Help with capacitor discharge units

[TEAMYAKIMA]

I have this capacitor discharge unit. I can't remember what brand it is.

 

 

At times I need to fire 4 PECO point motors at once and this just doesn't cope. Where can I obtain a more powerful unit?

[Dagworth]

Looks like you could add another pair of capacitors to this one.

 

Andi

[Andy Hayter]

https://www.ebay.co.uk/itm/363141050083?hash=item548ce4aee3:g:bowAAOSw0WFjuE~F&amdata=enc%3AAQAHAAAAsLfKf8N4abqeOzoOgAZgv6S3hUWkkLU%2FU2UNB5%2FXCYYsMMOp7NiRFQJ%2FwUHv9jqbkhDUco7UBcGE0Vg%2BHpYq%2FlaCPRnBxxmn5DRfov0wzlogZybd5DMBMc8kTvrELPQ2%2BOZJ1YNjRiGaVC%2BAQHA2iiEH0NIRctRVKdLss0ZsJNpJ2U%2FN7NGMKOUGhqtJ7e4raWVq2L7msl04R961P4Qfej7OAUfc4IY0inu9RCN0rAvk|tkp%3ABk9SR5K449fMYQ

 

claims to fire up to 6 points.

I have not used one of these so cannot vouch for it and I am pretty sure mine was a high power Gaugemaster which seems to be no longer available.  But it was bought a long time ago so perhaps no surprise.

[Michael Hodgson]

I am wary of trying to fire too many (more than 2 or 3) solenoids simultaneously from one CDU by feeding them in parallel, perhaps through a diode matrix.  The problem is that although the solenoids are supposed to identical, there are slight difference because of manufacturing tolerances, so one offers marginally less resistance than the next.  So more of the power goes through that one than the others, and in my experience it becomes a reliability problem once you reach about 4 or 5 point motors at the same time.

 

You can overcome this to some extent by increasing the capacitance, or the voltage*, but because the result is that the point goes over more forcefuly to the point that it sounds like a rifle shot and will do mechanical damage to the point in time.

 

I realise this is perhaps not what you want to hear if you've already wired it, but a better solution is to have several separate CDUs each driving one one or two points.

 

One detail that may be more helpful to you with your particular setup is to check whether you have removed the over centre spring on Peco points.  These are there so that a point naturally sits at one or pother position rather than sitting somewhere in the middle).   It is usually recommended that they be removed for CDU operation, as the spring resists  the throw and if the solenoid doesn't generate quite enough kick, the point bounces back to where it already was. 

 

* the voltage must not be increased beyond the rating of the capacitor, and you need a pretty big margin if the supply is rectified AC as commonly used, because the peak voltage of AC is quite a bit higher than the RMS (=average) voltage.  I would use capacitors rated at 25v if I was using a 12 v supply or 35v if I was using 16v AC.

[Dagworth]

50 minutes ago, Michael Hodgson said:

It is usually recommended that they be removed for CDU operation, as the spring resists  the throw and if the solenoid doesn't generate quite enough kick, the point bounces back to where it already was. 

I'm afraid I have to disagree here. Remove the spring for servo/slow action/stall motors yes, these have sufficient resistance at the end of the throw to keep the switches against the stock rails but with solenoid motors there is no pressure once the motor has thrown and they will wander and cause derailments without the spring.

 

Andi

[Michael Hodgson]

5 minutes ago, Dagworth said:

 with solenoid motors there is no pressure once the motor has thrown and they will wander and cause derailments without the spring.

 

Andi

Sorry, yes the OP did say Peco point motors, which lack a spring. 

My Seep solenoid motors do have a spring which causes them latch.

The over centre springs in Peco points can be very stiff requiring more force to throw them.

[Dagworth]

1 minute ago, Michael Hodgson said:

The over centre springs in Peco points can be very stiff requiring more force to throw them.

The older Peco points were adjustable in that the spring cover could be moved closer or further from the tie-bar to change the tension but the newer versions have the spring underneath where it can't be adjusted (or changed/replaced if it fails once laid) which is a step backwards IMHO

 

Andi

[Pete the Elaner]

I build my own & have used this as a soldering exercise at the club. I provided one to another layout group who were struggling with their Peco CDU which seemed a bit gutless & they were well pleased with 1 of mine.
I have more components than I need (especially capacitors) so maybe I could build some with double capacitors for you or maybe you can simply use 2 CDUs in parallel?

[TEAMYAKIMA]

Hello 'Pete'

 

I'll email you about that.

 

BW

 

Paul

[DCB]

I don't have trouble throwing the points, up to 6 at a time.  But if only 2 are thrown by the CDU then the force can rip the point blades from the tie bar.   My work around is a couple of spare point motor solenoid coils wired in to the Diode Matrix so if only 2 points are to be changed then two spare coils are energised as well. Its worked with no problems for over 30 years    I tend to use 44 volt capacitors charged by 24 volts max, as the 12 volt caps can blow up spectacularly when used on nominal 12 volts which can turn out to be actually 20 volts plus  on some common controllers like the H&M Duette.

Edited February 23, 2023 by DCB
Tpyo

[DavidB-AU]

Can you get a clear photo of the markings on the capacitors and the track side of the board? It might be possible to replace them with something larger or put more in parallel in the spare spots.

 

Another relatively cheap option is to build a new CDU yourself. They are not hard to build.

 

As mentioned above, when being charged on AC it's important to note that the nominal 12V is 12V RMS and the peak voltage is about 17V. Whatever input voltage is used, the capacitor needs to be rated for at least 1.4 times the AC input voltage plus another 10% margin then rounded up to at least the next available voltage rating.

[TEAMYAKIMA]

7 hours ago, DCB said:

I don't have trouble throwing the points, up to 6 at a time.  But if only 2 are thrown by the CDU then the force can rip the point blades from the tie bar. 

6 hours ago, DavidB-AU said:

Can you get a clear photo of the markings on the capacitors and the track side of the board? It might be possible to replace them with something larger or put more in parallel in the spare spots.

 

Thank you both for your input. I have received an offer of a self-build which I have gratefully accepted - job done, but thank you for your interest in my problem.

[Crosland]

If the capacitors are rated high enough then you get more bang for your buck by increasing the voltage.

[Bino]

Great advice here.

 

If I may, I have a related question. How many solenoid point motors can be fed through a Gaugemaster CDU? I have approx 30 points. Do I need more than one CDU?

[smokebox]

You only need 1 CDU, no matter how many points you have.  Only the points that are being operated take any power.