CDU for Peco Points Query

[Redford73]

I have 12 Peco PL-10 point motors on my layout and wont ever be throwing/using more than one at a time.

 

I have bought a CDU as I know they can help focus the power and stop the buzzing when the switches/point motors are activated but how many can I run to a single CDU?

 

I am using 16V AC terminal on my Gaugemaster D Controller to power the points and the CDU is also a Gaugemaster.

 

At present the point motor neg/black wires all go via terminal blocks with 7/0.2mm multicore wire then with 16/0.2mm multicore (bus wire) from terminal blocks to controller.  The pos/red wires from the switches are also 7/0.2mm and are also linked to a terminal block with a single 7/0.2mm (bus wire) feed back to the D Controller which is near the switches.

 

Can I just link up the above 'bus wires' to the CDU or are there too many points/switches for a single CDU of this type?    

[newbryford]

I have 12 Peco PL-10 point motors on my layout and wont ever be throwing/using more than one at a time.

 

I have bought a CDU as I know they can help focus the power and stop the buzzing when the switches/point motors are activated but how many can I run to a single CDU?

 

I am using 16V AC terminal on my Gaugemaster D Controller to power the points and the CDU is also a Gaugemaster.

 

At present the point motor neg/black wires all go via terminal blocks with 7/0.2mm multicore wire then with 16/0.2mm multicore (bus wire) from terminal blocks to controller.  The pos/red wires from the switches are also 7/0.2mm and are also linked to a terminal block with a single 7/0.2mm (bus wire) feed back to the D Controller which is near the switches.

 

Can I just link up the above 'bus wires' to the CDU or are there too many points/switches for a single CDU of this type?    

 

If you're only ever throwing one point at once, then I would say that you could fit as many as you want.

Also, no problem with running a common wire back from all the motors as it's only going to be carrying the current from one motor at once.

 

Cheers,

Mick

[Brian]

Hi

You can have hundreds of point motors and their switches all connected to the one CDU circuit as you normally only operate one or two motors at any one time.

 

Each points operation switch has to be in the Off position when not being used - not moving, therefore no power flows past that switch until it is moved, then only a momentary pulse of power (discharge for the CDU) is sent out along one of the two operation wires to the point motors coil, This then moves the motor and point to the left or right.  

All the point motor return wires can be connected together ideally at various places that are convenient around the layout and all are then linked together by one wire (the Return wire) then this return wire eventually runs back to the CDUs negative output terminal.  The positive output feed of the CDU goes to all the switches or levers.

 

Depending on the size of your layout 7/0.2mm equipment wire (Sometime called "Layout wire" by some retailers) can be rather on the small size.  So to avoid operation problem like intermittent failure to throw or total failure to throw when the switch is moved, I always recommend using 16/0.2mm wire for all the feeds and where more than one motor is to move together from one switch movement I recommend using  24/0.2mm or better still 32/0.2mm wire for the single return wire. Note: if you have plenty of 16/0.2mm wire you can always double up this making a larger wire size for the return.

 

My web sites Point Wiring detail may help?.... http://www.brian-lambert.co.uk/Electrical.html#Motor  Scroll down for more detail wiring of the return.

[kevinlms]

Hi

You can have hundreds of point motors and their switches all connected to the one CDU circuit as you normally only operate one or two motors at any one time.

 

Not really, because if there are 100s of points, then the operating distance & thus resistance is going to cause voltage drop. So while possible, in such a case, it would be better to have a number of CDU's & probably local control.

I agree with your basic advice though, just not true for '100s'.

[Redford73]

Thanks for advice.  I pretty much thought you could and as I only have 12 points it wont be a problem.  Have already wired the points using 16/0.2mm wire on the long stretches round the layout but it is only 12' by 8' so not all that big. 

 

My mind is at rest now and I will start wiring up the points/switches to the CDU.

[phixer64]

Got myself a gauge master CDU installed on my layout, even though its only got 9 points, 2 off them are wired as a pair. Works like a treat, i made sure that the switches or toggles are spring loaded, so there return to the centre (off) position.

 

Regards Jeff

 

[28XX]

I use 2 core loudspeaker wire for the Normal / Reverse connections to solenoid motors, keeps wiring neater. Many gauges available depending on the number of motors which fire together / length of run. The common can be daisy-chained to as many points as practicable, so long as it is at least as heavy a gauge as the longest run/ heaviest load.

