I am working with a DC motor that is rated 2A and an H bridge that has a rating of 1A, what i'm wondering if it is the h bridge or the motor that draws current from the batteries? would there be 2A going through the 1A hbridge or 1A going through the 2A motor? Simple question but i can't seem to find any clear answers!
Thanks
It that the normal motor current or the stall current ?
You have to know the stall current. That is the maximum current the motor will ever request.
When you know that, find a motor driver (the H-bridge) that is able to supply such a current.
Suppose a motor uses 4A nominal current, and the stall current is 20A. Then you need a motor driver that is at least 20A, but a little more is preferred, like 25A or more.
When you use a 1A H-bridge and a 2A motor, the H-bridge will go up in smoke.
I can't find the exact model of the motor that i'm using but the other models stall currents are all way above 1A. thanks for the reply!
It's a good question 
It can go wrong, but that also depends on the H-bridge that you use. When the H-bridge has mosfets the output can be considered as a normal digital output with the full voltage range output (full swing). I think that can be used to drive transistors. When the collectors are connected to the motor, perhaps some extra components are needed to prevent a shortcut.
When using complementary darlington transistors, the emitters can be connected to the motor so the circuit prevents a shortcut.
Sometimes an extra driver chip can be soldered on the H-bridge chip for more current. Only for H-bridge chips that allow to be used parallel with extra chips.
What's the power supply? If the power supply or motor stall current are the limiting
factors the H-bridge will survive. If the H-bridge is the lowest current rating it will
burn up since you'll put too much current through it.
The load doesn't pull current from the supply, nor the supply push current through
the load, the current depends both on the supply's voltage and the load's resistance,
so both are guilty(!)
MatthewScollay:
Would it be possible to put the outputs from the hbridge through a transistor taking the 1A current rating of the bridge up to the stall current of the motor? maybe a stupid question.
No, H-bridges have 4 control inputs and two power outputs, you cannot chain them
together naively, you need a more powerful H-bridge in the first place.
MarkT is right. A normal H-bridge has 4 inputs and 2 outputs. I didn't think of that. When the H-bridge is used in a simple way, it might be possible to add extra transistors ]
But in the end you might run into a deep pit of troubles.
a H-Bridge shiled Schematic for your reference ?http://www.elecrow.com/wiki/images/5/51/H-bridge_Shield.pdf
hope it helps.
Peter_n:
MarkT is right. A normal H-bridge has 4 inputs and 2 outputs. I didn't think of that. When the H-bridge is used in a simple way, it might be possible to add extra transistors ]
Yes, its called shoot-through...