H-Bridge with low current output

Projects General Guidance
1

Hello,

I have an H-Bridge using 4 2N4401 Transistors with a 9V battery power source that delivers 1.5 amps. The motor is drawing around 1.5 amps but the bridge is only outputting around 0.5 amps. Is this because of my transistors? Im looking at replacing them with 4 TIP120 Transistors. Will this work?

URGENT!

2

"I have an H-Bridge using 4 2N4401 Transistors with a 9V battery power source that delivers 1.5 amps. "

Well, that setup sounds a little sketchy. Is this a DIY H=bridge? Is the 9v battery a smoke detector sized one? You might search for "H-bridge" in the upper right search function to see more about previous similar H-bridge projects and issues.

3

I used help from this

4

Does the 2N4401 get warm? I would guess that the transisitors are not getting enough of base current.Using a battory like that is really bad. It is not designed to deliver 1.5 Ampere. Get a better powersupply for the motor.

5

achubler1548:
URGENT!

Right... You basically are saying "help me before you help others".

Fail...
Only an electronics noob would design a H-bridge directly driven by 5volt logic with four NPN transistors.
You will never get more than a few volts to the motor, because of the high-side emitter followers.
The high-side transistors are also potentially prone to overheating, especially with a 9volt supply.
The omited back-emf protection diodes put the transistors further in danger of popping their tops.
Leo..

6

How do you advise I deliver more current to the motor while still being able to reverse the polarity?

7

I would use a H bridge motor driver built for the purpose. Pololu has a good line of DC brushed motor drives. Choose one that will handle the motor stall current.

8

achubler1548:
How do you advise I deliver more current to the motor while still being able to reverse the polarity?

  1. Use an appropriate power source, not a 9V smoke alarm battery

  2. Pick a good MOSFET-based H Bridge, preferably already on a carrier board. I like the VNH5019 at the moment although it's a bit big for your application.

  3. Use appropriate wiring between power, H bridge and motor.

9

achubler1548:
The motor is drawing around 1.5 amps but the bridge is only outputting around 0.5 amps.

That does not make sense.

If the motor is drawing 1.5 amps and the h-bridge is only providing 0.5 amps where is the other 1 amp coming from?

Are you driving the H-bridge with PWM from analogWrite()?

How are you measuring the two currents?

...R

10

It will NEVER work to control a 1.5A motor with those transistors, as they're rated max 600 mA. That also means that to get them into saturation you're over-driving your Arduino outputs. The TIP120 can handle the current but being a Darlington is still a crappy choice for its high voltage drop doing so.

Solution: use a proper H-bridge. This one can handle 1.2A so maybe not enough for your motor. Your specs are too sketchy.