Using 3 batteries 9v in same circuit (arduino & L293d)

Thread Starter

naitsab

Joined Sep 7, 2017
9
Hello,
I am pretty new in electronic so I may not used correct terms but here is my problem:
my project consists of an RC car using arduino and L293D motor driver with brushed 12v DC motor.
I have a 9v battery with voltage regulator (5v and 3.3v like this) for the arduino and the L293D internal voltage.
I would like to use 2*9volts battery for the motor power.

here is really simplifed schema and my question regards the question mark on right

If I put the 2 batteries in parallel to get more voltage for the motor, can I plug the ground of the batteries to the voltage regulator used for the arduino?
Can it damage anything?

Thanks
 

Bernard

Joined Aug 7, 2008
5,788
The 2- 9V batteries are shown in series for a weak 18 V depending on what type of 9 V batteries they are.
You could check with an ohmmeter to be sure that all neg. & grounds are common on the V reg. IF they are , no problem of connecting all neg. & grounds together, except for the series mid connection of 2 - 9V batteries.
 

wayneh

Joined Sep 9, 2010
17,160
My read of the L293D datasheet says yes, that Vcc1 and Vcc2 should share ground. That's what the chip is designed for.
 

philba

Joined Aug 17, 2017
960
Here's two ways to do it. The second one will allow using only 2 batteries. If there is more current draw from the regulator than the arduino, you might want to keep the 3 battery solution.
bats.png

You probably know this but 9V batteries are terrible for powering motors. A typical 9V battery only has 500 mA hours of current and really isn't designed for even moderate current draw. They are nice and compact, though. But, you will probably run through batteries pretty quickly. I'd look at rechargeable battery packs designed for RC use.
 

Reloadron

Joined Jan 15, 2015
6,307
A note about powering your Arduino:
"The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V)".

Using the Arduino Uno board pictured below we can see the board has an on board regulator and that regulator has a 2.0 volt dropout. This is why external power to the board should be 7 to 12 volts and actually 9.0 volts is a popular choice.

Arduino PWR.png

There is no need for an external 5.0 volt regulator. Using below 7.0 VDC is not a good idea so you may want to rethink your circuit. Additionally using the 5.0 Volt on board regulator the Arduino board offers a 5.0 Volt low current output.

Ron
 

Thread Starter

naitsab

Joined Sep 7, 2017
9
Thanks Philba and Ron.
@philba yes you got me, I am using Alkaline 9v and it doesnt help hehe, already ordered some new one for rc.
The motor draw a lot, the l293d drop doesnt help (counting 7.1volt with new battery from motor pins) I thougt that with a bit of volts more it could help.

@Ron thanks, actually the schema does not entirely reflects what I have (tried to explain big picture about my grounds issues). The arduino is powered directly to the vin of the regulator (9v), I use the regulator for some leds, servos and the L293D itself.
 

crutschow

Joined Mar 14, 2008
28,474
For driving the motor it would likely be better so use larger batteries, such as 9AA's (or 9AAA's if space is of concern) in series.
Those will power the motor a lot longer than two 9V batteries in series.
 

Reloadron

Joined Jan 15, 2015
6,307
Thanks Philba and Ron.
@philba yes you got me, I am using Alkaline 9v and it doesnt help hehe, already ordered some new one for rc.
The motor draw a lot, the l293d drop doesnt help (counting 7.1volt with new battery from motor pins) I thougt that with a bit of volts more it could help.

@Ron thanks, actually the schema does not entirely reflects what I have (tried to explain big picture about my grounds issues). The arduino is powered directly to the vin of the regulator (9v), I use the regulator for some leds, servos and the L293D itself.
OK, that should work fine. The downside of generic 9 Volt batteries, as mentioned, is their inability to deliver current for motors. You may want to consider:
"The L293D has two +V pins (8 and 16). The pin '+Vmotor (8) provides the power for the motors, and +V (16) for the chip's logic. We have connected both of these to the Arduino 5V pin. However, if you were using a more powerful motor, or a higher voltage motor, you would provide the motor with a separate power supply using pin 8 connected to the positive power supply and the ground of the second power supply is connected to the ground of the Arduino".

Now in your case you may want to consider using a 9 Volt battery to power the Arduino. Then if your motor likes current consider a
Philmore Battery Holder for (6) AA with Standard Snap Connector : BH363 (1) and if needed pair up a few. All of your grounds would be a common ground, with the exception of putting two batteries or battery packs in series. Just as Philba shows in his drawing.Battery packs for AA batteries are common for 4 or 6 batteries.

Here is a link to using the L293 where them mention powering the L293 off the Arduino 5 Volts out and using a separate supply for the motor.

<EDIT> I see crutschow covered this as I slowly typed. :) </EDIT>

Ron
 

Thread Starter

naitsab

Joined Sep 7, 2017
9
Thanks guys, I will try to use the 6* packs, my L293D already use external power supply (the 2*9v batteries in series+12v reg), the 2*5v connections are for E1(1) and v+(16) ;) - Cant wait for those new batteries I ordered :)

Thanks again !
 

Thread Starter

naitsab

Joined Sep 7, 2017
9
I couldn't wait for the batteries to arrive, I went to shop and bought 10*1.2v@2500mah put them in series and it works great. Motor is weak and behave strangely but that will be for another post ! :)

Thanks!
 
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