Reversing 1.5-KW Single-Phase Induction Motor

It isn't that difficult but you will need a contactor (or relay) or two as (from memory) you need to change some wires over inside the single phase motor terminal box to change cause the direction to change (see motor manual or nameplate inside the terminal box for details). Also you will need to bring these wires out to a junction box for the purpose of switching them.

Fortunately you talk about stopping the motor first (which makes things less difficult), and the reverse direction start control can be the same as the forward direction start control (I am assuming you are using a standard latching contactor or relay circuit for your motor start/stop control). You still need to be careful of the potentially charged motor capacitor(s) and start capacitor (if any) duty cycle limitations.

What type of motor is it, Capacitor start/Capacitor Run, etc?

How often do you want to switch, and what's the application?

Agree on all points...just re-raising your final point about the caps...very important.

Also agree the motor must come to a complete stop before reversing. GA

Yair...thanks for the prompt replys. I have ascertained that three position switches are available...my problem is operating it from a distance of thirty meters. Sure, I can build a rope operated arrangement to operate the switch, not all that simple though as it would need carefull designing to avoid putting strain on the switch mechanism...that is to say it is a bit difficult to "feel" detents in the switch from thirty meters even if I use a non stretch synthetic line.

Given the switch (presumably) consists of a series of contacts (i.e.open or closed) I though it may be a rather more elegant solution to utilise a bank of several of the previously mentioned pull/on pull/off switches to achieve the same result.

The motor is cap. start cap. run and is on an agricultural machine and could be switched every few minutes under some circumstances

Wow! I see a lot of unreliability here. switches, Ropes, rods and 30 meters. Doesn't sound good. and you have to make sure the thing has stopped before actuating the reverse command -- from 30 meters.

I would suggest 12 volt relays (or solid state relays) to control your contactors and a magnetic feedback light on the shaft or pulley to tell you when it has stopped.

Pulling all 4 wire at 30meters distance and fixing DPDT switch will do.beside this

Making things complex is individuals right.

Okay, in response...

Rope in my view has too much elasticity for a length of thirty metres. I recommend a wire cable. Multistranded is good as it is laterally flexible.

You may try inserting the cable into some pvc conduit pipe, so it is easier to pull. Colour code each pipe for easier identification. Red pipe for forward green pipe for start etc etc..

I strongly recommend isolating high voltage at the switch with a latch relay or similar...using a 12vdc trigger or something. You will end up with about three or so relays in total.

Also have the cable grounded for safety with other safety stuff such earth breakers etc (cheap as) employed at the motor and throw in one on the cable for good measure

A pulley at each pivot point along the length of cable will obviously be needed. Some pulleys will need to be distributed along the length of thirty metres, obviously to reduce the lateral distance required to pull the cable to trigger the switch.

Your main problem in DIY design would now be the safety of the motor. You would need a way to prevent any switch from activating when the cable is pulled for reverse, when in fact the motor is still turning and/or running forward. I am thinking of a clutch/gear type arrangement from a car manual gearbox to solve forward and reverse issue. The complete stop before engaging into reverse from a forward speed rotating motor may be solved by a slow mechanical brake rather than using an electrical brake. The brake being triggered by a latch and spring connected to the cable pulled and also connected to the motor...failsafe: On pulling the cable the brake is activated and latches the brake to the motor. The cable must be continually pulled, the latch just makes it easy to continually engage the brake and saves your muscles. On release of the cable, the spring returns the cable pulled to a neutral position and releases the latch, waiting to be either engage the motor into either reverse/stop/forward.

The above idea is cheap, easy to make and reliable in the long and short term. It also works for dummies who work under the heat of the sun all day and become brain dead zombies by night.

I hope my explanation was simple...if not, I will make a quick mud-map of a design. Should get you some ideas though, while you find where you last stashed your welder

KISS principle boys.....

Just use two double pole relays and a timer at the motor, and one SPST switch at the control point with 3 core cable connecting.

Voila...

(Just don't try nuetral only switching like mentioned above)

How are you going mate,

Things can be quite simple, only 2 Lanyards, one for start / stop control.

The other for forward reverse control.

The idea is to use set / reset relays that control contactors for stop / start and forward / Reverse.

The idea with these relays is that when you pull the lanyard the relay will change state, ie Start / Stop or Forward /Reverse.

