I am using a NEMA17 stepper motor with 1.7A/Phase 3.06 V rated voltage . I need to use a battery since I have 2 motors driving wheels for a small cart. The battery I have is a 11.1V 2200mAh and my motor is an L298 based dual H-bridge. My question what type of configuration or how can I limit the current so my I don't fry anything up.
The L298 driver can't handle the current required by your low voltage, high current stepper. It will overheat and shut down. There are a couple of other options. The first is to put a resistor (e.g. 6 ohms, 10 or more watts) in series with each winding to reduce the current, which wastes power. The other is to use a modern stepper driver like the A4988 or DRV8825 from Pololu Pololu - DRV8825 Stepper Motor Driver Carrier, High Current
With the latter option, you still need to cool the motor driver to get the full current through the motors. However you can reduce the motor current to a reasonable level (for the motor driver) using the on-board adjustment.
Finally, if you discharge the LiPo batteries much below 2.5 V/cell, they will be destroyed. You will need a battery protection PCB to avoid that. See Tenergy Battery Pack PCB
Thank you for your response. Right now I am in a tight position and I'll probably go with the first options, I don't have to worry about power loss at the moment. But how did you calculate the resistance that I needed for this driver? Like for example if I wanted to run my motor on 1 A what resistor values should I choose?
The motor takes 1.7 amps at 3 volts. That means its winding resistance is (by Ohm's law V=IR) 3/1.7 = 1.8 Ohms.
The L298 H bridge will "consume" 3-4 volts, as it is very inefficient. Assuming the battery voltage is 11 V, about 11-3 = 8 volts maximum are available for the motor + resistor.
The current is 1 amp so the total resistance (motor plus resistor) should be 8V / 1A = 8 ohms.
That leaves 8-1.8 = 6.2 ohms for the resistor. That happens to be a standard value.
The power dissipated by the resistor is P = I^2 R = 6.2 watts. Choose a 10 watt resistor to be safe.
You my friend are awesome! Thank you that cleared so many things. Lastly, is it a good idea if I use one battery to run 2 identical motors along with their drivers since I would be dropping the current this way by half? And is the current sensing option for the drivers of any use here or is it just for connecting an external circuit like the L297?
The current sense output isn't much use unless you connect the L297.
When using "full steps", both motor coils are activated at the same time, which means that each motor will draw 2 amps total. In theory a single 2200 mAh (2.2 Ah) battery will provide 2.2 amps for one hour but in practice, less than that. With two motors the situation is quite a bit worse (I would guess perhaps 10-15 minutes).
@jremington,
Can you clarify something for me. I'm trying to understand your statement that the L298 cannot handle the 1.7A current. As you know , a stepper motor requires two windings energized at all times so 1.7A/2=0.85A /per phase =<1A max/output. Why are you saying it can't handle the current ?
Stepper motors are rated in terms of maximum average current per winding, so a 1.7 amp motor can at most be run at 3.4 amps (both windings) in full step mode. Any more current and the motor will overheat. They can run hot, sometimes too hot to touch.
The product data sheets for the L298 motor driver chip are "overly optimistic" (to be generous) in quoting 2 amps total per motor or winding. They overheat when more than about 1 amp is drawn, as documented by these guys The Motor Driver Myth — Rugged CircuitsRugged Industrial Arduino Microcontrollers and by hundreds if not thousands of posts on the Arduino and other forums.
1.7A is just a bit high for single-chip drivers to handle, alas, but
if you stick to a device with a heatsink built-in and provide forced-air
cooling you are most likely to succeed.
For such a motor from such a voltage a chopper driver is undoubtedly best,
the BigEasyDriver is one such possibility, but you will need to attach a metal
heatsink to the chip and cool it to get anywhere close to 1.7A. There are
other similar motor controller boards using stepper chopper-driver chips.
For higher current operation you need a proper motor driver using
discrete power MOSFETs, and there's a bit of a lack of commercial options
at hobby prices here, the Gecko Drives seem to be reasonable and there
are some cheap chinese units on eBay.
Hey guys,
I have a similar issue. I use canakit H-bridge L298 (4A Dual Bi-Directional Motor Driver (L298 H-Bridge), btw. I also tried BigEasy driver, and it exploded... motors didn't even rotate once, and I had 3 of those. 2 exploded, and i keep the third one in the drawer), and NEMA23 stepper with a 4:1 gearbox. I know... these drivers aren't the best option, however, I will probably order something like: http://www.ebay.com/itm/130959628870. Anyway.... . I fitted large heat-sinks with fans to cool this down so overheat is handled. The thing works fine while using power supply (12V - max 15amp, converted PC PSU). However, if i connect it to 16V of 5000mAh 25C LiPo (Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking)
Any idea? The stepper driver behaves very weird. Control leds are blinking very dimly. And the motor doesn't show any interest to run. However, when back on 12V PSU, works fine. What's the problem with LiPo? I also tried to fit 10ohm, 10w ressistor in series, however, the same thing repeats. Any ideas?