[Brian]

It was meant as an example kevinlms.  Not to be taken too seriously  :-)

Though in theory you could have a 100 plus points operated by one CDU especially with larger feed wires to each motor!

But reality says most would limit it to 20 - 30 etc.

[Bernard Lamb]

Thanks for advice.  I pretty much thought you could and as I only have 12 points it wont be a problem.  Have already wired the points using 16/0.2mm wire on the long stretches round the layout but it is only 12' by 8' so not all that big. 

 

My mind is at rest now and I will start wiring up the points/switches to the CDU.

Just take care that you do not touch the "hot" part of the CDU while working on the wiring. It can give you a kick even when you think it might be sleeping.

What switches are you using?

Brass screws and a small screwdriver is a cheap and effective method that has stood the test of time.

Bernard

[Colin_McLeod]

Just take care that you do not touch the "hot" part of the CDU while working on the wiring. It can give you a kick even when you think it might be sleeping.

When I had  CDU with a previous layout I got into the habit at the end of a session of changing one point after I had switched everything off. This discharged the CDU.

[kevinlms]

Just take care that you do not touch the "hot" part of the CDU while working on the wiring. It can give you a kick even when you think it might be sleeping.

What switches are you using?

Brass screws and a small screwdriver is a cheap and effective method that has stood the test of time.

Bernard

Agreed, it doesn't do soldering iron tips much good, nor the nerves!

[kevinlms]

It was meant as an example kevinlms.  Not to be taken too seriously  :-)

Though in theory you could have a 100 plus points operated by one CDU especially with larger feed wires to each motor!

But reality says most would limit it to 20 - 30 etc.

Oh yes I agree, but I was just clarifying. Sometimes if the seemingly obvious isn't stated, somewhere, sometime...

 

[DCB]

Speaker wires are marginal for power transmission, I think some are only 1/4 amp, I have managed to set some on fire on occasions.

 

Some point switches are passing contact and unsuitable for use with a CDU. The problem being as you move the lever it first gives the motor pulse in the wrong direction, which discharges the CDU and then as the switch nears the far end of its travel it gives it a pulse in the correct direction, while the Capacitor is recharging. The only way around it is to pause part way through the movement to allow the CDU to recharge, which is pretty impractical.

I use stud and probe using a brass probe made from a ball point pen and the spring loaded contact from a domestic light fitting on dome head brass bolts, 

[kevinlms]

Speaker wires are marginal for power transmission, I think some are only 1/4 amp, I have managed to set some on fire on occasions.

 

Some point switches are passing contact and unsuitable for use with a CDU. The problem being as you move the lever it first gives the motor pulse in the wrong direction, which discharges the CDU and then as the switch nears the far end of its travel it gives it a pulse in the correct direction, while the Capacitor is recharging. The only way around it is to pause part way through the movement to allow the CDU to recharge, which is pretty impractical.

I use stud and probe using a brass probe made from a ball point pen and the spring loaded contact from a domestic light fitting on dome head brass bolts, 

Speaker wire comes in a large range of sizes & ratings. Agree that the lower ratings are useless for solenoid motors. Larger sizes are excellent.

 

For a probe, I've even used a length of mains cable with the end soldered, to keep the strands together. Works well & if the end gets pitted, just cut the end off & resolder!

[Crosland]

Speaker wires are marginal for power transmission, I think some are only 1/4 amp, I have managed to set some on fire on occasions.

So you chose the wrong type. Get over it.

[Oldddudders]

Speaker wires are marginal for power transmission, I think some are only 1/4 amp, I have managed to set some on fire on occasions.

 

Some point switches are passing contact and unsuitable for use with a CDU. The problem being as you move the lever it first gives the motor pulse in the wrong direction, which discharges the CDU and then as the switch nears the far end of its travel it gives it a pulse in the correct direction, while the Capacitor is recharging. The only way around it is to pause part way through the movement to allow the CDU to recharge, which is pretty impractical.

I use stud and probe using a brass probe made from a ball point pen and the spring loaded contact from a domestic light fitting on dome head brass bolts, 

The switch should be single pole two-way, centre off, non-latching. Maplin have served me well over the years.

