[alanw]

Originally Posted by Fomen

Here is a picture of the voltage step down device I made. It's a pretty simple electrolytic component. It's basically a couple of resistors in series. Then I encapsulate it in a 2 part casting resin. It's impervious to water. The battery I have it hooked up to is 12.9 VDC. The output of the component is 6.6 VDC.

Sounds like a simple voltage divider. If it is, it's very inefficient and shouldn't be used as a power supply for a load. Every bit of current used by the pump also has to run through a resistor, and all that wasted power is dissipated as heat.