reducing electrical power to motor

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  #1  
Old 04-05-06, 07:37 AM
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reducing electrical power to motor

'they' put in an ejector pump that was too large - a 1/2 horse for a normal 3 foot deep well, and it's way too noisy. i am wondering about:

1. would it work to put an attenuator at the wall outlet, to reduce the power to the motor, so it 'acts' like a smaller unit more appropriate to the job?

2. do they even make such adapters?

thanks
 
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Old 04-05-06, 10:03 AM
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Nope, but it is possible you could replace the motor with a smaller or quieter model.
 
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Old 04-05-06, 05:36 PM
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What steps have you taken to reduce the transmission of vibrations/sound?

Acoustic isolation/insulation is important too.
 
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Old 04-05-06, 05:56 PM
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what's an ejector pump?

in any case, a fractional hp motor in good condition is virtually silent. Maybe you have a 3400rpm and you want a 1700??
 
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Old 04-05-06, 08:09 PM
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an 'ejector pump' is a sump pump. it's located in the basement, and serves to pump laundry water (the washing machine is in the basement) and sewage from the lower level bathroom, up into the overhead sewers.

the noise is normal, except that in such a shallow well, i have been told, a 1/2 horse motor is just too big.

i haven't done anything else to it, but will be securing the whole pipe assembly more rigidly to adjoining walls, etc, to quiet it down.

i thought about replacing the pump with a smaller unit, but the whole idea is to avoid the expecnse!

anyway, thanks for all your comments.

but one other informational question: why can't i use an attenuator? would it hurt the motor on the pump? would it reduce power so the pump wouldn't drive the water out? or do they just not make 'dimmer switches' that plug into the wall?

thanks again.
 
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Old 04-05-06, 08:48 PM
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A motor is very different than a simple resistive load like a light bulb. You can dim a bulb: less current, less light. No worries, mate.

A motor is a compled electromagnetic device...there is a stationary part ( stator ) and a rotating part (rotor). There are fixed magnetic fields, and electromagnetic fields involved. Simply reducing the votage causes too many interacting results which can cause overheating and failure to turn at all.

Variable speed motors are made: they usually have multiple windings. The full line voltage, applied to different windings, is used to run the motor at different speeds.
 
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Old 04-05-06, 09:52 PM
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Originally Posted by 594tough
A motor is very different than a simple resistive load like a light bulb. You can dim a bulb: less current, less light. No worries, mate.

A motor is a compled electromagnetic device...there is a stationary part ( stator ) and a rotating part (rotor). There are fixed magnetic fields, and electromagnetic fields involved. Simply reducing the votage causes too many interacting results which can cause overheating and failure to turn at all.

Variable speed motors are made: they usually have multiple windings. The full line voltage, applied to different windings, is used to run the motor at different speeds.
thanks! an interesting and convincing answer - unfortunately (unfortunately, because i was still hopeing for an easy way out!).
 
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Old 04-05-06, 11:22 PM
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Originally Posted by bwv11
I ... will be securing the whole pipe assembly more rigidly to adjoining walls, etc, to quiet it down.
That doesn't always work the way you want.

If the walls are massive (concrete), they will absorb the energy.
If the walls are light (wood, paneling), they will resonate.

Rubber, foam, and insulation absorb energy.

Air transmits sound. If you can seal off the air around the sump (well), that will help to deaden the sound.
 
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Old 04-06-06, 05:02 AM
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I am going to modify 594tough's reply:

There exist speed controls for motors. I use them all the time.

The problem is (as 594tough stated) that a motor is a complex electromechanical thing, and what is worse, there are many different types of motor. Each different type of motor requires a potentially different type of speed control.

For some particularly easy to control motors, you can use what is essentially a beefed up dimmer. You often find these sorts of motor on fans and blowers.

Your ejector pump motor is quite likely a single phase induction motor, which is very difficult to control for speed. To change the speed of an induction motor you need to change the frequency of the power fed to the motor, but single phase motors have starting components which will probably not be happy with the frequency change.

You might try checking the wiring diagram on the motor itself. Some motors may be connected for different speeds by changing connections on the motor itself. However this is a slim chance; it is far more likely that if the motor can be re-connected, it is for different voltages or for changing _direction_, which could damage your pump.

-Jon
 
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Old 04-06-06, 08:43 AM
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Originally Posted by bolide
That doesn't always work the way you want.

If the walls are massive (concrete), they will absorb the energy.
If the walls are light (wood, paneling), they will resonate.

Rubber, foam, and insulation absorb energy.

Air transmits sound. If you can seal off the air around the sump (well), that will help to deaden the sound.
I agree. That is the opposite of what you want to do. You need to isolate it from the walls etc. to prevent the sound transmission. Use rubber coupling in the pipe to isolate them and if you secure it to the wall use rubber isolation mounts. Old truck mud flaps cut up work well for this.
 
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