By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
Dear Mike,
I’m stuck at a campground with only a 30-amp pedestal outlet, but I usually run on a 50-amp plug. Seems like I can hardly run anything more than one air conditioner at a time and a few other things. But running the microwave at the same time doesn’t work without popping the campground circuit breaker. And even running a second air conditioner is a problem. Is there that big of a difference between 30-amp and 50-amp power? Are air conditioners really that much of an energy hog? —Texas Pete
Dear Tex,
Yes, air conditioners are generally your biggest RV power hog. So you’ve run into the limitations of what a pedestal can and can’t power. And you’re also the victim of the name game. The thing to remember is that calling a pedestal 50 amps is really a bit of a misnomer. Actually it should be called a 100-amp pedestal because there are indeed 100 amps of 120-volt power available for your RV from a 50-amp outlet, instead of the 30-amps of 120-volt power available from a 30-amp outlet.
Confused? Let me explain a little better. The only thing that counts is watts, and you can calculate the watts available if you simply multiply volts times amps. So in the case of your 30-amp outlet all we have to do is multiply 30 amps times 120 volts which equals 3,600 watts. Sounds like a lot, doesn’t it? Well, no, because the lowly outlet in the bedroom of your sticks-and-bricks house can supply 20 amps at 120 volts, so that works out to 2,400 watts. Yikes! So that big, heavy 30-amp outlet on the campground pedestal is only 50% more power than the outlet in my house? Exactly right…
Now let’s move up to the 50-amp pedestal outlet you’re used to. It’s actually 50 amps at 240 volts, which is split into two separate legs of 120 volts each with 50 amps of current. Since each leg can supply 50 amps at 120 volts, we just multiply 50 amps times 120 volts and calculate that there are 6,000 watts available FROM EACH LEG. So add the two legs together and you get 12,000 watts of power available from a 50-amp shore power outlet compared to 3,600 watts from a 30-amp outlet, and 2,400 watts from a 20-amp outlet at your house. No wonder you’re running out of available power quickly.
Here’s a chart comparing each of the pedestal power services available to you. As you can see, there’s a HUGE difference between the 12,000 watts you’re used to having compared to the 3,600 watts you now have available. For comparison, most houses nowadays have a 200-amp/240-volt service which is 48,000 watts. That’s 4 times as much power as even a 50-amp pedestal outlet, which is why we’re used to running everything at once in our houses but have to practice load-shedding in our RVs, even with a 50-amp plug.
I have been experimenting with an air conditioner upgrade that can be helpful when you need to run both air conditioners from a 30-amp service, and I’m getting ready to make a comparison video next week. But right now I can tell you that SoftStartRV™ by NetworkRV is getting great reports from the field. I’ll have mine wired up in another week or so and will report back how it works along with a real time graphic video of startup current draw for both stock and SoftStartRV modified air conditioners. Gonna be interesting.
In the meantime here’s a video of me explaining how air conditioner SoftStartRV technology works. This could do the trick and let you run both air conditioners at the same time from a single 30-amp shore power outlet. And you can visit a discount page setup if you’re interested in purchasing a SoftStartRV HERE
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ 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.
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I’ve asked in several places, no answer, if the Power Management system we have on our GD Momentum has to be changed, modified or whatever if softstarts are added. It won’t know they’ve been installed, and I’m wondering if it will continue to shed power, thinking that the A/C’s will use more than expected.
My SoftStart experience- with the diesel 7500 generator on when starting with 1 15kw Coleman heat pump no noticeable increase to generator output. Next start up of 2nd 15kw heat pump only a slight uptick to generator db. Both units did not have the usual start up surge issues.
2nd test.- I have 2 Honda eu 2000″s companioned together from a previous motor home and carry them as emergency spares to use or lend out to friends at the dog trials we boondock at. On echo mode the first HP started with a small uptick and settled back to echo mode. Starting the 2nd hp with the first still running went to about 3/4 of capacity for 2 to 3 seconds and settled back to 1/3 to 1/2 output. These are guestimates as no test equipment was available. My point is that the 2 SoftStarts with the eu2000 Hondas do actually what they promise and at a noise level that rivals the onboard diesel generator so as to not create havoc with our boondocking companions.
Thanks Mike, the illustrations really helped me understand it. I knew before reading how it worked but putting them comparisons together made it hit home.
Mike, it will be interesting to know if you need one of these on each of your AC units or will having it on just on unit allow you to run on 30 amps.
You would need one on each air conditioner if you want to run both of them at the same time, which of course you do.