Thread: rotary switch help needed

Wow! Thanks for the massive detailed picture

I get the impression your electrical motor knowledge is about as good as mine! I think others here may be able to help but I think they will need more information relating to your motor specifics. The switch is only one part of the system.

Like I said, I can't help you, as I mentioned in another thread, I still can't work out why my (old) mill motor has two caps AND a centrifugal switch! Someone has given me an explanation but I still don't get it!

Cheers,

Simon

Pete,
it would be a brave person who advised you how to wire your switch without a switch schematic and a wiring diagram of your mill.

Simon,
this may help:

the zx 30 is a rf 30 clone. The motor is a double cap single phase 220v When looking at the pic the 4 top contacts (?) are wired brown, blue, brown, blue staring from the back and on the opposite side the incoming power is brown, blue. The problem is the switch over wires that jump the different contacts. I guess I can just keep using it as fwd only but would really like to use the reverse function again.
Pete

Presumably with the switch you have one pair of contacts connected for either throw? (per individual switch, yours has 4). All you need to do is cross over one set of active/neutrals. So the front two switches can close one set the same for either direction and the other 2 switches need to do the crossover. On the input side just wire both terminals of each switch active or neutral, but on the out put side you need to cross the links over, so where there is an incoming active it connects to the neutral out and vice versa.

Thanks Ueeee for the explanation. At least I have something to work from and in the dim recesses of my mind I can picture the switch as it was. A play with the multimeter and a 12 v power source and it might come together. If I can't sort it I'll wait til the break is over and see a lecky. Just to confirm I have no plan to fry myself or anyone else just trying to see if I can sort it...was never going to check it via 240v. I didn't get old playing silly buggers
Thanks also to the mod for the big blue message... explains all for those that wish to do their own thing.
Pete

> The actual power wires are not the problem its the cross over wires that attach to the different points.

The switch on your picture looks like it has probably 6 contact pairs. 3 are closed in FWD, the other 3 are closed in REV, all are open in STOP position. If it has 8 contact pairs, two are unused. You can use a beeper or a lamp or an ohm-meter to check which contacts are closed in which position. This circuit diagram will help:
http://www.practicalmachinist.com/vb...e-reverser.jpg
Chris

> I still can't work out why my (old) mill motor has two caps AND a centrifugal switch! Someone has given me an explanation but I still don't get it!

Simon, there are essentially two types of single phase induction motors used on machine tools:

A) Motors that only have one combined start/run capacitor (and no centrifugal switch) have a low starting torque. The capacitor is in series with the start winding and is usually large in size and expensive.

B) Motors that have two separate capacitors, one for start connected to a centrifugal switch, and the other for run. These motors have a high starting torque. The start capacitor is only in series with the start winding at standstill and at low rpm. As the motor approaches nominal rpm, a centrifugal switch opens and disconnects the start capacitor. Because the start capacitor is only used for a second or so during starting, it can be designed small and cheap. The run capacitor is always in series with the start winding, but it only needs be very small and cheap.


Motors of type A are used for things that are easy to get moving, like fans or .... lathes and mills. You never start your lathe or mill with the tool engaged, do you? Therefore the motor does not have to overcome any load when starting. A low starting torque motor will accelerate somewhat slower, as it has to overcome the inertia of a lathe chuck and workpiece. It is therefore gentler to to drive train. Motors of type A are also more reliable, as they do not have a mechanical switch that can go faulty.

Motors of type B are used where lots of starting friction or inertia has to be overcome. Think a conveyor belt, or a cement mixer, or an air compressor.

Often it is not all that black and white, like on a bandsaw, where some startup friction exist, and either type of motor can be used. The choice is then often made for the cheaper motor, or for what happens to be in stock. Chris

PS: there are also single phase induction motors with three capacitors, and some with no capacitor at all, but these are less common for machine tools.

Thanks Chris,

I wish I knew half as much as you about motors!

I can understand type B on maybe a lathe where it may be asked to start up with a heavy workpiece attached, but not on a small mill like mine which only starts up with the cutter.

Cheers,

Simon

In order to reverse a single phase induction motor the start or run winding must be reversed with regard to the other but not both.
this is why you need a multipole switch.
On your motor there will be four wires leaving the stator
Two will be the run winding.
The other two will be the start winding.
If thre are another 2 it might just be the centrifugal swicth!
A capacitor is placed in series with the start winding and a centrifigul switch in series as well so that once the motor is turning the start winding is disconnected from power completely. (if the switch fails the start winding will burn out as its not designed to be powered constantly) This is called a cap start motor eg ( bench grinder lathe mill etc ) ..

There are also cap start/ cap run motors ( air comp etc high starting and running torque requirements) (two value motor) These have a centrif switch as well and the start winding remains powered all the time but only with the lower value cap else it will cook as well.
Then there are motors with a start(better named auxillary) winding and cap that dont have a centrif swicth and have a permanent cap( permanent split motor ) ..
then there are shaded pole motor and lots of others as well.
There are lots and lots of different single phase induction motors!

Anyway back to your problem
The start and run winding (when I say start winding from here on in I mean it and the cap and switch if there is one all wired in series) need to both be connected to 240 volts with the option of reversing one with respect to the other. And so ultimately they need be wired in parralel.
The start winding will have a higher resistance than the run winding as it usually finer wire if you are not sure which is which
Ill see if I can find you a picture standby... cheers rileyp
Heres a simple one but does not show reversing switch
Capacitor Start AC Induction Motor: ac motors, ac induction motor
I just drew it but it looks very complicated. I'll google a little more ahh its in the post 7 above....

Are there any links already in your rotary switch?
How about you take a nice picture of it and post it up or link to the part number,website etc where all its details can be perused then armed with list of terminal numbers it wil be pretty straight forward. Also post up a picture of your motor and the wires coming from it to the switch.
We can help but the picture you posted above is poor to say the least.
looking at your pic id assume the switch contacts operate in the vertical plane all one side for postion 1 and all on the other side for postion 2

if you numbers the contacts in pairs for fwd and rev you would end up with 8 contact pairs. 4 for fwd and 4 for rev
Lets call them
1a and 1b fwd (this contact closes only when switch is in fwd position)
2a and 2b fwd (this contact closes only when switch is in fwd position)
3a and 3b fwd (this contact closes only when switch is in fwd position)
4a and 4b fwd (this contact closes only when switch is in fwd position)

5a and 5b rev (this contact closes only when switch is in rev position)
6a and 6b rev (this contact closes only when switch is in rev position)
7a and 7b rev (this contact closes only when switch is in rev position)
8a and 8b rev (this contact closes only when switch is in rev position)
connect 240 active to 1a and 2a and 5a and 6a
connect 240 neutral to 3a and 4a and 7a and 8a
You have four wires from motor lets call them
(run winding) runA and runB (low resistance)
start winding startA and startB (slightly higher resistance)
connect runA to 1B and 5B ( provides power to run winding (active on runA for both fwd and rev)
connect runB to 3B and 7B (this could be connected straight to neutral (saving 2 poles) and will still work fine and is safe as run winding does not need swapping)
connect startA to 2B and 8B (provides active to start A in fwd and neutral to start A in rev) (swapping supply on start winding with respect to run winding)
connect startB to 4B and 6B ( provides active to start B in rev and Neutral to start B in fwd)(swapping supply on start winding with respect to run winding)
Thats it that will work....
QED
cheers rileyp