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Old 01-25-2015, 09:19 PM   #1
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Trying to understand generators...

We have a small 5th wheel. We've never owned a generator. I don't understand the whole output starting/running/reality thing... We've stayed for years in a variety of state parks with 15 amp service. Always ran the A/C with no problem. Or the TV and lights and whatever. Yes, we had to pay attention and couldn't run the A/C AND the toaster, but with a little attention we got along just fine on 15 amps.

I read several topics in the forum, and someone would say "I want to run my microwave" and 5 people would tell them it required a 4000 watt, $2000 generator. Why?

I found a topic that said a 13,500 btu A/C was something like 11.? amps to start and 9.? amps to run... I looked at some "inexpensive" basic 2000 watt generators and they say they have a 2000 watt peak and 1400 watt rating. Does 2000 watts equate to 16.6 amps at 120v? And 1400 = 11.7 amps?

How long CAN a generator produce the peak wattage? 10 seconds? 30 seconds? 2 seconds?

If so, why can't you run the 13,500 but A/C with that?

Or the small, 1200 watt microwave for 30 seconds? Or even a normal 1500 watt microwave for 30 seconds?

There's gotta be something obvious I'm missing, but we're looking at being able to use the 5th wheel at events where we're in a show haul parking area without electricity. We need to run some lights, a computer or 2, charge the batteries, stuff like that... Having the A/C would be nice, as would the microwave occasionally so I'm trying to figure out whats really NECESSARY if this isn't going to be a lifetime, 7 day-a-week constantly running thing... Just a half dozen or fewer weekends per year...

If it's gonna take a $1000 unit, the idea is dead before it even starts. If I can do it with a 2000 watt, $300 unit that I put between the hitch and tailgate it's probably feasible... So what's the real scoop if I'm not looking for the Corvette or Cadillac of generators - just a Kia that'll provide the basics?

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Old 01-25-2015, 10:37 PM   #2
Join Date: Mar 2013
Location: Edge of Hill Country
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When AC units 'start', there is the 'load' of the compressor and a fan motor to provide. Not having 'adequte' power can...and over time, not necessarily the first time, cause a failure in one of the AC components through 'inadequate' power, you cause overheating of components... or, slow startup of compressor which equates to higher/faster wear pattern and subsequent failure.

The AC unit can 'run' on a standard generator. Your PC's and other items with 'circuitry' like your MW control panel and TV, 'can' be run on a standard 'generator', but it is advisable to use 'inverter' style as they can provide proper '60 cycle' sine wave power your 'electronic necessities of modern life' demand...and your AC will work too... if your genny has adequate capacity.

So, if your AC specs show 110vac and 13AMPS, you can see, the draw can exceed 1000 watt generator in short order and will be running near 'max' when 'cruising'.

Now, imagine, you are running your AC... it's warm outside.. and your AC does a 'short cycle'.... meaning the freon pressures are still high when the compressor attempts to start again!!! This is known as a 'Hot Start' by some folks... you can install 'hot start' features which can 'protect' by ensuring enough time has elapsed since the last time the AC compressor ran before trying to start...

This 'hot start' will put an even greater load on your genny... better have enough capacity or you risk a burnout of components.

Bottom line, having more 'capacity' than you 'think' you will use will mean your genny will run better, last longer, and the components in your RV should last longer... You just can't cheat it.

I had a Home Depot coupon for a 6000 watt, diesel, portable Generator this weekend. It was $800. I 'passed' because it was NOT an 'Inverter' style.

now, some tech stuff...

