8mm Forum: Single Phase/3 phase

8mm Forum

my profile | my password | search | faq | register | forum home

next oldest topic

next newest topic

»	8mm Forum » General Yak » Single Phase/3 phase

UBBFriend: Email this page to someone!

Author

Topic: Single Phase/3 phase

Terry Sills
Phenomenal Film Handler

Posts: 1423
From: Weymouth,Dorset,England
Registered: Oct 2012

posted March 01, 2016 06:55 AM

Send New Private Message

Edit/Delete Post

I was wondering whether it is possible to use a single phase variac/variable transformer to power a 16mm projector but I am electrically illiterate in these matters. I just thought it would be good to gently bring up the power to full. Surely this would be good to conserve lamp life and would probably be beneficial for all electrical components. I understand that the transformer would have to be of sufficient capacity (probably 10amps). I know there are very competent members in these matters, so can someone enlighten me? Or tell me that it wouldn't work perhaps!

| IP: Logged

Paul Mason
Jedi Master Film Handler

Posts: 540
From: Aldershot, Hampshire, UK
Registered: Nov 2013

posted March 01, 2016 08:03 AM

Send New Private Message

Edit/Delete Post

Terry,

Martyn Stevens of the Cinerdistan website has recommended using a variac to power up an untested projector to avoid burning out a faulty amplifier.

It seems a good idea to me for a new untried projector but it shouldn't be used permanently as there is a risk of mechanically overloading the motor. You could disconnect the drive belt temporarily.

Applying a low voltage causes motors to draw a heavy current when stalled or running very slowly. I tried it once with a Bell & Howell 626 to see if it could runs slowly for copying but not for long as it seemd likely to cause eventual motor failure.

--------------------
Paul.

| IP: Logged

Terry Sills
Phenomenal Film Handler

Posts: 1423
From: Weymouth,Dorset,England
Registered: Oct 2012

posted March 01, 2016 09:23 AM

Send New Private Message

Edit/Delete Post

Thanks Paul
What's the difference between single and three phase and which is the one for this particular application?
I wasn't intendeding to run the machine slowly for any length of time though. Just to run it up so that it avoids the sudden change from stationary to full on, which to my mind can surely be the cause of mechanical and electrical stress and premature failure. What do you think?

| IP: Logged

Paul Mason
Jedi Master Film Handler

Posts: 540
From: Aldershot, Hampshire, UK
Registered: Nov 2013

posted March 01, 2016 10:33 AM

Send New Private Message

Edit/Delete Post

Single phase is the normal 230-240 volts normal household mains with two "Live" wires (live and neutral). 3 phase is usually 400/230V with four wires L1, L2, L3 and Neutral. It can provide three times the power of the single phase supply of the same volts/current ratings and is ideal for motors rated more than 1 or 2 kilowatts. You won't have a 400V 3 phase supply unless you live in a farm, large shop, garage etc

Portable projectors use single phase, some floor standing cinema types use 3 phase.

I guess the mechanical shock is less of a problem than the electrical one but I think a variac is a good idea.

--------------------
Paul.

| IP: Logged

Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted March 01, 2016 10:39 AM

Email Steve Klare

Send New Private Message

Edit/Delete Post

Three phase is primarily industrial: large motors, big power supplies, etc. You see single phase in devices up to about 1,800 Watts, above that three phase.

-you will very rarely find 3 phase in somebody's home, although if electric cars really take off and people want to charge them at home that may change.

I agree: bringing up un unknown machine on a variac is a smart thing to do, but in day to day usage it would just be kind of a pain in the butt.

--------------------
All I ask is a wide screen and a projector to light her by...

| IP: Logged

Terry Sills
Phenomenal Film Handler

Posts: 1423
From: Weymouth,Dorset,England
Registered: Oct 2012

posted March 01, 2016 12:23 PM

Send New Private Message

Edit/Delete Post

Thanks Paul and Steve
I know that some 16mm projectors have a start capacitor for the motor. How would that be affected if you did use a variac? Would the motor not work until it got up to the full voltage?

| IP: Logged

Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted March 01, 2016 05:46 PM

Email Steve Klare

Send New Private Message

Edit/Delete Post

I've never tried this with an AC motor.

