Is resistor realy have voltage rating?
Based on power rating, a 2M2 1/8W resistor working on 300Vdc isn't exceeding their power rating, its only 41mW dissipation, so, why a resistor has its own voltage rating whether the power rating not exceeded?
Any corellation with noise performance?
Different type and/or manufacturer has different nominal voltage rating?
or I can use whatever type and/or manufacture with the same power rating?
I'll be back later, working time...
Thx folks...
Based on power rating, a 2M2 1/8W resistor working on 300Vdc isn't exceeding their power rating, its only 41mW dissipation, so, why a resistor has its own voltage rating whether the power rating not exceeded?
Any corellation with noise performance?
Different type and/or manufacturer has different nominal voltage rating?
or I can use whatever type and/or manufacture with the same power rating?
I'll be back later, working time...
Thx folks...
also many resistors can tolerate considerable "surge" - dynamic peak power over their continuous power rating but as pointed out could still fail due to over Voltage
power related failures likely will result in an open, over voltage failures permit huge currents during arcing, and may result in permanently lower resistance due to carbon tracking after the overvoltage is gone
the difference can be critical in a safety analysis
power related failures likely will result in an open, over voltage failures permit huge currents during arcing, and may result in permanently lower resistance due to carbon tracking after the overvoltage is gone
the difference can be critical in a safety analysis
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Just think about a resistor where R= infinity.
The package, construction, and surface (paint?) finish will sensibly have a maximum working voltage before breakdown, arcing etc, as already mentioned. This obviously has nothing to do with power dissipation as there isn't any!
So that rating is for the package / construction and becomes moot as the resistance value falls to where Pd becomes real.
Cliff
COnsider that film resistors are made as a helical stripe around a ceramic form. (or other insulating material) Like the stripes around a baber pole.
The current flows through that stripe. Each turn of the stripe finds itself next to the previous turn and the following turn. As voltage drops along the length of the resistive stripe, a potential difference exists between the adjacent turns. The space between them is tiny. If the voltages across the resistor are high enough, there can be arcs between the turns.
The current flows through that stripe. Each turn of the stripe finds itself next to the previous turn and the following turn. As voltage drops along the length of the resistive stripe, a potential difference exists between the adjacent turns. The space between them is tiny. If the voltages across the resistor are high enough, there can be arcs between the turns.
An externally hosted image should be here but it was not working when we last tested it.
you mean like that helix line?
well, any suggestion for the voltage rating per watt package?
I mean in general, I don't know who is the manufacturer though...
I've been read in ESP website that for safety, max operating voltage of 75V for 1/4W Resistor and 150V for 1/2W.
Am I can safely use that terms for any manufacturer?
Resistors do have a voltage rating... I have seen countless failures due to this in commercial equipment. Switch mode PSU's often have high value start up resistors, and these are a classic failure item.
On the basis of power dissipated only, they were well within their limits.
Yes, and therefore the best way is to perform a serial connecting of several 1W resistors (I prefer 6 pieces in series. Now each resistor works with arround 50-55 volts).
The reason for failures after a certainly time of use is a chemical decomposition of the resistor material by the emergence of a blue corona, when using only one normal (not special made for high voltage) resistor (and not an overload due to overheating).
In darker surroundings this corona is sometimes visible, especially in the case of high humidity and the use of one very small resistor version (like the below link, last pic, but much less pronounced).
http://www.celnav.de/hv/hv4.htm
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The voltage limitation on resistors can be overcome in a similar manner as with electrolytic capacitors - just put multiple units in series, adjusting the values to yield the required total effective ohms or volts. For example, three 1-megohm resistors in series gives the same 3M resistance as a single 3M resistor, but at three times the rated voltage as the single resistor. Added benefit of the wattage rating of the string also being multiplied by the number of resistors...
Bud
Bud
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