Anything wrong with connecting L298Ns in parallel?

Question

Although L298Ns are very inefficient, they're very cheap. I have two motors that require 4A+ current at load combined. Can I connect multiple L298Ns in parallel in this way to increase the overall current output? Am I going to run into any problems?

How can you guarantee they will share the load current equally? (Hint - you can't). — Andy aka, Commented Mar 27, 2021 at 14:47
Tip: the illustration you have posted is referred to here as a "cartoon" or wiring diagram. A schematic diagram reveals the schema or purpose of the circuit with part numbers and pin designations and is the "language" of circuits. Meanwhile your diagram shows us that you have a breadboard, two motors, an Arduino, a red PCB and a green thing. Most of the cartoon generators have schematic export functions although you will need to spend some time laying out the components sensibly and untangling the mess of wires they generate. — Transistor, Commented Mar 27, 2021 at 14:52
you should probably not be running the current for motors through breadboard traces. — Hearth, Commented Mar 27, 2021 at 14:53
You could probably bolt them to a common heatsink (so as they heat due to their horrible performance they more-or-less heat together) and get a slight (maybe 30-50%) improvement in output current, but they are really horrible parts. Did I mention they are horrible? — Spehro 'speff' Pefhany, Commented Mar 27, 2021 at 14:55
this sounds like a very bad idea: instead of parallelling three 1970s, very inefficient (since high-loss) motor controllers, why not simply spend a fraction of the money on something modern? If L298N is the answer, then the question started with "Let's book time travel to the year 1978..." — Marcus Müller, Commented Mar 27, 2021 at 15:03

Math Keeps Me Busy · Accepted Answer · 2021-03-27 20:39:46Z

I am not endorsing wiring the L298Ns in parallel, but simply discussing the issues involved, and how it might be accomplished. As others have pointed out, an easier solution is to purchase a more robust driver.

Simply wiring the L298Ns in parallel will cause problems. A partial schematic of one of the motors, and one of the drivers, driven in one direction looks like this:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

With multiple drivers connected in parallel, a partial circuit would look like this:

schematic

^{simulate this circuit}

A big problem with this arrangement is that the currents through the transistors may be unbalanced. Suppose Q2A is slightly warmer than Q2B or Q2C. It is likely to conduct more than 1/3 of the current. Conducting more current means that it will get hotter than Q2B and Q2C. Which will cause it conduct more of the current, etc.

If you are willing to trade some motor speed (voltage) for torque (current), you can balance the transistors to some extent by adding small value resistors between the transistors and the tie-points to the motor, like so:

schematic

^{simulate this circuit}

The larger the resistors, the more voltage you will lose, and hence the lower the maximum rpm of your motor. However, the larger the resistor, the greater the current balance you can achieve. Sufficient balance, and you can safely connect multiple drivers to drive your motor, thus increasing your torque. However, this only works to a point. Obviously too large a value for the resistors, and you will lose more power in the resistors than you gain by having extra transistors.

You say that the two motors will require 4A combined. You don't say whether the motors will ever require more than 2A individually. (It could be that only one motor operates at a time, and when it does it requires 4A). I will assume that you only need 2A. (BTW the L298 is advertised as capable of 4A total (for 2 drivers), so if the modules actually behaved as advertised, you could get the 4A out of a single module, but that is another story).

Assuming each transistor needs to conduct, say 0.7A, and you want, say 0.3V across each resistor, the resistor values should be 0.3/0.7 = 427m\$\Omega\$ or something in that vicinity. Although they should only dissipate 210mW, I would use 1/2 watt rated resistors. The resistors need to be matched. Tight tolerance 0.5\$\Omega\$, 0.5W resistors are commercially available.

That takes care of the issue of transistor balancing.

There is another issue that must be addressed. Shoot-through. If both transistors in a half-bridge are on simultaneously, shoot-through will occur. A large current will flow through the transistors without encountering the impedance of the motor. This is bad, so you want to ensure that shoot-through doesn't occur. By connecting the modules in parallel, you increase the possibility that a high side transistor in some module is on, while a low side transistor on the same side of the motor, but perhaps in a different module, is also on. It is important when changing voltage directions, that there is sufficient "dead-time", so that all of the transistors are off, before any new transistor is turned on. It is your responsibility to ensure that.

Once again, I am only explaining how wiring the modules in parallel might be accomplished, but I am not endorsing this as a solution to the higher level problem of how to drive the motors.