Resistor for airpump motor

[redboat219]

Hi guys'
I'm new to the hobby and I'm building my first sub- a Trumpeter Kilo with a RCABS. My problem is that the airpump I have has a F130 type motor attached to it. I'm planning to run my system on 6 volts but I'm afraid I'll fry the motor. U812 suggested that I put a resistor to lower the voltage to a safe level. Does anyone have an idea on the rating of the resistor i need and where i need to solder it in relation to the 0.1 uf capacitors w/c i also need to install . Thanks.

[jsl]

I may be wrong here,

I may be wrong here, but the pump does require at least a few Amps when running under stress, right?

You said the pump was 6 volts, but not what your main power supply voltage in your sub is. I'm guessing 12 volts.

The resistor is a rather crude way to lower the voltage, as the excess power is burned of as heat in the resistor. This puts some demands on the resistor. First of all you need to know the current used by the pump under stress, and then calculate a value for your resistor. Then you have to find a resistor with the right power rating.

Choose a normal 1/4 W resistor, and there's a chance of it going of like a nice flare if burn of 10W of excess power in it, even though it has the right resistance value.

As said, the resistor solution is crude, not very accurate and may involve at least one component potentially getting very hot. Not very accurate, as the voltage drop it caused is proportional to the stress on the pump motor. But it is a reasonable and simple solution.

A 6V voltage regulator could deliver a smooth 6V performance in all situations, but it is somewhat more difficult to make...

[guillermo pelaez]

I do agree with Jacob,

I do agree with Jacob, a voltage regulator will be best. But since you are building a trumpeter kilo and space is something that you want to save as much as you can, I will also consider a few diodes in series, this will be also dependant on the battery remaining charge, but will do the job without generating that much heat. I guess the best compromise solution will depend on the current requirements (Amps) of your pump. To messure that you need an Amperimeter and put as much stress as possible on the pump when working, take note of the maximum value reached, add at least a 10% and you should have your minimum requirements. If you have access to the motor and you can stall it, that is even better, take the stall value and that is the maximum current required, I think.
Hope this helps.

Cheers,