Can I drive a Seep motor from a lever frame?

Julian Roberts
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Can I drive a Seep motor from a lever frame?

Postby Julian Roberts » Sat Sep 07, 2019 1:54 pm

A probably very basic question. With a Seep or Peco or similar design point motor, only a momentary pulse of power is needed to throw the point. An "electric pencil" is a convenient way to apply this pulse of power, where one just touches the "pencil" to a stud to briefly make the connection.

Is there a convenient but equally reliable way of actuating such a motor from a lever frame?

Can't see an answer to this question from the past in this part of the Forum. Probably so simple and basically no one has needed to ask!

No need to suggest alternative actuation systems like Tortoises and servos. Just wondering if these really basic old style motors can be controlled like this too.

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grovenor-2685
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Re: Can I drive a Seep motor from a lever frame?

Postby grovenor-2685 » Sat Sep 07, 2019 3:27 pm

The simplest solution is to use a Capacitor Discharge device designed to be the interface between a simple switch, ie the microswitch on the lever frame, and a solenoid type point motor.
MERG has kits for this, PD3 at approx £9, that can link 2 levers to up to 4 points, eg 2 crossovers.

An alternative is to use the old Hornby Dublo or Triang/Hornby levers designed for the job but not so elegant as a Scalefour Society frame kit.
Rgds

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Tim V
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Re: Can I drive a Seep motor from a lever frame?

Postby Tim V » Sat Sep 07, 2019 3:33 pm

An electric pencil is actually an extremely unreliable method of contact - see 'Design for reliability' by Stewart Hine, February 1976 Model Railways.
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Martin Wynne
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Re: Can I drive a Seep motor from a lever frame?

Postby Martin Wynne » Sat Sep 07, 2019 8:44 pm

Julian Roberts wrote:Is there a convenient but equally reliable way of actuating such a motor from a lever frame?

Hi Julian,

Well obviously the lever needs some form of electrical switch attached. An SPDT microswitch perhaps, or a home-made on-off contact controlling an SPDT relay.

Given that much, this design is a simple way to drive impulse point-motors, requiring only one capacitor per point-motor.

The capacitor is charged through one motor coil and discharged through the other. It needs a beefy power supply able to deliver the charge current. A 15-volt 50VA transformer and 4 amp bridge rectifier is ideal. This design needs only a SPDT switch, so if a DPDT switch or relay is used the other pole can be used for crossing (frog) polarity switching:

A POINT-MOTOR CIRCUIT

Image
© Martin Wynne

This circuit operates an impulse solenoid point-motor using an ordinary 2-way toggle or slide switch, or relay contacts. The advantage over sprung momentary-contact switches, electric pencils and other devices is that the switch setting indicates the points setting. The switch never breaks any current, so it can be a low-cost switch. The coil inductance limits the make current. (It must be "break-before-make" action, which rules out some types of rotary switch.)

Another advantage of this design is that it allows impulse point-motors to be operated via relays, multipole switches, computer or hard-wired logic, etc.

The only disadvantage is that it needs a separate capacitor for each point motor. Otherwise this circuit is simple, safe and reliable -- it is impossible to burn out the point motor and it will last forever.

After first switching on the power, it is necessary to work the switch once each way to synchronize it with the points.

Do not work the switch rapidly to and fro, as this is likely to lose the synchronization. If this happens work the switch slowly to restore sync.

The capacitor can be at the panel end next to the switch, or on the baseboard next to the point-motor. It needs to be a few thousand uF or so, rated at least 30 volts -- a suitable common size is a 4700uF 35V high-ripple-current capacitor, which costs typically around £1.25 each:

https://www.rapidonline.com/Suntan-TS13 ... 8?IncVat=1

https://www.rapidonline.com/Catalogue/P ... Id=11-3106 (higher ripple)

Some trial and error of capacitor size with specific point-motors may be needed, and a smaller lower-cost capacitor may be adequate in many cases. The power supply must be DC (usually rectified AC), and the capacitor must be connected the right way round, as shown.

N.B. after switching off the power, the capacitor may remain in the charged condition. For safety if the layout is to be moved, stored, etc., work the switch once each way after switching off.

regards,

Martin.
40 years developing Templot. And counting ...

Julian Roberts
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Re: Can I drive a Seep motor from a lever frame?

Postby Julian Roberts » Sun Sep 08, 2019 7:00 am

I'm very grateful for your replies, particularly Martin for your very detailed one. I must confess I'm really asking on behalf of someone else, and although this is all quite simple I'm sure I have not personally made a layout since a 00 one 20 years ago, where I had a single Capacitor Discharge Unit and electric pencil or momentary contact push button switches. The layout I now have in mind has S4 Society lever frame control with a central pair of capacitors and H&M motors; I do not know what type of switch is used with the lever frame. This system is not adequately reliable but the cause of most issues is that the H&M units are just too old and prone to jamming.

Could I check Martin (this will show my lack of understanding I'm afraid) that if using your system, in the case of a crossover (with single lever to control both points), each point will need its own capacitor?

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Martin Wynne
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Re: Can I drive a Seep motor from a lever frame?

Postby Martin Wynne » Sun Sep 08, 2019 9:19 am

Julian Roberts wrote:I'm very grateful for your replies, particularly Martin for your very detailed one. I must confess I'm really asking on behalf of someone else, and although this is all quite simple I'm sure I have not personally made a layout since a 00 one 20 years ago, where I had a single Capacitor Discharge Unit and electric pencil or momentary contact push button switches. The layout I now have in mind has S4 Society lever frame control with a central pair of capacitors and H&M motors; I do not know what type of switch is used with the lever frame. This system is not adequately reliable but the cause of most issues is that the H&M units are just too old and prone to jamming. Could I check Martin (this will show my lack of understanding I'm afraid) that if using your system, in the case of a crossover (with single lever to control both points), each point will need its own capacitor?

