T-Series/Commands/Set Running Current/General

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Instruction Name Set Running Current
Applies to All motorized devices
Firmware Version 5.00 and up
Command Number 38
Command Type Setting
Command Data Value
Reply Data Value
Safe to retry? Yes
Returns Current Position? No
Persistence Non-Volatile
Summary Sets the desired current to be used when the device is moving.

The specified current limit is applied per motor phase. If your application does not require high torque, it is best to decrease the driving current to reduce power consumption, vibration, and motor heating. If higher torque is required, it is generally safe to overdrive motors as long as they are not operated continuously and do not get too hot; please refer to your product’s specifications for current and temperature limits.

Zaber devices use two different techniques for controlling current: proportional and fractional. The easiest way to tell is to look at the device's power jack: a three-prong rectangular jack means that it uses the proportional technique, and a round jack means that it uses the fractional technique. Each section below lists the devices that use the technique and describes how the current is controlled. If you really want to be certain which technique is used, you can send the command with data value 1. If 1 returns an error, then the device is using the fractional technique. If 1 returns success, then the device is using the proportional technique.


Proportional: This technique is used by T-LSQ, T-LST, T-MCA, as well as A-series and X-Series motorized devices.

The value of this setting is in 14.1 mA RMS (20 mA peak) increments. As an example, to convert a desired run current of 1.2 A RMS into a data value for this setting:

data value = 1200 mA RMS ÷ 14.1 mA RMS/data = 85

To determine the actual current given the data value 40:

current = 40 × 14.1 mA RMS/data = 564 mA RMS

Fractional: This technique is used by all T-series motorized devices, with the exception of T-LSQ, T-LST, T-MCA.

The current is related to the data by the formula:

Current = CurrentCapacity * 10 / CommandData

The range of accepted values is 0 (no current), 10 (max) - 127 (min). CurrentCapacity is the hardware's maximum capability of output current.

To prevent damage, some devices limit the maximum output current to a lower value. In that case the valid range is 0, Limit - 127. Current limits are listed under the device specifications.

Some devices limit the voltage rather than the current. In this case the same formula can be used by replacing Current and CurrentCapacity with Voltage and PowerSupplyVoltage.


For example, Suppose you connect a stepper motor rated for 420mA per phase to a T-CD2500. Reversing the equation above and using 420mA as Current gives:

CommandData

= 10 * CurrentCapacity / Current
= 10 * 2500mA / 420mA
= 59.5 (round to 60)

Therefore CommandData = 60.