h-bridge vs single MOSFET DC water pump


What are the pros and cons of using a H-bridge vs a single MOSFET to control the speed of a DC water pump?


I'm going to go out on a limb here and say it depends if you need bi-directional control. You can't do that with one mosfet. If you don't need both directions, then a single mosfet is just the thing, much simpler.

Volts and Amps ?


I have an IMS-1 H-bridge and several IRL540 MOSFETs… the pumps spin in one direction… I have been able to control speed with both methods.

The IRL540 datasheet shows a (relatively) high Rds of 77 mOhms at 5V Vgs so pulling 9 Amps through it would result in over 6 Watts dissipated as heat, probably need a heat sink. An IRLB8721PbF MOSFET shows Rds of 13 mOhms, only about 1 Watt at 9 Amps, May not need any heat sinking. Can't comment on IMS-1.

And MOSFETs are available down to <1milliohm if you need even less heat dissipation. Hint: choosing a 100V
MOSFET for a 12V circuit is going to mean much higher on-resistances. Choose a 30V device with < 10 milliohm
on resistance maybe?

Thanks for all the feedback. For right now, I am going to use the IRL540 with a heat sink mostly because that is what I have on hand. I might end up choosing something with a lower resistance for the final build.