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Topic: H-bridge (L298N DUAL FULL-BRIDGE DRIVER) gets very hot - help! (Read 4901 times) previous topic - next topic

gruppe2

Hi,
We are a group of students doing a project with three Bipolar 76mm Stepper motors. To controle the motors we use three H-bridge (L298N DUAL FULL-BRIDGE DRIVER). These are connected to an arduino board. We have connected the components according to the attached schematic. We are connecting a power supply to power the H-bridge. This power supply is set to 5 volts. We can change this voltage, since the power supply can be set to different voltages.
We are using an adjustable DC power supply to power up the stepper motors. I have attached the datasheet for the stepper motors. We have set the adjustable DC power supply to power the motors with 3,96 volts. It should just take the amperes it needs to power the motors.
We are able to run the motors via the attached code.
We have a problem, though. The H-bridge is getting very hot. We have tried to adjust the voltage in the power supplies that are powering the H-bridge, but it still gets very hot.

Does anyone know what might be causing this? We are making an art installation which have to be able to run for three weeks (with breaks, though..) so we are worried that they heat up already after a few minutes.

Kind regards, group 2, Art and Technology.



mmcp42

a couple of observations

a)
3.96 volts is not enough to supply that current
that's the DC voltage, but you are driving an inductance (the motor windings) so you need a much higher voltage)

b)
the wiring diagram for the motor would be useful
maybe you have it wired incorrectly?

c)
does the motor actually turn?

d)
interesting delay in the code - what are you trying to do there?
there are only 10 types of people
them that understands binary
and them that doesn't

cr0sh

You didn't mention whether you have the L298 devices attached to a heatsink...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

RuggedCircuits

L298 drivers will get extremely hot at that kind of current (3.96V / 1.8ohms --> 2.2A). Here's a more detailed explanation:

http://ruggedcircuits.com/html/anmd01.html

I think you will either need to run the motors at lower current or a more powerful motor driver.

--
The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

gruppe2

Thanks for all the answers - we really appreciate the help.


Here are some replies to your questions.
Answers:

You didn't mention whether you have the L298 devices attached to a heatsink...
     We do not have the L298N attached to a heatsink. Can you recommend a link sayng how to do this?
     We think a heat sink sound as a good thing to add to our system, since our research on the L298N on the internet has showed that many people have problems with the L298N being very hot.

a)
3.96 volts is not enough to supply that current
that's the DC voltage, but you are driving an inductance (the motor windings) so you need a much higher voltage)

     Okay, we maybe have read the datasheet wrong. We thought that when the datasheet said: Rated Voltage: 3,96 V, that we should feed the motor with 3,96 volt from the adjustable DC powersupply. So if this is wrong, how can we know how high voltage we need? And in connection to your question regarding whether the motors have been up and running: yes. They run nicely with the code we attached to this forum.

d)
interesting delay in the code - what are you trying to do there

We are using the delay to control the speed of the motors. The bigger the number that is divided by 1000 the slower the motor drives.

We have attached a diadram of the wiring. Maybe this link is also useful: http://let-elektronik.dk/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=348&category_id=22&keyword=stepper+motor&option=com_virtuemart&Itemid=81

I think you will either need to run the motors at lower current or a more powerful motor driver.


In the datasheet for the motors we read that the rated current is: 2,2 amp. So can we run it at a lower current?

RuggedCircuits

Quote
We do not have the L298N attached to a heatsink. Can you recommend a link sayng how to do this?


I'm assuming you have the L298N in the through-hole package (not the surface-mount). You will need to get something that looks like this:

http://www.aavidthermalloy.com/cgi-bin/stdisp_print.pl?Pnum=530510b00000g

This bolts on to the package using a nut and bolt, and you should also apply thermal grease between the two to fill in any air gaps and improve thermal conduction:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=345-1006-ND

If you have a machine shop you can just make yourself a big block of aluminum to bolt on instead of trying to find a proper heatsink (it's not a standard package so finding a heatsink for it could be challenging).

Quote
We thought that when the datasheet said: Rated Voltage: 3,96 V, that we should feed the motor with 3,96 volt from the adjustable DC powersupply.


That is just the maximum steady voltage you should be applying, and really it's a sideways way of telling you the maximum current, which is more important (I=V/R). You can always operate a motor at a lower voltage/current to get lower torque.

