Scalefour lever frame & Cobalt point motors

Andrew Ullyott
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Re: Scalefour lever frame & Cobalt point motors

Postby Andrew Ullyott » Fri Sep 28, 2018 7:11 pm

I built one of the mark 1 SHAG lever frames for Wheal Elizabeth, the tails of which were connected to DPDT slide switches mounted in a line behind the frame. The linkage was 0.9mm nickel silver wire hooked into a hole drilled in the switch slide and the lever tail. With careful selection of the switch, omega loops weren't required. I used this to operate the feeds to Tortoise motors so I see no need why it couldn't work for Cobalts. What I couldn't do is fit a switch integral to the frame to do this since it was set up for SPDT lever switches as far as I could tell. Someone cleverer than me may have achieved it though.

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grovenor-2685
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Re: Scalefour lever frame & Cobalt point motors

Postby grovenor-2685 » Fri Sep 28, 2018 8:11 pm

You can certainly operate a tortoise with a single pole switch, eg the microswitch that is intended to be fitted to the frame, so I would expect that to be equally doable with a Cobalt, if there is a problem with the Cobalt design putting a cheap relay in between will sort it.
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Keith
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junctionmad

Re: Scalefour lever frame & Cobalt point motors

Postby junctionmad » Fri Sep 28, 2018 8:28 pm

The lever frame is designed for a SPDT microswitch. In order for this to operate a colbalt directly , you will need a split DC supply ( ie , +12, -12, 0v )
Alternatively you can use the microswitch to operate a DPDT relay , and hence use conventional single sided DC power supplies
Dave

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Re: Scalefour lever frame & Cobalt point motors

Postby grovenor-2685 » Fri Sep 28, 2018 8:59 pm

you will need a split DC supply ( ie , +12, -12, 0v )

Yes, and simply obtained from a transformer by using two diodes, abeit more of an issue with switch mode PSUs.
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Keith
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Andrew Ullyott
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Re: Scalefour lever frame & Cobalt point motors

Postby Andrew Ullyott » Sat Sep 29, 2018 10:49 am

grovenor-2685 wrote:
you will need a split DC supply ( ie , +12, -12, 0v )

Yes, and simply obtained from a transformer by using two diodes, abeit more of an issue with switch mode PSUs.

For the electronically ignorant amongst us (and I am very firmly in that category), is there a wiring diagram/'how to guide' anywhere that hopefully uses words of a single syllable?
I don't remember ever having seen one in either the lever frame or tortoise instructions.
Apologies if this seems an incredibly basic question, but split D.C. was something I'd not been aware of until your post. I can see the theory behind using a switch to 'choose' either +12v or -12v and presumably having 0v as the common return?

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Re: Scalefour lever frame & Cobalt point motors

Postby grovenor-2685 » Sat Sep 29, 2018 12:44 pm

The diagram is in the tortoise instructions,
See diagrams 2 and 3 on attached.
800-6000ins.pdf

Rgds
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Keith
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Andrew Ullyott
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Re: Scalefour lever frame & Cobalt point motors

Postby Andrew Ullyott » Sat Sep 29, 2018 3:58 pm

grovenor-2685 wrote:The diagram is in the tortoise instructions,
See diagrams 2 and 3 on attached. 800-6000ins.pdf
Rgds

Thanks. It kind of makes sense. Told you I was a luddite!

Tony Wilkins
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Re: Scalefour lever frame & Cobalt point motors

Postby Tony Wilkins » Sat Sep 29, 2018 4:09 pm

Split potential or dual rail power supplies are commonly used in audio amplifiers.
I used them on Green Street for the Fulgurex point motors. This has the advantage of only needing one wire to feed a point motor (rather than two) and a common return.
Diagram of the power supply wiring attached.
Dual rail supply.GIF

This design utilises a bridge rectifier for full wave rectification. The transformer has two separate secondary windings but a center tapped winding would do equally well.
The numbers to the right are the connector pin numbers in my case.
Pin 8 is the 0v rail and is connected to the point motor common return.
The +10v rail is connected to one pole (N/O) of the control switch and the -10v rail is connected to the other pole (N/C).
The common switch pole (C) is connected to one terminal of the point motor and the other motor terminal is connected to the point motor common return.
If the motor operates the wrong way round simply reverse the point motor terminal connections.
A word about switches. Toggle switches generally have the common pole (C) in the middle and the changing poles to the sides.
Micro switches however generally have the common pole (C) at one end and the (N/C) normally closed and (N/O) normally open poles toward the other end of the switch body.
It is far preferable to use a contact on the point motor to indicate the position of the point on the control panel as this provides positive feedback that something has happened at the far end. Albeit at the cost of extra wiring.
Cobalt IP motors have a built in terminal specifically for this function.
Regards
Tony.
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junctionmad

Re: Scalefour lever frame & Cobalt point motors

Postby junctionmad » Sat Sep 29, 2018 4:43 pm

Cobalt IP motors have a built in terminal specifically for this function


In the case of the classic omega , the pin marked feedback is simply a ½ resistive divider of the motor supply voltage

Hence on split supplies you get a +5 and -5v from the feedback pin but only as long as the motor voltage is present


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