My best guess is it will not work until the motor is near full voltage.

In a reasonable range around rated voltage the speed of an AC motor tries to follow the frequency of the voltage.

-but as soon as you apply 10V @50Hz to a 240V motor the thing isn't going to immediately jump up to 3000 RPM. Probably for a long time it'll just sit there and buzz until it finally starts to roll when the voltage gets high enough.

--------------------
All I ask is a wide screen and a projector to light her by...

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 01, 2016 06:19 PM

Edit/Delete Post

What a surprise Terry!

Let's remember the principles by which ANY ac induction motor works by in the first place!

Very well documented already here!

A Variac will do nothing to assist any ac motor except make it believe it is time to stall.
All you are achieving by delaying it's start up time is placing the motor into a false state of correct start up and assisting it to stall as well as drawing excess current through it's circuit in doing so by reducing it's nameplate voltage!.
It requires the full rated voltage to achieve it's rated speed and nothing less.

The very same principle in which they work by, also teaches us all why they should NEVER have been fitted to any machinery where close speed control is beyond essential!

This is the very same reasons as to why ALL the very best projectors ever made NEVER used ac induction motors, full stop.

How many times??? [Confused]

[Confused]

The Japanese in their infinate early 70's wisdom believed "brushless" was the future!

How little did they know!!!

Crickey, I'm beginning to sound like Hugh! [Big Grin]

[Big Grin]

[Big Grin]

[Big Grin]

a
But not without good reason, some folk read a lot, and learn very little apparently!!
[Eek!]

[Eek!]

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted March 01, 2016 06:46 PM

Email Steve Klare

Send New Private Message

Edit/Delete Post

It depends on how closely the utility regulates the frequency. Being that line frequency is used to time a lot of diffeent things, it's can't be allowed to get too far out of hand.

I agree it's certainly not exact enough for frame accurate sync, but I've been told that the human ear can't detect a variation of pitch within +/-5%, especially if the difference isn't a step change so it's fine for playback.

For a playback only machine, especially one for a single frame rate, I'd go with the AC motor every time. It' simpler, it's more rugged, without the DC speed regulator it's semiconductor free too.

-as much as I enjoy a good regulator circuit (I mean...doesn't everybody?!), they are a lot more fragile than a brushless motor.

--------------------
All I ask is a wide screen and a projector to light her by...

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 01, 2016 06:51 PM

Edit/Delete Post

No, not at all Steve. Try the alternative Steve, then come back here to us all and tell us the same!

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted March 01, 2016 06:53 PM

Email Steve Klare

Send New Private Message

Edit/Delete Post

I have DC motored machines too. The difference is not overwhelming me.

--------------------
All I ask is a wide screen and a projector to light her by...

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 01, 2016 06:58 PM

Edit/Delete Post

Well it OUGHT to be Steve..especially as you are an electrician!
You have the wisdom to work these matters out for yourself, quite besides the obvious evidence afore your eyes.

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted March 01, 2016 07:05 PM

Email Steve Klare

Send New Private Message

Edit/Delete Post

Electrician?

THAT explains the van out in my driveway with my name on the side!

All those years in Engineering College when I had a career the whole time!

-but seriously, I run the same films through multiple different projectors and the variation of frame rate is nothing that is troublesome: even for soundtracks with music where it should be.

What's going on with your power line frequency there?

--------------------
All I ask is a wide screen and a projector to light her by...

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 01, 2016 07:11 PM

Edit/Delete Post

Look Steve, if you you think for one millisecond that I speak Bullshit here, ..just try a recording on ANY 600ft reel of film and then get back to me Sir! (and I say this with the the highest respect for you as you know now, all too well, I hold you in the highest regard!!)

But Steve, c'mon... seriously??

