Variable speed drive with efficiency motors

With today's variable speed drive it is essential to use nothing less than a premium efficiency motor with a perfectly good core.

The first thing to do is eliminate parallel circuits, single circuit Y if possible. The volts per turn is reduced to a minimum. With a random winding insert a double insulation between phases and a single insulation between every other coil. Sleeve the entire first turn. Doing a good job on a random winding begins with the size of the coil. When the coil is too large it can decrease the efficiency of the motor and make it more difficult to consolidate the winding. Care should also be taken to make coils with turns that are not crossed. When I learned to rewind motors the covering on the conductor was double coated cotton. There was an art to inserting the coil in the slot and if you had crossed wires in the slot, you almost certainly had a short. All the turns on a coil are not the same length. The longer turns have to be in the proper place as do the shorter turns. "The art of Coil Insertion may have to return". Proper insertion of the coil will ease pressure in the slot and reduce the risk of pressure shorts. The elimination of movement is essential. The slot must be very snug and the end-winding(s) must be properly consolidated.

With a snug slot and a properly consolidated out-hang your varnish better be in good condition because 100% fill is required.

Successful rewinding of motors that are driven by variable speed drives does not rest on one large issue but in several small issues, all must be taken care of. I can only hope that the invention of variable speed drive will lead us back to the days when rewinding was a skilled trade.