L298n h-bridge BLOWING UP, need help - Page 1
Forum section: electronics / projects

author: Beninot
author_rank: Newbie
timestamp: February 14, 2016, 07:27:55 pm
content: Hi guys, I 'm trying to use a l298n h-bridge module to drive a medium size stepper with a 12v battery, so I plugged my arduino, asking to the h-bridge to rotate the stepper 360°, when I plug the stepper, it's blowing up after a few seconds of driving, anybody havve an idea what's going on?

author: uncle_bob
author_rank: Unknown
timestamp: February 14, 2016, 07:41:26 pm
content: HiAs a quick guess ... to much current ?Yes, that's completely unhelpful.The stepper you have likely has a rated current, a rated inductance, a rated resistance, and a rated voltage. For various really bizarre reasons, turning those numbers into something straightforward is not as easy as it should be.When you look at the resistance of the stepper and it's rated current, you get some magic voltage. That voltage, if applied long enough will magnetize the armature and you will get a step. The time constant between the L of the winding and the R will be the reason for the "apply the voltage long enough" qualifier.The step speed you get running at a "long enough" pulse rate normally is not fast enough. Next step is to increase the voltage so the L-R gets up to current faster. Now you need to current limit things to keep from burning stuff up.Part of getting the pulses fast is sequencing the H bridge. Turning both devices in a leg on at the same time is not a good idea (over current) . Turning all the devices off at once is also not a good idea (voltage spike). Of the two, over current is the more likely issue.Ok so far or have I headed off into the weeds already?Bob

author: wraper
author_rank: Unknown
timestamp: February 14, 2016, 07:49:09 pm
content: What is your stepper motor model? Most of them cannot take 12V DC. Usually they have current spec, and operate the best (fast rotation with good torque) when PWMed with current control. So as long as you don't use some additional chip (like L297) for PWM and current sense together with L298, most likely, you will blow it.

author: Beninot
author_rank: Newbie
timestamp: February 21, 2016, 04:53:53 am
content: Thanks bob, it was a pretty great explanation of what's going on, but sorry, I can't find the specs of the stepper, I got it in a teardown and it looks like it's custom to the product, I can't find any info about it on the web, only thing I know is that it's rated 12v and that it's from JapanServo corp. i think, but a friend of mine already got it to work with the same setup, with a different program(different speeds, ect...) so could a - 3v voltage difference could have caused it to blow(I plugged it on a battery that was not used for a long time)Thank you

author: Molenaar
author_rank: Regular Contributor
timestamp: February 21, 2016, 10:26:06 am
content: Is it a bipolar motor? Could it be shoot-through related?

author: uncle_bob
author_rank: Unknown
timestamp: February 21, 2016, 01:11:28 pm
content: Quote from: Beninot on February 21, 2016, 04:53:53 amHiBest guess ... the motor has about a max of 3V on the windings (steady state) before they blow. The 12V is the "normal operating voltage for rated speed". That assumes a current limited driver and a few other things. If anything stalls the stepping process and does not cut back the current quickly .... motor is toast. Firmware wasn't written by some guy named Bob was it ...Bob ( the firmware guy with the unknown forwarding address ...)

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2016, 01:34:15 pm
content: What are you using to control the L298?Using firmware to limit the current is generally not a good idea. How about using a stepper motor driver IC such as the L297?

author: Ribster
author_rank: Frequent Contributor
timestamp: February 28, 2016, 10:18:41 am
content: Don't forget the flyback diodes!!