L293D Motor Supply Voltage Drop [SOLVED again]

Hey all-
I have been trying to get my L293D chip (actually several) to work and I've double and triple checked the connections per the data sheet and various diagrams on the internets.

I can get the chip to work when I control a tiny lil' motor and use a tiny lil' 5v power supply as the motor voltage. But, as soon as I try to control my bigger RC car motor with its 9v power supply, the voltage of the supply dips to about 2-3 volts and the motor subsequently spins really really slow.

I've got my volt meter connected to the motor supply input pin (pin 8) and ground. That's where I see the voltage drop from 9v down to about 2-3 volts when I turn on the chip and try to provide a control input.

I've tried this several times (all weekend and most of last weekend) and dug through several examples to make sure that I'm following the right procedure. And I've tried 4 different chips just to make sure that I didn't fry them. Anyone have any idea what could be going on ? (I also tried giving up and building my own H-bridge by hand but that failed miserably as well.)

The L293D chip cannot possibly supply the current that a (brushed) RC motor requires. For those, you need an Electronic Speed Controller (ESC) or a dedicated, high current brushed motor driver like those sold by Pololu.

The L293D is a chip from the stone-age. It has a large voltage drop.
You can use it for small 12V motors, but that's about it.

Using the L293D with 5V for the motor power is a problem, the voltage is too low.
Using the L293D at 9V with more current is also a problem, since the voltage drop can be 2.6V.

A normal 9V battery can not supply enough current for a motor. Even a normal RC car motor requires more current than a 9V battery can supply.

Hmmm, well the data sheet (http://www.ti.com/lit/ds/symlink/l293d.pdf) says it can handle motor voltage up to 36v and up to 600mA of current. My motor battery is actually a rechargeable 1600mAH (not the transistor radio type) and works fine on the car w/o the L293D. I measured about 200mA stall current when the motor's in its nominal state (i.e. again no L923D).

So when I have the 9v motor supply and 5v chip supply connected, the supply drops by 6-7 volts, not the 2-3 volts that would/could be expected.

And I've seen a few postings out on the internets where people connect one of these chips to a 12v motor. So I'm stumped.
Thanks for the input.

A 9V motor with only 200mA stall current and a 1600mAh battery ? Well, that should work, even with the stone-age L293D XD

Can you give a link to the motor and the battery ?

What is a "nominal state" ? Even Google Translate didn't help me there. The stall current is when the motor gets the maximum voltage and the axis is blocked. It is the maximum current the motor can ever request.
I think it is hard to believe that a 9V motor for an RC car has a stall current of 200mA. Is that RC car only running down-hill ?

I'm confused what voltage is dropping by 6-7V. The voltage over the motor or the voltage of the battery ?

Can you upload a schematic or scan a drawing of a make a photo of the wiring ?
If you have your circuit for example on a breadboard, you can have bad connections.

You can do many tests: measure the current supplied by the battery, when the motor is fully on, and also with the motor fully on in the opposite direction. Do the same test and measure the current through the motor.

All these posts and test might be useless. If for example the stall current is 2A instead of 0.2A, you can't use the L293D, and you need a H-bridge motor driver with mosfets. Perhaps you should try such a motor driver and forget about the L293D.

In my response, I assumed that you had a much larger R/C vehicle than you seem to -- many of the racing type vehicles consume up to 50 amperes!

However, the L293 should be able to handle 400 mA with no hitches (never believe the maximum values of the datasheet), so I'm surprised that your smaller motor doesn't run with it. On the other hand, I have trouble believing the figure of 200 mA for the stall current. Most toy vehicle motors, even the small ones, consume 1 or more amperes at 3-6 V.

How, exactly did you measure the stall current? Was this with a fully charged R/C 9 V battery? If so, did you measure the battery voltage at the same time that you did the stall current measurement? You need to do that to account for any internal voltage drops in the battery.

In any case, the L293D and L298 chips are old, inefficient technology, and you will have much better luck with the newer MOSFET devices on the market. I've had excellent success with the motor drivers from Pololu.

