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Topic: L293D Getting Really Hot, Really Fast (Read 2015 times) previous topic - next topic

dgelman

Hello

I am using a DUE and using the following shield:

Shield
http://yourduino.com/sunshop2/index.php?l=product_detail&p=292

I am controlling a 24V motor.  Because the shield max is 16V, I am operating this motor at 16V.  It seems to be moving, and my current is not limiting at all.  Running both motors I am getting a maximum of 800mA draw from my power source but the driver is extremely hot!

Motor
http://www.faulhaber.com/uploadpk/EN_3863_C_DFF.pdf

For the link above, I am using the 024C version.  Also I configured the timers on the DUE to run the PWM at 36KHz, not sure if this is a useful peice of information.

I am slowly learning about drivers and motors and would like some help on why this is happening and what can I do to fix this?

Thanks,
Daniel

Dialup is the future.

MarkT

Well that motor has a design full-load current of 9A (at 24V) and a stall current of 25A (at 16V), so you'll need
a motor controller able to handle those currents (and probably an over-current sensor to detect stalls).  The L293D
can only handle the no-load current really - not very useful.

A motor that size is probably OK to PWM at 4kHz - the L293D won't handle 36kHz efficiently, its has slow darlington
outputs, not MOSFETs.
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Justscary

Another thing to remember is some driver boards come without heatsinks on the chips and they leave it up to you to fit them afterwards. With this in mind you'll find a driver board that can handle 25A may only handle 1-5A without the heatsinks installed. Some boards have them factory and I'm not sure why they supply others without
, maybe to save on cost?

JimboZA

The 4 centre pins on the 293D (2 each side) are for heatsinking.

But with them mounted as they are in the middle of the shield, it might not be possible to use them for heat. Maybe hook up a 5v pc cooling fan on top somehow?
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MarkT

The L293D won't handle the currents this motor is designed for at all, however big a heatsink you use!
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Justscary

Sorry, I was not saying it would, I'm not familiar with the L293D. I have however, been caught out by the lack of heatsinks in cases before. Even some of the high end vfd boards I use for CNC conversions come without the heatsinks which is kind of frustrating, but sometimes it can be handy as you can mount them all on a tunnel type heatsink with a pc fan blowing down it.

JimboZA

But even when the 293 can handle the current in a particular set of circumstances, what are the ways of heatsinking it when it's on a board? It's not like a 298 where there's a hole in the back to attach a sink, even an ersatz nut and bolt and a chunk of metal.

With a 293 on a board, where there's probably limited access to the 4 pins, how to protect it?
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Justscary

That's always the fun part, as I have said before, I'm not farmilliar with this board, but I know that in some cases you have to get really creative. I have had to mill up my own aluminum sinks specially shaped and use a bit more thermal paste than I would like, but it works. Mostly tho, if the board was supposed to have a heatsink, it normally has some kind of provision for mounting it, even if that is just a small flat surface to "glue" it on the chip.

JimboZA

@dgelman.... perhaps you could post a photo of the underside of the shield to see what the heatsink arrangements are, if any. I know the board's not suitable for your needs regardless of heatsinking, but I'm curious to see if they made provision for it. The link you gave shows a top view only. With the board being a shield, there's very little chance, it seems to me, of any kind of heat transfer from underneath, since it'll be right on top of the Arduino.
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JimboZA

Looks like the attached pic is one of the ways of sinking a chip like that.....
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Justscary

Jimbo, I just saw the link above for the board, I don't see any probs heat sinking these chips, if it was me, I would get an allum sink the right size to go across the three processors and use heatsink compound to "glue" it on. Ok it's not ideal, but it would be better than nothing.

JimboZA

Quote
I would get an allum sink the right size to go across the three processors and use heatsink compound to "glue" it on


Yep and that's what my later post shows too Justscary.

I'm just curious though, that the 293 datasheet says the middle four pins are electrical ground and heatsink.... so is the ideal (or theoretical) plan to solder those leads to the heatsink? I can't visualise how to do that on a board where to say the least, space is at a premium.

Gluing a chunk of metal on top seems eminently sensible to me....
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Justscary

I don't think it would matter too much if you did or didn't connect the sink to the pins, I think the idea behind the data sheet specs is to show that it is the common ground and, as some heatsinks need to be earthed to stop noise, and sometimes the sink that is used is the ground, like the side of an allum enclosure, it's showing it can have a ground link there to help prevent ground loops or just bad earth.

cr0sh


But even when the 293 can handle the current in a particular set of circumstances, what are the ways of heatsinking it when it's on a board? It's not like a 298 where there's a hole in the back to attach a sink, even an ersatz nut and bolt and a chunk of metal.

With a 293 on a board, where there's probably limited access to the 4 pins, how to protect it?


I don't know if you can still buy them, but back in the day there were clip-on heatsinks for DIP ICs like the 293 (I have a 16K core memory board that has a couple on some on-board driver ICs).
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dgelman

Hello Community,

First off thank you all for your help.

I recently encountered a couple of issues which lead to me changing my design a little. I would extremely appreciate any comment on my build.

So using L293D I am limited to 0.6 A continuous current, as maximum of 16V motor voltage supply.  I decided to switch the motors, and before I purchase them I was wondering these motors (link below) will cause any same issue (over-heating).

Motor
http://www.pololu.com/catalog/product/1443

These motors run 300 mA free-run with a 5A stall current at 12V voltage supply.  My only issue with using these motors with this shield is the 5A stall current.  I don't think I will stall the motor (in regards to my application), especially with 110 oz-in torque.

BUT, 300mA free-run is still pretty close to 600mA supply.  I always went with a rule of thumb that my driver should at least be 4-5 times current provided over the motor free-run.

Would this driver and motor work nicely together? (I am planning on using 3 of them, if that means anything)

Daniel
Dialup is the future.

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