Hi so i wanted to use stepper motors with the arduino but i dont know exactly how i should power them
So i wanted to use a A4988 Driver with Nema17 Steppers which are 1.5 A rated current and have a resistance of 2.4 ohms but the problem would be that i would want to connect 3-6 stepper.
Could someone maybe help me with the calculations and choosing the right supply?
Hi @ColiderMite,
do you want to use 3 to 6 steps motors with a single A4988?
Or do you want to use 3 to 6 step motors with 3 to 6 A4988?
According to the datasheet the A4988 supports currents up to 2A.
About power supplies:
The A4988 requires 2 power supplies.
One for his logic and must be from + 3v to + 5.5V.
Another one for the motors and it should be from +8v to +35V.
The consumption of the logic part is very small and the consumption of 6 A4988 modules should be around 50 mA total.
The consumption of the engines, with 6 of 1.5A motors, will be around 9 A.
So think of a power supply with at least 30% more. 12A
RV mineirin
Not true.
Stepper drivers are power converters, you need to do the calculation in terms of power consumption, not current.
The motors are 1.5A and 2.4 ohms, so they use I-squared-R power, named 1.5x1.5x2.4 = 5.4W.
So the power supply needs to be at least 6 x 5.4 = 33W for six motors. Then you need to
allow for the driver inefficiency and the extra power drawn by the motors under load, perhaps double that to 70W or so, which at 24V would be 3A, not 9A.
Higher voltage supply allows for faster operation of the steppers, 24V is a commonly
chosen supply voltage for a reasonable compromise. If you chose 12V supply, 6A would be appropriate.
Higher motor supply voltage, up to the max allowed for the driver, will give more speed and torque.
The A4988 driver might handle 2A with good heat sinking and forced air cooling. For a 1.5A motor, a DRV8825 may be better.
Robin2's stepper basics tutorial may be of interest.
edit: fixed typos, added informational page
1A is about it for A4988, DRV8825 will handle somewhat more (1.5A).
Unless you're going to liquid-cool the chip!
Description
The A4988 is a complete microstepping motor driver with
built-in translator for easy operation. It is designed to operate
bipolar stepper motors in full-, half-, quarter-, eighth-, and
sixteenth-step modes, with an output drive capacity of up to
35 V and ±2 A. The A4988 includes a fixed off-time current
regulator which has the ability to operate in Slow or Mixed
decay modes.
This is from the Pololu web site product page on their A4988 module.
It operates from 8 V to 35 V and can deliver up to approximately 1 A per phase without a heat sink or forced air flow (it is rated for 2 A per coil with sufficient additional cooling).
Not true...
This calculation is valid for a single fase, but for 2 fase motors the value should be:
5.4 W * 2 = 10.8 W.
So the power supply needs to be at least 6 x 10.8 = 65 W for six motors. Then you need to
allow for the driver inefficiency and the extra power drawn by the motors under load, perhaps double that to 130W or so, which at 24V would be 5.4A, not 3A.
At 12V = 11A .....
RV mineirin
ye sry I should have been more precise
yes i would like to use an A4988 per motor
So i dont worry much about powering the driver because i can just power them with the arduino or come up with something but the stepper were the thing
Does that mean i could use somthing like a Universal Regulated Switching Power Supply Transformer to power all of them?
Power supply currente formula;
Power supply current =......((Vmotor / VPsupply)* Itotal)* Ep
Vmotor =......Volts motor coil
VPsupply =......Volts power supply
Itotal =......Total motor currente (Motor current per fase * 2 = Itotal )
Ep extra power = ......(maybe 1,5 to 2,5 -recomended 2)
Current/ phase.................A........1.50
Coil resistence /fase..Ohms........2.40
V motor...............................A........3.60
W motor............................ W........5.40
Power supply........................V........8.00.......12.00 ....24.00......32.00
Total motor current.............A....... 3.00.......3.00........3.00........3.00
Extra power ...................................2............2.............2..............2
Power current for 1 motor..A........2.70.......1.80.......0.90........0.68
6 motors current..................A........16.20.....10.80.....5.40........4.05
wait so 24V 10A would be more then enough?
Yes.
Which is complete marketing BS as the datasheet clearly states 2A is the "absolute maximum never exceed" specification, not the recommended operating current - in practice on the small breakout boards that A4988's come on 1A is the sensible limit - they will still be searing hot, so you need to stick on the little heatsink anyway.
If you delve more carefully into the datasheet you'll see the output devices on the chip are rated at upto 0.43 ohms. Thus with 2A flowing in one winding, 2 devices are each carrying 2A and dropping 0.86V, leading to a worst-case total dissipation of about 3.5W, well above what the tiny little SMT package can handle without water-cooling.... The A4988 cannot handle 2A, basically, except as a very temporary overload. The bond-wires may fail above 2A in fact, that might be the reason for the absolute-maximum rating.
Unfortunately many people don't distinguish between operating values and maximum values. The maximum values in the datasheet means that the device will not be damaged if these values are not exceeded. or - the other way round - it can be damaged if these values are exceeded. It does not mean that the device operates ordinarily at these values.
I think the A4988 is not suitable für a 1,5A stepper - at least if you want the full tourque of the motor.
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