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Discussion Starter · #1 ·
I'm testing and re-testing my 2 generators, being cautious before winter. My 1996 Hurricane Fran era Coleman Powermate Maxa ER is putting out 268 volts with no load. I use an interlock to connect to my breaker panel. I connected 3000 watts worth of resistance space heaters and the voltage dropped to 240. But it takes every bit of 3000 watts to do the trick. This engine is a 10 hp Tecumseh HM100, no AVR. No adjustable carb either. Only thing I can do is adjust the governor screw to bring the RPM's down. Before I do that, I wanted to be better informed, so:
1. Is acceptable practice to get the gen to 240 volts with NO load, and just let it drop under load?
2. If so, how low is it safe to let it drop under full load?
3. Is it acceptable practice to set the gen at a sweet spot in between?
4. Is there a website where I can find accepted best practices for setting up a generators' output? i.e voltage and Hz?
Thank you,
Tom

PS: I've used the Coleman all these years with no problems. Should I just leave well enough alone?
 

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# coxt
yea you are better off saving your bucks and getting a late model gen set.
and sell the old unit.
the new inverter gens are a good choice.
rock solid on voltage too.
I prefer Honda EU inverter series in the gens.
they just work well with a modern house setup.

just remember you do get what you pay for when buying a gen set.
so choose wisely and select a gen that you can find parts for as well and performs well too.
 

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Yes i would expect the frequency to be high. I am not an expert but I believe the generator should run at 3600 RPM with output voltage of 240 volts. If you increase the rpm both the voltage and frequency will increase.
 

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Yes, 3600RPM is the nominal engine speed to get 60Hz. But in practice, it's acceptable and even advisable to set it a little higher at no load to take into account the eventual sag under load. No mechanical governor is 100% perfect at maintaining 3600RPM exactly from 0-100% load.

So 3600RPM (60Hz) + 3-4% at no load is a good place to start.
 

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Discussion Starter · #8 ·
# coxt
yea you are better off saving your bucks and getting a late model gen set.
and sell the old unit.
the new inverter gens are a good choice.
rock solid on voltage too.
I prefer Honda EU inverter series in the gens.
they just work well with a modern house setup.

just remember you do get what you pay for when buying a gen set.
so choose wisely and select a gen that you can find parts for as well and performs well too.
Thank you for the tips on new generators. Fortunately, I did happen across a great sale at Costco a year or so ago on a Firman 7571 tri-fuel. On gasoline it's rated 9400/7500 and it displays watts and frequency, which are both spot on. This 26 year old Coleman is just a back up to a back up. But it's been a great generator. Still starts on first pull. I just wondered about the high voltage. Also, I wanted to LEARN for sure about what's right and what's not when it comes to setting voltage/frequency and whether to set it under load or no load. Until I got to this forum, I saw lots of directly conflicting posts and advice. Many said +- 5%. Another one said for a generator like this 130 volts or even 135 was acceptable since it would drop so much under load. Also some said the over voltage would damage electronics devices but not appliances while others claimed the exact opposite. Makes me want to go back to school and get an EE so I'll KNOW for sure. But I'd be pushing 80 when I finished so yeah maybe not.
 

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Discussion Starter · #9 ·
You may already have a multimeter that can measure frequency or Hz. This feature is often overlooked.
Good suggestion. Unfortunately, my meter is an el cheap. My Christmas present to myself this year is going to be the meter I've always wanted with a LOUD continuity beeper and all the bells and whistles.
 

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Alternatively, you get one of those small engine tach-hour meter. It's self-contained and the only wiring necessary is to wrap the wire "antenna" around the sparkplug wire. It detects the pulses and gives you the RPM readings. Also, as the name suggests, it serves as a engine hour-meter. Makes it easy to track oil changes and other necessary periodic maintenance.
 

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Discussion Starter · #11 ·
Yes, 3600RPM is the nominal engine speed to get 60Hz. But in practice, it's acceptable and even advisable to set it a little higher at no load to take into account the eventual sag under load. No mechanical governor is 100% perfect at maintaining 3600RPM exactly from 0-100% load.

So 3600RPM (60Hz) + 3-4% at no load is a good place to start.
Thanks to both of your for the 3600 RPM figure. Along with the new multimeter, I will treat myself to a good tachometer and a Kill a Wat meter. BTW, in Champion's technical bulletin, I read that if you don't have a frequency meter, you can take an electric clock with a second hand - but it has to be corded - plug it into the generator and watch 60 seconds go by while looking at another trusted clock. If gen is at 60 hz. then 60 seconds elapsed time will show up.
 

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It has to be a synchronous clock (one that relies on the 120V AC 60Hz frequency for timing). If the clock gets its timing independent of the AC input, that method is not going to work.
 

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Thank you for the tips on new generators. Fortunately, I did happen across a great sale at Costco a year or so ago on a Firman 7571 tri-fuel. On gasoline it's rated 9400/7500 and it displays watts and frequency, which are both spot on. This 26 year old Coleman is just a back up to a back up. But it's been a great generator. Still starts on first pull. I just wondered about the high voltage. Also, I wanted to LEARN for sure about what's right and what's not when it comes to setting voltage/frequency and whether to set it under load or no load. Until I got to this forum, I saw lots of directly conflicting posts and advice. Many said +- 5%. Another one said for a generator like this 130 volts or even 135 was acceptable since it would drop so much under load. Also some said the over voltage would damage electronics devices but not appliances while others claimed the exact opposite. Makes me want to go back to school and get an EE so I'll KNOW for sure. But I'd be pushing 80 when I finished so yeah maybe not.
never too late to learn!
lol
yea it depends on what you are running for a load and what it will stand for the voltage and HZ.
i try to keep things at the exact 60 hz as that is where things are happy.
on voltage on grid 119-126 is the normal here at my location.

and when on honda inverter gen it is a solid 123.0 volts ac with exact 60 hz.

higher voltage will erode electronics over time.

lower voltage is hard on some motors and they may over heat.

same on some electronics that have "buck boost" on the boards.
heating issues on the parts as they make up or regulate down the voltage.

these days with led lighting unless they have a WIDE operation voltage
they need to be spot on to work right with no flicker.
 

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That's an easy fix! Use a good volt meter and read your 240 volt outlet while adjusting the posture on the regulator. I set mine at 242 volts . Make sure to watch a video first on YouTube so you don't get hurt. The regulator is a half moon looking block on the back of the genset head. Good luck.
 
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