Over voltage input protection for the Current Ranger

[dmketting]

Hi all,

I have the Current Ranger and intend to use it to measure and log current going into a system which drives stepper motors and a lot of electronics. The issue I'm having is that the system is generating inrush currents over 7 amps (All DC). I read that the max voltage difference is 33mV or we might damage the CR. Placing diodes back to back will not limit the voltage differential to 33mV as far as I can tell.

Any ideas on how we could "clamp" the differential voltage to 33mV during the inrush currents?

Thanks for any ideas upfront.

[Felix]

Hi dmketting,

The warning in the guide is there more as cautionary since some folks may not be aware that a voltage source cannot be applied to the input, and this is where damage can occur.

Technically there is no damage done to the amplifiers if you overload them with current, but keep the inputs to the amps to a differential below their VCC (3.3v in this case).

For transients above 33mV in the mA range (corresponding to ~3.3A loads) the output of the second amp will be overdriven. There will be recovery time of up to 10ms for the amp after such a condition, this is undesirable, but won't do damage.

Anyway in your case of 7A transients I am not worried you will actually do damage. I would however not use the CR in applications where large sustained currents over 3.3A are expected. It is just not designed to measure more than 3.3A. It could be modified to power the amps from the battery, or even up to 5.5V (from another such power source) and then it could do 5.5A but I doubt that's a common case. After all, the CR is intended to range from very low currents, up to a few amps which seems plenty in most DC electronics projects.

I hope this helps make it more clear what the limits are.