SN754410 H Bridge + Small Stepper HOT

Hello everyone-

I recently purchased a SN754410 Dual H-bridge AKA quad half H-bridge (https://www.sparkfun.com/products/315)

I purchased with it 2 small stepper motors: https://www.sparkfun.com/products/10551

The motors are bipolar, 400mA, 12V. From what I can tell it should work great with the bridge, and it… kind of does. It will step with my Arduino UNO, using the stepper library, but within about 10 seconds, the bridge gets HOT. Burn your fingers hot. I don’t think this should be happening. I measured with my meter and they are drawing between .3 and 1.2A during operation.

A little more technical idea of how I have things wired:

I’m using a 12V battery to power the bridge directly, then drawing power to the UNO using Vin.

For wiring, I have Arduino pins connected as: D9 to IC 2, D10 to IC 7, D11 to IC 10, D12 to IC 15. This correspond to D9-12 to inputs 1-4 on the SN754410.

I then have the motor connected as: black to IC 3, brown to IC 6, orange to IC 11, yellow to IC 14. This should correspond to the 4 pins being connected to outputs 1-4. I couldn’t find much information on how best to hook this up, the datasheet for the motor is terrible. From my measurement, the coils are black-brown and orange-yellow, not necessarily in that order.

The enables are connected to the 5v rail (from UNO) via 10k resistor, as was suggested in the datasheet.

Other weird things, the motor makes weird squeaking sounds, and gets warm as well.

Here is my code:

#include <Stepper.h>
 
int in1Pin = 9;
int in2Pin = 10;
int in3Pin = 11;
int in4Pin = 12;
Stepper motor(48, in1Pin, in2Pin, in3Pin, in4Pin);  
void setup() {
  pinMode(in1Pin, OUTPUT);
  pinMode(in2Pin, OUTPUT);
  pinMode(in3Pin, OUTPUT);
  pinMode(in4Pin, OUTPUT);
  motor.setSpeed(20);
}
void loop() {
  delay(1000);
  motor.step(100);
}

Very sorry for the long post, just wanted to include as much as I could. Any suggestions of help are much appreciated.

From some more investigation, I’m guessing that the issues arises from the coil resistance being 4Ohms. Because at 12V, the current would be 3A, not 400mA as the Spark Fun page and datasheet suggest. I saw comments about this on a forum post over at ADAFruit, but could not find anything on the forums here.

Has anyone been able to get this small stepper motor working?

If the issue is the current, would it be better to add a 6-10Ohm 5W resistor in series with each coil, or try to setup a current chopper?

Thank you for any help you can provide