Now for steppers, it is common to use a higher voltage but just not leave it on all the time. That is, use pulse-width modulation (PWM) to deliver an effective average current that is within the motor specifications but turn it on and off quickly so that the current does not rise beyond the rated current.

Quote
In the datasheet for the motors we read that the rated current is: 2,2 amp. So can we run it at a lower current?


Absolutely. The lower the current you run at the less hot your driver will get, and the less torque you will get from your motors.

--
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cr0sh

[If you have a machine shop you can just make yourself a big block of aluminum to bolt on instead of trying to find a proper heatsink (it's not a standard package so finding a heatsink for it could be challenging).


While it would be easiest to just bolt it to something (whether from a shop or otherwise - you could probably take a piece of thin aluminum bar stock (maybe 1 mm thick, a few centimeters tall), then cut slits along one edge, and alternately fan out the sections), the package is somewhat "standard" - its known as a Multiwatt package (Multiwatt 15 - IIRC), and was pretty common of the era of the L298 for those ICs, as well as a few audio amplifiers and other devices.

If you look around, you can find "Multiwatt" heatsinks, but they aren't cheap. You can also look around and find places that sell aluminum and copper heatsink extrusions, some of which can fit the L298, once you chop off a chunk and machine a bolthole into it.

I did a bit of research on this for an L298 setup I was (am? I need to get back to my project - so lazy) working on; I ended up finding some heatsinks instead at my favorite local haunt (Apache Reclamation and Electronics here in Phoenix) instead...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

zoomkat

For a heatsink, you might stop by Radio Shack and check the below.

http://www.radioshack.com/product/index.jsp?productId=2102856
http://www.radioshack.com/product/index.jsp?productId=2102857
Google forum search: Use Google Advanced Search and use Http://forum.arduino.cc/index in the "site or domain:" box.

roypardi

Those Radio Shack ones look good but they may be an online only thing - have never seen them in the bins at a RS store.

cr0sh


Those Radio Shack ones look good but they may be an online only thing - have never seen them in the bins at a RS store.


I think both are too small, anyhow. The 220 heatsink you'd have to mount backwards on the L298 to get it to fit, and it would be undersized. The other one looks like something you are meant to bond to the part with heat-conductive epoxy (and I still think it would be undersized). Then again, maybe the heatsinks I've seen on L298 driver boards and shields have been waaay oversized for the application?

One thing I've never been able to find, though, is where those board makers get their heatsinks from. Digikey and Mouser (IIRC) both do sell supposed "multiwatt" heatsinks, but neither give any good details on them to know if they'd be worth buying...

:)
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

zoomkat

Quote
Those Radio Shack ones look good but they may be an online only thing - have never seen them in the bins at a RS store.


Use the "find it in store" button to see your local stores that list them in stock. If it is listed in stock at the store, call the store and have the clerk verify they actually have it (actually touch one) if it is a long ride to the store. Worse case one probably could make a heatsink from the flat area of a can lid.
Google forum search: Use Google Advanced Search and use Http://forum.arduino.cc/index in the "site or domain:" box.

MarkT

For a high-current low-voltage bipolar motor like that the L298 is simply not the right controller - you ideally want a switch-mode stepper motor driver with current limiting - or at least an H-bridge designed for low voltage.

The L298 is meant for higher voltages and is very inefficient at low voltage due to the Darlington output stages that drop about 3.7V at 2A - that's about the same power wasted in the chip as goes to the motor, requiring a big heatsink.

There are many stepper motor switchmode (also called PWM) controller chips like the A4983 (Pololu have a breakout board for this), the L6208 and many others - although 2.5A is quite a lot for most of them.  These can be run from upto 40V and efficiently convert to whatever voltage the motor wants with automatic current limiting.  This means the motor can be stepped at much much faster rates as the back EMF can be overcome, yet little power is lost.

If you don't want high step rates it is easier to use a stepper motor with a higher winding resistance than can be driven directly from 5V, 12V or whatever.
[ I won't respond to messages, use the forum please ]

gruppe2

Hi guys,
Thanks for the help.
For now your replies have been very helpful.

We might return for some more help..

Kind regards,
group 2

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