Help for god sake !!!

Discussion in 'Homework Help' started by tracker, Jun 9, 2011.

Jun 1, 2011
41
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I'm posting here to help me solve my problem.
my project is designing a stepper motor driver , everythink is O.K but still one think freaking me out.
__a stepper motor is supposed tu run under a suply voltage higher tenfold or more than the rated voltage.
__my stepper motor power supply is 24V ( i do not have any information about my motor or it's rated voltage, it's a rare motor i did not found any datasheet so i have no idea about the rated current too).
__the resistance of a coil is 1.3Ω.
__so the amount of current that will flow through the winding is :
I=V/R=24/1.3=20A!! that's too much.
__so i have to limit the current to a constant value (better be the rated current but i don't know it if somebody tells me how can i calculate it, a will appreciate).
__just proposing to limit the current to 2A, then the resistor that i have to add is : 2=24/(R+1.3)--->R=(24-2.6)/2=10.7Ω that's fine BUT
the power dissipated as JOULE EFFECT (heat) is P=R*I²= 10.7*(2)² = 42.8 WATTS!!! that's toooooo much heat despite the use of POWER RESISTOR it's getting too hot.
__ so a friend of mine tells me to put a lightbulb that will dissipat that power but i don't see how.
if i put a light bulb(small resistance) it's will light up and will not limit much current.so i have to add a power resistor again en series and the current flowing it's big enough to make that power resistor to overheat.

i'm confused a little bit the idea of a lightbulb is good but i don't see how to use it please somebody give me a suggestions i will be thankfull.
that's my CIRCUIT here :
http://www.imagup.com/data/1122323635.html : sorry it's very big

http://www.mediafire.com/?66lssa171szqqaw
any information is welcome.

2. beenthere Retired Moderator

Apr 20, 2004
15,815
290
Where do you get this information from? The current is the critical thing, so any voltage able to cause that current to flow is enough.

You might try the information at this link - http://www.cs.uiowa.edu/~jones/step/

3. SgtWookie Expert

Jul 17, 2007
22,194
1,761
I told him about the lightbulb trick. It's a low-tech way of getting high voltage across the motor yet limiting the current; not nearly as good as a chopper drive, but I don't think our OP understands how a chopper drive works.

I referred them to the L297/L298 series drivers just to get an idea of how they work. I'm afraid that I simply don't have the time to spoon-feed information like I used to; my online-time for today is about gone.

[eta]
There is another thread in this same forum started the day before this one, and tracker was getting help:

all about trackers' desire to design a stepper motor driver; or at least various parts of it.

I don't know why tracker started this thread; it's just wasting people's time when multiple threads are opened for the same topic.

Last edited: Jun 9, 2011

Jun 1, 2011
41
1
hello
you just have to know i don't mean to waste any body's time here, i'm just asking for help. frankly i'm a beginner (2sd year electrical engineering), i appreciate you helping for me many times.. when you told me about the chopper circuit i didnot sleep i made some researchs , gather informations, know how it works, but it's just not the right time to use it for pedagogic reasons .
i have to make this driver with the lowest price possible.
i'm sorry if i waste your time i'm not a bad fella i'm just curious and like to know stuff from priciples.

Jun 1, 2011
41
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no body you must run it under a high voltage to get big torque and high top speed and avercome the inductance...dt=(L*di/V) when V increase dt decreases.

Jun 1, 2011
41
1
There is good reason to run a stepping motor at a supply voltage above that needed to push the maximum rated current through the motor windings. Running a motor at higher voltages leads to a faster rise in the current through the windings when they are turned on, and this, in turn, leads to a higher cutoff speed for the motor and higher torques at speeds above the cutoff.

Jun 1, 2011
41
1
today i put the light bulb the motor turn at low frequency , when i increase the frequency i hear like the motor it's turning but it is not

8. SgtWookie Expert

Jul 17, 2007
22,194
1,761
Get light bulbs with a higher wattage rating.

This is an interesting integrated driver IC:
http://www.toshiba-components.com/motorcontrol/pdfs/TB6560AHQ_AFG_E_2003_20080407.pdf
I have suggested this driver to others on the forum, and they've used it with good results.
However, you also have to read this document:
http://www.glyn.de/data/glyn/media/doc/TB6560AHQ-E_en_090324.pdf
If you don't follow the instructions, you can burn up the driver instantly.

They cost around \$4.75 each at Digikey. You can spend a LOT of time trying to "make something cheap", not to mention burning up lots of stuff - and never come close to as efficient as that driver will be.

9. Papabravo Expert

Feb 24, 2006
11,079
2,158
You cannot START and STOP a stepper motor at high speed. There is insufficient torque developed to overcome the rotor inertia. You must accelerate and decelerate the motor and you must avoid both the mechanical and electrical resonance regions. Look for the mechanical resonance in the 200 Hz. region and the electrical resonance in the 5 kHz. region.