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Topic: Weird motor problem (Read 901 times) previous topic - next topic

vek11

Hi,
I have a 1.5-3v dc motor, and I am using a SN754410 to control them. The problem is that when I hook up 1 motor with a 3v power supply(2 AA batteries), the motor does not move but it makes a tiny noise when I put it near my ear. (I thought the motor no longer worked, but then I used 2 motors with a 6v power supply, and the motors ran at full speed.) Any help clearing this up for me? thanks.

dc42

Why oh why do people persist in using ancient bipolar H-bridge chips such as L293, L298 and SN754410? These chips have high voltage drop, which also means that they get hot and can't take much current. My advice is to forget bipolar motor driver chips and use modern mosfet-based chips instead. If you really want to use a bipolar chip, then read the datasheet to see how much voltage drop it has, and increase the power supply voltage over and above the motor voltage by that amount.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Drew Davis

Hello!!!

The reason you'r hearing that noise is because your not giving the motor enough voltage. Due to the fact that your AA batteries probably are not really 1.5v more like 1.2v and because of the voltage drop due to The SN754410 your motors are not getting enough voltage. When you use the 6v your motors are getting plenty of voltage (probably to much). Keep in mind that voltage is not split up between the motors like amperage is. Each one is getting 6v. I would recommend using 3 AA batters. After voltage drop your motors should each get around 3V.

Best of luck,
Drew Davis

vek11

Thank you Drew Davis, that helps a lot.

Drew Davis

No problem!!!! Just out of curiosity what are you building?

cr0sh


Why oh why do people persist in using ancient bipolar H-bridge chips such as L293, L298 and SN754410? These chips have high voltage drop, which also means that they get hot and can't take much current.


Probably because they are cheap, easy to obtain, come in thru-hole packages, and are well documented with tons of example designs; in other words, they have real "staying power". The L293/SN74410 works great for most hobby designs at 1 amp per channel (perfect for most small DC motors); the L298 is good for 2 amps per channel, or 4 amps in bridged mode (granted, you need one helluva heatsink for it, though). Even though they aren't the most efficient, for most hobby purposes, both work well.

Used right - the L293 can even be used as a driver for a MOSFET h-bridge (or a larger bipolar bridge)...


My advice is to forget bipolar motor driver chips and use modern mosfet-based chips instead.


If you have links to a good replacement MOSFET-based h-bridge driver chip in a thru-hole package variant that compare to the aforementioned bipolar devices, please post a link or some part numbers - I'm sure that tons of people would appreciate it!


If you really want to use a bipolar chip, then read the datasheet to see how much voltage drop it has, and increase the power supply voltage over and above the motor voltage by that amount.


Can't argue there; honestly, this applies to any and all parts - not just h-bridge ICs...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

dc42

#6
Dec 30, 2012, 10:35 am Last Edit: Dec 30, 2012, 12:27 pm by dc42 Reason: 1

If you have links to a good replacement MOSFET-based h-bridge driver chip in a thru-hole package variant that compare to the aforementioned bipolar devices, please post a link or some part numbers - I'm sure that tons of people would appreciate it!


This one http://uk.farnell.com/allegro-microsystems/a3959sb-t/motor-driver-full-bridge-pwm-smd/dp/1521714 handles up to 50V and 3A, and does current limiting internally if you provide a sense resistor. Minimum motor supply voltage is 9.5V.

For anyone prepared to use SMD breakout boards (available from Sparkfun, eBay etc.), a much wider choice is available.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

vek11

Hey Drew, right now, i'm building a tank that will just move forward and turn for certain periods of time. Then im planning on hooking up a simple claw so it can pick up random things like a bottle of water...thanks for asking!

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