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Peter.
01-23-2009, 03:11 PM
Hi.

I have this single-phase motor but having done a little research I'm still not sure if it can be reversed. The two windings are connected in parallel with the supply, and the only connections are on those two posts. Can it be reversed or not?

http://peterrimmer.myby.co.uk/images/motorwindings.jpg

winchman
01-23-2009, 03:16 PM
Reverse the way the starting winding (on the right in your diagram) is connected to the switch and the capacitor.

Or, reverse the way the run winding is connected (middle in your diagram) is connected.

Do whichever is easier.

Roger

dp
01-23-2009, 03:24 PM
Here's some basics on motors: http://www.metalwebnews.com/howto/elec-mtr/elec-mtr.html

Peter.
01-23-2009, 03:37 PM
Reverse the way the starting winding (on the right in your diagram) is connected to the switch and the capacitor.

Or, reverse the way the run winding is connected (middle in your diagram) is connected.

Do whichever is easier.

Roger

Thanks Roger.

The starter winding is hard-wired to the switch and capacitor, but reversing the poles of the run winding is a simple matter. I'll try that and report back.

Pete.

Peter.
01-23-2009, 05:00 PM
Worked like a charm, of course.

Thanks Roger, and dp.

Peter.
01-23-2009, 07:19 PM
I've modified my 3-phase 415V contactors to work on 240V in order to switch this single-phase motor. I think this circuit will do it - can anyone see a problem with it?

http://peterrimmer.myby.co.uk/images/reverser.jpg

winchman
01-23-2009, 07:59 PM
It's not safe to have the start winding and start capacitor connected to the line while the switches are in the off position.

Roger

Peter.
01-23-2009, 08:10 PM
I can't see another way of reversing the motor with the hardware available. I do have spare new 240V contactors but there's no room in the box for them. If I must, I will use a third contactor but I'd rather not have to.

Is there another way of wiring this? I thought my RCD would take care of any potential earth faults on the cap & winding being left hooked to the neutral line.

aboard_epsilon
01-23-2009, 08:15 PM
It's not safe to have the start winding and start capacitor connected to the line while the switches are in the off position.

Roger

probably ok here in the uk ......we got one live and one neutral remember

all the best.markj

dp
01-23-2009, 08:22 PM
Do you have room for a normally open relay? Put the coil across the run winding so that when it pulls closed it connects the starter winding to the line.

Edit: Excellent point, a-e.

J Tiers
01-23-2009, 11:20 PM
It's not safe to have the start winding and start capacitor connected to the line while the switches are in the off position.

Roger

Don't sweat it.... About half the equipment in the world has only ONE switch element in its power switching...... Thus only switching one line.

Sure that one probably SHOULD be connected to neutral, but you can't count on that in Germany, for instance, the Schuko plug has no polarity......

I would, for choice, be sure that the unswitched line went to neutral. That's better.

But, the mains switch is NOT a "disconnect". In CE countries, you cannot have BOTH the "I" and the "0" marked on the switch actuator UNLESS it breaks both mains lines. That distinction obviously shows that not all do.

All equipment passing CE or UL or CSA has to pass all insulation tests in such a way that it does not matter whether what you THINK is the neutral really is.

The only item I can think of in the US that really makes any difference that way is a floor or table lamp. The screw shell is supposed to be to neutral. But the bozo electrician may have had a hangover and wired wrong, even if your lamp has a polarized plug.

As for the UK, there may be some issues locally that I am not aware of. But we sold-in equipment that opened BOTH mains leads, AND equipment that opened only one. All got marked CE with the approval of our NRTL.

rdfeil
01-24-2009, 02:04 AM
Like J said, there is nothing wrong with that design due to the start circuit. I design and build industrial control panels with UL508 and ETL listings and that design would pass without a problem. The only thing I see that might be a potential safety problem is that there is no lockout on the contactors to prevent BOTH from being activated at the same time. This all depends on how you plan on switching from forward to reverse. If it is with a mechanical switch that won't allow both to be on at the same time then problem solved. If however you plan to use pushbuttons then there is a problem. If both contactors are activated at the same time the mains will be shorted out and Boom Boom:eek: Also you should have a disconnect switch for safety, this is a switch that completely disconnects the mains or a plug in would also serve this purpose.

Robin

Peter.
01-24-2009, 04:48 AM
Hi.

Here in the UK all 240V equipment must be either earthed or double-insulated. Mine will be earthed and protected by the RCD both in the workshop and in the board in the house, so I think I'm good. The two breakers are mounted right alongside each other and each has a mechanical plastic arm that springs out the side and locks the other out.

Many thanks to everyone who has replied.
Pete.

winchman
01-24-2009, 05:46 AM
What's a RCD?

I didn't know the electrical system in Europe had 240AC with one side as a neutral.

There's SO much I don't know.

Roger

Peter.
01-24-2009, 05:54 AM
Sorry Roger, and RCD is a residual current device. It's purpose is to detect any tiny current going to earth and isolate the supply. They are typically installed in the domestic distribution panel, but we also have standalone RCD's and plug-point ones for using electric mowers etc. They don't provide overload protection though, unless it creates a fault to earth.

http://en.wikipedia.org/wiki/Residual-current_device

SDL
01-24-2009, 05:59 AM
[quote=winchman]What's a RCD?

I didn't know the electrical system in Europe had 240AC with one side as a neutral.

There's SO much I don't know.

Roger[/qu

Yep Houses get 230 V one phase and the star point from 400V 3ph street i am in are on alternate phases, one phase went on the underground cable a while back every 3rd hose had the power out.

Most houses are fed underground except out in small villages not off poles.

On our building sites we have to use 110V tools which are fed off a transformer that does 230V to 110 which is actually A 55-0-55V earthed centre tan so that there is only 55V to Ground.

I buy 110V tools to take home when I go to USA as they are less than half price.

Steve Larner

Doozer
01-24-2009, 10:28 AM
"How can I reverse this motor?"

Replace the capacitor with an inductor.
--Doozer

winchman
01-24-2009, 01:15 PM
So, your RCD is the equivalent of our Ground Fault Interrupter.

Roger

aboard_epsilon
01-24-2009, 01:56 PM
I'm no electrician

we have/had two types

ELCB...old.. earth leakage circuit breaker
RCD........residual current device

wiki explanation .

Current-operated ELCBs are generally known today as RCDs (http://en.wikipedia.org/wiki/Residual-current_device) (residual current device). These also protect against earth leakage (http://en.wikipedia.org/wiki/Earthing_system), though the details and method of operation are different.
When the term ELCB is used it usually means a voltage-operated device. Similar devices that are current operated are called Residual-current devices (http://en.wikipedia.org/wiki/Residual-current_device).

all the best.mark

Circlip
01-24-2009, 02:03 PM
And we also have NVR switches.( No Volt Release) So if you have a mains power out, the machine doesn't start up "On it's own" on return of supply.

Regards Ian.

aboard_epsilon
01-24-2009, 02:15 PM
NO VOLT RELEASE
pics show control for my southbend .......the green and red switch is the NVR rated at 16 amps 240 volts .....this one also has posts for emergency stop.

http://img.photobucket.com/albums/v190/aboard_epsilon/workbench/frontswitch.jpg

http://img.photobucket.com/albums/v190/aboard_epsilon/workbench/insideswitch.jpg

all the best.markj

Circlip
01-24-2009, 02:26 PM
And when excretae is circulating from the propellor, how small that BIG red button becomes! :D

Regards Ian.