Using Zener Diode for Control Voltage?

[jevs]

Is there anything negative about using a Zener diode off your motor supply voltage to supply voltage for the Control? I am using R90H drives. I can have another tap on my power transformer to make a 24 Volt supply for the controller, but in the instructions it says it is fine to just use a zener to jump over from the Motor supply voltage. Just wondering if anyone used the zener diode method and if there is any drawbacks. Like I will probobly kill the motor voltage with the Estop, which would also kill the control voltage then. Any probolem with this? The zener diode is just simpler to me than making yet another DC supply.

Thanks

[Al_The_Man]

Originally Posted by jevs Is there anything negative about using a Zener diode Thanks

Only if you are using NEGATIVE voltage

Seriously, I have used zener supplies in some applications, The draw back is if the current varies greatly, then there is a lot of wasted energy across the high wattage resister required, you have to design the resistor required for the maximum load, in other words the load at max. will drop the voltage required and the zener will be hardly conducting, but at minimum current the zener will be conducting and dropping the required voltage across the series resitor, this can result in high wattage resistors and high wattage zener.
Only working the required numbers will tell you if it is feasable.
Al

[ViperTX]

Is the Zener wired in series? If so then it's just being used to drop the voltage to the controller by the value of the zener.

[Al_The_Man]

Originally Posted by ViperTX Is the Zener wired in series? If so then it's just being used to drop the voltage to the controller by the value of the zener.

How would that work? surely if the load in series with the zener the voltage would be constant across the zener but the load voltage would vary?
I have always used them parallel to the load.
Al

[jevs]

The zener diode should only conduct as much current as the controller pulls across it. It shouldn't really vary much. All your doing is parralelling it off the voltage feeding the motor input. The current through the diode shouldn't have anything to do with the current the motors are pulling. I don't see any reason you need a high wattage resistor or zener. Just a regular little zener should work. This thing probobly needs 100 mA or less. I am going to call Rutex and ask them.

[Al_The_Man]

You didn't explain sufficiently to give a qualified answer, it depends on the max. current you want to draw, what voltage you are coming from and going to, it is simple ohms law once you know the parameters you are working with.
Al

[jevs]

I just talked to the Rutex guy and he recommends using a seperate 24 Volt supply. The drives draw approximatly 300 mA each. This would put the zener needed at kind of a hard value to find and also he said this would eliminate possible "intereference" problems, so I am just going to locate a 24 Volt supply that can put out an amp or 2. Should be easy to find.

Thanks

[ViperTX]

So, the way this works is: Let's say you have a 24 volt power supply and also need a low current 12 VDC supply, you would take the 24 volt supply connect the cathode of a zener to it and then you could use the anode side as your 12 VDC supply. It is only a simple solution for very low current applications (zener diodes are usually of fairly low wattage) and allows you to have 2 output voltages from a single source.

[Al_The_Man]

I take it you are calling for the load to be placed on the anode I do not see how that will work. there will not necessarily be 12v from anode to ground.
Al