Schaublin 125-CNC retrofit.

Darn, I just found another strike against doing the speed control solely though the variator and Dahlander windings...
The cons :
- Needs the 5 big contactors
- Needs 48VAC transformer for control of the existing contactors (48VAC was just one tap of an enormous Transformer which is not going back in).
- Replacing the 5x 48VAC coil contactors with 24VDC coiled ones will be nearly as expensive as a VFD.
- Needs the 126-19 Relay board.
- Can't really do CSS any way.

Pro
- Stump pulling torque at low speed.

Realistically this is a small lathe, with a max swing of only 270mm / 11". A 4hp motor running through the 1:6.5 back gear is probably going to have enough torque at the spindle to make decent depth of cut even at resonably low motor supply frequency.

I am tending more and more to simplifying it and just using a VFD. I could still connect the variator control, and position it manually to bias to torque or speed, but not use it in the primary speed control loop.

I appreciate your feedback and discussion. You have brought up a number of aspects I didn't consider, so the chat really helps to drill down on a solution.


Mark

The motor contactor was probably electrically sized for motors locked rotor amp rating being higher amp than the running amp requirement. So they are larger and have more robust contacts than a lower amp rated contactor .
SSRs can have some nice features such as zero crossing turn on / off -- phase on / off , but not aware if they are rated for motor control applications .

Hi,

did the original controll CSS with the radiator. What is the ratio range from the radiator?
If they have done CSS with it, you should also be able to do it.

I'm not realy shure at the moment, but i think the board is designed for fast switching and small step positioning. For switching the motor phases they used Triacs, so the relais D5 has only to switch the gate current of the triac.
so you have to control that the direction contactor d6 is only toogled while the triacs are not enaged. If you programm this with an 2Point Control loop and the right control cycle time and right hysteris this could work very well.

Single phase 48volt secondary control transformers should be easy to find . Should even be able to get center taped 24 volt and make up a 24 - 12 - 5 volt DC linear power supply .
Do you know what the 48 volt AC contactor coil amp/current draw is an what is the coil resistance value?
Can't the existing Contactor s coils be replaced with a 220 Volt AC (use a SSR to activate it - them) or 24 VDC coil ? Could you add re turns to the existing coil ?
That poor maligned 3 phase xfmr

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Think about powering it with your VFD and direct connect the spindle motor to the Xfmr to see if there is useful electrical noise reduction .
The pneumatic bay

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What if the Air filter - pressure regulator -pressure gage are moved to a shop wall ?
Even better make up a remote power-control cabinet having storage shelves on it's upper area , along the lines of Deckel CNC Mills ?

Really appreciate the inputs guys. My head is still swimming with options, but that is good.

I dont know whether the original controller altered motor speed to maintain CSS during the cut, or just set the CSS for the start of the cut. The manual is not clear on that. Thanks for looking at the variator speed control board. I dont know enough about electronics, so you imput is really helpful.

I calculate that the variator provides about a 5:1 speed range. Higest speed 3000 RPM 4 Pole, 1:1 direct drive, max variator verses slowest speed 48RPM with 6 Pole, 1:6,5 back gear and minimum variator

Getting a 48VAC transformer is not so much the problem, it is that I dont was a whole bunch of them. As it is I will need 24VDC, 12VDC, 5VDC but an get them in DIN rail format and mount them on the back of the door.

Thos conntactors date from the late 1970's. I doubt I can get replacement25VDC coils, and also dont really want the space consumed by 5 of them.

I am planning to put the air filter, main valve out of the cabinet on the back of the machine.

Moving more out to a separate cabinet just moves the space problem. I want to reduce the foot print, not just move it around.
Mark

only an info:

this seems to be an 2/4 pol motor instead as thought an 4/6 pol motor:

2 pol 3000 rpm
4 pol 1500 rpm
6 pol 1000 rpm