You may have known these facts below... I lifted it from this website: How to Convert Watts to Amps Simplified -- Converting Amps to Watts the easy way
Converting Watts to Amps

The conversion of Watts to Amps at fixed voltage is governed by the equation Amps = Watts/Volts

For example 12 watts/12 volts = 1 amp
Converting Amps to Watts

The conversion of Amps to Watts at fixed voltage is governed by the equation Watts = Amps x Volts

For example 1 amp * 110 volts = 110 watts

Converting Watts to Volts

The conversion of Watts to Volts at fixed amperage is governed by the equation Volts = Watts/Amps

For example 100 watts/10 amps = 10 volts

Converting Volts to Watts

The conversion of Volts to Watts at fixed amperage is governed by the equation Watts = Amps x Volts

For example 1.5 amps * 12 volts = 18 watts

Converting Volts to Amps at fixed wattage

The conversion of Volts to Amps if the wattage is known is governed by the equations Amps = Watts/Volts

For example 120 watts/110 volts = 1.09 amps

Converting Amps to Volts at fixed wattage

The conversion of Amps to Volts if the wattage is know is governed by the equation Volts = Watts/Amps

For Example, 48 watts / 12 Amps = 4 Volts

Converting Volts to Amps at a fixed resistance

If you know the volts and the load of the resistance the amps are found by Ohm's law: Amps = Volts / Resistance

Converting Amps to Volts at fixed resistance

If you know the amps and the resistance Ohm's law becomes Volts = Amps * Resistance


Amps are how many electrons flow past a certain point per second. It is equal to one coulomb of charge per second, or 6.24 x 10^18 electrons per second. Volts is a measure of how much force that each electron is under, which we call "potential". Power (watts) is volts times amps. A few electrons under a lot of potential can supply a lot of power, or a lot of electrons at a low potential can supply the same power. Think of water in a hose. A gallon a minute (think amps) just dribbles out if it is under low pressure (think low voltage). But if you restrict the end of the hose, letting the pressure build up, the water can have more power (like watts), even though it is still only one gallon a minute. In fact the power can grow enormous as the pressure builds, to the point that a water knife can cut a sheet of glass. In the same manner as the voltage is increased a small amount of current can turn into a lot of watts.

This is also why increasing the volts does not necessarily increase the available power. Power is amps times volts, so if you double the volts you halve the amps unless something in your circuit actually creates power, such as a battery, solar panel or nuclear power plant.

Convert amps to watts. Convert watts to amps. Convert watts to volts, convert volts to watts, convert amps to volts at fixed wattage. How to convert watt to amps. How do I convert amps to watt? Amps converting watt. Volt to watt conversion.

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Old 01-26-2015, 03:45 AM   #3
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Got all that?

Check the tag on the AC unit, your biggest power user. If it says 12 amps or less, you can probably use a 2000 watt generator from Home Depot or Costco. Spend a little extra for the quiet one that looks like a suit case, the open ones are LOUD.

Example, amps ( 8.3 ) times volts ( 120 ) equals watts ( 996 )

Volts will alwsys be 120 so look at your stuff and find the amps it uses. If it lists watts, there is no math.

If you have the AC running and turn on the microwave, the generator will probably kick out, from to many watts. Just learn to manage your power.
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Old 01-26-2015, 05:17 AM   #4
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I use a Champion 3500/4000 watt generator and have not had any problems with anything. Cost was 273.00 at HD.
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Old 01-26-2015, 05:27 AM   #5
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total usage

from the labels on the items you intend to use, add up what they draw

and match a generator that matches it + 25%.

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Old 01-26-2015, 05:46 AM   #6
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This will meet your needs. This one also has a 30 amp twist lock outlet. Be aware that it will be LOUD! Generators which are quiet cost $$$$$ more than this one.

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Old 01-26-2015, 06:48 AM   #7
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I have the champion version of this generator. I can tell you there are times my 13.5k btu ac sounds scary when it starts when powered by this. --Mine has 15min run time on it, always used stabil in the gas. Starts on the first pull or two. Yours for $275 w/wheel kit and cover
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Old 01-26-2015, 08:50 AM   #8
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Awesome. Thanks for the information. So, if I'm reading correctly (always risky for me), my 13,500 btu has some startup requirement. I need a generator that'll meet that, and 25% extra would be good... Is there ANY correlation between being able to run any (not together but individually) of the A/C, toaster, microwave on 15 amp campground power, and running any of them on a generator?

