Mixing
Difference between [W] and [WS] power rating of resistors
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I see some datasheets of power resistors where power ratings are in Watts [W] and some in [WS] which I don't know what they mean.
What is the difference between them?
Example of datasheet
Some screenshots from datasheets:
power resistors datasheet ratings
asked 3 hours ago
Chupacabras
3,65421034
 |Â
show 3 more comments
up vote
4
down vote
favorite
I see some datasheets of power resistors where power ratings are in Watts [W] and some in [WS] which I don't know what they mean.
What is the difference between them?
Example of datasheet
Some screenshots from datasheets:
power resistors datasheet ratings
asked 3 hours ago
Chupacabras
3,65421034
Perhaps "small"? i.e. the physical size is the same as the next rating down.
– Tom Carpenter
2 hours ago
@TomCarpenter Size is size, and power rating is power rating. Why to mix it together?
– Chupacabras
2 hours ago
2
I suspect Watt-seconds. I.e., you can give it 1/4W continuously, or you can blast it with 10W for 1/20th of a second.
– TimWescott
2 hours ago
Not sure, other that many resistors from different manufacturers for a given power rating are similar in size. So it's plausible.
– Tom Carpenter
2 hours ago
@Chupacabras - I believe most Wattage sizes are "standard"/common. Same goes for SMD resistors. But they are only conventions and plenty break the mold.
– Bort
2 hours ago
 |Â
show 3 more comments
up vote
4
down vote
favorite
up vote
4
down vote
favorite
I see some datasheets of power resistors where power ratings are in Watts [W] and some in [WS] which I don't know what they mean.
What is the difference between them?
Example of datasheet
Some screenshots from datasheets:
power resistors datasheet ratings
asked 3 hours ago
Chupacabras
3,65421034
I see some datasheets of power resistors where power ratings are in Watts [W] and some in [WS] which I don't know what they mean.
What is the difference between them?
Example of datasheet
Some screenshots from datasheets:
power resistors datasheet ratings
power resistors datasheet ratings
asked 3 hours ago
Chupacabras
3,65421034
asked 3 hours ago
Chupacabras
3,65421034
asked 3 hours ago
Chupacabras
3,65421034
asked 3 hours ago
Chupacabras
3,65421034
asked 3 hours ago
Chupacabras
3,65421034
3,65421034
Perhaps "small"? i.e. the physical size is the same as the next rating down.
– Tom Carpenter
2 hours ago
@TomCarpenter Size is size, and power rating is power rating. Why to mix it together?
– Chupacabras
2 hours ago
2
I suspect Watt-seconds. I.e., you can give it 1/4W continuously, or you can blast it with 10W for 1/20th of a second.
– TimWescott
2 hours ago
Not sure, other that many resistors from different manufacturers for a given power rating are similar in size. So it's plausible.
– Tom Carpenter
2 hours ago
@Chupacabras - I believe most Wattage sizes are "standard"/common. Same goes for SMD resistors. But they are only conventions and plenty break the mold.
– Bort
2 hours ago
 |Â
show 3 more comments
Perhaps "small"? i.e. the physical size is the same as the next rating down.
– Tom Carpenter
2 hours ago
@TomCarpenter Size is size, and power rating is power rating. Why to mix it together?
– Chupacabras
2 hours ago
2
I suspect Watt-seconds. I.e., you can give it 1/4W continuously, or you can blast it with 10W for 1/20th of a second.
– TimWescott
2 hours ago
Not sure, other that many resistors from different manufacturers for a given power rating are similar in size. So it's plausible.
– Tom Carpenter
2 hours ago
@Chupacabras - I believe most Wattage sizes are "standard"/common. Same goes for SMD resistors. But they are only conventions and plenty break the mold.
– Bort
2 hours ago
Perhaps "small"? i.e. the physical size is the same as the next rating down.
– Tom Carpenter
2 hours ago
Perhaps "small"? i.e. the physical size is the same as the next rating down.
