Motor Current Parameter

The motor current of stepper motors can be adapted to the requirements of each axis via the current scale parameters in the Firmware Parameter Configuration. The most important factors are required torque, motor size and generated heat: If the current is set too high or if the motor does too few cooling breaks with lower current the motor and electronics can overheat and get damaged.

The following current parameters can be configured:

• CSLoad: current scale under load conditions
• CSStart: current scale at start of motion
• CSIdle: current scale when not moving
• CSRef: current scale when referencing

IMPORTANT: Do a stress test (e.g. 1hr) after changing the current scale parameter and watch the temperature at the motor. Since the motors do not have temperature sensors the electronics only monitors the temperatures of the electronic modules.

Current Scale and Actual Current

The current scale parameter is a number 1-31 that translates to a current as the following measurements show. This is independent from motor size and voltage.

Current Scale	Actual Current (A)	Current Scale	Actual Current (A)
1	0.5	16	3.6
2	0.7	17	3.8
3	0.9	18	4.0
4	1.1	19	4.2
5	1.3	20	4.4
6	1.5	21	4.6
7	1.7	22	4.8
8	1.9	23	5.0
9	2.1	24	5.2
10	2.3	25	5.4
11	2.5	26	5.6
12	2.7	27	5.8
13	2.9	28	6.0
14	3.1	29	6.2
15	3.3	30	6.4
		31	6.6

Recommended Current Scale

We recommend the following values for the different motor types:

Motor	Current Scale	Actual Current
NEMA17	8	1.9A
NEMA24	19	4.2A

At low RPM the generated torque does not depend on voltage, a higher voltage delays the effects of back EMF and allows faster motion. Therefore the recommended current scale values are equal for both 242V and 48V systems. However, since a higher voltage creates more heat in the motor control electronics the current scale may need to be limited.

Examples:

Robot Type	Motor	Voltage	Current Scale	Actual Current
DLE-RG-0014	NEMA24	24V	25	5.4A
		48V	16	3.6A
	NEMA23	24V	22	4.8A
		48V	15	3.3A
	NEMA17	24V	12	2.7A
		48V	6	1.5A
DLE-RG-0374	NEMA23	24V	25	5.4A
		48V	16	3.6A

Torque Loss at High Velocities

The available torque of stepper motors decreases after a certain speed. This is an effect of Back EMF: the motor induces a current that is opposed to the current that turns the motor, decreasing the effective current. The following diagram shows this effect; the usable current drops after 300 RPM in a 48V system. This can cause issues like motor stalls at the fastest part of a motion.

In 24V systems these effects start at even lower speeds as the following diagram shows.

These effects are considered in construction where motors, gears and voltage must be chosen for the appropriate speed range.