[ March 02, 2016, 04:32 AM: Message edited by: Andrew Woodcock ]

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted March 01, 2016 07:13 PM

Email Steve Klare

Send New Private Message

Edit/Delete Post

No,

I think you are not paying attention.

-I said "Playback only".

I would not record with an AC motored machine either.

--------------------
All I ask is a wide screen and a projector to light her by...

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 01, 2016 07:18 PM

Edit/Delete Post

Doh!! ok then if we could ever possibly for just one moment in our time on this planet put up with the GAWD awful Wow & flutter developed by these crude awful creatures!

Sooner you than me, that's all I can say!

Very much the end of any chance of any sensible conversation here now me thinks! [Mad]

[Mad]

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Pasquale DAlessio
Film God

Posts: 3523
From: Bristol,RI, USA
Registered: May 2010

posted March 01, 2016 07:18 PM

Send New Private Message

Edit/Delete Post

Can somebody translate all this electro stuff into English please? As it stands it doesn't phase me at all. Although I do find it over powering but not shocking. I'm just trying to keep up to current standards. [Big Grin]

[Big Grin]

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 01, 2016 07:24 PM

Edit/Delete Post

ack aaaaaaaaah!! There we go again eh Pat!!! [Wink]

[Wink]

Somehow Pat, I get the feeling you're not totally involved in this sport, though please do correct me if I'm wrong here?

No, I thought not. [Big Grin]

[Big Grin]

[Big Grin]

[Wink]

[ March 02, 2016, 04:22 AM: Message edited by: Andrew Woodcock ]

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Graham Ritchie
Film God

Posts: 4001
From: New Zealand
Registered: Feb 2006

posted March 01, 2016 11:14 PM

Email Graham Ritchie

Send New Private Message

Edit/Delete Post

That's interesting chaps.

Last month I was trying to figure out why there were 4 wires connected to the motor for the Westar 35mm projector. After a lot of [Roll Eyes]

[Roll Eyes]

and as someone with little electrical experience I thought...right the brown is live, the blue is neutral, and the green is earth, wire that lot up...so I did. Switched the motor on buzzzzzz not turning [Roll Eyes]

[Roll Eyes]

right I will try "plan B" make a jump wire from the white terminal to brown live on the motor terminals itself, and see what does [Roll Eyes]

[Roll Eyes]

...bingo, the motor went, and it even runs through a 5 amp fuse. Good thinking there Graham I thought [Big Grin]

[Big Grin]

Anyway one of the good things about "google" I later discovered that this mains motor came out in 1960 and has an internal switch, that as soon as the motor turns fast enough the 220volts running along that little internal jump wire which I guess is for the start up windings on the inertia switch cuts off. The motor is then running on its primary windings the brown, blue, and green.

So what you chaps are saying about the buzzing and the motor not getting a good kick to get it going sounds about right. [Smile]

[Smile]

| IP: Logged

Terry Sills
Phenomenal Film Handler

Posts: 1423
From: Weymouth,Dorset,England
Registered: Oct 2012

posted March 02, 2016 02:02 AM

Send New Private Message

Edit/Delete Post

I'm with Pat here! Most of this stuff is completely over my head bur Graham makes the point about startup windings. I don't know whether 16mm projectors have these windings but I do know that some have start capacitors. I thank all for the input but I'm still confused. It sounds like Andrew is saying don't do it, but then he talks about induction and brush motors. I thought all reasonabley modern machines use induction motors? The other point made is that a low voltage supplied would draw a high current. It sounds like that might cause damage to the windings. Am I right? But then what about projectors with variable speed? How does that work? Keep the info coming boys. It's an education for me, but keep it simple please. [Smile]

[Smile]

[Smile]

| IP: Logged

Paul Mason
Jedi Master Film Handler

Posts: 540
From: Aldershot, Hampshire, UK
Registered: Nov 2013

posted March 02, 2016 04:06 AM

Send New Private Message

Edit/Delete Post

My original answer has kind of got lost here that a Variac is most useful to power up an unknown ancient projector amp. An ac induction motor may stall unless you bring up the voltage reasonably quickly but there is little benefit using a variac just for the sake of the motor unless it's to reduce the voltage for a 110V motor. DC motors are different so I would say don't use a variac to supply a 8mm projector unless you know it has a mains induction motor.