– Tom Carpenter
2 hours ago
@TomCarpenter Size is size, and power rating is power rating. Why to mix it together?
– Chupacabras
2 hours ago
@TomCarpenter Size is size, and power rating is power rating. Why to mix it together?
– Chupacabras
2 hours ago
2
2
I suspect Watt-seconds. I.e., you can give it 1/4W continuously, or you can blast it with 10W for 1/20th of a second.
– TimWescott
2 hours ago
I suspect Watt-seconds. I.e., you can give it 1/4W continuously, or you can blast it with 10W for 1/20th of a second.
– TimWescott
2 hours ago
Not sure, other that many resistors from different manufacturers for a given power rating are similar in size. So it's plausible.
– Tom Carpenter
2 hours ago
Not sure, other that many resistors from different manufacturers for a given power rating are similar in size. So it's plausible.
– Tom Carpenter
2 hours ago
@Chupacabras - I believe most Wattage sizes are "standard"/common. Same goes for SMD resistors. But they are only conventions and plenty break the mold.
– Bort
2 hours ago
@Chupacabras - I believe most Wattage sizes are "standard"/common. Same goes for SMD resistors. But they are only conventions and plenty break the mold.
– Bort
2 hours ago
 |Â
show 3 more comments
2 Answers
2
active
oldest
votes
up vote
2
down vote
TL;DR; It's my thinking that the S is simply relating to the package being smaller.
Resistors from different manufacturers for a given power rating tend to be similar in size - the power rating effectively becomes a de facto way of identifying package size and vice versa.
As such it's plausible that they are using the prefix S to indicate that it is the higher rated resistor, but with the physical size of the next power rating down. If you go through all of the tables in your question, you'll find this holds true.
To back this up, if for example you take the SR Passives example, the part number for say a 1k 0.25W resistor differs between "CF1/4WS-1K" for the smaller package 3.2mm long package, and "CF1/4W-1K" for the larger 6mm long package. Both resistors are rated for 1/4W.
If you look at the Tecla & Chiara example, they seem to separate the two in a similar way - the ones without the S suffix are under the label "MF", and those with the suffix are under the label "MFS", which are likely the series names.
If it were representing an energy - Watt-seconds as suggested - then it would be Ws, not WS per SI unit capitalisation. I could understand if one failed to make this distinction, but the fact that three fail makes me highly sceptical. As a specification it also doesn't make much sense without context.
For example, could I run a 1Ω "2WS" resistor with 500V across it for 2ms? That would not exceed 2 Watt-second, nor exceed the voltage rating, however it would result in a 500A surge through the resistor. Is this allowed? Would the "2W" version be able to withstand this? Could it withstand more? It would be a meaningless specification.
answered 2 hours ago
Tom Carpenter
36.2k264109
+1 Tom for being correct, as I have to pay attention when buying 100 1% resistors at a time for maybe $3 USD. I noticed the same values in the Digi-key listing had 2 sizes but the same 1/4 watt rating (through-hole). One is short like a 1/8th watt, the other looks like a 'standard' 1/4 watt package. I would say better metal film materials allow the manufacture to do this, along with a tougher coating. Resistors with a FP (flame proof) rating tend to be standard size.
– Sparky256
56 mins ago
add a comment |Â
up vote
1
down vote
One rating (W) is average power over some poorly defined integration time, the other (Ws) is energy in a pulse application.
Note that voltage limits are also given and apply even in the pulse service.
Basically as long as you stay within the average power, the thing will not overheat and if you have chosen a pulse rated part the energy limit is specified in the Ws figure.
You typically see pulse rated parts used for things like inrush limiting.
answered 2 hours ago
Dan Mills
10.1k11023
+1. The datasheet's 'WS' reads as 'watt-siemens' which is nonsense. 'Ws' is correct. Capitals matter.
