Electronics > Electronics
quick driver current question
notgiven:
Been looking around the forum a lot to find out the answer to my question. Still not done yet actually. But might as well ask this is the mean time:
I have a driver that can only put out 1Amp at 1.5V (called L293D dual H-Bridge). I have a motor that needs 2.8 Amps at 2.1 volts. What happens when I put them together?
Will the driver chip burn out?
How about this combo: driver gives 1 Amp and 4.5V to 36V (called SN754410 quadruple Half H Driver) used with same motor.
I understand that voltage stats are not really important as motors are often run at voltages above their rated voltage. But rather the current is more important. That's what worries me here. I think a motor that takes more current than a driver can give will burn out the driver chip.
BTW thanks for all previous help. I just kinda left my previous thread dead as I found more reading material, and will be back to it eventually to beg more help.
newInRobotics:
Yes, the chip will burn if no protection is used. You can use weaker chip to drive stronger motor, however some current monitoring and adhusting system has to be in place, however that way motor torque/max velocity will suffer. It's best to mach motor and driver in order to get full performance.
notgiven:
Thanks for answering.
I don't care about the torque/max velocity.
I don't care about maximizing strength/efficiency. I'm a beginner and I'm almost at the point were I can get a motor to move. I just want that for now, so I can fiddle with it and learn.
Question: so how can I set up a " current monitoring and adhusting system"?
I can use transistors, yes? (I don't know enough about circuits yet. Still reading)
Tell me if the following is true: I just need to increase the current somewhere between the driver and the motor, right?
Then the thing will turn w/o anything burning up? (again, neglect efficiency).
Soeren:
Hi,
--- Quote from: notgiven on August 07, 2012, 03:53:36 PM ---I don't care about the torque/max velocity.
I don't care about maximizing strength/efficiency. I'm a beginner and I'm almost at the point were I can get a motor to move. I just want that for now, so I can fiddle with it and learn.
Question: so how can I set up a " current monitoring and adhusting system"?
I can use transistors, yes? (I don't know enough about circuits yet. Still reading)
Tell me if the following is true: I just need to increase the current somewhere between the driver and the motor, right?
Then the thing will turn w/o anything burning up? (again, neglect efficiency).
--- End quote ---
Take a look at this simple controller. If you think you can get this together (MOSFET can be replaced with a power BJT if that's easier for you).
If you think it's within your abilities, I can revise it for your supply, motor etc (just lay down the details). Then you'll have no problems with too little current :)
If you'd rather go with a currnt limiter, you need to detect the motor current and feed it to whatever controller you use to chop the current before it gets critical, but given that you just want to move things however inefficient, another option would be a simple power resistor (calculating value and power rating takes supply voltage/L293D output voltage, motor voltage and whether your L293 is actually the "D"-postfix version
The L293D can only handle 0.6A and both variants drops quite some voltage, so is poor for low supply voltages.
What is your supply voltage? (Battery or mains adapter? Voltage?)
Does your motor come with the specs you mention (2.8 Amps at 2.1 volts), or did you just measure it?
What do you drive the H-bridge with? (Microcontroller, 555 circuit or what?).
notgiven:
Thanks for the advise Soeren.
[/quote]
Take a look at this simple controller. If you think you can get this together (MOSFET can be replaced with a power BJT if that's easier for you).
If you think it's within your abilities, I can revise it for your supply, motor etc (just lay down the details). Then you'll have no problems with too little current :)
[/quote]
Actually I don't think I can do that first suggestion. I might not be able to make sense of the schematic. But maybe if I ask a few questions I might be able to, though it might be too much trouble for you to answer all of them:
- What do all the letters stand for? I know PWM and Gnd and I can identify a motor in there, and I guess the R1, R2, etc are resistors, but that's about it. What does UB, BD140, 1N4004, Schottky, etc mean?
-Do you have a more breadboard friendly representation? Cant solder for this project.
-Would all the grounds end up connecting to the same path to the Gnd on my microcontroller?
- Whats a BJT look like? Would I be using this?: http://www.semiconductor-today.com/news_items/2008/MAY/Transic.jpg
My supply will probably be this: http://www.radioshack.com/product/index.jsp?productId=3932578&gzq=CAT2818121_PartsAndToolsPower
My motor: http://www.automationdirect.com/adc/Shopping/Catalog/Motion_Control/Stepper_Systems/Motors_-z-_Cables/STP-MTR-23055
My drivers:
http://www.hobbyengineering.com/H1384.html
and
http://www.hobbyengineering.com/H1048.html
My microcontroller: Arduino UNO :http://arduino.cc/en/Main/ArduinoBoardUno/
The H bridge must be connected to both the microcontroller and the battery, right?
I think the second proposal would be easiest for me to do (and for you to explain for me). Except, I hope it doesn't involve PWM because I dont know how to apply that.
And when you say "both variants drops quite some voltage, so is poor for low supply voltages", why is it bad to run things at high voltage? Burns things up ?
So yeah, the bottom line is I screwed myself because I didn't have enough understanding before I started ordering stuff in the first place, and now I have to make it work with this stuff or I can't justify ordering more because its not my money.
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