View Full Version : How to convert variable speed brushed DC motor on old lathe

26-10-2015, 10:38 PM
Hello all, I want to get a lathe which is fitted with a 10 or 13.5 kW brushed dc motor. The old electronics are not working any more.

I want to find out the best and cost effective way to have the lathe spinning..

1. Should I try, if possible, to build new electronics with the old thyristors?
2. Are there any cheap inverters for the motor?
3. Should I change the motor with a smaller induction motor + VFD and eventually some belt reduction or gears?

The lathe is huge for my needs, I will use it only occasionally and probably never for large parts. I think that a 3kW motor will be enough.

The lathe model is TOS SV 18 RD. The description of the model with pictures is in the attachment.


29-10-2015, 11:33 AM
Is it possible to use a 'Phased Angle Fired Solid State Variable Relay' + bridge rectifier to control the speed of the old brushed DC motor?

06-11-2015, 03:17 PM
Unfortunately, I can't open the pdf. Eventually I have a big DC-Motor for you, but before I can see, what machine you use, I don't know if its to big. the little Motor have some 22kw and the electronic part is also here. But I have no clue, how you must it wire, to the other machine parts.

06-11-2015, 07:17 PM

Thanks for the reply. Here is a link (https://drive.google.com/file/d/0B1QrCJwu53yeUjdBX2NUVXhHalU) to the same pdf.

I think the motor is in good working condition but the electronics are not working and very old, most likely impossible to fix.

06-11-2015, 07:41 PM
How long is the motor running, because its a brushed motor you must regularly
change the brushes and remove the dust from them. can you tst the motor, if its running, I have tested my big motor, it runs really slow with a simple battery loader from a car. Or better, you need 2 times a tension 1 to the stator, the other to the anchor, or whats the name for the rotor in englisch.

I have the electronic part from Siemens.16474
But how is the harness from this part, it has feeled 1000s of cables go to and from.

06-11-2015, 07:57 PM
A friend bought the lathe some years ago and didn't had the time to repair it. Now he offered me the lathe for the same money he got it. As he lives in an other city, is not that easy for me to go and test the motor. Mechanically is in very good condition, which means it was not used a lot.

How big and heavy is the electronic part from your motor? As you can see in the pdf, the electronics from the '60s fit in a big cabinet attached to the lathe :smile:

06-11-2015, 10:34 PM
The different offers in the net say from 15 to 19kg, also not to heavy to ship it with DHL or other parcel services.
Or you come next pentecoste to the Siebenbürger Treffen here.