Determining Hall Sensor pinout

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I will be teaching a quick course on using Arduinos at a Hackerspace camp this summer, and want to use some small BLDCs that I've scavenged out of CD-ROM and DVD-ROM drives.

The motors come equipped with Hall sensors, but I have no way of determining which pin leads to what, and I can't get at the sensors to see what model the chips are. On most of the motors I can determine which pins have to be power and which are signal, but that doesn't tell me what the polarity is.

My problem is that I don't want to fry the Hall sensors while trying to guess which is positive and which is negative. Any suggestions, aside from being ready to chuck half of them in the e-cycling bin because I've destroyed the sensors?

Last Edited: Mon. Jul 19, 2010 - 11:51 AM
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I think you could drive them without feedback, maybe that way you could analyze wich sensor goes to wich winding. I think atmel have a appnote on sensorless BLDC driver, or you could buy a cheap controller for a model airplane.

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Oh, I know I can run them without hall sensors, that's no problem. But then you're into what is generally called sensorless BLDC (even though there are clearly sensors, they're just elsewhere than the motor) control.

Usually, the sensorless designs don't use hall sensors because they're more expensive than free and add another point of failure. For my purposes, I want to have access to the hall sensors. They're already there, so there's zero advantage to not using them.

Thanks anyway for taking the time to respond.

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I dont have any experience using hall sensors, so it all is a guess for me. Would it be possible to run the motore sensorless and then analysing the ouput from the hall sensors to find out where it belongs?

I think these motors allows you to just pull of the rotor casing without causing damage, should get a better view on how it is connected that way.

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The problem is that as far as I'm aware, the hall sensors won't make an output unless they're powered. I'm hoping to find out that that's not true, that somehow with some combination of pins that I can figure out which has to be the ground.

It's an idea to pull the casing. However, it's probably easier to just guess and if I get it wrong I chuck the motor in a bin and get another from the copious amount of computers we're always throwing away here at the university.

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Hehe, i used to pull out motors from university scrap computers too :D Never got to use them tough.

If you remove the sticker on the backside of the motor, it should be very easy to also remove the locking pin holding the axel in place. Worth a try i would say, 2minute job at most.

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Surely some hacker at the "Hackerspace camp" will get the motor apart (otherwise I volunteer my 2 yr old grandson) and then an inspection of tracks with a buzzer will identify the pins.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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LDEVRIES wrote:
Surely some hacker at the "Hackerspace camp" will get the motor apart (otherwise I volunteer my 2 yr old grandson) and then an inspection of tracks with a buzzer will identify the pins.

Not to worry, we're pretty good at getting them apart. Not that it does any good, as the only markings are things like "24".

And, sadly, connecting pins to pins isn't going to help as the problem of what voltage to connect to which pin still remains unsolved.

Does anyone know if Hall sensors will completely fry if I run them backwards? Are they likely to give ma signal, albeit a bad one, if I undervoltage them? If I had to guess, which would be the best strategy to ensure that on the 50% where I guess wrong on the first go that I don't completely fry the chip.

Or is there a common pinout to hall sensors such that if I had to guess, better to guess one over the other?

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use current limiting resistors on all three leads to prevent instantaneous burn out and You may very well be able to determine rentation...
Just keep in mind two sensors may give oppositie level depending on their bodily orientation with respect to the magnetic field

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In-circuit curve tracer such as the Tracker 2000 and successors utilize current limited ac to produce forward/reverse bias waveforms on the display without damaging the components. You could make a simple version like this.
http://www.google.com/url?sa=t&source=web&cd=4&ved=0CCMQFjAD&url=http%3A%2F%2Fwww.qsl.net%2Fkd7rem%2Fpdf%2Foctopus.pdf&ei=oONETNivA4OisQOxmKWJDA&usg=AFQjCNEpzlFOx2uAxihUOIldwJq9L4mLcg

I used > "in-circuit" component "curve tracer" < as a search string with google. Limit the current to no more than is necessary to overcome shunt capacitance and limit the voltage to just reach the reverse breakdown region. If you turn the motor shaft while doing this, you should see which polarity is correct.

Rick

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That's really neat, RickB. Thanks a lot for the tip. I'm sure this is the solution, but will report back with results.

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It is very easy to remove the spindle (just pull it with your hand) to be able to see the connections inside, this way you will be able to see the coil connection points but if the hall sensors have 4 pins like mine they have a bias pin, a ground pin (these are common in all sensors) and three + - output pins.
Look at the datasheet of the driver chip and then follow the lines of the pcb board to see which goes where, thats what i did.

Alex

"For every effect there is a root cause. Find and address the root cause rather than try to fix the effect, as there is no end to the latter."
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