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Thread: Voltage Drop?

  1. #1
    Join Date
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    Default Voltage Drop?

    So I just got a used UPS (Uninterrupted Power Supply) I put in fresh batteries and the unit seems to work great. My problem though started the other night I noticed that every time my well pump kicks on the UPS switches over to Battery power for a split second and then switches back to AC power. Just wondering what you guys think could be causing this. From the manual for the UPS the Error code says low voltage is the reason it is turning on. How can I fix that?

  2. #2
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    Default Re: Voltage Drop?

    The pump motor has what's known as a "high-inrush starting current." This is pretty normal for motors, and it can cause a momentary voltage drop on other circuits. You'll notice this if you have incandescent lights, they will momentarily dim when the pump starts.

    I'm assuming you have a single electrical panel. Is it circuit breakers or fuses? Do you know what the main amperage rating is?

    Usually, the only way to resolve this is to upgrade the service entrance cables coming from the utility transformer, and possibly even having the utility upgrade the transformer. I've seen older houses where the service has been upgraded to 200A, but the "drop" (the wires from the utility transformer) haven't been upgraded by the utility. The existing wires are not large enough to meet modern demands, resulting in voltage drop like you're seeing.

    You might be able to get the utility to send someone out to evaluate your service.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  3. #3
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    Default Re: Voltage Drop?

    I have a single panel and they are circuit breakers. My service is supposed to be 200amp but my main breaker is only 150 amp. Is there a way to tell what type of service I have and if it truly is 200 amp? I did follow my line back to the transformer and it appears I share one with my neighbor. Or would it be best to just call the electric company and have them check everything. (transformer, Lines to the house)

  4. #4
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    Default Re: Voltage Drop?

    This may not be a utility problem, it may be a problem with your pump instead. As Fencepost said, a pump can have a high inrush current and that will drop your voltage down for just a fraction of a second. You should notice that your lights dim when the pump comes on.

    If you have a large motor on the pump, then it should have a starting capacitor, sometimes called a condenser. It stores some current to help start the motor and also keeps the power factor in line which helps it to use less electricity when running. If you don't have a capacitor on the motor, you should check to see if one was ever offered on it. I should ask first if this is a submersible pump or a jet pump.

    Since you share your transformer with a neighbor, it should be a larger size transformer than one used to serve one home only. This is an advantage as it has more capacity to supply this in rush current. It is unlikely that both you and your neighbor would have your pumps come on at exactly the same time.

    If you have a whole house AC unit (central air) and it is not causing a low voltage condition, then I would tend to rule out the utility, the transformer or your service panel and concentrate on the pump motor.

  5. #5
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    Default Re: Voltage Drop?

    Quote Originally Posted by keith3267 View Post
    If you have a large motor on the pump, then it should have a starting capacitor, sometimes called a condenser. It stores some current to help start the motor and also keeps the power factor in line which helps it to use less electricity when running.
    A start capacitor is in series with the start windings and produces a phase shift to start the motor in the proper direction, it does not affect the power factor or reduce electricity used by the motor. To affect the power factor a capcitor must be across the line.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  6. #6
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    Default Re: Voltage Drop?

    check the capacitor to make sure it is up to speed.

  7. #7
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    Default Re: Voltage Drop?

    Quote Originally Posted by JLMCDANIEL View Post
    A start capacitor is in series with the start windings and produces a phase shift to start the motor in the proper direction, it does not affect the power factor or reduce electricity used by the motor. To affect the power factor a capcitor must be across the line.

    Jack
    A capacitor, whether in series with an inductor or in parallel, has an effect on the power factor. If sized properly for the application, it does increase the efficiency of the motor.

  8. #8
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    Default Re: Voltage Drop?

    Quote Originally Posted by keith3267 View Post
    A capacitor, whether in series with an inductor or in parallel, has an effect on the power factor. If sized properly for the application, it does increase the efficiency of the motor.
    A start capacitor decreases the efficiency, increases the torque, and provides a phase shift to provide direction of rotation of a motor but is only in the circuit for a few seconds. Most pumps are capacitive start and inductive run. Run capacitors increase efficiency of motors but produce phase shifts which is what you want to eliminate to improve the power factor. There is a difference between power factor and efficiency.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  9. #9
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    Default Re: Voltage Drop?

    The pump is submersible. It is in a Drilled Well. I haven't really noticed the AC causing the same issue, but I haven't really payed attention to that I will check that. The light bulbs dimming question I am no sure I have all CFL's in the house, Not sure if they will dim like an incandescent would. And to be honest I never really payed attention to that ether. I will check both tonight and post back what I find. Thanks for all the great responses though.

  10. #10
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    Default Re: Voltage Drop?

    Quote Originally Posted by JLMCDANIEL View Post
    A start capacitor decreases the efficiency, increases the torque, and provides a phase shift to provide direction of rotation of a motor but is only in the circuit for a few seconds. Most pumps are capacitive start and inductive run. Run capacitors increase efficiency of motors but produce phase shifts which is what you want to eliminate to improve the power factor. There is a difference between power factor and efficiency.

    Jack
    I have never seen a start capacitor that is switched out of the circuit once the motor is up to speed. It stays in the circuit and it increases the motor efficiency by correcting the phase shift caused by the windings of the motor.

    The inductive reactance of the windings in the motor cause voltage to lead current. The capacitor causes current to lead voltage. If the size of the capacitor is matched to the inductance of the motor, then voltage and current will be in phase.

    Power factor is not the only thing that affects the efficiency of a motor, but it is a factor. A motor still has core losses, I2R losses, stray losses and friction losses and none of those, except I2R are affected by the power factor.

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