– Transistor
2 hours ago
@Transistor It depends whether "S" stands for some unit, or simply for "small", as mentioned Tom Carpenter in his comment
– Chupacabras
2 hours ago
something got lost in the translation for "Maximun" too. If Ws =2xW for small parts then the thermal time constant is 0.5s ( depending on air gap or better with thermal conductance)
– Tony EE rocketscientist
2 hours ago
Another possibility is S stands for "surge". I know, for example, Vishay sells "surge-rated" resistors.
– The Photon
1 hour ago
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
TL;DR; It's my thinking that the S is simply relating to the package being smaller.
Resistors from different manufacturers for a given power rating tend to be similar in size - the power rating effectively becomes a de facto way of identifying package size and vice versa.
As such it's plausible that they are using the prefix S to indicate that it is the higher rated resistor, but with the physical size of the next power rating down. If you go through all of the tables in your question, you'll find this holds true.
To back this up, if for example you take the SR Passives example, the part number for say a 1k 0.25W resistor differs between "CF1/4WS-1K" for the smaller package 3.2mm long package, and "CF1/4W-1K" for the larger 6mm long package. Both resistors are rated for 1/4W.
If you look at the Tecla & Chiara example, they seem to separate the two in a similar way - the ones without the S suffix are under the label "MF", and those with the suffix are under the label "MFS", which are likely the series names.
If it were representing an energy - Watt-seconds as suggested - then it would be Ws, not WS per SI unit capitalisation. I could understand if one failed to make this distinction, but the fact that three fail makes me highly sceptical. As a specification it also doesn't make much sense without context.
For example, could I run a 1Ω "2WS" resistor with 500V across it for 2ms? That would not exceed 2 Watt-second, nor exceed the voltage rating, however it would result in a 500A surge through the resistor. Is this allowed? Would the "2W" version be able to withstand this? Could it withstand more? It would be a meaningless specification.
answered 2 hours ago
Tom Carpenter
36.2k264109
+1 Tom for being correct, as I have to pay attention when buying 100 1% resistors at a time for maybe $3 USD. I noticed the same values in the Digi-key listing had 2 sizes but the same 1/4 watt rating (through-hole). One is short like a 1/8th watt, the other looks like a 'standard' 1/4 watt package. I would say better metal film materials allow the manufacture to do this, along with a tougher coating. Resistors with a FP (flame proof) rating tend to be standard size.
– Sparky256
56 mins ago
add a comment |Â
up vote
2
down vote
TL;DR; It's my thinking that the S is simply relating to the package being smaller.
Resistors from different manufacturers for a given power rating tend to be similar in size - the power rating effectively becomes a de facto way of identifying package size and vice versa.
As such it's plausible that they are using the prefix S to indicate that it is the higher rated resistor, but with the physical size of the next power rating down. If you go through all of the tables in your question, you'll find this holds true.
To back this up, if for example you take the SR Passives example, the part number for say a 1k 0.25W resistor differs between "CF1/4WS-1K" for the smaller package 3.2mm long package, and "CF1/4W-1K" for the larger 6mm long package. Both resistors are rated for 1/4W.
If you look at the Tecla & Chiara example, they seem to separate the two in a similar way - the ones without the S suffix are under the label "MF", and those with the suffix are under the label "MFS", which are likely the series names.
If it were representing an energy - Watt-seconds as suggested - then it would be Ws, not WS per SI unit capitalisation. I could understand if one failed to make this distinction, but the fact that three fail makes me highly sceptical. As a specification it also doesn't make much sense without context.
For example, could I run a 1Ω "2WS" resistor with 500V across it for 2ms? That would not exceed 2 Watt-second, nor exceed the voltage rating, however it would result in a 500A surge through the resistor. Is this allowed? Would the "2W" version be able to withstand this? Could it withstand more? It would be a meaningless specification.
answered 2 hours ago
Tom Carpenter
36.2k264109
+1 Tom for being correct, as I have to pay attention when buying 100 1% resistors at a time for maybe $3 USD. I noticed the same values in the Digi-key listing had 2 sizes but the same 1/4 watt rating (through-hole). One is short like a 1/8th watt, the other looks like a 'standard' 1/4 watt package. I would say better metal film materials allow the manufacture to do this, along with a tougher coating. Resistors with a FP (flame proof) rating tend to be standard size.
