I am trying to use a L293D to drive a small 12v DC motor. Everything from sketch works fine, I'm pretty sure all connections are OK because I checked them multiple times. My problem is that while I'm feeding 12v to the L293D, only 7.9v are outputted to the motor drive.
Now, I''ve read that this chip can cause some current drop, but it seems to me that 12 to 7.9 is too high.
I've tried to connect the EN pin both in digital and as PWM, nothing changes. I've conected both EN pins top, but only one motor is connected.
Is this a power loss in an acceptable range for the L293D so I better head for a different chip? Is there anything on the connection that I should be checking better or can I suppose I somehow fried my L293D?
Thanks fopr any suggestion
Question 1. Is it a problem for you? Or does the motor work the way you want to.
Question 2. How do you measure output voltage? A motor is an inductive load. Also, the current through the motor will not be constant. Most meters do not handle that accurately. Replace motor with resistor and measure again...
Option1: go for mosfet equivalent of L293...
Option 2: (if using breadboard). Make a version with soldered connections. Breadboards are not the best connectors (especially for higher currents).
Answer to your question: voltage drop of this chip is considerable. 4V is higher than usual.
Hi,
What signal are you feeding the 293?
Put your DMM on AC range and measure the output voltage.
Can you please post your code?
Can we please have a circuit diagram?
An image of a hand drawn schematic will be fine, include ALL power supplies, component names and pin labels.
Thanks.. Tom... 
How small.
The L293D is still in specs if it drops 3.6volt at 600mA.
Leo..
That's typical for this old driver chip.
Newer MOSFET drivers don't drop that much voltage, if you need more motor power.
@s_bastian never said what size motor.
It could be 1hp motor drawing 5A for all we know
Speculating about what is wrong is pointless
If it would draw 5A the L239 would have gone up in smoke...
So why not assume it is a typical hobby motor...
And as always: assumptions are no evil, as long as they are explicit and checked afterwards...
With newbies, I never assume anything.
OK, trying now to give as many answers as I can:
With newbies, I never assume anything.
I'm NOT that newbie but good to point out that THAT might be an issue. I've try to do my homeworks before posting, nonetheless this comment can help others in the future
Foreword: I'm modifying a feeder, changing the present timer board (late medieval stuff, 4 buttons+display) with an ESP32 and a web interface. THAT part works fine. Full code here, it is plain copy/paste/adapt, I'm glad I could optimize some routines and use preferences.h instead if SPIFF, but don't expect wonders. It works easier than I expected and it does what I need it to do.
Ther pinout.png is the first version using a relay, will try to update ASAP
Presently there is only a test routine under the feed() function, that turns the motor left and right for given seconds. The machine has a rotaton sensor and that will be implemented in later phase, already tested with the relay but I switched to H-bridge because I need to brake the motor faster to "close" the feeder, and revert rotation in case the feeder gest stuck (->rotatrion takes longer than expected). This same code was successfuly tested using a relay, the only changes made are the pin declarations and the feed() function. Using it's onw original power supply the motor was fed full 12v and was turning faster. So there is not just a "tester" thing, is is also a visual one.
this is the motor:
The reason why I'm "blaming" the L293D for the power loss is thst, again, it has run for years under plain 12v and with the same power supply it was running fine with a relay. Unluckly the original board is sealed so I cannot see what they are using on that.
Some answers
is this I problem? Possibly. This is going to have to support some load in terms of weight/torque, I don't know yet how being fed less volt can affect the functionality
how did I test? Apart from visual verification (it turn slower than with the relay ) I tested it under load. Now upon your hints i retested on the pins directly after disconnecting the motor. Voltage improves but is still under 9v
this is soldered stuff, not breadboard. Solders has been checked and all potentially inaccurate ones has been redone and wire tested. So i would exclude that as the problem.
Now, I am not a prefessional, I'm just an amaterud trying my best. I am using a L293D bare chip because my dealer was out of L298n boards. This is what I was meaning to use
but since I' still prototyping buying one spare in shop was cheaper than one on amazon, and I still don't need 10s to drop the cost 
I thought preformance was about the same, but if you say that using a L298n board would improve the performance, I'm keeping the L293 for prototyping and reverting to that on "production"
Someone mentioned MOSFET, but as already told I'm not a professional and I don't know them as hardware, I'm still on the lower part of the learning curve. Any hint/axpalantion link on how using a MOSFET can affect my project compared to a L293/L298?
Thanks anyway for all your comments/hints so far!
Hi,
Please post your code.
Please post your schematic?
In a new post please.
Do you need to control the speed and or direction of the motor?
Motor Specs
Technical data
Compare in category
| Dim | (Ø x L) 37 mm x 77 mm | |
|---|---|---|
| (Ø) | 37 mm | |
| Length | 77 mm | |
| Max. transmission load | 18 kg/cm · permanent 6 kg/cm | |
| Gear reduction | 1:200 | |
| Nominal voltage | 12 V | |
| Max. load current | 2.1 A | |
| Gear reduction (details) | 200:1 | |
| Shaft length | 12 mm | |
| Shaft Ø | 6 mm | |
| Operating voltage | 12 V DC | |
| Peak torque | 180 Ncm | |
| Idle speed (nominal) | 30 U/min | |
| Load speed | 26 U/min | |
| Product type | Gearmotor |
Thanks.. Tom..
PS. The reason to post code and schematics is because some of our users have platforms that don't like going off forum to retrieve data.
The information posted on the website link you gave under Technical specifications does not match the information given in the data sheet, specifically max load current. Is it 2.1A or 290mA?
If the motor is not strong enough, move to mosfets or 16V power supply.
If your motor has a stall current of 2amps, the L293 might be underdimensioned. This might lead to failure immediately or on the longer term...
2 amps times 4V is 8W... that will get pretty hot without heat sink...
The Darlington transistors in the old L29x BJT chips have a voltage drop of about 2V each, 1 high side plus 1 low side switch drop 4V in total. MOSFET transistors in modern CMOS chips drop perhaps 4mV and consequentially mW where the L29x have power loss of W.
You don't have to worry about the chip technology, the driver chips or boards have about the same well known function pins.
Probably not, the chip has thermal limiting, and shuts down.
Try to piggy-back a second L293D chip on top.
Leo..
Ok so now that it is quite clear that the L293D has some pretty heavy power loss, since I don't need PWM my options are:
- relay-made H-bridge, as I was already using a dual relay module I already had
- a MOSFET module
Would you kindly suggest me one? Is there anything I need to pay attention to when choosing? For example, with relay the optocoupler is crucial, is it needed for MOSFETs too?
...
I don't know. All I know is that it works with minimum power (a small solar panel and minimum light) and that the difference between measuring V with and without the motor connected is less than a volt. So, the L293d is evidently NOT the way to go for.
Search for H-bridge motor driver and check for the requirements (V, A) of your motor.