Run current limitation

[BL1]

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?

[MM..1]

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]

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

Can I change them without risk of hardware damages ?

[MM..1]

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

[Cristiana SCARAMEL · Accepted solution]

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.

[BL1]

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]

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

[Cristiana SCARAMEL]

Hi @BL,

if you want to run the motor at 9A, you must change the resistors value.

For example using 15 mohm --> Psense = 0.015 x 9^2 = 1.215 W

[BL1]

Hi @Cristiana SCARAMEL​ ,

I'm a little confused, when you say "change the resistor value" is it only in the interface or is there some hardware modifications to do?

[Cristiana SCARAMEL]

Hi @BL​,

you have to physically change the sense resistors on your board according to your ratings.

Then you can select a custom value in the RSense list according to your board.

Pmax is used to check the power dissipation on the sense resistor.