# A question about motors and capacitors

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My neighbor has a well that's 200 feet deep. When he tries to run the pump from a generator located at the well head it works fine. But he moved the generator to his garage and this added another 150 feet of

10 gauge wire to the circuit. The pump will not start now. So it looks like the extra 150 feet drops the voltage too much. So I was wondering if it would be practical, or even possible, to use a capacitor to provide enough energy to start the motor. Anybody know? I don't know if his pump is running on 240 or 120 volts. Looking at the chart in my hand I see that for a 2% or less voltage drop using 10 gauge wire the pump must draw 6.7 amps or less for 120 volts and 13.4 amps for 240 volts. Of course if the cap idea is sound I'll need to measure the voltage and amperage. Thanks, Eric
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Does he have any of it formed into a coil? They block AC quite nicely.

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For AC? Not a good idea!

Nick

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Adding power factor correction caps at the well head will help. He could also add a boost transformer at the generator. If he is using

120 volts to run the pump, he will benefit by rewiring the motor to use 240 volts.

Dan

Eric R Snow wrote:

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10 gauge is around .1"+ right? 150' is a long ways. Try some wire around 3 times that size. Personally I wouldn't even try, I'd make it so the generator could stay out close to the well.
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"Dave Hinz" wrote: Does he have any of it formed into a coil? They block AC quite nicely. ^^^^^^^^^^^^^^^^ A coil of paired conductors should have almost zero inductance, so that, in itself, should not be the problem. However, having part of the cord coiled means that it is longer than necessary, which would add resistive voltage drop. Uncoiling the cord wouldn't help that--shortening the cord would.

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I've seen coiled up extension cords which melted together from heat. I've also seen an electric popcorn popper (the kind they use in carts for events) which wouldn't work; the extension cord was coiled up and HOT to the touch. I uncoiled it, the lights brightened on the cart, and it got hot enough to keep up. Same length cord, effect was gone, and the crowd got popcorn.

I think what I was seeing above was inductive loading; pairing notwithstanding.

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Hi Dave

Leo is right. You must have experienced some voltage drop in the closely coiled, parallel conductors that was due to something other than inductance. I would guess your increased voltage drop was due to heat of the conductors.

Jerry

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I did a quick browse of the inductance formulas, I think its plausible that a fairly large coil of extension cord carrying a goodly number of amps could exhibit a few ohms of reactance- enough to heat the wire up at least. Assuming a heavy load, that might be enough to drop the voltage significantly.

Its far from "blocking" the AC though, its more like increasing the wire's resistance by several ohms, probably less than 10, but thats enough to cause heating and voltage drop problems.

Gregm

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"Dave Hinz" wrote: in message news: snipped-for-privacy@individual.net...

I've seen coiled up extension cords which melted together from heat.

I think what I was seeing above was inductive loading; pairing notwithstanding. ^^^^^^^^^^^^^^^^^^^^^ Well, Dave, I can't argue with waht you actually have seen, but it still bothers me on THEORETICAL grounds: 1.) The coiled pair statement I made earlier 2.) Inductive voltage drop does not produce heat.

I can see that a cord that is coiled up would run hotter than one that is stretched out. Since resistance generally goes up with temperature, you could have positive feedback going on.

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Very interesting discussion.

I think that it would be useful to quantify the issues.

What is

- the operating voltage rating and HP of the motor

- Actual idle generator voltage

- Voltage at generator end during startup

- Voltage at pump end during startup

- Starting amps

Good suggestion in a possibility of rewiring the motor from 120 to 240 volts, if possible. Can the generator be possibly adjusted to produce higher voltage?

Besides long wire, the culprit could be some bad crimps, worth checking at least.

i
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Hi Greg

Did those "inductance formulas" account for the fact that the conductors are *parallel-side by side*?

Jerry

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Well, a few ohms resistance on a 10A load starts being a non-trivial percentage of the current draw.

Impedance.

(shrug) I'm just describing what I've seen and done myself. The electrician who showed me the coiled extension cord melted together had no doubts about the reason, and I have no reason to doubt him. And the popcorn popper in question went from barely heating to working fine with just that change. For whatever reason.

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Extension cord cools, its resistance drops -> element gets hotter, its resistance rises, current drops -> extension resistance drops further

-> etc., until the system settles at a new equilibrium point.

Ned Simmons

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not related to any previous post... Resistance of 300 ft of 10 gauge wire (150 ft away running there and back) is 0.3 ohm. At 20 amps current, voltage drop would be about 7 volts. At 40 amps, voltage drop would be about 14 volts.

Voltage drop = amps * 0.3.

Just wanted to inject some numbers into this discussion.

i
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"Dave Hinz" wrote: (shrug) I'm just describing what I've seen and done myself. The electrician who showed me the coiled extension cord melted together had no doubts about the reason, and I have no reason to doubt him. (clip) ^^^^^^^^^^^^^^^^^^ Well, now that I know that you base the melted extension cord on "heresay," I have every reason to doubt that it was caused by inductance.

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I'd agree with that. In that arrangement the individual inductances of the two conductors would largely cancel because nearly all of the field produced by either wire links the other wire as well.

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More numbers: the starting current of an induction motor can easily be 10X the rated run current. Circuit breakers and mains can handle that because the surge lasts for well under a second. Greater resistance in the line will extend the duration of the starting surge, and gennies don't handle even 2X overload well.

I have observed starting surge current of 190 amps on a brand-new 2-HP

115-volt capacitor-start capacitor-run 3450 RPM buffer motor.
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Yes.

I have observed a 120A starting current on an unloaded 10 HP motor (3 phase, starting with a capacitor on single phase).

I mentioned this in my previous post, the OP needs to measure quite a few things to be able to get some meaningful answers.

i
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Leo, that's fine. Really, it is. You don't know the electrician in question, I do. He's been my firefighting and EMT partner for nearly 15 years so I trust him completely, literally with my life. Maybe he doesn't know his topic and it wasn't inductance. Or maybe there's something going on you haven't seen.

I propose a test - 100 foot extension cord, 10A load. Measure the voltage across the load with the cord straight, and then with the cord coiled. This is analogous to the popcorn popper example I mentioned. I'm also not sure that the return current path eliminates inductance; it eliminates it picking up external signals, yes, but I'm not sure I understand how it would counter the effect. Either way, seen it, had it explained by someone who understands electrician-level signals _very_ well, and am inclined to believe it.

So, why don't you give that extendsion cord thing a try? I might if I get some spare time, but the cance of _that_ happening soon is low.

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