– Sparky256
56 mins ago
add a comment |Â
up vote
2
down vote
up vote
2
down vote
TL;DR; It's my thinking that the S is simply relating to the package being smaller.
Resistors from different manufacturers for a given power rating tend to be similar in size - the power rating effectively becomes a de facto way of identifying package size and vice versa.
As such it's plausible that they are using the prefix S to indicate that it is the higher rated resistor, but with the physical size of the next power rating down. If you go through all of the tables in your question, you'll find this holds true.
To back this up, if for example you take the SR Passives example, the part number for say a 1k 0.25W resistor differs between "CF1/4WS-1K" for the smaller package 3.2mm long package, and "CF1/4W-1K" for the larger 6mm long package. Both resistors are rated for 1/4W.
If you look at the Tecla & Chiara example, they seem to separate the two in a similar way - the ones without the S suffix are under the label "MF", and those with the suffix are under the label "MFS", which are likely the series names.
If it were representing an energy - Watt-seconds as suggested - then it would be Ws, not WS per SI unit capitalisation. I could understand if one failed to make this distinction, but the fact that three fail makes me highly sceptical. As a specification it also doesn't make much sense without context.
For example, could I run a 1Ω "2WS" resistor with 500V across it for 2ms? That would not exceed 2 Watt-second, nor exceed the voltage rating, however it would result in a 500A surge through the resistor. Is this allowed? Would the "2W" version be able to withstand this? Could it withstand more? It would be a meaningless specification.
answered 2 hours ago
Tom Carpenter
36.2k264109
TL;DR; It's my thinking that the S is simply relating to the package being smaller.
Resistors from different manufacturers for a given power rating tend to be similar in size - the power rating effectively becomes a de facto way of identifying package size and vice versa.
As such it's plausible that they are using the prefix S to indicate that it is the higher rated resistor, but with the physical size of the next power rating down. If you go through all of the tables in your question, you'll find this holds true.
To back this up, if for example you take the SR Passives example, the part number for say a 1k 0.25W resistor differs between "CF1/4WS-1K" for the smaller package 3.2mm long package, and "CF1/4W-1K" for the larger 6mm long package. Both resistors are rated for 1/4W.
If you look at the Tecla & Chiara example, they seem to separate the two in a similar way - the ones without the S suffix are under the label "MF", and those with the suffix are under the label "MFS", which are likely the series names.
If it were representing an energy - Watt-seconds as suggested - then it would be Ws, not WS per SI unit capitalisation. I could understand if one failed to make this distinction, but the fact that three fail makes me highly sceptical. As a specification it also doesn't make much sense without context.
For example, could I run a 1Ω "2WS" resistor with 500V across it for 2ms? That would not exceed 2 Watt-second, nor exceed the voltage rating, however it would result in a 500A surge through the resistor. Is this allowed? Would the "2W" version be able to withstand this? Could it withstand more? It would be a meaningless specification.
answered 2 hours ago
Tom Carpenter
36.2k264109
edited 2 hours ago
answered 2 hours ago
Tom Carpenter
36.2k264109
answered 2 hours ago
Tom Carpenter
36.2k264109
answered 2 hours ago
Tom Carpenter
36.2k264109
36.2k264109
+1 Tom for being correct, as I have to pay attention when buying 100 1% resistors at a time for maybe $3 USD. I noticed the same values in the Digi-key listing had 2 sizes but the same 1/4 watt rating (through-hole). One is short like a 1/8th watt, the other looks like a 'standard' 1/4 watt package. I would say better metal film materials allow the manufacture to do this, along with a tougher coating. Resistors with a FP (flame proof) rating tend to be standard size.
