Lately I’ve been seeing questions about the electrical power supply in RVs. Specifically, in one Facebook RV group, someone asked how large a generator should they buy for their travel trailer. The answers given by some people were confusing or downright incorrect. I’ll take a minute to try to explain how this works as simply as I can.
Recreational vehicles typically are wired for a 30 amp or 50 amp power supply. This is where the confusion begins. It seems like a 50 amp power supply would be capable of supplying 20 amps more than the 30 amp power supply. It doesn’t work that way. The 30 amp power supply uses a three-prong plug – a hot lead, a neutral and a ground. All current flows through one hot lead. A 50 amp power supply uses a four-prong lead – two hot leads (L1 and L2), a neutral and a ground. Each hot lead – L1 and L2 – can provide up to 50 amps of current.
An RV wired for 50 amp service has the power outlets and electrical consumers split into two separate circuits. Each circuit has the capability of providing up to 50 amps of current. For example, L1 might provide power to the front air conditioning unit, the microwave/convection oven and half of the wall outlets. L2 might provide power for the rear air conditioning unit, the converter/battery charger and the rest of the wall outlets. A 30 amp coach has all of the consumers and outlets on one power supply circuit. So, we can see that the 50 amp service can really supply up to 100 amps while the 30 amp service is limited to 30 amps.
Back to the question – how much power do I need from a generator? To answer this, we have to understand a few terms. First is voltage. Voltage is electromotive force – think of it as the pressure creating the flow of electricity. Amps describe current – it tells us how much current is flowing through the circuit. Watts describe power – the rate of electrical transfer. We need to understand watts because that’s how electrical consumers are rated and it’s also how generators are rated. The formula is simple – watts = volts X amps.
In a coach wired for 50 amp service we can use the formula to see that when the coach is plugged in to a 50 amp service, we have 120 volts times 50 amps = 6,000 watts on L1 and 6,000 watts on L2 – 12,000 total watts ( sometimes listed as 12kW). Does this mean I need a 12kW generator? That would be expensive.
Looking at the information regarding typical appliance loads in my Onan generator manual, I see the following:
Appliance Load (watts)
Air conditioner 1400 – 2000
Battery charger/converter 300 – 2000
Microwave/convection oven 1,000 – 1500
Electric hair dryer 1000 -1500
Television 200 -600
Coffee maker 550 – 750
As you can see, anything with a heating element will require quite a bit of power. Also, large electric motors like the one in an air conditioner also requires a lot of power. The power requirement drops after start-up. In other words, the maximum power requirement for an electric motor comes when the motor is first activated, then drops as the motor RPM stabilizes. Likewise, a heating element draws the highest amount of current at start-up and the power requirement drops as it heats up. Our Dometic Penguin II air conditioners have a delay built in on start-up and both units never start at the same time – there’s a few seconds of delay before the second unit kicks in.
Our coach is wired for 50 amp service, but our generator is a 7.5kW Onan Quiet Diesel. It provides about 30 amps of current on each circuit. So L1 can provide enough power to supply about 3,600 watts of electrical consumers. Likewise L2 can provide 3,600 watts. With the circuits on the coach split, I see that this should be adequate. The only issue I have is if I want to run the front air conditioner, the microwave/convection oven and the coffee maker at the same time, I may overload the circuit and trip the breaker on the generator. So, if we’re cooking breakfast and making coffee, I don’t run the front air conditioner at the same time. If we need AC, I can run the rear air conditioner as it’s wired to L2.
On shore power, we have more than enough power – 12,000 watts total – to run everything without concern. I hope this makes sense and my simplified explanation helps someone understand the power requirements and how to choose generator size.
We’re continuing to enjoy great weather here in Mesa. We really like Viewpoint Golf and RV Resort. I’m hitting the pickleball courts four or five times a week and Donna has been playing more and she’s really stepping her game up. That’s all for now.