Hi Julian,

Why do folks ask for help, but provide full information only after someone has gone to the trouble to write a reply based on partial information? It happens on all forums.

It's impossible to answer your original question without knowing what type of switch is currently attached to the lever frame.

Assuming you are willing to fit changeover switches of some sort to the lever frame, or alternatively if they are on-off switches to add a control relay, then yes you can drive two solenoid point motors simultaneously using the circuit I posted. Connect the motor coils in parallel. It is likely/possible that it will need a larger capacitor (more uF), or alternatively two capacitors in parallel (side-by-side), and also possibly a beefier power supply.

The old H&M solenoid motors include a changeover switch. It might be more reliable to use the changeover switch on the first motor to switch the second motor using a duplicate of the circuit. That way the impulses will be sequential and the original power supply will be adequate -- the more so if the connections are arranged so that one capacitor is in the discharged state when the other is in the charged state.

The changeover switches on H&M motors can be made more reliable by self-tapping two brass screws through the top plate, linking them together to provide the common connection instead of the loose central rivet. Round the tips of the screws to provide a new contact at the unused end of the wiper arm. Ensure that the wiper can't bridge the original contacts and the new ones simultaneously (break-before-make).

Jamming of H&M motors can be alleviated by generous greasing of the moving parts.

If I was doing it myself I would use a grounded frame with a simple home-made on-off contact on each lever, driving a separate SPCO control relay for each point motor circuit, plus similar relays for any additional switching needed. The control relays can all be slaved together off a single lever contact. They can be had for typically 60p each:

https://www.rapidonline.com/Catalogue/Product/60-4668

raising the total cost with the capacitor to about £2 for each point motor.

Using a separate SPCO relay for each function makes trouble-shooting much easier than with multi-pole switches or relays.

cheers,

Martin.
40 years developing Templot. And counting ...

martin goodall
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Re: Can I drive a Seep motor from a lever frame?

Postby martin goodall » Sun Sep 08, 2019 4:36 pm

Being a simple-minded soul, I shudder at the mention of relays, control circuits end other electronic complications.

The levers supplied more than 60 years ago by Tri-ang (some of which I still have in my spares box), and also the modern equivalent from Peco are simply passing contact switches.

It should not be too difficult to improvise a passing contact, which would be briefly connected by the sweep of a lever in a mechanical lever frame, so as to operated the SEEP (or similar) solenoid as the lever is reversed, and (in the opposite direction) when the lever is restored in the frame.

Rather than trying to incorporate it in the frame itself, the passing contact could be devised using copper-clad paxolin sleeper strip, suitably gapped, driven off the lever tail, with a fixed sprung contact which the 'live' part of the copper-clad strip will wipe against in mid-throw as it is moved by the point lever in the frame.

Julian Roberts
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Re: Can I drive a Seep motor from a lever frame?

Postby Julian Roberts » Sun Sep 08, 2019 5:01 pm

Very many thanks both Martins.

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Martin Wynne
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Re: Can I drive a Seep motor from a lever frame?

Postby Martin Wynne » Mon Sep 09, 2019 12:08 am

martin goodall wrote:It should not be too difficult to improvise a passing contact, which would be briefly connected by the sweep of a lever in a mechanical lever frame, so as to operated the SEEP (or similar) solenoid as the lever is reversed, and (in the opposite direction) when the lever is restored in the frame.

The big drawback to such a scheme is that should the lever happen to be left in a mid-position, the motor coil will rapidly overheat and burn out. There is a good chance that such a situation will arise at some time in the lifetime of a layout. To prevent that requires the additional complexity of an over-centre spring on each lever in a mechanical lever frame. Impulse solenoid coils are not continuously rated -- if the current flows for more than a few seconds they will at least burn out, and possibly represent a fire-risk to the baseboard.

Whereas once the energy stored in a capacitor has been discharged through the motor coil, the current falls to zero, and there is never any chance of a coil burning out. That's a system having a vastly greater long-term reliability than any passing contact switch.

Also any system using passing contact switches is going to need 2 wires to the baseboard per point-motor. Whereas if a control relay and capacitor are installed near the point-motor, that requires only 1 wire per point-motor. On a large layout with several baseboards and multi-pin plugs and sockets, that all adds up.

Rather than trying to incorporate it in the frame itself, the passing contact could be devised using copper-clad paxolin sleeper strip, suitably gapped, driven off the lever tail, with a fixed sprung contact which the 'live' part of the copper-clad strip will wipe against in mid-throw as it is moved by the point lever in the frame.

Copper foil is a poor contact material, especially in high-current inductive circuits. At the very least that design requires a quenching diode across each motor coil (on DC, or a resistor on AC). Otherwise the reliability will go rapidly downhill as sparking oxidises the copper, or even burns through it, leading to a high-resistance contact. Also making such a switch and maintaining it in alignment over the years is no 5-minute task -- the available stroke on most lever frames is not much more than 10mm.

Compared with the work and skill needed to do that, the capacitor scheme needs only the ability to use a glue gun. Dab a control relay and a capacitor in place somewhere under the baseboard, make a few wire connections between them, and job done. Fit and forget for the lifetime of the layout.

The one advantage for basic passing-contact switches, electric pencils, push-buttons, etc., is the ability to work directly on AC. Any system using capacitors needs a DC or rectified AC power supply. But that's only one decent-sized bridge rectifier for the whole layout.

cheers,

Martin.
40 years developing Templot. And counting ...


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