Hi. I am out of my depth trying to dial down my solar power water pump. I do not know if I need a brushless or brush DC motor controller.
My pump is as follows.
24V brushless motor submersible water pump
1/3 hp
Internal controller
Typical operating current is 10-11.00A.
The stall current is around 12.00A.
The pump can start around 150W. Max power is 250W
Only has two wires (Positive and Negative)
A brushless motor would logically need...
This however got an internal controller, and two wires + and -, so use a relay or a MOSFET to switch the power.
HI, @rockdoc
Welcome to the forum.
Can you please post a link to the equipment you have.
Most of the solar powered pumps have a MPPT (Maximum Power Point Tracking) controller, to optimise the PV output.
Try Google;
solar mppt arduino pump
Tom.... 