[Chimer]

Going back to the OP, I thought if you were only ever going to throw one solenoid point motor with one flick of a switch, push of a button or whatever, a CDU was unnecessary and the standard 15v AC output from the average train set controller would be fine?  It worked OK in the 1960s ..... (apart from burning one or two out of course   )

[Colin_McLeod]

Chimner even with just one point being changed the CDU produces a robust point change compared to a transformer alone. Also there are always one or two points that become sluggish over time bur with a CDU they still change reliably and none burn out.

[Crosland]

 It worked OK in the 1960s ..... (apart from burning one or two out of course   )

 

Once the CDU is discharged it can't burn out a point motor. That's one of the advantages.

 

Andrew

[Redford73]

Well, got the CDU installed on the layout and tested it on one point (I still need to wire up all the switches to a terminal block).

 

One query - when the D controller (to which the CDU is wired up via the 16V AC terminal) is switched on there seems to be a constant low buzzing (presumably the CDU as the D controller never did this before).  is this normal?  This is when it is 'idle' (i.e. no points being activated/used).  Is it because I haven't wired up al the switches to it yet?

[Brian]

It has nothing at all to do with the number of switches connected or not wired, so long as those already wired are of the (On)-Off-(On) switch style or are passing contact lever style switches such as the Peco PL26 and all the wiring is correct.  

Connect 16v AC to the input pair of terminals on the CDU.  CDUs Output pair of terminals are Positive (+) terminal to all the switches middle connections, linking first switch onto the next and so on until last switch is reached where the wire stops.  Negative (-) output on the CDU terminal runs out to the layout and links together all the solenoid point motors return connections. These are Seep 'C' terminal, Peco motors the Green wire and Hornby the Black wire.    The other two wires on the motor connect to the outside connections on the switch that works that motor.

 

The humming you're hearing is most likely to be the mains to low power transformer laminations vibrating at the 50Hz mains frequency. This in itself doesn't represent any issues, just a little annoying.

You could try powering up the unit and then while its humming removing one wire on the 16v ac connection that goes to the CDU, does the humming then stop? 

[Pete the Elaner]

For a probe, I've even used a length of mains cable with the end soldered, to keep the strands together. Works well & if the end gets pitted, just cut the end off & resolder!

Nothing wrong with this for a probe, but why would the end get pitted?

 

Without a CDU, the end gets pitted because the sudden current drop through the motor's winding causes the magnetic field to collapse suddenly which generates a large back emf which causes the spark which pits the connection.

The CDU gives an initial burst of current which then drops very quickly. Once discharged, there is very little left so the back emf is very low & you only get a very tiny spark when pulling the probe away from a stud.

 

I used this theory to swap from stud & probe to small push-button switches to create a much tidier control panel.

After several shows, these are still performing nicely. I am sure I would have needed to replace some if they were not protected by a CDU.

[kevinlms]

Nothing wrong with this for a probe, but why would the end get pitted?

 

Without a CDU, the end gets pitted because the sudden current drop through the motor's winding causes the magnetic field to collapse suddenly which generates a large back emf which causes the spark which pits the connection.

The CDU gives an initial burst of current which then drops very quickly. Once discharged, there is very little left so the back emf is very low & you only get a very tiny spark when pulling the probe away from a stud.

 

I used this theory to swap from stud & probe to small push-button switches to create a much tidier control panel.

After several shows, these are still performing nicely. I am sure I would have needed to replace some if they were not protected by a CDU.

Probably because I was using a diode matrix & switching both ends at once, on a set of storage loops and throwing up to 8 points at once. This required a large capacitor & the output was around 30-35 volts, using a suitably rated capacitor! If the probe was removed before the capacitor had fully discharged, you got a flash. It was never a problem & such a simple fix, I didn't investigate time on reducing the flash.

 

If only throwing a small number of points, then a more modest CDU would have done the job and no flashes.

[Ron Solly]

 

Some point switches are passing contact and unsuitable for use with a CDU. The problem being as you move the lever it first gives the motor pulse in the wrong direction, which discharges the CDU and then as the switch nears the far end of its travel it gives it a pulse in the correct direction, while the Capacitor is recharging. The only way around it is to pause part way through the movement to allow the CDU to recharge, which is pretty impractical.

I use stud and probe using a brass probe made from a ball point pen and the spring loaded contact from a domestic light fitting on dome head brass bolts, 

 

Peco passing contact switches are OK for use with a CDU but not the Hornby type which use the concept as mentioned above. Peco are internally different.  Good CDU's also recharge almost in an instant.