I need to add some wirewound resistor in series with a voltmeter to make it high range. I am converting the voltmeter from 300v FSD to 900v FSD.
As per my calculation the wattage should be 20W, but I am not getting only 10W resistors in market.

So my question is if I use the 10W resistors in place of 20W resistor, can I run it for a short duration?
If yes how much duration will be safe to run them ?
If I place a cooling FAN directly over the resistor will it help to extend the operating time ?
may be 5-10 second will be enough to complete the voltage measurement.

 

Use two 10W resistors in place of one 20W resistor.
You can put two in series (half the desired final resistance) or in parallel (two times the resistance).

 

Yes adding more resistors to make an equivalent resistor of desired wattage is possible, but that will make the unit bulky and cost will be 4 times. I can do that too, but I am just wandering how about running them for few seconds only to do the measurement and then let them cool down for 30 min before taking another measurement.

 

Why do they have to be wirewound?

 

I need to add some wirewound resistor in series with a voltmeter to make it high range. I am converting the voltmeter from 300v FSD to 900v FSD.
As per my calculation the wattage should be 20W, but I am not getting only 10W resistors in market.

So my question is if I use the 10W resistors in place of 20W resistor, can I run it for a short duration?
If yes how much duration will be safe to run them ?
If I place a cooling FAN directly over the resistor will it help to extend the operating time ?
may be 5-10 second will be enough to complete the voltage measurement.

So you're trying to drop 600V across the resistor, but what current is the meter taking, that way you can work out what Wattage you need?