DPDT to work Seep point motor.

[Trog]

Does anyone have a circuit I could use to drive a Seep point motor using a DPDT toggle switch?

I want the switch to stay at each end of the throw like a proper lever, so no (on) off (on) switches wanted.

 

I found a circuit using a capacitor and two diodes that worked but it used the capacitor in one direction and the feed power in the other giving an uneven amount of power in each direction.

 

So ideally I want a circuit powered by a capacitor in both directions, so I get a nice even throw. Has anyone got any ideas?

[Dukedog]

Try this link http://home.cogeco.ca/~rpaisley4/ToggleTwin.html

 

I have not tried this circuit myself but it should work.

 

Cheers

Frank

[Trog]

Thanks I had found that one and have made two, neither of which worked.

 

I have been puzzling over it and I can not figure out what the diodes are supposed to be doing.

 

They look like they would direct the power to one coil or the other if the power was applied and reversed over terminals A and B on a Seep.

 

But what they do when the power runs A-C or B-C I can not work out as the side of the circuit with the open switch is a dead end so no current will go that way anyway. On the other side with the closed switch where I assume the current is wanted to run through the coil, why have a bypass you dont use?

[smokebox]

The diodes across the point motor connections are to reduce/eliminate the back emf which is generated in the point motor coils

[Ron Heggs]

Having built two of these circuits and neither appeared to work, I was wondering whether your switch pole connections were correct

 

If the two live connections were wired to the centre/common switch terminals tand the two coil connections were wired to the switch terminal connections on the same side of the switch, then motor coils would appear not to throw, as with the switch throw in one direction neither coil would receive power and in the other direction both coils would receive power - acting in opposite directions hence no movement

 

I have modified the circuit diagram which I hope will make it clearer -

 

 

You will see that the coil connections are wired to opposing terminals

 

Hope this helps

 

Ron

[Trog]

The diodes across the point motor connections are to reduce/eliminate the back emf which is generated in the point motor coils

 

That makes sense.

 

thanks.

[Trog]

Having built two of these circuits and neither appeared to work, I was wondering whether your switch pole connections were correct

 

If the two live connections were wired to the centre/common switch terminals tand the two coil connections were wired to the switch terminal connections on the same side of the switch, then motor coils would appear not to throw, as with the switch throw in one direction neither coil would receive power and in the other direction both coils would receive power - acting in opposite directions hence no movement

 

I was using the two middle connections and two diagonally opposite outer ones, with the connections to each coil on the same side of the switch.

 

Will have to have a good look at what I have done and have a good long think about this.

[Dukedog]

Well done Ron for finding that error.

As I said I have not used any of these circuits. I use a conventional CDU with transistor assisted coil operation. similar to one of the other circuits in the link I provide

 

 

Let us know if Ron's mod works, I can't see why it shouldn't. The only drawback I can see is the time taken to charge the capacitors due to the relatively high value resistor,

it will be less than a second or two though, and unless you want to change point position very quickly should prove no problem.

 

Cheers

Frank

[martin_wynne]

This design requires 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 is used the other pole can be used for crossing (frog) polarity switching.

 

A POINT-MOTOR CIRCUIT

 

© 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. (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 25 volts or more -- a suitable common size is a 4700uF 25V capacitor, which costs typically around £1.25 each. 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 (rectified AC), and the capacitor must be connected the right way round, as shown. If the supply voltage is more than the nominal 12 volts DC shown (typically from 15v AC rectified), increase the capacitor voltage rating accordingly.

 

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.

[Trog]

Thanks for the help.

After some thought I came up with this which works nicely and gives a nice equal push in both directions.

 

[Donw]

An alternative approach I have used is to connect up the point motors via switches to the coils you can use a SPDT although there is no great cost saving. With the supply via a cdu through a push button. You set the switches to the road then press the push button and the points all fire. This works for six peco motors in 0 gauge. I use a house type push button and that is the only one to make or break the current so the other switches arranged like a single box only have to carry the current not interupt it and hence last longer.

Don

[Trog]

 

 

After a bit of experimentation I have come up with this to power a crossover with one of the new small Peco point motors on one end and a SEEP on the other.

 

The two black boxes are DPDT relays and are switched by powering them with a reversable DC supply as if they were a Cobalt or Tortise. So they can be wired into my control box the same way and/or used as replacements., The diode on the middle right changes the reversing current into an on - off signal to work the relays.

 

Each relay is wired so that one of a pair of capacitors is being charged while the other is connected through one of the coils of the motor. Reversing the relay switch discharges the charged capacitor through the point motor switching the point, and puts the other capacitor onto charge ready to bring the motor back.

 

I have another crossover with SEEP motors both ends where both ends are worked by the same pair of capacitors. But the missmatched pair require seperate capacitors hence the dual design.

 

It is powerful enough that when I miss timed changing a point the motor threw a loco that was on the point off the track, and the recharge time is almost instant. It is as fast as I can move the switch anyway.

[Dagworth]

This topic may be of help

http://www.rmweb.co.uk/community/index.php?/topic/17365-push-button-switches/page__p__165586__hl__cap__fromsearch__1&do=findComment&comment=165586

 

Andi