I'm still fairly new to electronics and I may be doing something wrong, but are we expected to lose some power from an h-bridge?
I say this because if I connect my motor directly to a battery, it goes fairly fast. But if I do it through the h-bridge (and I make sure the voltage is being sent to the h-bridge pin that powers the motor), and I set the h-bridge enable at 100%, I can't get it to rev as fast as it did when I did it directly. It is noticeably slower.
Is this expected? Am I perhaps doing something wrong?
Hello,
The H-Bridge is essentially two switches in between your motor and the power supply.
So there is always SOME loss.
A typical L298N H-Bridge used Bipolar power transistors internally and so the voltage drop can easily be 2 volts. If you are running 5V motors from a 5V supply that will be very noticeable. But they are inexpensive.
A high-end Power-FET based H-Bridge will have a lot less voltage drop.
That H-bridge has Darlington output stages so it will lose about 2 to 3V - pretty poor if you are using a 6V motor (I'm guessing you are). A MOSFET based H-bridge is much more suitable for low voltage motors.
Unfortunately there don't seem to be any good cheap MOSFET H-bridges in DIP packages, and a lot of people go with the L293, L298, SN754410 which are cheap and cheerful, but lose lots of voltage (and thus get hot at high currents). That TLE5206-2 sounds good (Farnell don't stock it alas...)
Some of the high performance MOSFET bridges are available as motor controller modules (Pololu is a good source of these BTW).
(A Darlington stage is a pair of transistors with high gain but minimum saturation voltage of about 1 to 1.5V)
actually the main motors I am using this on is a 1.5v to 3v motor.
The weird thing is despite if I connect a 9v battery or 4 AA batteries (6v), I still can't get it anywhere as close to the same speed if I was to connect it directly to the batterie, without the h-bridge. Is this expected?
Check the data sheet for the h-bridge chip you are using for the voltage drop across it and its internal resistance. Test the h-bridge making the input control pin high by direct connecion without using the arduino.