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. |
If your application does not require high torque, it is best to decrease the driving current to reduce power consumption, vibration, and motor heating. Trial and error should suggest an appropriate setting. If higher torque is required, it is generally safe to overdrive motors as long as they are not operated continuously. Motor temperature is typically the best indication of the degree to which overdriving can be employed. If the motor gets too hot to touch (>75°C), you should reduce the running current.
Zaber devices use two different techniques for controlling current: percentage 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 percentage 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 or 127. If 1 returns an error, then the device is using the fractional technique. If 127 returns an error, then the device is using the percentage technique.
Percentage: This technique is used by T-LSQ, T-LST, T-MCA, and A-series motorized devices.
The current is related to the data by the formula:
- Current = CurrentCapacity * CommandData / 100
The Command Data can be a value from 0 (no current) to 100 (max). 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. 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, the T-MCA has a CurrentCapacity of 2.5A. To apply a current of 0.5A to a motor, reverse the formula:
CommandData
- = Current / CurrentCapacity * 100
- = 0.5A / 2.5A * 100
- = 20
Therefore CommandData = 20.
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.
