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U Kaz
02/10/06 01:39
Read: 581 times
United Kingdom

#109678 - thankyou
Responding to: Andy Neil's previous message
Andy Neil said:

Use a relay with a 24V AC coil, connected to the transformer output (before the recfifier).
Then as soon as the mains goes off, the 24V AC goes off, and the relay disconnects the DC out.

You could have a little light connected across the capacitors - that would warn that they still have charge even though the load is off, and would also gently discharge the capacitors!

Fantastic, thankyou so much for the solution recommendation,

Kia Klaas said:

The very simplest methode would be to have a resistor permanently connected across storage cap

I will try this one as well, thanks Kia, what sort of resisitor value are we talking about here???

Kia Klaas said:

How long may the fall down of potential last? Why is a fast fall down needed at all?

At the moment it takes around 20 seconds for capacitors to discharge and I would like to do it in max 1 second, the reason I want to do is that I am using a micro PLC unit to control different motors, one of them is AC and one is DC, both motors are switched on using relays, I have emergency stop connected to mains in, so when I disconnect the main in by pressing emergency stop , the AC motor stops as emergency stops cuts the power to motor BUT relay is still connected via PLC which then takes 4 seconds to go dead and in case some one release the emergency stop during those 4 seconds the PLC stays alive and motor starts again, so emergency stop is not really acting like emergecny stop.

So I think if I cut the O/P of capacitor as well with emergency stop as you said below then I think it should be OK,

Kia Klaas said:

A good methode would be to combine the turn-off of power supply with the turn-off of motor by additional soft- or hardware: When you want to turn-off the power supply, first turn-off the motor. Then there will be no further current flow and the power supply to motor can be disconnected without sparking.
Turning-off power supply should turn-off both, (a) mains from primary side of transfomer and (b) connection between storage cap and motor. Use two separate relays for this.

Sounds like brilliant solution,

Kia Klaas said:

Also, do you already need a soft start, when switching the transformer to mains? I guess so.

At the moment I am switching transformer stright from the mains with no additional device, how can I acheive soft start, I guess I have to use soft cap for that ? Am I right? Please suggest.

Thank you very much all


List of 19 messages in thread
Discharging capacitors?      U Kaz      02/09/06 09:17      
   sorry I missed that..      U Kaz      02/09/06 09:35      
   many versions have been implemented      Erik Malund      02/09/06 09:40      
      Simplest        Andy Neil      02/09/06 09:55      
         Alternatively...      Hal Albach      02/09/06 12:23      
            Switch      Andy Neil      02/09/06 12:32      
         thankyou      U Kaz      02/10/06 01:39      
            Emergency stop      Per Guldmann      02/13/06 10:21      
            Soft start      Kai Klaas      02/13/06 19:34      
   Combine        Kai Klaas      02/09/06 19:46      
      if it has to be done the right wa      Erik Malund      02/10/06 06:36      
         SPS?      Kai Klaas      02/10/06 07:25      
            if a SPS is a switching power supply - y      Erik Malund      02/10/06 08:13      
      resistor value ??      U Kaz      02/13/06 08:53      
         DIY      Steve M. Taylor      02/13/06 17:02      
            Hmm...      Kai Klaas      02/14/06 20:11      
               the crux      Erik Malund      02/15/06 06:19      
   check current rating of capacitors ...      Frieder Ferlemann      02/13/06 09:13      
      search      Saif Ullah Khalid      02/14/06 09:13      

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