– Sparky256
56 mins ago
add a comment |Â
+1 Tom for being correct, as I have to pay attention when buying 100 1% resistors at a time for maybe $3 USD. I noticed the same values in the Digi-key listing had 2 sizes but the same 1/4 watt rating (through-hole). One is short like a 1/8th watt, the other looks like a 'standard' 1/4 watt package. I would say better metal film materials allow the manufacture to do this, along with a tougher coating. Resistors with a FP (flame proof) rating tend to be standard size.
– Sparky256
56 mins ago
+1 Tom for being correct, as I have to pay attention when buying 100 1% resistors at a time for maybe $3 USD. I noticed the same values in the Digi-key listing had 2 sizes but the same 1/4 watt rating (through-hole). One is short like a 1/8th watt, the other looks like a 'standard' 1/4 watt package. I would say better metal film materials allow the manufacture to do this, along with a tougher coating. Resistors with a FP (flame proof) rating tend to be standard size.
– Sparky256
56 mins ago
+1 Tom for being correct, as I have to pay attention when buying 100 1% resistors at a time for maybe $3 USD. I noticed the same values in the Digi-key listing had 2 sizes but the same 1/4 watt rating (through-hole). One is short like a 1/8th watt, the other looks like a 'standard' 1/4 watt package. I would say better metal film materials allow the manufacture to do this, along with a tougher coating. Resistors with a FP (flame proof) rating tend to be standard size.
– Sparky256
56 mins ago
add a comment |Â
up vote
1
down vote
One rating (W) is average power over some poorly defined integration time, the other (Ws) is energy in a pulse application.
Note that voltage limits are also given and apply even in the pulse service.
Basically as long as you stay within the average power, the thing will not overheat and if you have chosen a pulse rated part the energy limit is specified in the Ws figure.
You typically see pulse rated parts used for things like inrush limiting.
answered 2 hours ago
Dan Mills
10.1k11023
+1. The datasheet's 'WS' reads as 'watt-siemens' which is nonsense. 'Ws' is correct. Capitals matter.
– Transistor
2 hours ago
@Transistor It depends whether "S" stands for some unit, or simply for "small", as mentioned Tom Carpenter in his comment
– Chupacabras
2 hours ago
something got lost in the translation for "Maximun" too. If Ws =2xW for small parts then the thermal time constant is 0.5s ( depending on air gap or better with thermal conductance)
– Tony EE rocketscientist
2 hours ago
Another possibility is S stands for "surge". I know, for example, Vishay sells "surge-rated" resistors.
– The Photon
1 hour ago
add a comment |Â
up vote
1
down vote
One rating (W) is average power over some poorly defined integration time, the other (Ws) is energy in a pulse application.
Note that voltage limits are also given and apply even in the pulse service.
Basically as long as you stay within the average power, the thing will not overheat and if you have chosen a pulse rated part the energy limit is specified in the Ws figure.
You typically see pulse rated parts used for things like inrush limiting.
answered 2 hours ago
Dan Mills
10.1k11023
+1. The datasheet's 'WS' reads as 'watt-siemens' which is nonsense. 'Ws' is correct. Capitals matter.
– Transistor
2 hours ago
@Transistor It depends whether "S" stands for some unit, or simply for "small", as mentioned Tom Carpenter in his comment
– Chupacabras
2 hours ago
something got lost in the translation for "Maximun" too. If Ws =2xW for small parts then the thermal time constant is 0.5s ( depending on air gap or better with thermal conductance)
– Tony EE rocketscientist
2 hours ago
Another possibility is S stands for "surge". I know, for example, Vishay sells "surge-rated" resistors.
– The Photon
1 hour ago
add a comment |Â
up vote
1
down vote
up vote
1
down vote
One rating (W) is average power over some poorly defined integration time, the other (Ws) is energy in a pulse application.
Note that voltage limits are also given and apply even in the pulse service.
Basically as long as you stay within the average power, the thing will not overheat and if you have chosen a pulse rated part the energy limit is specified in the Ws figure.
