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Topic: Which Motor Relay to use?

Bernie Anderson Jr
Master Film Handler

Posts: 435
From: Woodbridge, New Jersey
Registered: Apr 2000

posted 05-15-2011 04:10 PM

What relay would you recommend as a motor relay to control the Digital sound changeover for a 2 projector booth?

Thanks

Bernie

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Dave Macaulay
Film God

Posts: 2321
From: Toronto, Canada
Registered: Apr 2001

posted 05-15-2011 05:13 PM

- coil voltage is whatever your motor voltage is.
- contact rated at a low amperage, 5A is OK. Lower is better, as large amperage contacts can corrode and fail to close with the tiny actual current switched in this application. The P&B KHU-17A11-120 (3A contacts) is good for a 120VAC motor, with the matching socket and a wire retainer. The KRP-14AGA-120 (10A contacts) works OK and also stays in its socket well without a retainer clip.
A socketed relay (with the socket!) makes trouble shooting and replacement easier.
Use shielded wire: shielded pair like the sound reader wire is great - belden 8451 or similar. The conductors can be mighty small (24ga is fine). Connect the shield to chassis ground only at the processor end and insulate it at the relay end, don't connect it to anything at that end.

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 05-17-2011 11:53 AM

Two semi-related questions:

- is there any advantage two using relays vs. DPST motor switches, with the second pole connected to the processor/DA20 (assuming no automation and only one motor switch per projector)?

- if using relays, what is the preferred place to mount them? On/in the projector base in electrical boxes? In the sound rack? Somewhere else?

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 05-17-2011 12:36 PM

Scott:

1: Yes, a relay provides a very high level of dielectric isolation to keep that pesky 120 volts from the motor away from the sensitive low voltage logic of the motor sense in the processor. [Big Grin]

DPST switches can and will suffer from contact failures and flashovers (remember you're switching a highly inductive load [motor] which makes for a lot of arcing in the switch) which will fry your very expensive sound processor. So would you rather save your processor or try to save the $10 for a set of relays?

2: Best place will be in the projector bases or in j-boxes near as possible to the motor. (Or if you have wall-mount automation, in the automation can if there is room.) You DO NOT want to run that 120v line from the motor to your sound rack...it is not cost-effective, and you now have a high voltage line with nice spikes on it every time the motor starts/stops mingling with your sound gear.

quote: Dave Macaulay
contact rated at a low amperage, 5A is OK. Lower is better, as large amperage contacts can corrode and fail to close with the tiny actual current switched in this application. The P&B KHU-17A11-120 (3A contacts) is good for a 120VAC motor, with the matching socket and a wire retainer. The KRP-14AGA-120 (10A contacts) works OK and also stays in its socket well without a retainer clip.

I agree with the part in bold. But DO NOT use the 10 amp relay as its contacts will not stay clean in this application! I have had to replace many of them as a service tech.

Finally, in a single-projector application, the motor start relay is really not 100% necessary, you can leave the Dolby-supplied jumper in and the Digital will work fine. (If you have no jumper or relay what will happen is if the DD drops out the sound will mute as it will assume there is no film running and thus no SR backup playing.)

And yes I did notice that Bernie is asking about a 2-projector setup. In which case the relays are essential as it also lets the processor know when to expect the changeover on the digital track.

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Andres Briano
Expert Film Handler

Posts: 162
From: Buenos Aires, Argentina
Registered: Jan 2008

posted 05-24-2011 10:07 AM

quote: Tony Bandiera Jr.
Finally, in a single-projector application, the motor start relay is really not 100% necessary, you can leave the Dolby-supplied jumper in and the Digital will work fine. (If you have no jumper or relay what will happen is if the DD drops out the sound will mute as it will assume there is no film running and thus no SR backup playing.)

Hey Tony,
Excuse my ignorance, but what is that relay for? I´ve always dealt with single projector systems and, as you´ve mentioned, they come with a factory jumper to the 9 pin connector labeled Motor Start. I have wondered about that before, but never asked anyone.
Thanks,
Andrés

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 05-24-2011 10:26 AM

I use a simple octal socket & Omron relay from Grainger. What you really need is wiping contacts since the current drain is so low. Louis

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 05-24-2011 02:18 PM

Andres, no need to feel ignorant. [Smile]

Here is the info from the DA-20 manual on what the motor relays are for:

"Because the data on the Dolby Digital track is normally read in advance of the picture gate, in a two-projector changeover system the DA20 requires signals in advance of a changeover. Motor Start contact closures provide those signals......In a single-projector system, the DA20 requires the MS1 signal to be valid when the projector motor is running in order to allow switching to the analog soundtrack when digital data is not present. If the MS1 signal is not connected to Digital Ground, the DA20 will not switch to analog if the digital signal is unreadable. "

By the same token, in a two-projector system if the proper MS signals are not given the DD will not pick up the incoming reels track in a timely manner, which may result in an extended dropout of sound or erratic switching from digital to analog during changeovers. Also, if the relays aren't present the running projector will not drop to analog if the digital data becomes unreadable.

The drawback to using the link (in a single-projector system) is that the system will be in analog instead of muted digital during projector startup.

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Andres Briano
Expert Film Handler

Posts: 162
From: Buenos Aires, Argentina
Registered: Jan 2008

posted 05-24-2011 02:49 PM

Thanks, man! Understood and learnt! [thumbsup]

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 05-24-2011 03:38 PM

You're welcome sir. [Big Grin]

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Bernie Anderson Jr
Master Film Handler

Posts: 435
From: Woodbridge, New Jersey
Registered: Apr 2000

posted 02-13-2012 11:03 PM

Hey Louis,

Which model Omron relay do you use?

Also , for clarity, so I totally understand the operation of the relays, you need two relays, one at each projector motor. When the motor turns on, it closes contacts in the relay telling DD that an incoming reel is about to go on screen. So for those 8 secs that both machines are running right before the changeover, both relays are energized, then when the outgoing machine shuts down, the only relay holding a closure is the incoming machine only. Right?

Thanks

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 02-14-2012 08:00 AM

That's right. 120volt (motor voltage) Omron octal relay from Grainger.

You will need 4 relays and sockets. The other two follow the picture changeover (120v) for the analog changeover. Louis

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 02-14-2012 08:49 AM

We've used the Omron LY2-F series for 120V motor systems and one can always double up on the contacts to lower the contact resistance. Likewise, if using the KHAU relays from P&B...double or triple or quadruple up on the contacts to reduce the contact resistance. I've actually had fewer problems with contacts with Omron relays than P&B (especially since the EPA killed off key ingredients in relay contacts like cadmium).

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 02-14-2012 10:19 AM

As to changeover, I usually use a microswitch inside the Kelmar douser instead of relays. Only one switch is needed, it's cheaper and there is not as much chance of the relay sticking, and if it does, you can mechanically clear it.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 02-14-2012 11:53 AM

For changeovers on CP650, I always use "Pulsed" logic as it always is right. For older stuff, I like mechanical latching relays like the KBP series by P&B. For Kinoton, we make our own PCB that monitors the button pushes and then turns that into motor/changover logic in either pulsed or latched.

-Steve

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Bernie Anderson Jr
Master Film Handler

Posts: 435
From: Woodbridge, New Jersey
Registered: Apr 2000

posted 02-14-2012 01:11 PM

I understand the reason for the use of motor relays for the DA20, but I thought the picture changeover contact happened between the CP65 and the DA20 internally, so when the 65 switched analog from projector 1 to 2 on picture and analog CO it would also send that signal to the DA 20 through pin 25 on J18 confirming it was on the second mahine

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