How to modify this L293D Motor Driver Shield to allow more voltage?

Thread Starter

fablau

Joined May 14, 2020
72
Hello everyone,
I am an electronics newbie, and I am working on an Arduino project involving the use of electromagnets.

The electromagnets I am using are custom made and at 20v they draw about 90mA. I'd need to be able to make them run up to 32v for my application, which means they can draw up to 150mA at that voltage.

Now, I'd like to create a custom made L293D Motor Driver Shield similar to this one:

http://wiki.sunfounder.cc/index.php?title=L293D_Motor_Driver_Shield

But I'd need to be rated for voltages up to 32v, or maybe even a little bit more for safety (35-36v?) (that one is rated up to 16v). I know that L293D chips are rated up to 36v, so they should be ok to be used. But I have no idea about the rest of the circuitry that'd need to be "upgraded" (i.e. resistors, capacitors, etc). Keep in mind that with two L293D I can drive up to 4 magnets at 32v drawing a total of 600mA when fired at the same time.

Here is the schematics of that shield (also present on the webpage above):




I could easily reproduce the same exact circuit from that schematics, but, as I wrote above, I'd need to modify it to be rated up to 35-36v.

Thank you in advance for any feedback on this. I already looked anywhere for an answer to my inquiry and couldn't find anything around.


All the best,
Fab.
 

bertus

Joined Apr 5, 2008
20,756
Hello,

The L293 is capable to work on 36 V absolute max.

L293_ratings.png

Working on 32 V would be no problem.
Change C7 and C8 with 50 V or higher types.
Also make R1 about twice as high value.
Raise V+ to the 32 Volts.

I can not see where the V+ is coming to the board.

Bertus
 

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shortbus

Joined Sep 30, 2009
7,936
My question to you would be why are you wanting to use the "motor shield"? Are you needing to reverse the polarity of your electromagnets? If the magnets are only being turned on and off why not just use a mosfet with it's gate controlled by the Arduino?

Also maybe explaining what your trying to accomplish would get some ideas to help you.
 

Thread Starter

fablau

Joined May 14, 2020
72
Hello,

The L293 is capable to work on 36 V absolute max.

View attachment 207169

Working on 32 V would be no problem.
Change C7 and C8 with 50 V or higher types.
Also make R1 about twice as high value.
Raise V+ to the 32 Volts.

I can not see where the V+ is coming to the board.

Bertus
Wow, thank you so much for your quick and in-depth reply!

Ok, sounds easy then... about the capacitors, do I just need to increase their voltage, but keep the same farads?

As for the power supply, I'll use an external DC power supply. The logic will be driven by an Arduino.

I'll post more pics of this job soon. Thank you again very much.

Fab.
 

Thread Starter

fablau

Joined May 14, 2020
72
My question to you would be why are you wanting to use the "motor shield"? Are you needing to reverse the polarity of your electromagnets? If the magnets are only being turned on and off why not just use a mosfet with it's gate controlled by the Arduino?

Also maybe explaining what your trying to accomplish would get some ideas to help you.
Good questions Shortbus.

Well, I need this kind of setup because the electromagnets are able to both attract and repel, that's why I need to use the L293D to invert the current flow (to repeal if I need to). The final goal is to be able to move objects on a flat surface with electromagnets.

Please, let me know if you have any further questions.

All the best,
Fab.
 

bertus

Joined Apr 5, 2008
20,756
Hello,

Yes, keep the 100 μF value and raise the voltage.
The next values for capacitors are 25 V and 35 V.
I am saying 50 Volts or higher as you want some headroom.

Bertus
 

shortbus

Joined Sep 30, 2009
7,936

Thread Starter

fablau

Joined May 14, 2020
72
The L293 is well know for it's voltage drop problems and it is very hard to heatsink it. Is there a reason you don't want to make a better H-bridge that can both handle your voltage and give better current output?
Or if your not comfortable making a circuit get one from Ebay ready made, just the first one that came up;
https://www.ebay.com/itm/10A-Dual-Motor-Driver-Module-Board-H-bridge-DC-MOSFET-IRF3205-3-36V-/332050977653
Good question, again! I didn't think about that kind of solution actually... it is my understanding with that kind of circuit I can still invert the current flow right? Exactly like with the L293D?

Thanks again very much.

Fab.
 

Thread Starter

fablau

Joined May 14, 2020
72
Sorry for the question above, I found my answer on the eBay page you gave me, it looks like those circuits can invert the flow and I can also control its power via PWM. Am I correct?

Thanks again!
 

shortbus

Joined Sep 30, 2009
7,936
Sorry for the question above, I found my answer on the eBay page you gave me, it looks like those circuits can invert the flow and I can also control its power via PWM. Am I correct?

Thanks again!
That's what they are for. All of the motor drivers using chips like L293 and others like them are limited in the power they can handle, since the mosfets/transistors are very small to fit in the chip. So when you need power you have to go with something made for power. Adding a heat sink to the mosfets would probably also be a good idea.
 

Thread Starter

fablau

Joined May 14, 2020
72
That's what they are for. All of the motor drivers using chips like L293 and others like them are limited in the power they can handle, since the mosfets/transistors are very small to fit in the chip. So when you need power you have to go with something made for power. Adding a heat sink to the mosfets would probably also be a good idea.
That makes sense! Thank you again very much. I'll try one of those boards as well.

Appreciated your help!
 
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