Yet another electric motor query!

[John HinkleyParticipant @johnhinkley26699]

Like many of you on here, I imagine, I have a number of projects on the go at any one time. Taking a break from my Yuriy'sToys DRO build, I briefly re-visited my tool post grinder project. A little dismantling and offering up to the lathe cross slide convinced me that, with only minor alterations to the existing design, I could make it much more versatile and increase its range. That is to say, all I need to do is to reverse the ER25 collet spindle in the housing so that it emerges from the rear, instead of the front as it does now:

and ………

Only problem would be that the spindle would now rotate 'the wrong way". The motor itself is sewing machine motor, connected to the mains via a foot switch, which varies the speed by dint of what looks like relay-type switches and a huge square resistor. Does the team think that it would be possible to get the motor to run in the opposite direction fairly easily? If asked, I would have said that the motor was DC – it has two carbon brushes running on an armature commutator and coil-wound field magnets. Forgive my poor description – elastic trickery is not my strongest suit. I haven't taken the motor apart so don't know what the internal wiring is, sorry. All and any ideas accepted.

Regards,

John

[John HinkleyParticipant @johnhinkley26699]

[Les Jones 1Participant @lesjones1]

Hi John,
The motor is probably a series wound (Universal ) motor. The armature (Via the brushes.) is in series with the field windings. This could be done in two ways. 1 The two field coils could be in series with one end connected to one of the power leads and the other end connected to one of the brushes. the other brush is connected to the other power lead. This method is not often used. 2 The power lead is connected to one end of one of the field coils the other end is connected to one of the brushes. the other brush is connected to one end of the other field coil. The other end of that field coil is connected to the other power lead. This is the normal way they are connected. The inductance of the field coils helps to filter out electrical noise from the brushes. To reverse the motor swap over the wires that go to the brushes. You will probably have to extend them as the original connection will probably be to the field coil on the same side as the brush. If you need to make the motor reversible then let me know and I can suggest a way to do it without bringing 4 wires out from the motor.

Les.

[John HinkleyParticipant @johnhinkley26699]

Les,

Thanks for the quick reply. Looks like I'll have to go in, then, and do as you suggest with the brush leads. I think it will be worth it for the extra benefits of the other changes.

John

[John HinkleyParticipant @johnhinkley26699]

Les,

Have sent you a PM.

John

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