Let's Make Robots!

burnt md23 :(

Ok, i burnt my brand new 50€ worth MD23 motor controller. I'm deeply desperate... I was all excited about its arrival with all the RD01 kit, i was all happy about the incoming testing and building and having fun with it, when suddendly all the magic smoke came out of it and dispersed for good. :(
BWAAAAAA :( i'm so saaaad :(

Sniff, ok.. So i'd like to at least have some idea of what happened, becouse i have none.. How can it happened ?
This is the chip that smoked:
37369566dded3f0378c85b4cb5b4b177.jpg


what is is ?
I was normally feeding the board with 12V for motors (logics use 5V, with internal regulator), i connected the SDA and SCL of the arduino and MD23 together.
The only strange thing i did was connecting the ground of the MD23 to the ground of the Arduino. Is it wrong? It wasn't working without it, and when i connected it worked for some time before smoking out. I did it becouse it was not communicating properly throu i2c, i thougt that maybe it wasn't able to drain the line or something like that (the lines are pulled up).
Did i lost my mind? If i have two board communicating with i2c, each with its own power source, should it be enought to just connect SDA and SCL, or also ground or 5v or anything?
Or what else could have gone wrong ?


Ok.. thanks everybody.. i'm going back to my sorrow..

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So something like that just happened to me. Both mnotors were working until I tried to connect a Serial LCD to teh Arduino which seems to be shorted somewhere :S When I connected everything Arduino failed and reboothed while one of the motor controllers of the MD23 didnt work at all... Trying it again later on both stopped working.. awsome :)

Can somebody explain me please which component I need to replace and how do I know if it is that one? cause it doesnt seem to be anything burnt!

thanks

HI, I just burnt my md23 I think the same way. Wierd thing is I've been using it fine for months connected to a power supply (12v), and I had been using it for one day with a battery pack that is only 9.6V. Could this be the reason why it went? Although I don't see how :-( if the voltages are lower surely there's less risk??

What I would say from the descriptions  of the hook-up of this board, is that everything is being driven by an inadequate power supply. A 12V 500 mA power supply certainly won't over-current anything, but it might undervolt the device as it is trying to drive the FETs and the motor. The board probably won't draw much itself, but the EMG30 motors have a 2.5 Amp stall, which they attempt to draw at least briefly everytime they start up. Trying to get 2.5 A from a 500 mA supply will drop the voltage down pretty substantially. The gate voltage Vgs of the FET really needs to be up around 10-12 volts to ensure complete turn on. Otherwise, they can operate in a "linear" region, that allows a lot of heat being dissipated in the device, and eventual burn out.

In John_ posts, the power supply is not specified, but stated to limit to 2.5 A, not sure what is happening there. It is interesting that the same FET blew, and I wonder about the trace length from the driver to the FET, and any possible PCB errors.  Found the LM5104 driver but can't see any real probs there. It has an Under Voltage LockOut that should have helped some, but may not have been able to shut down in time. Just a weird problem, and thought I'd throw another possible issue out there. What I would suggest is to have 12 volts worth of fresh charged batteries, rather than any type of power supply for running an h-bridge. Maybe with a fuse or PTC device or some other current monitor if you wanted to be safer.

I used a bench supply and it was working well, i.e. both motors responding perfectly to tilt (I’m making an inverted pendulum robot).  As soon as i load tested it to check max current draw, just on one motor the mosfet died.  The most likely cause is no back emf diode... I have designed a 30amp PWm motor drive, i used a Scotty diode which heated more than the mosfet because of  the back emf.

This reveres voltage (back emf) can be up to 7times the input voltage i.e. 7*12volts (84V), and the max reverse voltage for the mosfets used is 30V. 

any way i will be soldering some diodes (8), one per mosfet to the MD23 once i replace the mosfet. Which has to be shipped from another country. This is all because i assumed the MD23 design would feature a protection diode which is a fundamental feature to any semiconductor that is switching a inductive load.

As to the first post with a 500ma supply this would still be enough to cause a reveres voltage from the inductance of the motor to destroy the mosfet. 

 also my MD23 did work fine for over 30mins. in this time i had it running at full speed in both directions no probs.  Until it was load tested.... than it died.  since the power supply was limited well under the ratings of the mosfets, if the controls (i.e.  mosfet driver) or the microcontroller stuffed up and latched on side of the H-Bridge on then the still would be fine as they could handle much more current that what was supplied.  And the fact that the unit worked fine until it was loaded shows that the H-Bridge and driver was working fine. 

Only conclusion i can make is that the lack of revers voltage protection killed the mosfet.

 

Hi there,

The final answer is that the MD23 appers to have no from of "back emf" (flywheel diode) proection.  The mosfets used have a body diode but when switching and inductive load an external fast switching diode such as a schottky diode. 

Ne way im ordering new mosfets today and some fast recovery diodes to prevent this happening again

 

The best way to remove and resolder SMT DIPs and other chips is use a hot air gun. just heat the area up enough to melt the solder, but dont bump other components, you'll need some tweesers or something to pick the chip up.

After you have removed the old one, put the new one in its place, you may need to add some solder with your iron to each pin but its not to difficult.

Godd luck. 

I don't have the equipment to do this.. I don't think i'll be able too.

I think i'll write to the place where i purchased it and ask if they can do something.. maybe replacing with a discount or just changing it or such.

Thanks!

so yeah Nicola,with the below mentioned tutorials read from sparkfun.com were' back to a soldering iron,solder wick and a new Chip and this thing will be humming right along again.

my guess is that either Latchup,Heat or BackEMF Killed the poor wittle mos-Fet. Power MOSFETS are sort of my favorite thing to pop so i cannot help to think they are pretty fragile little creatures.

Soldering SMT with just an iron and Solder Wick is very good to know how to do in general. then i would send an email saying HEY i burned my board out. give me a replacement. at the same time i would order my $1.00 Part so that if they do turn you down and say nope you're stuck buy a another. you will have your replacement component in just a day or so and will have found the fastest way back in action and as cheaply as you possibly can. which without them promising you the motor controller will not ever burn out by clamping down and limiting pulsewidth i don't *THINK* they will. a motor controler is the most often destroyed component in robotics applications. 

you should read about this 400 pound BEAST of a robot and this guys $500usd - 1000USD motorcontroller's he kept smoking.

http://www.eigenspace.net/robot/ 

Hi there,

 

I just got a MD23, and blew the same mosfet.  I think there must be a design flaw as the module was taking less than 2.5 amps when the mosfet blew. 

 Anyway ordering new ones tomorow.

Probably it depends on the voltage. How were you feeding the board ?