--------------------
Paul.

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 02, 2016 04:15 AM

Edit/Delete Post

Terry, to put it very straightforward, any a.c. induction motor will not have any brushes as it has no commutator to the rear of it in the way you may have been used to seeing on your washing machine etc at home.
A.c. motors use induction as the principle by which they work.
Think of induction as magnetism almost.They have no brushes or indeed any physical connection from the turning part ( rotor) to the stationary part ( stator).
This is physically how a.c. motors differ from their dc counterparts.

You could argue that therefore due to the lack of any physical connection between running parts and stationary part, that a.c. motors are both an advancement and are superior in requiring far less maintenance than their dc counterparts, and you'd be correct for many applications.

In many ways in the early 70's a.c. motors were seen to be the "modern" solution to make something turn and still are in certain applications. Far less maintenance required on these type of motors for a start.

There is nothing at all wrong with a.c. motors until you find yourself in need to drive something at varying speeds but very accurately and with a need to control the speed accurately.

That is when a.c. induction motors cannot possibly begin to compete with their older designed and superior for purpose, dc counterparts or better still, servo motors, but that's another story further.

And to Paul's statement above, I completely agree Sir!
For motor alone, no benefit whatsoever and quite possibly a tremendous strain on older windings by forcing them to draw excess current for longer than ordinarily would be necessary.

Thanks for the reassurance btw Graham! [Big Grin]

[Big Grin]

[Big Grin]

[Wink]

[ March 02, 2016, 05:20 AM: Message edited by: Andrew Woodcock ]

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Terry Sills
Phenomenal Film Handler

Posts: 1423
From: Weymouth,Dorset,England
Registered: Oct 2012

posted March 02, 2016 08:22 AM

Send New Private Message

Edit/Delete Post

I think I am getting the picture that unless the projector has got a DC motor (with brushes) then using a variac has no advantage other than to gently bring up an old valve amp? Without switching on the motor. I'm told that this can sometimes help revitalise old dry capacitors and resistors. But my main aim was to gently bring up the motor speed and lamp brightness. We all know that the sudden surge of switching lamps on is the reason that lamps blow prematurely. As I first stated this thread is related to older 16mm projectors that I have, so I guess that I will have to ascertain what type of motor they use in order to have any success.
I hope I am understanding your replies correctly?

| IP: Logged

Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted March 02, 2016 08:31 AM

Edit/Delete Post

For everything other than the motor, using a variac may be a good way to go Terry for these aging 16mm machines, but yes, do check the motor first.
You may well be doing more harm than good to the actual motor if it is an ac type which is highly likely I suspect on this type of machine.

--------------------
"C'mon Baggy..Get with the beat"

| IP: Logged

Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted March 03, 2016 06:19 PM

Email Steve Klare

Send New Private Message

Edit/Delete Post

A long time ago I had a job at a power supply company where we were evaluating prototypes for a new product line.

Everybody had a variac and you can just bet when we got something brand new in for test we twisted that knob slowly and listened for trouble.

-the problem you'd run into is other than a series breaker or fuse you really had no current limiting and if 3/4 the way up something broke down things went south really fast!

It worked best when you had a hard short all along: You'd twist it up to 5V and pop a fuse, then you'd go back and start over with an ohmmeter and try again later.

A friend there was more gung-ho: "Plug it in full voltage, fix whatever blows up!"

-twenty years later he's still at, he doesn't always have eyebrows, but it hasn't killed him so far!

--------------------
All I ask is a wide screen and a projector to light her by...

| IP: Logged

All times are Central

Move Topic

Delete Topic

next oldest topic

next newest topic

Printer-friendly view of this topic

Visit www.film-tech.com for free equipment manual downloads. Copyright 2003-2019 Film-Tech Cinema Systems LLC

UBB.classic^TM 6.3.1.2