L298N no amperage?

So i am trying to make a 24VDC pulse generator for teaching myself how to properly use high speed inputs on Remote telemetry units. Specifically the Micrologix 1100 with 24VDC high speed inputs (BWA version).

However i seem to have hit a slight snag. I have an L298N H-Bridge that should be perfect for this as it is rated to 46VDC.

I have it hooked up, and when I run it through a multimeter I get my input (around 26V) minus 2V which puts me right in my target range. Not to mention through everything the H-Bridge stay fairly cool, I can hold a finger on it no problem.

HOWEVER, I seem to not be getting any amperage, I hook a motor up to it, and nothing happens even if my multimeter was just reading 9V output (testing voltage for my motor as I have a variable power supply).

Thinking it could have been maybe my power supply I hooked the motor directly to it and it jsut spun up and ran like a champ.

What gives?

Picture failed security check apparently, here is a dropbox link to it. Hbridge

You have set the relevant enable input?

Enable A is currently set to high with +5VDC.


It reminds me that the last time my multimeter was saying 0A... one of the two fuses was dead :P Maybe you have already checked, if not it's quickly-done :)

Less of my multimeter showing no amperage, and more it not spinning a 9V motor whether it have 9v or 16v pushed to it through the h-bridge, but spinning its heart out when hooked directly to the power supply.

So measure the voltage across your motor when it is connected to the H-bridge.

With: With Motor

Without: Without Motor

Looks to me like a bad connection on the solder less bread board, they are known for this.

Have you made sure the current sense pins 1 and 15 are properly tied to ground? Otherwise you wont be able to run any current through the L298N.

HEEEEYYYY look at that! I actually didn't know the current sense pins HAD to go to ground!

I thought they were meant as an output to the controller for reading load amount.

Thank you to everyone who made suggestions and to kamelryttarn!

I'm out a motor cause i just started it at 27V but motors are cheap and I'm glad the circuit works now.

Just take care so you don't fry the L298. It can't handle more than 3A (absolute max) and the current rush at 27V may have been too much.