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Discussion Starter · #1 ·
Hey guys, first post!

I just finished installing a 30 amp inlet and interlock kit in my panel today. Anyway, I was taking some readings with my clamp meter, and I noticed that my well pump draws ~19.x amps when running on the generator, but only ~10.x when running on utility power. The generator is regulating voltage well (drops from ~245 to ~234 under load, some of which is no doubt loss in the wiring), so it's not due to undervoltage. Any ideas? I did take a peak on my oscilloscope and saw that there was some harmonic distortion in the power when under load -- it looked kind of like a shark fin, similar to this: http://stevepedwards.com/wp/wp-content/uploads/2013/05/052713_1709_Recognisabl6.jpg -- but with a little more sine wave and a little less sawtooth. Could that account for it? Could it be an artifact from my meter (it's not true RMS, but I wouldn't expect that big of a difference)? I'm really worried about this, because I don't want to damage my well pump. My well is ~300 ft deep, and replacing the pump would cost quite a bit.
 

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What kind of generator are you running?
 

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It appears your generator has high THD and yes, it can damage or burn out your motor.

Check your oscilloscope against line power.
 

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Discussion Starter · #5 ·
I think that maybe the aux start winding is remaining energized after the pump starts. I plan to test this theory tomorrow.
 

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Discussion Starter · #6 ·
I think that maybe the aux start winding is remaining energized after the pump starts. I plan to test this theory tomorrow.
Sorry to resurrect an ancient thread, but I had to work on my well pump controller today, and I remembered this and wondered if I ever posted the solution - turns out I did not. This information is critical for anyone who has a well pump that had a high current draw (draws too many amps), draws too many watts, or doesn't start on a reasonably sized backup generator. Sorry for loading with keywords there, but even knowing exactly what to search for now, I can't find whatever bit of information helped me solve this two years ago, so I want to try to make sure people can find this.

Anyway, it turns out that Franklin solid state QD submersible well pump controllers (and probably many other solid state controllers) are adversely affected by the poor power quality produced by cheap backup generators. These things make a lot of harmonic distortion (high THD), which means that the output isn't a sine wave. For some reason solid state well controllers don't disengage the starting winding when subjected to this poor quality power, which can cause the generator to bog down, the pump to draw extremely high amperage, and will probably kill the pump pretty quickly.

The solution that I found was to refit my pump control box from using a QD solid state relay to use a voltage relay kit - this is an older style, has an actual mechanical relay, and will not last as long ... but it will make your well pump work with your cheap portable generator. At the time I found some Franklin documentation that mentioned the issue with using a QD Relay based control box with a backup generator, but now I can't find it even though I know exactly what to search for.

Before you drop $60-$90 on a voltage relay, you may want to verify that this is the problem you actually have. This can be accomplished by using a clamp meter to check the current draw on the leg of the 3-wire pump connection that's going to the starting / auxiliary winding - if it doesn't go to zero in less than a second, you have a problem, and you should quit using your well pump with your backup generator immediately until you resolve it.

The 'better' solution is to buy a generator with low THD / harmonic distortion (large inverter, or a high-quality alternator based model that has a published THD spec).
 

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Thd

Hi danjayh,

Thanks a lot, the information given in this thead is very illustrative, every step has been well explained and easy to understand. It is an important consideration that must be included in the generator selection process, to avoid surprises after the installation.

Best regards.
 
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