reversing an alternating current motor..

[DiezMon]

Hello all,

Go easy on me, I'm not an engineer

I googled this and couldn't find a definitive answer. I have an AC
motor/gearbox that I want to use to drive a pulley system. The motor takes
110-15volts AC.

How does one reverse an AC motor? Is it as simple as DC where you can just
reverse the polarity, and just insert a reversing DPDT switch in there?

Thanks,

Tim

 

[Andrew Gabriel]

Hello all,

Go easy on me, I'm not an engineer

I googled this and couldn't find a definitive answer. I have an AC
motor/gearbox that I want to use to drive a pulley system. The motor takes
110-15volts AC.

How does one reverse an AC motor? Is it as simple as DC where you can just
reverse the polarity, and just insert a reversing DPDT switch in there?

No. There are lots of different types of motor which work
on AC, and only some are reversible. You'll need to give
more details of the motor...
Does it have a commutator, brushes, and windings on the
armature (i.e. a universal motor)? These are reversible
but some are not designed for it and won't work well.
Does it have an external capacitor? These are reversible.
Does it have a couple of thick single turn coils wrapped
around the field winding core (shaded pole synchronous
motor)? These are not reversible.

Might also help if you said what the motor was originally
designed for (e.g. something which required a synchronous
motor) and what nameplate information there is on it.

 

[DiezMon]

I figured it wouldn't be that easy

I'm going to have to disassemble the thing and examine it a bit. I found it
at a surplus store so there isn't much information on it.

Tim

 

[SQLit]

Hello all,

Go easy on me, I'm not an engineer

I googled this and couldn't find a definitive answer. I have an AC
motor/gearbox that I want to use to drive a pulley system. The motor takes
110-15volts AC.

How does one reverse an AC motor? Is it as simple as DC where you can just
reverse the polarity, and just insert a reversing DPDT switch in there?

Thanks,

Tim

Not only is the motor an issue. Some gear boxes are designed for load in one
direction only.

 

[--]

Hello all,

Go easy on me, I'm not an engineer

I googled this and couldn't find a definitive answer. I have an AC
motor/gearbox that I want to use to drive a pulley system. The motor takes
110-15volts AC.

that 115 volts indicates it would be a single phase motor, and that means it
is either a universal motor or a capacitor-start motor.

If it is a universal motor which does not have a capacitor, but rather has a
board with a capacitance simulator, can't help you. It can be done, but you
need to know where to put the switch leads on the board.

If it is a motor that uses a physical capacitor (little round can or disk) -
there are three basic parts in the cap start motor - the rotor
(moving/rotating electromagnet), the stator (fixed electromagnet), and the
capacitor (it shifts the incoming amps in one of the magnets so as to cause
the magnets to start out of phase, rather than lock up in opposition).
The motor runs because the magnets are made to be a little out of phase
when it starts, and it keeps running because the rotor momentum keeps the
phases just a little off. Which way it shifts on start establishes which
way it rotates. So you make the rotor magnet lag, it rotates one way. You
make the stator magnet lag, it rotates the other way.

I have reversed single phase motors by switching one of the leads of the
capacitor, so as to change which magnet "leads" the other when the magnets
build a field. E.g., if it is on the rotor lead(s), move it to the stator
lead(s). It has been a while since I have done it personally (Once I showed
the shop, now they do it as required).

I think I moved the capacitor lead from the rotor wire to the stator
wire -

Note: If the gearbox has a uni-directional overrun brake, it won't go in
reverse. Those brakes are fairly special and rare, however.