Shunt size for peak or continuous amps

[hwy17]

I am looking at a BMS with generic programmable shunt compatibility.

The pack would have a 150A Class T on it so no more than 150 continuous amps but it could surge to 250 sometimes during inrush currents and excursions.

Should I use a 200A shunt or 500A shunt?

 

[BentleyJ]

Inrush is a very short duration event and usually does not need to be considered.
Conventional wisdom indicates the shunt should be sized so the maximum continuous current does not exceed 75 to 80% of the shunt rating. Ambient temperature and shunt resistance are factors also. A 50mv shunt will produce less heat than a 100mv device at a given current.

See attached PDF for a derating calculation.

 

[hwy17]

Thanks, is it fair to say that a 200A shunt should remain pretty accurate during a 300A excursion then?

The accuracy during overload is my concern, rather than the safety aspect. I am comfortable with the safety of 150A fused battery on 200A device.

My hesitation is that with Hall Effect sensors Orion recommends that they be sized for the max pulse. But not all of Ewert's opinions make sense.

Whispers: Eddy Currents

 

[BentleyJ]

The shunt itself is a passive device. A 200A, 50mv shunt will produce 75mv at 300A for those few milliseconds of inrush like a motor starting up so in that sense would be accurate. The better question is what is the upper measuring limit of the ADC input and would it be able to capture that data.

Curious why its necessary to have that degree of accuracy where every electron needs to be counted?

 

[Brett V]

Riedon is my employers choice for precision DC shunts.

https://www.digikey.com/en/product-highlight/r/riedon/precision-dc-current-shunts

 

[hwy17]

Riedon is my employers choice for precision DC shunts.

https://www.digikey.com/en/product-highlight/r/riedon/precision-dc-current-shunts

That's the ones I'm looking at, the RSB-200-50.

 

[hwy17]

Curious why its necessary to have that degree of accuracy where every electron needs to be counted?

Nah it's not, just another battery build. I just want to understand the conceptual boundaries and tradeoffs. I really enjoyed the ease of installation of the Hall effect sensor with the Orion and not needing to put another pair of lugs in the circuit. But Nuvation seems committed to shunts and I'm sure they have some smart people who are convinced of that for a reason. So they are my next learning topic at hand.