I was being a bit sloppy with my terminology, when I wrote "nominal" I meant holding on to the tire so the motor could not move while measuring the current when the L293 was not in the loop. I agree that the amp rating for the stalled motor should have been in the 1A range. Of course I was on my fifth chip by then and was getting fed up, so I could have buggered up that test.

And yah, my motor is a smallish one-- I picked up the car (a RadioShack monster truck with motor in tact) at a garbage sale and bought this battery pack for it:

When I say that there's a voltage drop when using the L293 I meant that while measuring the battery's voltage when the L293 is in the circuit loop, that value drops to about 3-4 (closer to 3) volts, even when the motor is not running.

I did order this from sparkfun since I'm about to give up:

I also saw on several posts that said that the L293 will drop 2-3 volts due to its darlington design (by nature and expected) and that to get around massive current drain (more than 1 A) you can piggy-back them on top of each other, if that helps anyone else having issues.

That is either wrong wiring or a broken L293D. Perhaps you misunderstood the datasheet and wires all them wrong so all of them are broken ?

That could be, and I was hoping that was the case (i.e. that I have it wired up wrong).
This is how I've got it set up:

pin 1: +5v
pin 2: +5 or gnd (for control)
pin 3: + motor
pin 4: ground (common with 9v and 5v supplies)
pin 5: ground (ditto re common)
pin 6: - motor
pin 7: +5 or gnd (for control)
pin 8: +9v

pin 9: not used yet
pin 10: not used yet
pin 11: not used yet
pin 12: ground (again, common)
pin 13: ground
pin 14: not used yet
pin 15: not used yet
pin 16: +5v

I've also used several chips in case I did have it accidentally wired wrong and had blown it up.

Datasheet says to expect motor out to be 1.4 to 1.8V below Vcc2, so with 5V source you're down to 3.2 to 3.6V.

The part on the sparkfun board

will have much less voltage drop across it, see page 5 of the data sheet.
Basically: 1A x 0.5 ohm Rds = 0.5V loss.

Yah, but my Vcc2 is set at 9v (the motor power), not 5v (the logic power), so I'm confused about that big drop.

Thanks for the sparkfun link, I'm just surprised that more people hadn't had this issue with the L293D for as "popular" as it appears to be.

The L293D was popular.... in the stone-age.

You didn't connect the second part of the L293D, if you have not connected the inputs, the output might be floating and draw a lot of current, or the output might be in high frequency resonance, also drawing a lot of current.

You connected the enable to +5V, but the PWM signal is normally connected to that enable. The two other pins are used for the direction with two other Arduino pins (not pwm).

That was it!

So I tied the unused pins all low and voila! No more major drop. Thanks for the tip!

I also just rx'd the sparkfun TB6612fng driver but haven't seen too many how-to's on the interwebs using it. For some reason the L293x's seem more prevalent.

Anyway, thanks for all the help!

For some reason the L293x's seem more prevalent.

Mainly because they are cheap, well understood, and there are a ton of them out there - basically, the L293 (and the L298) are the "555" of motor drivers...

Yah, that would make sense. The sparkfun driver I bought in desperation was $8 and didn't have the protective diodes. Plus it requires some soldering to header pins, and you have to be careful of static discharges when handling it.

I do have to remove the [SOLVED] adjective from the subject line: after my elation of getting a single motor to work properly, the the thing started acting weird again when I hooked up the second motor. I'm wondering if the chips that I bought could be faulty.

Acting weird is often the power supply not being strong enough, sometimes also dropping the voltage of the Arduino.

Right again. Long story short, my 9V supply was wacked. I replaced it and VR-RRRRROOOOOOOMMMMM!
Thanks for the info, NOW marking as solved.

I have same issue with L298. Qunqi L298N Motor Drive Controller Board Module Dual H Bridge DC Stepper For Arduino. Voltage drops from 10v to 4.5v. Any help..