Demonstration Cell - Variable Spacing Plate Cell

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scrs need a circuit to turn them off 

with the circuit shown in the diagram the circuit will turn on  and will stay on until the voltage goes back to zero again  which makes the circuit absolutly useless cause your doing the exact samething with the bridge rectifer without the circuit

their  are numerous ways to turn scrs off some are resonant turn off, commutation or reverse biasing the gate pin of the scr  crow baring  the possibilites  are endless  thats why their is no diagram of the scr network card

the circuit  card shows 4 opto coupler so their are more than likely  more than one scr  so the circuit  could be a  phase angle latching circuit

i have 7 phonebook size books on scr type circuit   none of the ones in the books

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yes there was four opto's,but there was only one hooked up to the circuit.
The other three weren't hooked up,just mounted on the board
Don

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were their 3 stud mounted diodes

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no,there was only one stud mounted diode on a heat sink in the left rear corner of the box beside the scr on it's own heat sink
Don

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the unit will not work  as described in the schematic that much is definate the scr will stay latched open till cycle ends

any form of scr turn of circuit needs at least 2 scr to turn off  when you wanted it to   

or  the unit would have to have 2 optocouplers hooked up  to one to turn on scr and one to reverse bias the gate turning scr off   making the scr  into  a GTO thyristor

the only other way is to crowbar from positive to negative which will blow that little scr to hell

my quess is some one took something out of the box 

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from what i thought i understood about scr is they need a  second scr to fire  as they call it back to back in order to shut a scr off in a standard load (amps)  from what i understand is one must drop current to turn off a scr ?so if there were enough impeadance in a coil would it not be able to shut it self off due to the fact the coil it is apply power to restrics current?

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the back to back method you mentioned is called inverse parralell    that circuit will not turn off with out forced commutation

yes outlaw the circuit will not turn off because of the retricted amp flow   also back emf will keep it latched open 

 the circuit would have probably some type of snubber   a large elctrolytic capacitor  and resistor  if it is only using one scr

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So Dudley , what is the basic goal of that scr , to gate properly and to not interfere and cut a off beat wave ?

What did your circuit do anyways ,what was its purpose in detail plz ?

You said something about the voltage reaching zero , is there a  problem with that ?

Did you connect the  bifilar as shown in the diagram ? The 'scalar' type bifilar .