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Old 08-10-2017, 10:52 AM   #1
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Generator 110v vs 120v

If you were to set engine RPM at 110 or 120 volts (AC power, N. America). Just for discussion, a value in between is not an option. Which would you choose and why? Assumes rpm is set at working load.

In my case a little single cylinder Kubota running at approx 3600rpm.
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Old 08-10-2017, 10:57 AM   #2
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Set rpm to 3600 to 3650 running a normal load. That equates to 60-61Hz. A gennie like that likely is capacitor excited so no adjustment for voltage. 110 is fine, 120 is fine. If there is a regulator with adjustment for volts, I set to 120.
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Old 08-10-2017, 12:11 PM   #3
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110 and 120 are "nominal" voltage numbers and mean essentially the same thing. Check the voltage in your home and it will be anywhere around these numbers.


I suggest 120 if you can't get an explanation from the manual or the company.
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Old 08-10-2017, 01:50 PM   #4
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Higher voltage draws less amps. Watts = Amps x Volts Watts/Volts = Amps
Whatever you're running on the AC power has a need in watts. If you lower the voltage, it draws more amps. 1500w/120v = 12.5 amps 1500w/110v = 13.6 amps
The lower voltage could cause marginal wiring to heat up, cause pitting in contacts in switches and breakers and so on.
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Old 08-10-2017, 03:16 PM   #5
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The standard in the United States is 120 volts, not 110 volts.

People seem to interchange 110 and 120 frequently, but in reality 120 volts is the standard.

120 volts is derived mathematically

In a three phase system you can take phase to neutral voltage of 120 volts and multiply it by the square root of three (1.73) and get the common 208 volts.

In a single phase system you use a 30:1 transformer from a 7200 volt primary line to make 240 volts. Then you center tap and ground the secondary of the transformer to get two 180 degree opposite legs of 120 volts each, with 240 between them. As a FYI they call it single phase because you use a single phase off of the primary lines which are what runs down your street.

In a 3 phase 208 volt system they use three 60:1 transformers each producing 120 volts from the 7200 volt primary. They then tie one side of each of the secondarys together and ground that. This is called a WYE system, and the phases are 120 degrees apart. As I indicated above if you multiply 120 times the square root of three you will get the phase to phase voltage which is 208. The square root of 3 constant was derived by performing phasor trig on the phases.

So... The correct voltage is 120 volts, and now you know the rest of the story
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Old 08-11-2017, 08:44 AM   #6
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"The standard in the United States is 120 volts, not 110 volts."


True but the actual measured voltage at your home can vary quite a bit, perhaps from 110 volts to 125 volts. Marina voltage is notorious for varying because of varying loads on the docks and long wiring runs. 105 volts is not uncommon at the end of a long dock.
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Old 08-11-2017, 09:57 AM   #7
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Ski is correct, the useful number is 60 Hertz, the frequency of north American AC Current. Set your genny to 60Hz plus or minus 1 on a normal load.
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Old 08-11-2017, 10:12 AM   #8
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Quote:
Originally Posted by WesK View Post
"The standard in the United States is 120 volts, not 110 volts."


True but the actual measured voltage at your home can vary quite a bit, perhaps from 110 volts to 125 volts. Marina voltage is notorious for varying because of varying loads on the docks and long wiring runs. 105 volts is not uncommon at the end of a long dock.
Agreed

As a FYI, the reglatory requirement for energy delivery at the meter base is +- 5% or on a nominal 120V phase to neutral voltage 114-126 volts.

The actual voltage delivered will vary based on many factors such as line loading of primary and transmission systems, etc..., but must always fall within the 114-126 range.
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Old 08-11-2017, 11:01 AM   #9
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Just checked my house with a Fluke, 122Vac. My boat gennie is set at 118. Seen many boats with gennies with sloppy voltage control range from 110 to 130. Get below 105 and time to fix something.
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Old 08-11-2017, 11:07 AM   #10
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Quote:
Originally Posted by Ski in NC View Post
Just checked my house with a Fluke, 122Vac. My boat gennie is set at 118. Seen many boats with gennies with sloppy voltage control range from 110 to 130. Get below 105 and time to fix something.
The voltage you see at your house is set at the substation. Our local utility sets the voltage at 124.5V with a one volt dead band. Above or below and the substation transformer ratchets up or down a notch to keep the voltage within the dead band.

People near the substation get closer to 124 volts, end of the line might be 118.
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Old 08-11-2017, 12:13 PM   #11
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I always set the genny at half load for 60 Hz and then checked to make sure that they were within 62 nd 58 Hz at no load and full load levels.
Also checking the voltages as a byproduct to make sure they were within spec as well but as per Ski's first post the frequency is the key check.
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Old 08-11-2017, 12:41 PM   #12
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A handy tool for verifying voltage and frequency of the generator is the "kill-a-watt" power monitor. Plug it into a receptical and monitor the gen output while you load up the gen. Compare results to your owners manual specifications.
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Old 08-11-2017, 06:47 PM   #13
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When "writing" directions and making labels...

When we might have 12 volts, and 24 volts, and 120 volts and 240 volts...

It has been my habit to downgrade the AC numbers to 110 and 220, in order to defend against bad printing, part label smeared, and triggering better recognition of the system at hand.

Then we get 12/24/110/220

Avoiding miscommunication depends on eliminating those devilish similarities?

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