Motor driver won't drive...

[Tracy Walker]

I decided to build an H-bridge motor driver out of transisters, since I have half a dozen TIP41c's and 42c's. Before I did, though, I breadboarded a single TIP41c hooked up to the motor I was planning on using; basically just a switch. It would't drive it at all, though the same set-up worked fine with a smaller motor.
The one I want to use comes out of a 6v power screwdriver. I measured the stall current at about 4 amps and unloaded current at 400 ma. Seems like the TIP 41c should handle that, though maybe the stall current is making it fail to start?
Any help?

 

[penoy_balut]

if it can drive a small motor and not a bigger one your TIP' base current is not enough , with its current gain of 40 you must drive the base at least 100mA to run 4 amps load, don't forget to put diode for back emf in your motor

 

[Boris]

I had the same problems.I used schematick H-bridge driver with FET transistors. Works much better.

 

[audioguru]

your TIP' base current is not enough , with its current gain of 40 you must drive the base at least 100mA to run 4 amps load

Its minimum current gain at 3A is only 15, and then it will have 4V across it. Its current gain is less at 4A. If you want it to saturate properly then use a base current of 400mA like the datasheet shows for a 4A load.

 

[Hero999]

I had the same problems.I used schematick H-bridge driver with FET transistors. Works much better.

Yes, MOSFETs are a much better idea, you get lower saturation losses and lower drive requirements, so your driver will be >95% efficient rather than <85% efficient.

 

[penoy_balut]

Its minimum current gain at 3A is only 15, and then it will have 4V across it. Its current gain is less at 4A. If you want it to saturate properly then use a base current of 400mA like the datasheet shows for a 4A load.

it could have been a different datasheet that i have looked to, thanks audioguru
i think Tracey should try darlington connection for his TIPs for higher current gain

 

[Hero999]

No, try using MOSFETs.

**broken link removed**