And why is bjlakatos, who is using the Champion equivalent of a 4000 watt behemoth getting "scary" noises from the A/C when running on it?

Unfortunately, in the end, from what I've read in here and elsewhere, I have the feeling this is going to be DOA... If the "open" generators, which are far more reasonably priced are loud, it won't work 'cause my wife will have a fit. If the "quiet" ones cost a lot more and I need 3000 or 4000 watts that requires a hoist to get out of the truck, that's not gonna fly either... I THINK I was living in fantasy world where I could get a small-ish, reasonably light, pretty quiet, adequate unit for a "reasonable" cost. Doesn't sound like it's gonna happen. But, at least I have more information now.
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Old 01-26-2015, 09:08 AM   #9
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A lot of good information above, but let me try to simplify this for you.

* Cheap = loud, as in lawn mower loud.
* If you want to run the microwave, lights, etc. EXCEPT the A/C, then a 2000 watt generator will work fine. The Honda EU2000 is a popular one, is pretty small, and only weighs 45 pounds. And it's very quiet (for a generator) and reliable.
* If you want to run a single A/C, then you'll want *at least* 2400 watts (and that may not be enough, but I've done it before). A popular solution here is TWO Honda UE2000 generators. They can be connected to provide double the output (4000 watts), enough to run a single A/C. Plus, it's easier to move around and store 2 small generators than a single huge one.

If noise is a huge concern, I'd go with the double Honda 2000's. They run around $1K each. Yamaha also makes similar generators that can be joined together. I currently have 2 Honda's but a Yamaha previously; I actually thought the Yamaha was quieter but not by much.
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Old 01-26-2015, 09:08 AM   #10
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A RV friend of mine who owns a 5ver with 50 amp service decided to purchase a generator for his rig. He bought a portable 3000 Watt PowerHouse Generator.

His objective was to have one that would power up some stuff plus run at least ONE of his rooftop A/C's.

I helped him wire it into his ATS and once finished it would power the stuff in his coach with EXCEPTION of his roof-top A/C's.

I asked him to retrieve the literature on his A/C's and after reading the brochure it clearly stated that his A/C's require a 3500 watt Generator to start and run ONE roof-top A/C.

So he kept the generator for about 2 years and then recently sold it for a loss.

An expensive lesson as it cost him over $1000 for that unit.

Do your homework and research PRIOR to deciding on what generator to purchase so you don't make the same mistake as my friend did.


Dr4Film ----- Richard
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Old 01-26-2015, 09:34 AM   #11
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Keep in mind that these "loud" generators that you are thinking of are normally rated at 70db and normal conversation is about 65db at 6 feet. Yes, you can hear them, but you can stand right next to it and talk to someone, not yell at them. If you get one get the one with the large (small car size) muffler. Running it when you are in a parking lot I would have no problem being beside it. After all, I run mine right next to my trailer.
edit: I for got to tell you, on the type of generator you are looking at the digital clocks probably won't keep accurate time. They use the 60 cycles per second for time keeping and the generator may or may not be putting out exactly 60 cycles per second.
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Old 01-26-2015, 09:36 AM   #12
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Dr4Film: Too late for your buddy, but did he by chance try adding a hard start capacitor to his A/Cs? They're around $15 and reduce the initial electrical surge when the A/C starts up. I did this for a window A/C unit and it made the difference between being able to run it off a Yamaha generator I used to have.
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Old 01-26-2015, 09:44 AM   #13
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Holy cow, a muffler the size of a small car, where do you pack that!

Could`nt help it.
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Old 01-26-2015, 09:48 AM   #14
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Sorry, my fingers can't type as fast as I was thinking...... It should have said the size USED on a small car.......

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