If the fault is in the constant current section, use a resistor and a transistor that gets activated when the voltage drops below a certain value. This way you will have a 20v range and the LED will still work.

 

If these things blow up in the field, which they will, you could easily be up for $250 to field-replace each one and you will be bankrupt in a month.
As I said in the beginning, you have diode junctions across 24v and the surface mount transistors can fail at any time due to a spike in voltage. It only takes a microsecond to voltage-fail. It takes a lot longer to current-fail.
The transistors are obsolete - and no wonder. They proved to be failures.
You need some sort of current limiting resistors to at-least prevent instant failures. You can't expect 5v to 24v with simple current limiting but certainly 12v to 24v can be achieved with protection resistors.

 

There is nothing really wrong with the constant current circuit the the manufacturer has in the drive as far as I can see. If there was a problem, the other inputs would pop too. As it is only the one input, I suspect it is a large spike, maybe induced from another cable running against the signal wire. That is why I reckon a tranzorb is needed to clip the spike.
There are not just a couple of diode junctions across 24V.

 

Hi Lafaver14,
Do you have page 7 of the schematic so we can see the connections to the PLC ?
I do not agree with Colin55's comments.

Les.

 

This is just rubbish:
There is nothing really wrong with the constant current circuit the the manufacturer has in the drive as far as I can see. If there was a problem, the other inputs would pop too. As it is only the one input, I suspect it is a large spike, maybe induced from another cable running against the signal wire. That is why I reckon a tranzorb is needed to clip the spike.
How is a tranzorb going to be faster than a transistor?

"There are not just a couple of diode junctions across 24V."
Oh ?????

 

The constant current driver circuit is designed for when you have no control over the input voltage.
Since this is a fixed application with known 24V drive, I would simply replace the driver circuit with a 1kΩ series resistor.

If you must insist on wanting to use the driver circuit, then install a 470Ω resistor in series with the 24V input.

 

Hi Lafaver14,
Do you have page 7 of the schematic so we can see the connections to the PLC ?
I do not agree with Colin55's comments.

Les.

No problem - attached

 

Why would the voltage spikes be so inconsistent? This is what makes me feel like we are over amping (cooking) the drive after running for a while. The only thing that scratches my theory is that we put a 1amp fuse before the direction input.

Also, you guys can hopefully help me understand why over voltage is ONLY damaging the direction input?

 

Hi Lafaver14,
The signal labels do not seem to match up between the page showing the stepper driver an the PLC outputs on sheet 7 that you have posted in post #27


Signal Stepper input Page 7
Clock From P7 Y2 Y0 (Y2 on sheet 7 No signal name shown.)
Direction From P7 Y10 (Y10 on sheet 7 is marked Work lights)

I have noticed that there seems to be two +24 volts supplies. +24 and Safe +24 As we can only see part of the full wiring diagram I don't know if they are seperate supplies or if the Safe +24 comes from the +24 via relay contacts etc. If this is the case if the Safe +24 is supplying some inductive load when the contacts open it could pulse to a high voltage causing the damage. One think I have noticed is that the most significant digit of the three digit number on the left hand side seems to correspond with the sheet number. Am I correct ? If I am the sheet that you posted in post #27 is sheet 6 instead of sheet 7.
If you cant find the real cause of the problem then a workround may be connect a 24 volt zener diode (1 Watt.) between the - and + 24 volt direction inputs And put a 470 ohm resistor in series with the + direction input signal. Any voltage spike above 24 volts would then be across the resistor. The constsnt current input circuit would still give the same drive current through the LED in the opto isolator.

Les.

 

Hi Lafaver14,
The signal labels do not seem to match up between the page showing the stepper driver an the PLC outputs on sheet 7 that you have posted in post #27

.

Yes, I noted that in #6 but no answer!
Max.

 

Sorry Max,
I had forgotten that comment. At the time I trying to see if there was any sense in Colin55's comments about the constant current LED driver circuit. It would be a great help if we had the FULL schematic rather than just parts.

Les.

 

Adding a 470R in the 24v is doing exactly what I suggested in the first place. Remove the diode junctions from the supply. The resistor is simply a "safety resistor" and reduces the high current to save the transistors.

 

Just curious but in your installation does the stepper motor ever get mechanically back-driven by the machinery? I have seen that blow drivers. Driving a stepper through it's shaft can generate voltages way beyond what a lot of designers put in for protection.