L298N Parallel Mode - Possible Solution or Alternative

Thread Starter

KidCanada

Joined Mar 14, 2024
6
For a school project we are trying to stabilize a dual axis inverted pendulum using reaction wheels.

We are using these motors:

Model : RS555-EN 12V
No-load speed : 8000 RPM
No-load current : 0.4A
Rated torque : 0.4 Kg.cm
Rated speed : 6700 RPM
Rated current : 3.5A
Stall torque : 2 Kg.cm
Stall current : 18.5A
Weight approx. 230g

We were planning on using the L298N H-Bridge, but we are finding that we need to add additional weight to the reaction wheels, and it doesn't seem like the L298N can supply enough torque to the wheels while running 2 motors off a single L298N. We are using the boards that are commonly found on Amazon:

1710435042559.png

I saw in the datasheet for the L298N that the 2 channels can be run in parallel to achieve a higher output current, which is found on page 7 of the datasheet:

https://www.sparkfun.com/datasheets/Robotics/L298_H_Bridge.pdf

We had the idea of running each motor in this configuration on its own board. Can this board be modified easily to achieve this? Or does a custom integrated circuit need to be created (I tried wiring the terminals as indicated but the motor won't spin). The system will never be running for longer than 30 seconds or so.

If this isn't a good option, I'm wondering if I could get a suggestion on a better H-Bridge for this application that can handle constant direction changes.

Thanks.
 

Reloadron

Joined Jan 15, 2015
7,544
Just a few things you may want to consider. The L298 H Bridge was a neat as sliced bread when it was first available but if we look closely at the L298N data sheet you will notice the basic schematic on page 2/13 that it uses Transistors and there is considerable loss in the circuit or simply put your motors will not see the applied motor voltage. Pololu has a huge range, all tabulated so you can search and sort on characteristics like voltage and current. Remember when choosing a motor driver it needs rated for your motor's stall current. The maximum current it will ever see. I would be looking at the Pololu selection or at least use it as a reference of what is new design and available. The link includes Low, Medium and High Power motor drivers.

Ron
 

Thread Starter

KidCanada

Joined Mar 14, 2024
6
Just a few things you may want to consider. The L298 H Bridge was a neat as sliced bread when it was first available but if we look closely at the L298N data sheet you will notice the basic schematic on page 2/13 that it uses Transistors and there is considerable loss in the circuit or simply put your motors will not see the applied motor voltage. Pololu has a huge range, all tabulated so you can search and sort on characteristics like voltage and current. Remember when choosing a motor driver it needs rated for your motor's stall current. The maximum current it will ever see. I would be looking at the Pololu selection or at least use it as a reference of what is new design and available. The link includes Low, Medium and High Power motor drivers.

Ron
I appreciate it.

Just to make sure I'm clear... since our motors have a stall current of 18.5A, we should be looking for a dual channel driver that can deliver 18.5A peak per channel, correct?
 

Reloadron

Joined Jan 15, 2015
7,544
That would be correct and that is a high current motor driver. Yes, you want dual motor with a rated current of at least 18.5 amps. There are some high current versions in the link I posted.

Ton
 

Reloadron

Joined Jan 15, 2015
7,544
We are using these motors:

Model : RS555-EN 12V
No-load speed : 8000 RPM
No-load current : 0.4A
Rated torque : 0.4 Kg.cm
Rated speed : 6700 RPM
Rated current : 3.5A
Stall torque : 2 Kg.cm
Stall current : 18.5A
Weight approx. 230g
Whoa? These are what you originally posted. No load current is 0.4 Amp and normal run current is 3.5 Amps and yes, Stall Current is 18.5 Amps based on the data you initially posted. When choosing motor drivers you want a driver which will handle your stall current and it would be wise to fuse your motors. I was working from your data to come up with 18.5 Amps.

Ron
 

Reloadron

Joined Jan 15, 2015
7,544
Why do you need that much current?
Hi Ya Al and how goes it? Yes, I suggested 18.5 amps based on the motor's stall current from post #1 at the beginning. Normal run current is 3.5 amps and stall or locked rotor current is 18.5 amps. So I suggested an 18.5 amp motor driver. No clue as to the motor's start current or if the motor starts under load or what the load is. :)

Ron
 

MaxHeadRoom

Joined Jul 18, 2013
28,759
One problem with those boards, they do not use the Sense-A lines-B lines of the IC in order to limit the current.
I have lifted the pins off the board in order to use them with a suitable sense resistor.
.
 
Last edited:

Reloadron

Joined Jan 15, 2015
7,544
One problem with those boards, they do not use the Sense-A lines-B lines of the IC in order to limit the current.
I have lifted the pins off the board in order to use them with a suitable sense resistor.
.
I actually have an old L298 board and it's made by Cana (insert maple leaf) Kit and it's one of the better L298 boards, it includes two 0.5 Ohm 5.0 Watt resistors labeled CSA and CSB (Current Sense A & B). It included a nice data sheet with schematic. Made up in your neighborhood Canada. Apparently CanaKit is still around making good stuff.

Ron
 

MrAl

Joined Jun 17, 2014
11,564
Hi Ya Al and how goes it? Yes, I suggested 18.5 amps based on the motor's stall current from post #1 at the beginning. Normal run current is 3.5 amps and stall or locked rotor current is 18.5 amps. So I suggested an 18.5 amp motor driver. No clue as to the motor's start current or if the motor starts under load or what the load is. :)

Ron
Hi there Ron,

It goes OK i guess, I hope you are doing well also.

Oh, yes, I had forgotten about the stall current so that makes a lot of sense. That makes me think the original choice of driver IC is not a very good one at all :)

Oh BTW, that L398 chip has a sense for current so it can limit the total current. Not sure if that makes too much difference with a really heavy duty motor though because it still has to be able to put out the full normal run current.
 

MaxHeadRoom

Joined Jul 18, 2013
28,759
Oh BTW, that L398 chip has a sense for current so it can limit the total current. Not sure if that makes too much difference with a really heavy duty motor though because it still has to be able to put out the full normal run current.
That is what I referred to in #13, I lifted the two L298 sense pins up and connected a couple of 0.51Ω resistors for current sense, when used in conjunction with the L297, which has the dual Comparator, it can be set precisely for current control.
Or back into a picmicro etc.
 

sarahMCML

Joined May 11, 2019
391
That is what I referred to in #13, I lifted the two L298 sense pins up and connected a couple of 0.51Ω resistors for current sense, when used in conjunction with the L297, which has the dual Comparator, it can be set precisely for current control.
Or back into a picmicro etc.
I did the same just over a year ago when I was learning about steppers. I faked the matching L6505 Stepper Motor Current Controller I.C. with what I had available (half a LS76, a couple of LS11's, a TLC555, and a TLC3704 (push/pull LM339)). It works beautifully!
If you don't need the Enable input you can use a single Quad, 2-input LS08 instead, and save a package!
The 8.2 Ohm carbon resistors were the lowest I could find at the time, and as I only wanted 0.5A max through each motor coil, 4 in parallel were fine.

Pics attached. Sorry for the grid!


DiscreteL6506B.jpg


Chopper Pix.jpg
 

Thread Starter

KidCanada

Joined Mar 14, 2024
6
Thanks for all the help folks. We ended up ordering new motors that are significantly lighter and a new dual H Bridge from Pololu. Really wish I had found that site sooner. Going to redesign our assembly to get the weight as low as possible.
 
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