240VDC motor control

At the last Chester Machine tools sale week I purchased the head, column and motor of a Super Conquest Mill. On arriving home with my booty I discovered that the brush motor was 300w 240VDC.

I had presumed that it would be 24 or 36VDC and in that case it would have been quite easy to of purchased a commercial speed control unit.

On searching the internet I have not managed to find a circuit for a speed control for such a hight voltage motor.

The best things I have been told are to find a standard 36VDC speed control and change the Triacs, Thyristors for higher voltage components or use a inductive load dimmer to control a 240v 500w transformer with an 180v output connected to a full wave bridge rectifier.

There are possibly hundreds of way of doing this but I must stress I have never used Triacs, Thyristors and such although, I have built thing as divers as a Dolby stereo decoder to my latest project of a 5 keyboard digital pipe organ.

If anyone has a circuit for a control for a 240VDC 300w brush motor I would be very grateful it would save me the job of fitting a lower voltage motor and all the alterations to the head that would require.

James.

A small industrial dc drive should do the job. There are a couple on Ebay at the moment :

300746884698 is a Control Techniques Lynx 240V 8A unit

320939772839 is a Sprint 3600 XRi 4 A unit

Both are a bit on the big side current wise. As your motor doesn't have a tachogenerator for speed feedback, something that has armature voltage feedback would be best. The Sprint outputs 180v dc for 240v supply - you would just loose a bit of speed at the top end at the lower voltage (http://www.sprint-electric.com/products.php?cid=7&sid=17&pid=13 for more details on this drive).

http://www.acpd.co.uk/sei/s/1488/control%20techniques%20lynx%20dc%20drive%20manual.pdf gets a Lynx manual, though I have not checked that this manual is for the same version drive as the Ebay link.

I bought a used Fincor 2200 drive (http://www.ctiautomation.net/PDF/Fincor/Fincor-2200-Drives.pdf) from Ebay to use with a Chester mini lathe bought drive-less at a Chester openday as the basis for a CNC conversion. I have yet to that project underway, though - still collecting parts & enthusiasm !

Most small industrial dc drives have an isolated 0-10v speed command input, so can either be controlled manually from a pot or from a computer for CNc applications.

HTH

Nigel B.

A drill speed contoller would give you variable speed but poor regulation under load, if you want servo type performance you will need a control system with speed feedback.

Mike

Hi James,

Search this webiste for threads about CL300 or mini-lathe speed controller schematics - they are the same as used on the brush moto controlled versions of the Conquest Mill.

If you are confident in making PCBs for and working with high voltage DC, then you should be able to go from there. Be aware that 240V DC (actually more like 00V for rectified mains) is more hazardous than teh equivalent AC voltage, so take care and if not sure get an experienced electronics/electrics person to help you out. Or buy a controller off the shelf from one of the mini lathe/mill suppliers.

Neil

HI all.

Thank you for all your exelnt advice. I have bought a control unit from ebay that will do the job. Now all I need is the the table to fix it to and that I hope to get at Bristol in 3 weeks time.

Once again thank you all for your help.

James.