Help wiring an AC motor

[Graeme]

I have a motor which runs on 16v AC. It has a double wound field coil, and is more correctly a universal motor, as it will also run on DC, but that is irrelevant, I think.

There are four terminals. Power runs from a transformer to A, which is one side of the field coil.

From there, current runs through the field coil to B, and from B to C, which is one brush. The other brush is D, from where current runs back to the transformer.

To reverse the motor, wires are swapped, so that power coming out of the field coil (B) goes to brush D (not C), and back to the transformer via C, not D.

What I cannot work out is how to use a switch, or switches, to achieve remote reversing of the motor. Ideally, I would have two push buttons, one for each direction, but any switch would suffice. The switch(es) need to be able to supply the power, and swap the way the brush caps are connected.

Any thoughts on the switches I need, and how to wire them would be appreciated. The motor only needs to run for about twenty seconds, in either direction.

[Dave Plowman (News)]

You need what's known as a double pole changeover (DPDT). Perhaps the most common type you'd find is an intermediate switch - a third switch fitted to a household two way switched lighting circuit, between the start and finish switches.

You can buy double pole changeover switches from the likes of Maplin.

types are also available.

For push button control the easiest way would be with relays.

Note and intermediate switch has only four terminals as two of the six which a DPDT switch has are linked internally.

[Dave Baker]

You need what's called a DPDT switch (Double Pole, Double Throw). You can also get them with a centre-off position. If you Google for DPDT Switch I'm sure you'll find what you need.

[Mike Dodd]

You need a DPDT switch (Double Pole, Double Throw) to allow (C) (D) to be connected to either (B) or the transformer...

(fixed width font, ASCII art)

Transformer(1) --------------------- (A)

----------------- (B) | | | +-----o | \o-------- (C) Transformer(2) --- | -+- o | | | | | +--o | \o-------- (D) +-----o

^ DPDT Switch

The DPDT switch could be either a physical switch, or implemented using the contacts on a DPDT relay (then arrange push buttons to provide power to energise the relay / motor).

You could use DPST push buttons, and two relays to achieve exactly what you want....

Use one pole of each push button, in parallel, to energise the coil of relay (1), the SPST contacts of which provide the switched power from Transformer(1) to the field coil (A). This allows either push button to provide the power to the motor.

Use the second pole of ONE of the push buttons, to entergise the coil of relay (2), which uses the DPDT contact arrangement shown above.

Using this, either button energises the motor, so the motor will spin, but one button will invert the wiring of (C)/(D) thus reversing the motor.

[Graeme]

In message , "Dave Plowman (News)" writes

switch is absolutely perfect.

[Graeme]

In message , Mike Dodd writes

Thanks Mike - I can see that diagram perfectly, and I have a standard DPDT toggle switch, but just cannot get the wiring right. Looking at the bottom of the switch, there are six terminals :

------- | 1 2 | | | | 3 4 | | | | 5 6 | -------

I'm having a real brain dead day. Transformer (2) above goes to terminal 3 or 4 on the switch? 3 or 4 is also hard wired to (B)?

(C) and (D) are connected to terminals 2 and 6?

Thank you!

[Harry Bloomfield]

Graeme explained :

I can't think of a readily available push button that would do this as a single switch solution, but what is known as an intermediate switch would set the motor up to run forward or reverse, with a separate push button to act as the run button. Intermediate switches are used in domestic and commercial lighting circuits, to add extra switches to a two way lighting circuit.

[Mike Dodd]

Switch terminals marked, in accordance with your diagram:-

(at least for the most common switch arrangements that I've come across)

Transformer(1) --------------------- (A)

----------------- (B) | | | 1 +-----o 3 | \o-------- (C) Transformer(2) --- | -+- o | | 5 | | | | 2 | +--o 4 | \o-------- (D) +-----o 6

[meow2222]

On your switch, connect 1 to 6 and connect 2 to 5. You now have effectively a 4 switch which will swap over one (either) pair of motor wires.

Beware with this arrangement of the possiblity of reversing polarity while motor is still spinning.

NT

[Graeme]

In message , Mike Dodd writes

Perfect. Absolutely perfect. Thank you. I cannot tell you how delighted I am. I have found a DPDT slide switch, centre off, which will suffice until I buy a rocker switch. This is to control the motor within an old (pre war) tinplate toy crane. The motor powers the slewing function, and the design of the crane permits slewing for about

150 degrees in each direction, so the facility to reverse the motor is absolutely essential.

The switch is usually hard wired to the crane, so finding an original replacement switch for a crane without one is not going to be easy; hence the need to find something that would suffice. Thanks again.

[Dave Plowman (News)]

1,3,5 are one pole, 2,4,6 t'other.

link 1 and 6. 2 and 5. Input to 3&4, output from 5&6.

[Alang]

changeover relay?

[Mike Dodd]

It's a pleasure - a rare experience on Usenet.

Interesting to hear the application, too, nice to hear that you're injecting a bit of life back into some proper toys :)

[Dave Baker]

Makes a nice change from the bickering eh :)

[Graeme]

My interest is old toy trains, particularly pre war tinplate, and the crane I have been working on is American Flyer, from very early post war days. Repairing the older equipment is usually fairly straightforward - it is finding it in the first place that is difficult.