current-sense resistor for space with a rated pulse power

[DHambley]

Most of us know that a resistor can take very high pulse power if the pulse width is much less than the thermal time constant. My problem is, if the thermal time-constant isn't specified or tested, or if there's no chart of pulse power vs time, we can't use it. (per our customers reliability Engineer). The peak power of these pulses could be 10 or 20 times higher than the rating of the part.
Does anyone know of a current-sense resistor (< 0.1 Ohm) which has curves published in the data sheet for pulse duty cycle?

 

[MikeHalloran]

Terrestrial test data wouldn't do you any good "in space", where atmospheric pressure and gravity are greatly reduced.

... unless you're dissipating heat by conduction through the spacecraft structure, etc.





Mike Halloran
Pembroke Pines, FL, USA

 

[Skogsgurra]

These guys may have the data you are looking for:

http://www.isabellenhuette.de/en/resistors/

Their text mentions high pulse power. For pulse load, the absence of surrounding air is of no or little consequence because the energy is absorbed in the resistor body and no transfer to the surrounding air takes place (adiabatic process).

Their brochure says: "Small temperature coefficient, low thermoelectric voltage, high long-term stability, low inductance and high (pulse-)loadability..."

They are German and knowing Germans in general, I would be surprised if there isn't a detailed pulse load specification.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Warpspeed]

I cannot answer your question directly.
But for less than 0.1 ohm, I would be looking at purpose built current shunts rather than "ordinary" electrical resistors.

These tend to have far more thermal mass, far lower current density and operate at much lower rated temperature rises (for specified accuracy).

A far more robust and better made part than the bit of thin curly wire that usually makes up the ubiquitous power resistor.

 

[DHambley]

Skogsgurra,
Thanks for the link. Isabellenhutte's BVT series may work for my application and they do have a set of continuous pulse curves.

 

[DHambley]

I searched around some more.
These all have continuous pulse curves.

KOA KSE series
Ohmite TFS series
TT PWC and WHPC series
Vishay CRCW-HP-e3 resistors.

Mike, For space applications, all thermal paths are considered to be conductive, from the part junction to the heat sink mating of the PCB. Now the funny thing; I often see the data for ambient (25C, sea level) thermal characteristics used for worst-case calculations of junction temperature for space applications. The reliability engineers either forgot to notice this or they ignore this because the numbers work out right. This has recently become one of my pet peeves - extremely expensive analysis of very expensive screened parts, and the analysis is full of incorrect equations!

 

[DPolak]

Can you use HALL?
Yes, for 50A range I used resistor as sensor.
But for 400A (yes, for SPACE!!!) I used good, Europe made Halls.
(Just need to BS with customer for approval....)

and with Hall you you can put sensor any place, on high 140V cable without any isolation optos (7800 or similar)...