You typically see pulse rated parts used for things like inrush limiting.
answered 2 hours ago
Dan Mills
10.1k11023
One rating (W) is average power over some poorly defined integration time, the other (Ws) is energy in a pulse application.
Note that voltage limits are also given and apply even in the pulse service.
Basically as long as you stay within the average power, the thing will not overheat and if you have chosen a pulse rated part the energy limit is specified in the Ws figure.
You typically see pulse rated parts used for things like inrush limiting.
answered 2 hours ago
Dan Mills
10.1k11023
answered 2 hours ago
Dan Mills
10.1k11023
answered 2 hours ago
Dan Mills
10.1k11023
answered 2 hours ago
Dan Mills
10.1k11023
10.1k11023
+1. The datasheet's 'WS' reads as 'watt-siemens' which is nonsense. 'Ws' is correct. Capitals matter.
– Transistor
2 hours ago
@Transistor It depends whether "S" stands for some unit, or simply for "small", as mentioned Tom Carpenter in his comment
– Chupacabras
2 hours ago
something got lost in the translation for "Maximun" too. If Ws =2xW for small parts then the thermal time constant is 0.5s ( depending on air gap or better with thermal conductance)
– Tony EE rocketscientist
2 hours ago
Another possibility is S stands for "surge". I know, for example, Vishay sells "surge-rated" resistors.
– The Photon
1 hour ago
add a comment |Â
+1. The datasheet's 'WS' reads as 'watt-siemens' which is nonsense. 'Ws' is correct. Capitals matter.
– Transistor
2 hours ago
@Transistor It depends whether "S" stands for some unit, or simply for "small", as mentioned Tom Carpenter in his comment
– Chupacabras
2 hours ago
something got lost in the translation for "Maximun" too. If Ws =2xW for small parts then the thermal time constant is 0.5s ( depending on air gap or better with thermal conductance)
– Tony EE rocketscientist
2 hours ago
Another possibility is S stands for "surge". I know, for example, Vishay sells "surge-rated" resistors.
– The Photon
1 hour ago
+1. The datasheet's 'WS' reads as 'watt-siemens' which is nonsense. 'Ws' is correct. Capitals matter.
– Transistor
2 hours ago
+1. The datasheet's 'WS' reads as 'watt-siemens' which is nonsense. 'Ws' is correct. Capitals matter.
– Transistor
2 hours ago
@Transistor It depends whether "S" stands for some unit, or simply for "small", as mentioned Tom Carpenter in his comment
– Chupacabras
2 hours ago
@Transistor It depends whether "S" stands for some unit, or simply for "small", as mentioned Tom Carpenter in his comment
– Chupacabras
2 hours ago
something got lost in the translation for "Maximun" too. If Ws =2xW for small parts then the thermal time constant is 0.5s ( depending on air gap or better with thermal conductance)
– Tony EE rocketscientist
2 hours ago
something got lost in the translation for "Maximun" too. If Ws =2xW for small parts then the thermal time constant is 0.5s ( depending on air gap or better with thermal conductance)
– Tony EE rocketscientist
2 hours ago
Another possibility is S stands for "surge". I know, for example, Vishay sells "surge-rated" resistors.
– The Photon
1 hour ago
Another possibility is S stands for "surge". I know, for example, Vishay sells "surge-rated" resistors.
– The Photon
1 hour ago
add a comment |Â
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Perhaps "small"? i.e. the physical size is the same as the next rating down.
– Tom Carpenter
2 hours ago
@TomCarpenter Size is size, and power rating is power rating. Why to mix it together?
– Chupacabras
2 hours ago
2
I suspect Watt-seconds. I.e., you can give it 1/4W continuously, or you can blast it with 10W for 1/20th of a second.
– TimWescott
2 hours ago
Not sure, other that many resistors from different manufacturers for a given power rating are similar in size. So it's plausible.
– Tom Carpenter
2 hours ago
@Chupacabras - I believe most Wattage sizes are "standard"/common. Same goes for SMD resistors. But they are only conventions and plenty break the mold.
– Bort
2 hours ago