Jump to content
 

Capacitor discharge unit - wiring instructions?


TEAMYAKIMA
 Share

Recommended Posts

I've found a very old ECM capacitor discharge unit which might solve a problem I have with a very stiff device operated by a PECO point motor.

 

The instructions are long gone. It has one set of terminals marked something like ' power in - 24v AC max '

 

post-4476-0-56234400-1515677912_thumb.jpg

 

It's 30 odd years since I've used one of these and TBH I'm ashamed to say that I'm not sure how to wire this in, can someone remind me please?

Edited by TEAMYAKIMA
Link to post
Share on other sites

  • RMweb Premium

After 30 years that capacitor will be well down in performance at best. If it is clear how to connect it to the board, a replacement is advised. They dry out and at best lose their capacitance at worst become a short circuit.

Link to post
Share on other sites

  • RMweb Premium

It looks like the capacitor itself has been disconnected.

The AC supply should go the the power in sockets & the other terminals should connect across the motor/switch.

 

Having worked out exactly how a CDU works, I would not operate a solenoid motor without one again.

Here's the typical wiring diagram of a CDU kit.

 

http://www.talkingelectronics.com/projects/CDU-2/CDU-2.html

 

A couple of differences to OP's version. The two wires directly from OP's capacitor are definitely wrong, as OP's bypasses the output diode. I wonder why?

 

This circuit uses 4 low wattage resistors at a higher resistance, compared to your single higher wattage resistor. It of little consequence either way.

 

The explanation is quite could and accurate, but take note in regard the voltage rating of the capacitor(s). This is very important.

This kit is available (from Australia - so may not be worth it for you), or buy a new one, as previously suggested.

Edited by kevinlms
Link to post
Share on other sites

Here's the typical wiring diagram of a CDU kit.

 

http://www.talkingelectronics.com/projects/CDU-2/CDU-2.html

 

A couple of differences to OP's version. The two wires directly from OP's capacitor are definitely wrong, as OP's bypasses the output diode. I wonder why?

 

This circuit uses 4 low wattage resistors at a higher resistance, compared to your single higher wattage resistor. It of little consequence either way.

 

The explanation is quite could and accurate, but take note in regard the voltage rating of the capacitor(s). This is very important.

This kit is available (from Australia - so may not be worth it for you), or buy a new one, as previously suggested.

I suspect that at some time it's possible a second capacitor was connected across the existing one to give a bigger pulse to the solenoid or solenoids.

Link to post
Share on other sites

It looks like someone has disconnected the Capacitor from the PCB and  and simply used the Capacitor to operate the point motors.

 

These Capacitors are polarity conscious and go bang and spray nasty yellow liquid if over charged (yes I did it)  or shorted out so be careful.

 

I just connect a Capacitor across the 12 volt DC uncontrolled output of a transformer, positive to positive etc  and use it to power the point motors via a push button however the Cap does need to be at least twice the rated voltage of the Transformers 12 volt DC output as the "12 volt" output is often a lot more than 12 volt off load and can overcharge a Cap quite easily.   I find 24 volts provides a bit of a safety margin.

I used them 40 years ago on my Triumph and Ariel motorcycles to provide a battery free electrical system, again using 24 volt caps as the proper Lucas 12 volt items were prone to explode.

Link to post
Share on other sites

  • RMweb Premium

It looks like someone has disconnected the Capacitor from the PCB and  and simply used the Capacitor to operate the point motors.

 

These Capacitors are polarity conscious and go bang and spray nasty yellow liquid if over charged (yes I did it)  or shorted out so be careful.

 

I just connect a Capacitor across the 12 volt DC uncontrolled output of a transformer, positive to positive etc  and use it to power the point motors via a push button however the Cap does need to be at least twice the rated voltage of the Transformers 12 volt DC output as the "12 volt" output is often a lot more than 12 volt off load and can overcharge a Cap quite easily.   I find 24 volts provides a bit of a safety margin.

I used them 40 years ago on my Triumph and Ariel motorcycles to provide a battery free electrical system, again using 24 volt caps as the proper Lucas 12 volt items were prone to explode.

But simply putting a capacitor across a DC supply, doesn't turn the solenoid off if the switch (or whatever means to control) fails. The diodes & transistor are there for a reason.

Edited by kevinlms
Link to post
Share on other sites

I just connect a Capacitor across the 12 volt DC uncontrolled output of a transformer, positive to positive etc  and use it to power the point motors via a push button however the Cap does need to be at least twice the rated voltage of the Transformers 12 volt DC output as the "12 volt" output is often a lot more than 12 volt off load and can overcharge a Cap quite easily.  

 

Yes, we know that you do all sorts of things that should never be recommended to others.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...