Resistors

Do any of you electrical genius types know what value resistor I would need to drop voltage 1.1V? In treaty, pumps are measured by capacity in GPM. My current build gets a 1.25GPM pump. The pump I am ordering is rated 1.26GPM @ 12.2V, but the power source I am using is 13.2V. Any input would be helpful. Thanks!
EDIT: I was thinking about using a potentiometer in the correct range, but I decided that the risk of corrosion to the contacts was too great.

 

Use a BEC or ESC that will provide constant voltage output.

 

Why not just use a reducer to restrict the flow output?

 

V=IR (voltage = Current x Resistance)
The only problem with using a resistor to drop voltage is that the voltage it drops will change as the load on the motor changes. When the motor is loaded down, it will draw more current. As the current through the motor (and the resistor) goes up, so will the voltage dropped by the resistor. Is it possible? Yes. However, if you want to restrict the pump electrically, it would be best to use a ESC that can be set to provide a constant voltage output. The other option would be to mechanically restrict the output, such as by using a nozzle. It should be possible to use a nozzle with a setscrew in the path of the flow. By adjusting the screw into or out of the path, you can control the flow to get exactly the flow you need, even if you are a bit over the voltage you would otherwise need.

 

This. I plan to use a small hose clamp with a piece of dowl to restrict my output flow. I should be able to just tighten it down until my flow is legal.

 

Don't use a potentiometer, they will not handle the wattage that will be dissipated.
Example: say you at 13.2 volts you draw 3 amps. At 12.1 volts you will draw a little less, let's guess 2.8 amps. To drop 1.1 volts at 2.8 amps, you need a resistor of 0.4 ohms (R=V/I). The power dissipated in the resistor is 2.8 *2.8*0.4 (I^2R) = 3.1 watts, so I would say you need at least a 5 watt resistor.
Measure how many amps the pump draws while loaded and then we can make an educated guess on the resistor. Wire wound adjustable resistors are also available at the local surplus store, which will allow you to fine tune the resistor without buying a bunch of fixed resistors.

 

Diodes drop voltage. Make sure the power handling is adequate.

 

Thanks for all the replies. I think I will start looking at cheap airplane ESCs. I was looking at resistors in the first place because of my experience lighting model spaceships (one day, I will finish that 36" movie era 1/350 Enterprise).

 

Mike's solution is the most cost effective, but I just like to make things difficult

 

Ok-cost effective solution possibly found. I traded a spare item for a 30A Turingy ESC yesterday. No out of pocket cash.
However, I got into the instructions tonight and it states 3 cell LiPo or 10 cell NiMH. There is a jumper to select cell type. LiFE is listed at 3.3V or 3.2 depending on the source, so 12.8v to 13.2v. 3 cell LiPo would be 11.1V and 10 cell NiMH would be 12V.
NiMH with a fresh charge hits about 1.4V per cell, so about 14V.
LiPo freshly charged are 4.2V per cell, so 12.6V.
LiFE peaks at 3.6V per cell, so 14.4V.
The big question is: Can I run 4 cells of LiFE on this without burning it up?
If so, how would you jump it? NiMH ot LiPo