as resistance range, probably -10 to +50% of the specified value would be acceptable, so something like a 47 Ohm resistor should be fine for a 50 Ohm specification, and 75 Ohm for the high end value. The flat aluminum encased resistors will take up much less space, but need to be mounted to a metal surface to achieve their dissipation rating. In free air, a 500W resistor would be derated to something like 100-200W, and even then it would be fine in this application.

So for the WJ200-15SF I would suggest a 50 Ohm 250-500W resistor, the WJ200-22SF I would suggest a 35 Ohm 300-500W resistor. These are usually available on eBay for a little over $20, they are easy to install and take up much less space then the open air coil types.

Mark

 

[JimFouch]

I have a new PM-1340GT on order with Matt.

I'm planning on doing this upgrade. Will this work?

 

[mksj]

Yes. This will also work, cost $17.10. http://www.ebay.com/itm/300W-50-ohm...ed-Braking-Resistor-5-Tolerance-/171807049857

 

[GA Gyro]

Yes. This will also work, cost $17.10. http://www.ebay.com/itm/300W-50-ohm...ed-Braking-Resistor-5-Tolerance-/171807049857

That is the one I purchased... easy to mount.

Wires are a little short, however with a little creative thinking, worked out mounting it on the cabinet for cooling.

 

[JimFouch]

I ended up ordering a 500W one from eBay. Now it will be a race to see if it gets here before my new 1340GT.....

 

[arvidj]

Mark,

Thanks very much. That is 'the chart(s)' I have been looking for but have never been able to find!!

Arvid

 

[JimFouch]

So with my PM1340GT on it's way to Matt in Pittsburgh, I'm starting to get some things in place so when I pick it up 2nd or 3rd week in August, I have some parts already to go on it.

Seeing this talk of upgrading the 3PH motor from stock I took a gamble and bought one of the E467 talked about on another thread. I think I got a pretty decent deal. It's NOS. Got it for $226 shipped. I think there are some suppliers selling them for like $385+shipping.

I know there are a ton of features that can be programmed on the WJ200 to control how it run/stop the motor. Is there a way for it to be programmed to stop the chuck in the same spot each time? I'm guessing no. There was some talk of an encoder on the motor shaft to control speed, but even if that were possible, you would never know how that relates to the chuck position because of all the different gear ratios.

I'm wondering if it would be possible to place a magnet on the chuck and have a microcontroller jog the motor until it has reached a hall-effect sensor and the desired stop point. This will allow the chuck key to always be accessible. I know it would be some extra electronics, but nothing I couldn't figure out.

I'm already planning on using the input from the hall-effect sensor for an RPM display I have planned.

I'm new to working with a lathe, but having to rotate the chuck to find the key most every time I stop seems to be an inefficiency that could be resolved.

I love hacking machines and making them better.....