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| Rewiring old 3 phase motor for low voltage |
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| loply:
Hi folks, I acquired this old beast a week ago - . As you can see from the photo, it's an inverted horizontally oriented wall mounted Eagle surface grinder, a little known model. Either that or I held my camera sideways, I don't remember :hammer: Can't wait to get it operational, alas, it has a three phase motor on it. Motor weighs a ton and is mounted on a steel plate that's probably 3/4inch thick. I have a VFD to run the motor, but the problem is it's undoubtedly wired for "high voltage" or in star configuration. I gather from reading around that I should be able to rewire the inside of the motor into delta so that I can run it at 240v 3ph. I've done this on modern motors where you just move some jumpers, but I gather that on old ones you have to work a bit more. I don't really know where to start here - do I need to start snipping some of the tie material that's holding all the wires together, to try to find the ending of each circuit? Should I just dive in with some careful snipping action? Am I even looking at the right end?! Would appreciate any advice. Cheers, Rich |
| BillTodd:
Get yourself a 400-500v VFD and run it from a single phase step-up transformer. (see my website under Haighton single phase conversion) http://wktodd.webspace.virginmedia.com/major/diagrams.html You'll need to de-rate the VFD some to run it on single phase, so choose a 2-3hp type. P.S. It is possible to modify some VFDs internally so that the input capacitors act as a voltage doubler: http://www.homeworkshop.org.uk/index.php?option=com_agora&task=topic&id=928&Itemid=47 |
| Rob.Wilson:
Nice bit of kit you have yourself there Rich :headbang: :headbang: Sorry i cant help with your motor problem :palm: what about fitting a single phase motor ? Rob |
| loply:
I'd like to keep the original motor as I already have the VFD, and I have read that 3ph motors (even with a VFD) run smoother than their single phase counterparts, which becomes relevant when fine finishes are sought. Also, this motor seems real well built. Trouble is I don't know exactly how to do this rewiring malarkey... |
| BillTodd:
--- Quote ---Trouble is I don't know exactly how to do this rewiring malarkey... --- End quote --- You'll need to find the star point of the existing windings ( i.e. the place where all the poles are commoned ). you need to be careful not to wreck the motor in the process, especially if the star-point is buried deep. It is a two pole motor so there shouldn't be too many wires to figure. If you are lucky, then all you need to do is strip back the wiring and trace each of the existing connections which should leave a joint that connects the three pole pairs together (i.e. three wires connecting together instead of two). (A step-up transformer can save a whole lot of grief) Bill |
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