Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

H Bridge for Motor Control

Status
Not open for further replies.

ag93ds

New Member
Hello ET,

I am building a lightweight robot using the Tamiya 70168 dual motor/gearbox combo. The motors will be running at 3v provided by 2 AA batteries. They have already been measured to pull 2.4 amps each at stall. I would like to use an H bridge circuit to control the forward and reverse functions, rather than use relays, to keep the size and weight at an absolute minimum.

My question is: would ET recommend building the circuit myself with transistors and if so, what types, or, would using an H bridge IC, like an L298, work best? Also, what other components will be necessary to make this work? Using a logic board like Arduino is not allowed either. My knowledge on this topic is limited so any and all information is appreciated.

Thanks,

Matt
 
Last edited:
Didn't you look at the datasheet for the L298?
Its max allowed continuous current is only 2A and its max saturation voltage for a bridge is a loss of 5V.

You might find some low-loss Mosfets that work from a voltage as low as 2V to 3V.
 
You don't run 3V motors at 2A. that's ridiculous. That 2A is for it in stall mode. From that page you provided:
Free-run current @ 3V: 150 mA
That is the typical no-load current, it'll take a bit more when it is under load, but it certainly doesn't use 2A for normal loads!
Use L293 push pull drivers. They give out 600mA typical output, and my 6V motors run beautifully with a load. DON'T build your own H-Bridge, it is a complete waste of time and money if you're just driving 3V motors.
 
I have a cheap little fan with a floppy propeller. It uses two AA cells (3.0V) and draws 1.0A.
That's still twice as less (or is that the no-load current?). But I'll take your word for it.

Please describe how the OP will get L293 working on 2AA cells.
2AA cells only provide about half the required voltage for L293.

I didn't say he should use 3V. He can use a 6V, mine's running from 9V. Unless his "competition" specifies any why should it be a problem?

Thanks all. So does anyone know of an H bridge IC that will work with 3v but handle 2.5a safely?
Buy a H-Bridge IC (like L293), connect the motors, increase the supply for the IC until it runs properly. Voila! Solved.
 
Last edited:
Have a look at Bill's you will see the schematic including the H-Bridge. It does however use 4 AA cells.

Mike.
 
To address some questions: I cannot use more than 2 AA batteries to keep weight down. I can use any voltage to supply signal to the H bridge (i.e. 9v) so is it agreed that the L293 /298 it the best choice? Does anyone have a schematic for wiring this IC up?
 
The H-bridge ICs waste 5V so cannot use only 2V to 3V from two AA cells.
A little 9V battery cannot supply enough current for more than a minute so it also cannot be used.

You need to use the custom-made IC used in those tiny RC cars about 12 years ago. Then make a tiny robot that uses a low current.
 
The motor draws 150mA when it is idling with the gears disconnected, not when it is driving the robot.
Here is a 9V alkaline battery with a 400mA load:
 

Attachments

  • 9V alkaline, 400mA load.PNG
    9V alkaline, 400mA load.PNG
    7.7 KB · Views: 167
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top