CDU capacitor size

[spikey]

All things being equal, would a bigger capacitor deliver more current to each of my solenoid motors, or just enable me to power more of them from the same source? I'm thinking of a separate (larger capacity) CDU to supply a fan of sidings, but am concerned lest that would give each solenoid a bigger belt and thereby perhaps introduce reliability issues.

Edited August 16, 2018 by spikey

[Jinty3f]

This thread may be useful........

http://www.rmweb.co.uk/community/index.php?/topic/100367-changing-capacitors-on-cdu-feasible-or-not/

[DCB]

All other things being equal a bigger capacitor gives a bigger belt to the solenoid.  It can rip the point blades out of the tie bar on Peco points and completely destroy hand built points. It also takes longer to recharge

 

If using it to power more solenoids at once you need to balance the load. My system using a diode matrix throws two three or four points at a time so  I have two dead loads which are simply two point motor coils so when just two points are to be thrown the two dead loads are also energised, If you don't balance the load you risk points not throwing when too many points are trying to throw or as previously stated  the point blades being knocked out of the tie bars when too few are thrown. 

 

Watch the voltage rating when changing Capacitors, they charge to the very peak of the applied voltage not the average.  I found out the hard way that they explode when over charged.  However I use big bulky 50 ish volt capacitors connected across my 16 volt nominal power unit for point motor operation through a diode matrix and electric pencil or rotary selector, matrix and push button, without a CDU and it works really well.  It was even better before the 24 volt transformer failed.

[kevinlms]

 

 It also takes longer to recharge

 

 

A decent CDU uses a transistor to recharge the capacitor quickly, then goes to trickle charge. So it should recharge the capacitor very quickly.

[Crosland]

A decent CDU uses a transistor to recharge the capacitor quickly, then goes to trickle charge. So it should recharge the capacitor very quickly.

 

The transistor circuit limits the charging current so actually slows it down, compared to simply connecting the cap across the supply (which DavidCBroad has stated he does in the past), but it protects the power supply. Having said that, you are correct that a well designed CDU with an adequate supply will recharge quickly.

 

Now, I wonder why DavidCBroad's transformer failed

[DCB]

The transistor circuit limits the charging current so actually slows it down, compared to simply connecting the cap across the supply (which DavidCBroad has stated he does in the past), but it protects the power supply. Having said that, you are correct that a well designed CDU with an adequate supply will recharge quickly.

 

Now, I wonder why DavidCBroad's transformer failed

Absolutely I connect a big capacitor across the transformer and throw up to six big meaty H&M point motors at a time, using a probe and stud system.  The failed transformer lacked any overload protection which wasn't very clever.

I have to count two seconds between between operating points to let the cap recharge as I have 4 separate diode matrixes fed by the same cap and stud probe set up.

Edited August 29, 2018 by DavidCBroad

[Crosland]

The failed transformer lacked any overload protection which wasn't very clever.

 

It's not the transformer that wasn't very clever!

 

A transformer, by definition, has no overload protection. See my answer in this thread http://www.rmweb.co.uk/community/index.php?/topic/137010-trouble-with-12v-transformers/