Hi
What is the right value of resistor required to protect high voltage power supply rated up to 11kv. To protect it from no load. In the same time not to effect the power on the output load.
Thanks

 

Voltage bleed resistors are usually not there to protect the supply, but to protect humans that come into contact with it when it is powered down. They do this by providing a discharge path for the output capacitors (I'm assuming your are talking about a HVDC supply, right?).

With that in mind, what considerations do you think would impose minimum and maximum values on the size of the resistors used?

If you are talking about a different purpose for this bleeder resistor, you really need to provide a lot more detail before we can possibly help you.

 

Thanks for the reply.
Yes it is HVDC.
This device for plasma generator , some times the vacuum goes lower and the plasma stops working(this is normal) . To protect the HVDC from no load . I was thinking about 100m ohm 10w resistors ( 10m ohm x10 1w). Maybe this enough? Some devices have no load protection. But I don't trust the Chinese devices too much.

 

I don't have experience with so high voltages but 11kV (max) at 100MOhm is 1mA of current.. the capacitor of the supply will take like forever to discharge... ?!

 

Bleeder resistors would not be a good choice to protect against a possible but rare over-voltage condition, because the simple bleeder resistor would need to impose a major load on the supply during all of the non-over-voltage operation.
So there are two questions: How much of an over-voltage is possible, and how much over voltage would cause any damage??

One scheme that will not detract from normal operation would be a spark gap in series with a load resistor to avoid any short-circuit damage to the high voltage source. The spark gap would be set to break down at a bit over the acceptable working voltage, and the resistor would be sized to pull the supply voltage to some value below 11 KV. The power rating of the resistor will need to exceed the output power capability of the high voltage supply.

A second scheme would be to make the high voltage system able to withstand it's no-load voltage level.