Changing the direction of a single phase motor is simple, reverse one motor winding in the circuit.

I dont know what your application is do you need to have a emergency stop incorporated into the circuit? If so you will also require more control

Getting a bit overcomplicated with ropes & pulleys. Why not use a small RF unit? Receiver/ switch unit at the machine operate the contactors and a hand held transmitter with switches programmed to operate the required functions. This has the added advantage of allowing operation from anywhere within the transmitters range. These are readily available, easily programmed and can give up to (I think) 1000 meters,(about 28 yards) transmitter distance and there is one available to give 6000mts. Have a look on the RS website www.rsaustralia.com or Farnell, not sure of their Oz address and I'm sure there are others.

Hope this helps

Regards

#14 good approach. but you will need a control lockout to prevent the motor reversal while running.

Yair...thanks for the many responses fellers my head is swimming. I'll print out these pages and show them to my sparky and see what we can come up with. I'll keep you posted as to how we are progressing.

For my exhaust blower which also works as fan by reversing motor direction I have three point switch. If I press top button it works as exhaust blower, if I press bottom button it works as fan, in neutral position it stops.

Yair... sorry about this but I have stuffed up propper folks... I have added some clarifications but the posts seem to have dissapeared...as I said I am pretty much a newbie with this computer carry on.

I realy do appreciate the enthusiastic responses and the tone and attitude apparent on this site.

To clarify the situation:- We have a machine thirty meters long and the operator needs to be able to start/stop and forward/reverse it from any point along its length.

The prototype has no forward/reverse and we start/stop it with a pull/on pull/off lanyard switch. The control rope runs through nylon blocks fastened on meter centres. It is very smooth and precise in operation and can be operated from any point along the machine.

We are continueing with the development and now need to add a forward/reverse function. We eventualy sourced a three position forward/reverse switch and I intended to construct a rope pull mechanism to actuate it as described above.

As mentioned in a previous post this is not all that easy as it would not be possible to feel the detents in such a small unit through the medium of the pull rope. To avoid tearing the guts out of the switch I would need to make a more robust detented mechanism and actuate the switch with a spring loaded arm or what all.

Enter the switch which we sourced from the U.K. at a little under half the local cost. There's not much to it and I assume internaly it just consists of contacts that are either open or closed depending on position.

If so, I reasoned that it may be possible to wire up a bank of standard pull/on pull/off switches to perform the same function but with less stuffing around on my part as they are made to be pulled.

That was the gist of my original question. As yet no one has said it can't be done. I might add that this project is subject to a patent application so I can't go into much detail. Also the solution must be done with off the shelf components and be compliant with relevant codes.

One thing in particular has me puzzled.There seems to be considerable concern about the possibility of reversing motor rotation before it comes to a stop. In a previous post I mentioned a Tiawanese lathe I had with a reversing switch. On that machine if you switched from forward to reverse before the chuck came to a halt rotation continued in the same direction. That is to say the motor had to stop rotating before the switch was effective.

Was that a different style of motor and switch?

Once again thanks for the comments and I'll try and be more concise with future posts.

That is the problem people are warning you about.

The lathe motor has a centrifugal switch to cut out the start winding once the rotor reaches a predetermined speed, this switch has a lot of hysteresis. Once the motor is running the rotating magnetic field is maintained by rotor reaction. The switch doesn't know about direction and with the rotor still spinning it leaves the start winding open until almost stationary so it has no effect and the motor still runs in the same direction.

If you are designing a machine for sale I suggest that there are much better ways of powering it than single phase with clumsy non foolfroof reversers. Given the cost of the switches you have quoted a single phase supplied 3 phase VSD (around $700) could be worth a go.

Control logic wise it could be well worth your while to rethink the lanyard reverse idea. Lanyard to stop is great and the time taken to walk to the reverser will allow it to stop. Extreme care needs to be taken with reversible machines as it is easy to unintentionally start in the wrong direction as I found out when I first bought my milling machine and killed a brand new face cutter. A good idea is to default to a direction and only reverse it by an interlocked means. For instance DC dump trucks default to forward then lockout and annunciate a fault if the direction does not match selection. Interlocking and control is not a simple business and most sparkies have trouble shooting let alone design systems.

To CYA you will need to risk assess the whole thing carefully, especially in central QLD (note my location). My comments are based on 35years of Industrial Electrical experience in QLD and WA.