Wednesday, November 30, 2022

RV Electricity: How much generator do I need?

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By Mike Sokol

Dear Mike (and the RV Electricity Group),
I hope this is not off topic. A question about generators. The on-board generator in my Class A is not working right now. I wanted to buy a portable generator until I can figure out what is wrong with the one that is in there. The on-board is a 5,000-watt Kohler. The rig has a 50-amp system. I know that Mike and others recommend inverter generators because they are quieter. Besides the cost, the largest I can find is around 3,000 watt. Can I get away with that capacity or should I just go for a 5-Kw open frame (contractor) generator to make sure I have enough power? This would be just for an overnight at a Walmart and would not be in a campground or boondocking. The more I can plug into shore power the better. Opinions? —Steve C.

Dear Steve C. (and everyone),
There’s a bunch of other answers on this thread from other members of the group, but I’ll cover a few of the most relevant ones here. To read the complete thread, go HERE.

First let’s do a little data mining of your original question. If this was a 5,000-watt generator, then it was likely capable of providing around 42 amperes of total current at 120 volts (5,000 watts / 120 volts = 41.6 amperes). Doesn’t really matter if this is a single pole or 2-pole or even split-phase output. Watts is watts.

So, if your existing 5,000-watt generator was able to power everything you need in boondocking mode, then you’ve already made a lot of power sacrifices compared to the 50+50 amperes of current available on a standard 50-amp, 120/240-volt shore power pedestal. As I’ve written recently, that’s actually 12,000 watts of power since each 50-amp leg can supply 6,000 watts. So, good job at cutting back on power for generator operation.

Now let’s take the contractor generators off the table. They’re not only gas guzzlers (compared to an inverter generator, which can go into eco-throttle mode to save gas), contractor generators are LOUD and can be heard many hundreds of feet away. Can you even sleep with a contractor generator right beside your rig? Want to make enemies in a parking lot where you need to “pavement camp” for the night? Then get a loud generator and see how quickly the store manager asks you to move along. I know they’re expensive, but inverter generators allow you to operate in stealth mode since they’re often no louder than a car engine at idle.

Next, let’s consider quiet inverter generators and how much power you really need. Yes, I do recommend good inverter generators like the Honda, Yamaha and some of the Champion units, and I’ve been told that the Predator inverter generators are also pretty quiet (though I haven’t measured one for myself yet).

But your statement about 3,000 watts being the largest inverter generator you can find isn’t the case. In fact, I installed a Honda EU7000is generator as backup power for my dad, and it is indeed super-quiet and will run his entire house with only a few appliances turned off via its 120/240-volt split phase output. But this thing is HEAVY at 262 pounds. I mean, it’s got big wheels and a wheelbarrow handle and even I don’t like to roll it around much. While I can guarantee that an EU7000is would easily power anything your Kohler 5,000 would, I’m pretty sure you don’t want to be lifting this beast. Plus, it’s pretty expensive at around \$5,000.

So the question should be, can you run in boondocking mode on a good 3,000-watt inverter generator? For example, I have a Honda EU3000is and it has a 30-amp twist lock outlet (in addition to a few 20-amp Edison outlets). And at 134 lbs. it’s a LOT easier to move around compared to its 7,000-watt big brother. It easily starts a 15,000 BTU air conditioner with plenty of power to spare for several smaller appliances at the same time. However, it won’t start a big rooftop air conditioner with the microwave running at the same time. And it won’t start and run two rooftop air conditioners at the same time unless you add a soft-start circuit to the air conditioner compressors.

I’ve been doing some experiments with the Micro-Air EasyStart, and it does appear to reduce the starting current from air conditioners sufficiently that a Honda EU2000i generator will easily start a 15,000 BTU air conditioner. Depending on your air conditioner situation, you might find that adding an EasyStart to each of your air conditioners (I assume you have two), just might let you run both of them on a 3,000-watt inverter generator. But I don’t know for sure. In any case, the EasyStart is a smart investment since it will reduce the strain on your electrical system no matter if you’re running from a generator or a campground pedestal.

What would I do if I were you? Well, I would find a rental house that can supply you with a Honda EU3000 generator for a few hours and try it on your RV. Hey, see if they’ll let you drive your RV to the parking lot with the appropriate twist-lock 30- to 50-amp adapter and try to power up your RV. Don’t forget the G-N bonding plug just in case your RV electronics aren’t happy with a floating neutral. If the EU3000is will run your RV with whatever boondocking appliances you want for an hour in the middle of the day, then it should be good overnight. The rental fee will probably be less than \$50, and then you’ll be able to judge for yourself. Or if you know someone with a 3,000-watt Predator generator, see if they’ll let you try to power your RV with it for an hour or so. The generator will protect itself if you get too power hungry, and only you can determine just how power hungry you are (I’m not judging…).

Hope this helps you figure it out.  Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 40+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

##RVT897

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Andrew Harris
3 years ago

We have generally camped in campgrounds and have never needed a generator. This year we’d like to take our Travel trailer to some NASCAR and NHRA races and will have to be self sufficient. We used to just tent camp at the tracks so we feel that we won’t need much in the way of power, just a couple hours of lights each day and perhaps the fridge and our water pump. It would be nice to be able to charge our Cell phones. How much do we really need for a 3 or 4 day trip?

Wolfe
3 years ago

I’ll agree the \$650 Predator 3500 beats the heck out of \$2000 Hondas for 30A trailers. I believe there is a larger Predator for 50A as well.

So many people have asked me about sizing generators that I made up a TT30 plug with an \$8 digital wattmeter so people can live-test their own rig’s draw, easier than doing math of what things “should” draw.

John
3 years ago

The bigger question at this point is why the RV industry hasn’t adopted inverter generators instead of the noisy old technology that has been around forever? Obviously, for diesel powered coaches, there aren’t any inverter models on the market, but I have no doubt that Honda and others could build a propane fueled unit that would be almost maintenance free. Gas powered coaches and toy haulers could easily mount an inverter unit. Why aren’t these an option? Why has Onan ignored this technology?