How can I slow down my shower pump?

[James86004]

I am a mechanical engineer getting into trouble with electrical stuff...

The shower pump I made from a headlight washer pump is too fast and draws a lot of power. The motor in it has a resistance of 2 Ohms. I put a 10 Ohm resistor in series with it, and the pump doesn't turn. I put a 5 Ohm resistor in it and it turns too slow. I would like to put maybe a 2 or 3 Ohm resistor in it, but if I did my math right I would need a 36 Watt resistor, which Radio Shack does not carry.

Is this the way I should be doing this, or is there a better way to slow it down?

 

[Robthebrit]

Its exactly what multispeed heater box fans do, its a viable solition to your problem. What it won't fix is the power consumption.

Mount the resistor away from anything, its going to get hot. In the heater box scenario they are mounted in the air flow which helps keep them cool.

Rob

 

[DaveInDenver]

That's certainly the easiest way to do it. The fan control works that way, just a big multiple step resistor. You might look for a ballast resistor for an ignition system. Those are usually a couple of ohms and can dissipate a tens of watts. No matter what, the sucker is gonna be hot if the motor draws 3 amps and you want to drop significant voltage.

 

[UK4X4]

adding resistors to the circuit will as Rob says not save current draw, it just gets expended as heat.


resistors can be put in parralel to absorb more power

But for me


Just add a valve and reycycle some of the flow back through the pump

ie loop the water system from container to pump and back to container.

put in a T and a valve in line to the shower head.

 

[Travelmore]

I think what you really want is a current divider. This should allow you to move the dissipation over multiple resistors or a capacitor and a resistor. I will let wiki explain.
http://en.wikipedia.org/wiki/Current_divider

 

[spressomon]

How about restricting water flow at your shower head instead? Then you get the bonus of higher pressure and lower volume. That's what I did on mine...works great.

 

[DaveInDenver]

I think what you really want is a current divider. This should allow you to move the dissipation over multiple resistors or a capacitor and a resistor. I will let wiki explain.
http://en.wikipedia.org/wiki/Current_divider

Motor speed is proportional to voltage, not current. Gotta drop the voltage somewhere and the simplest is a voltage divider, which is what you're doing by putting in a series resistor. The downside is primarily that excess energy is dissipated as heat. The better way is to build a motor controller, but that's not a one-device solution. Not difficult, if you want to do that I can sketch up something (or just Google 'motor controller' or 'PWM controller'). I'd recommend for a neophyte to find a motor controller kit, maybe check Alltronics or school lab supply places.

 

[StumpXJ]

Tie a knot in the power wire. That should slow down the flow of electricity. The tighter the knot, the less voltage.


kinda off topic hi-jack: I was working as a "Meter Reader" while in high school in the not-so-fortunate side of town. I am minding my own business, reading the meters, and this old man comes storming out of his house complaining loudly to me about something. Apparently his neighbor was stealing electricity from him via an extension chord that the neighbor hard wired into this old mans service box on the outside of his house. The old man was furious (rightfully so), and was telling me to unhook the chord from his service box. Me being a lowly meter reader did not have the authority or knowledge to do this safely, so I told him he would have to call the electrical company and file a complaint and they would have an electrician come out an fix it.

The old man is completely PO'd at this point, and snatches up the extension chord... and.... you guessed it. Tied it into a big ole knot right in front of me. Threw it back down on the ground and said to me in a serious face. "There you go, that will teach him to steal my power!" Then, turned around and stormed back into his house. :yikes:

True story.

Hi-jack over. Thanks.