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BL1
Associate III
Nov 17, 2021 10:12 AM UTC
Solved

Run current limitation

Using SPINFamily Evaluation Tool 3.2, STnucleo-f401re and IHM03A1, I try to drive a 48V-9A motor.

In SPINFamily interface, I choosed current mode and tried to set run current to 9A. But an error show up in the interface: "Power dissipation on sense resistor to High for RUN Current".

With run current to 7A, all is working fine, but not higher. Do you know why?

This topic has been closed for replies.
Cristiana SCARAMEL
ST Employee
Nov 18, 2021 8:29 AM UTC

Hi @BL​,

pay attention that in your screenshot you have selected the EVLPOWERSTEP01, but you are using X-NUCLEO-IHM03A1.

This Nucleo expansion board mount a 100 mohm / 2W sense resistors.

The sensing resistor power rating should be chosen taking into account the peak value of the dissipated power:

Psense = Rsense x Ipk^2

where Ipk is the peak value of the load current.

Using multiple resistors in parallel will help obtaining the required power rating with standard resistors, and reduce the inductance.

Rsense tolerance reflects on the peak current error: 1% resistors should be preferred.

"If you feel a post has answered your question, please click ""Accept as Solution"""

16 replies

MM..1
Super User
Nov 17, 2021 3:14 PM UTC

dissipation on sense resistor is real element with max power for example 2W and your calculation for 9A is over this and windoww report you 3W = blown.

Change it to more W or less mOhms

BL1
BL1Author
Associate III
Nov 17, 2021 4:00 PM UTC

But Rsense and PMax were predefined according to the board I'm using

Can I change them without risk of hardware damages ?

MM..1
Super User
Nov 17, 2021 5:08 PM UTC

I dont recomm change in window, but change real hardware components and then enter changed values

BL1
BL1Author
Associate III
Nov 18, 2021 1:59 PM UTC

Hi @Cristiana SCARAMEL​ ,

I through this was the same, thanks

Can I simply change Rsense and PMax value to respectively 100(mOhm) and 2 (W) ? or do I need to do some hardware modifications on the board to safely reach 9A ?

MM..1
Super User
Nov 18, 2021 2:33 PM UTC

Realy 0.1Ohm x 9^2 = 8,1W Your Rsense blown when is 2W.

BL1
BL1Author
Associate III
Nov 19, 2021 2:24 PM UTC

Hi @Cristiana SCARAMEL​ / @MM..1​ ,

Thank you very much for useful help :)

MM..1
Super User
Nov 19, 2021 2:37 PM UTC

@BL​ for complete clear , maybe you need stop work with 10Amps , when you need ask this questions. Start learn use multimeter, Ohm law and scope.

And FYI 30mA can kill your heart.