A quick circuit please...

[tramcar trev]

With my trams I want to make them able to be run from 2 rail or rail and overhead. Ok simple enough with a spdt switch BUT due to the way I have sectioned my track the pick up wheels need to be on the side that has power in it so I want to be able to switch them so both sides ( all the wheels) can be switched to the - which is the track and the + comes via the trolley pole without shorting out.... I started out with a DPDT switch and the trolley pole permanently connected to the + at the motor, then I got a headache and lost the plot..... One of you bright sparks will know exactly what I'm trying to do..... I hope....

 

[Tony]

First question is why ?

First answer..... simples solution..... 3 wires connected to each of the rails and overhead and two socket holes from transformer ....plug each into each depending on your mood

second answer..... see question 1

 

[ntpntpntp]

First question is why ?

Sounds like Trev has his track sectioned with just a singe rail isolated on one side, and a common rail. Therefore need to be able to choose which side the wheels are picking up when running on overhead + common, depending on which way the tram is facing when it runs into a track section which is switched off?

Off the top of my head, I'd say use a Double Pole Triple Throw switch (DP3T). The common connections go to the motor. 1 position links each common pole to a rail (wheels), one position links one pole to one rail and the other pole to the overhead (trolley pole), the 3rd position swaps which pole is linked to rail and which to the overhead. Can't draw it now as I'm at work and can't post links to DP3T switches on ebay, but they do exist.

 

[rjstott]

Trev,
I guess questions are in order, so here are the key ones.
1) I'm guessing you're using simple AC? Not DC and not DCC?
2) Why do want to use the pole as a pickup, it seems to me it will be a very weak link?
3) If you are happy with a dpst switch does this mean you run sessions with track feed only?
For some reason a centre-tapped transformer comes to mind with the pole going to the centre tap. This would be aboard the tram with the other winding feeding the motor. A similar arrangement would be used to feed the track and overhead?

Richard

 

[Tony Walsham]

Yes, it is probably best to do it with a SPDT switch.
One side of switch goes to track power pick up.
The other side of the switch goes to the Trolley pick up.
Middle goes to Motor terminal.
Other motor terminal goes to the return power pick up.

Assuming the motor is straight DC, the tram will behave the same.
No need to worry about track polarity using the same track side speed and polarity controller.

 

[Nodrog1826]

It sounds to me as if you are wanting to run something like the old Trix Twin system.

http://www.trix.co.uk/Operating.htm

Not sure if you could in essence modify your system to work in the same way.

 

[tramcar trev]

Trev,
I guess questions are in order, so here are the key ones.
1) I'm guessing you're using simple AC? Not DC and not DCC? No simple PWM DC power supply
2) Why do want to use the pole as a pickup, it seems to me it will be a very weak link? well trams traditionally use a trolley pole and as my track is hand laid on PCB sleepers I really only need the facility if mt trams ever visit a 2 rail layout
3) If you are happy with a dpst switch does this mean you run sessions with track feed only? No at present I use the trolley pole and one side of the wheels to pick up, I want to be able to use both sides of wheels to pick up and the pole...
For some reason a centre-tapped transformer comes to mind with the pole going to the centre tap. This would be aboard the tram with the other winding feeding the motor. A similar arrangement would be used to feed the track and overhead?

Richard

I guess I should rephrase the question. I want to be able to switch both sides of the pick up wheels to be able to be electrically joined, and retain the ability to switch to 2 rail mode.

 

[tramcar trev]

First question is why ?

Sounds like Trev has his track sectioned with just a singe rail isolated on one side, and a common rail. Therefore need to be able to choose which side the wheels are picking up when running on overhead + common, depending on which way the tram is facing when it runs into a track section which is switched off?

Yes excactly and as I have balloon loops the tram comes back to an isolated section of track and stops because the wheels on that side are insulated.... I have heaps of DPDT but now the quest is on for DPTT....
Im quite prepared to swap some of my Hindsight for some foresight, I should have thought of this before I paved my roadways and filled in between the rails with cobblestones...

 

[Neil Robinson]

I started out with a DPDT switch and the trolley pole permanently connected to the + at the motor, then I got a headache and lost the plot.....

How about switching the trolley pole and leaving one side of the track permanently connected to the motor - ?
I think this is possible with a DPDT switch provided the trolley pole is electrically redundant when operating in two rail mode.
Unless I misunderstand your requirements I think this circuit should work.

 

[ntpntpntp]

Don't think that would work if the tram is running on overhead and in the same section as a 2 rail tram - you'd get a short across the tracks?

I'm assuming Trev wants the ability to run both types of power on the same section, as you can do with overhead locos in the small scales. I have several N gauge locos which can do this, but you cannot physically reverse the direction of the loco on the track which Trev would be doing with his balloon loops. Hence the need to switch and choose which side of the loco acts as the common wheel pickup.

 

[Neil Robinson]

Hi Nick,
Point taken, If Trev wishes to use both systems simultaneously he has a problem.

<snip>I want to be able to switch them so both sides ( all the wheels) can be switched to the - which is the track and the + comes via the trolley pole <snip>

By definition doing the above shorts out the track.

 

[ntpntpntp]

My first thought was something like this:

 

[rjstott]

Ok everyone's gone DC so why not use a full wave diode rectifier across the track to power the motor and connect the pole to the positive side of the motor. That's assuming the trams always go the same way (if not then a DPDT switch can reverse the motor at the same time you swing the pole. It doesn't connect the tracks together but would allow track only running and the pole gets priority to feed the tram ('cos the diode drops 0.7V) And of course the track polarity is no longer an issue.
Regards

Richard

 

[Dtsteam]

Trev,
Neil's post #9 is the way to go if you are running live overhead, but want to run 2 rail on other layouts. The most successful tram layouts I've seen have gone down this route. Its a PITA isolating both rails, but its less unsightly than too many section breakers in the overhead.