Blowing up my H-bridge with a stepper motor?

Dear All,

I have built the scheme as mentioned by Tom Igoe to control a stepper motor with an Arduino and a SN754410NE H-Bridge.

The stepper motor is a NEMA17 (42BYGHW609) and has a current rating of 1.7 amp. It all runs nice and does the things I want.

However, the current for the H-bridge IC is specified to be a maximum of about 1.1 A and only short peaks of 2 A are allowed.

As I recently learned from this forum that a stepper motor basically always draws the rated current, it would mean that I am always overloading the IC by 70%. It gets pretty hot and I can just (not) hold my finger on it (estimated 60 Celcius).

Question: can I build this safely in my project without the whole thing catching fire or stopping after a few hours?

I would be very gratefull for any tips!

a stepper motor basically always draws the rated current,

Actually, the stepper obeys Ohm's law, and if the power supply allows, can draw much more than the rated current, overheating and possibly destroying itself.

For that stepper you need a modern motor driver. Follow the instructions to set the current limit to 1.5 amperes/winding or less.

Hmm, that indeed sounds not too promising for the current set-up. Bit strange that this scheme is then mentioned on the tutorial section of the Arduino site?

Anyway, the stepper motor drivers that you mention are compatible with the Arduino I presume?

And thanks for your input!

H-Bridge drivers are not ideal for stepper motor control, as I recently (re)learned. At one point I knew this because I built a 3D printer that uses 4 of them, but, well, I forgot.

I just switched from using an expensive H- Bridge driver to a $2 chinese A4988 driver and its way better, in part because it has the ability to limit current, but also has a number of other useful features like micro stepping (which will limit your max RPM). The current draw on my bipolar stepper is 3 ohms per coil, I have yet to determine if this lil driver can handle it, but so far so good, little if any heat after running it for 30 min. Its pulling under 1A @ 24V in my application.

Here are the ones I picked up: http://www.amazon.com/Robotlinking-Stepstick-Stepper-Driver-Printer/dp/B0166QZ5HO/ref=sr_1_fkmr1_2?ie=UTF8&qid=1459788504&sr=8-2-fkmr1&keywords=a9488+stepper+driver

artelectro:
As I recently learned from this forum that a stepper motor basically always draws the rated current, it would mean that I am always overloading the IC by 70%. It gets pretty hot and I can just (not) hold my finger on it (estimated 60 Celcius).

Question: can I build this safely in my project without the whole thing catching fire or stopping after a few hours?

A stepper doesn't necessarily draw rated current. If you limit the current.... then less magnetic field strength and less force/ torque etc. As long as the stepper has adequate current to do its thing reliably... then it's ok.

If you're concerned about temperature.... then could use a thermal fuse taped to the heatsink. Or use bigger heatsink.... or use some fan cooling (backed up by temperature monitoring).

If you feel that your system is uncomfortably hot.... then do something to sort it out...... ie... need more cooling.... or use some other driver that could solve the problem.

H-Bridge drivers are not ideal for stepper motor control, as I recently (re)learned.

All modern stepper drivers are H-bridge, including the A4988. The main difference is that the modern ones use fast, efficient MOSFET transistors, rather that the bipolar transistors used in older designs.

jremington:
All modern stepper drivers are H-bridge, including the A4988. The main difference is that the modern ones use fast, efficient MOSFET transistors, rather that the bipolar transistors used in older designs.

Oh ok.

jremington:
All modern stepper drivers are H-bridge, including the A4988. The main difference is that the modern ones use fast, efficient MOSFET transistors, rather that the bipolar transistors used in older designs.

The point is stepper drivers implement a current-drive, not voltage drive, by sensing the current and
chopping the voltage to maintain the programmed average current. That requires current sensing,
comparators, clocking, feedback, decay-mode logic and so forth, as well as an H-bridge to do the
actual switching. Whether the H-bridge is MOSFET or bipolar is not very crucial (MOSFETs happen
to be better, that's all).

High performance steppers are designed for the resistive EMF across the winding to be small
compared to the motional back-EMF, allowing greater speeds (if current driven).

Looking at the datasheet for your motor, it will draw the rated 1.7A for a voltage of 3.4V (it has a 2Ω winding resistance).

You haven’t told us what what supply voltage you are driving the motor from, but I suspect that it is likely to be more than 3.4V.

If it is, then the current drawn could be higher than the rated 1.7A, and might only be limited by the internal resistances of the supply and the H bridge transistors.

You could get around this by adding a high power resistor in series with each motor winding to limit the current to a safe value for the H bridge.

I am running a NEMA23 motor rated at 5V, 1A from a 13.8V supply by adding a 10Ω/10W resistor in series with each winding.

You may find some useful stuff in Stepper Motor Basics

...R

The point is stepper drivers implement a current-drive, not voltage drive, by sensing the current and
chopping the voltage to maintain the programmed average current. That requires current sensing,
comparators, clocking, feedback, decay-mode logic and so forth, as well as an H-bridge to do the
actual switching.

Yep, all done many, many years before efficient MOSFET power drivers became available on chips, with integrated sensing circuitry.

Ok.... the current in the winding is linked to torque.