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I've been working on a voltage divider circuit that will hopefully allow me to measure voltages between 0-60 kV DC (80 W) as 0-889 volts DC.

The voltage divider section that is used to measure the voltage is circled in red, the rest of the circuit is included to show the other components in the circuit:

enter image description here

The R2 is rated for 65 kV and 60 W (nominal) while the R1 is rated for 17 W (nominal). The multimeter, of course, is able to handle 1000 V nominal (4 kV peak).

My primary concern is with the power ratings of the resistors. Are the resistor power ratings high enough for the circuit?

Also, how much power would be dissipated by the R1 and R2 resistors?

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    \$\begingroup\$ You work with 60kV and don't know how to calculate the power dissipation in a resistor? I hope I misunderstand your question, otherwise I'd strongly advise not to work with lethal voltages. \$\endgroup\$
    – Huisman
    Commented Dec 7, 2019 at 21:37
  • \$\begingroup\$ I'm not working with it, I'm just setting up the resistors. \$\endgroup\$
    – James Li
    Commented Dec 7, 2019 at 21:41
  • \$\begingroup\$ @Huisman Purchasing them, that is \$\endgroup\$
    – James Li
    Commented Dec 7, 2019 at 21:42
  • \$\begingroup\$ I read your profile: with regards to experience being a hard teacher: don't get taught by 60kV. \$\endgroup\$
    – Huisman
    Commented Dec 7, 2019 at 21:55
  • \$\begingroup\$ But to help you on the way gaining knowledge (which i think is to not provide a direct answer): In case of no load, all current will run through R4, R2 and R1. That will give the highest power dissipation in R2 and R1. Also, the highest output voltage (60 kV) will give the highest dissipation. So, apply Ohm's law and find the voltage and current per resistor and calculate the dissipation. \$\endgroup\$
    – Huisman
    Commented Dec 7, 2019 at 21:57

1 Answer 1

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Since the resistance of the load is unknown, exact calculations cannot be made. However, as a matter of safety, it is reasonable to assume that all of the voltage (60 kV) will be dropped across R2 since it is much larger than R1 and R4. Using Ohm's law, it is easy to calculate that R2 will dissipate 300 watts. Clearly then, your proposed resistor is severely underrated. R1, on the other hand, has about 890 volts across it and will dissipate only 4.4 watts. R4 is probably OK as it has a smaller value than R1 and 6 times the power rating. We would need to know the load resistance to be sure.

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  • \$\begingroup\$ In this situation, worst case is bound to happen at least once... So I would go with this answer. \$\endgroup\$
    – MadHatter
    Commented Dec 8, 2019 at 19:02

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