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 a newbie so please be gentle with me. I keep hearing about inverters and converters, but I’m confused as to the difference. Can you explain what they are in simple language?
Thanks… Tony
Dear Tony,
Yes, RV terminology can be very confusing for a newbie. After all, your house doesn’t have a converter or an inverter or house batteries. In a house you just plug in and go. But in an RV you have to think about running from 120-volt AC power or 12-volt DC power, and that’s where inverters and converters come in.
Basically, most of the smaller gadgets in your RV (interior lighting, television, ventilation fans, water pump, etc.) all run from 12 volts DC. Yes, this is exactly like the 12 volts DC from your car battery that powers the headlights, radio, blower motor, etc. And your car has a way to recharge its battery whenever the engine is running. This is called the alternator, which is belt-driven from the engine. Without an alternator to recharge your car battery it would soon be dead.
Your RV does something similar, with a 12-volt DC battery (called the house battery) and a set of fuses and/or circuit breakers to feed power to your fans, lights, television, etc. But instead of an alternator driven by the car engine to recharge this house battery, at the minimum you’ll have something called a converter. Its job is to take 120 volts AC from the pedestal or outlet that your shore power cord is plugged into, and convert it down to 12 volts DC or so (actually, a little closer to 14 volts, but who’s counting?). This is so that it can do two things: recharge your house battery (or batteries), and provide power to run the aforementioned 12 volt DC accessories such as your interior lights, fans, etc. With me so far?
Now, not all of your RV accessories will run from 12 volts DC. Some insist on needing 120 volts AC at 60 Hz to operate, just like you get from a wall outlet in your home. One big example would be the new residential refrigerators showing up in many RVs lately. If your RV is plugged into shore power it’s no big deal. But what if you’re boondocking (camping without campground electricity or water supply) and don’t want to start up a generator for 120-volt AC power?
Since these bigger appliances won’t run on 12 volts DC directly from your house battery, you need something that will “invert” the 12 volt DC battery power into 120 volt AC power. And yes, it’s called an inverter. Its job is to make 120 volts for the larger appliances in your RV – that might also include things like your microwave oven and large-screen television. However, there’s no practical way to be able to afford enough batteries in a normal RV to run a rooftop air conditioner for more than 10 or 20 minutes before the battery goes dead (maybe up to 60 minutes with a large battery bank).
So, a “converter” converts the 120-volt AC power from the campground pedestal into 12 volts DC to charge your RV’s house battery (or batteries) as well as run all of your DC appliances. An “inverter” does the opposite and inverts the 12-volts DC from the RV’s house battery into 120-volts AC that bigger appliances such as your residential refrigerator and maybe your microwave oven can use.
But don’t go crazy with running lots of appliances at once when you’re operating on battery power alone since you’ll soon run out of juice.
Hope this helps.
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 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.
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I had read your RV Electricity – RV fire safety THIA interview: Part 1 of June 29, 2019 and never could find the Part 2. I looked for the promised YouTube interviews and found zilch… Where are the updates to the THIA products?
I think the product has very limited applications, but want to see what you had found.
Thanks
Stay cool
Thank you, Mike, I find your articles fascinating and very helpful.
We have a small trailer with a small Dometic fridge. It has three settings; AC, DC, and Gas (propane). It has been my understanding that, in fact, all three use DC power to cool in some way. If I’m driving it runs off the house battery, if I’m stopped and off the grid, it’s either using house battery or propane, and if I’m using propane, it’s also using the house battery to run the cooling fans and to ignite the burner.
Does that sound correct?
Oh, for crying out loud! I forgot something!
It is also my understanding that it I have the unit set to AC it is actually running off 12V from the converter. In other words, it’s a 12V or propane and 12V refrigerator. Possibly correct?
We are going to upgrade to a 5th wheel in the future. We now have a refrigerator that runs on electric and gas TT. My question is if we get a residential refrigerator in our new RV will it run while traveling? If not how do people keep things cold?
Thank you
If you want the Residential Refrigerator, you will need to have and INVERTER installed. And once you disconnect from Shore Power, your Inverter will kick in and Run your Refrigerator while going down the road.
The Inverter should give you up to 8 hours on the batteries, provided your batteries are fully charged and in good shape!
You will also need to make sure you have a Good Set of DEEP CYCLE Batteries to power the inverter!
The modern Residential Refrigerators are insulated very well these days, so if your Fridge is cold when you depart down the road, it won’t require must energy to stay cold while on the road!
We have a Residential Fridge in our 5th Wheel and would have nothing else!
Also do not forget that if you are moving, the vehicle should be continually charging the batteries.
Stay cool
Be aware that unless you have a DC-to-DC charger between your tow vehicle and trailer, you’ll probably be limited to around 10 amps of charging current. That’s less than 1 amp on the 120-volt side of the inverter, so that’s probably not enough to keep up with your refrigerator’s power needs on long drives. But you won’t know until you try it for yourself.
Yes, you are so right. Sorry for the confusion.
Stay cool
If your 5th wheel has a residential fridge, I’m pretty sure there’s an inverter onboard that will power the fridge while traveling. But there’s a chance you will need to turn the inverter on prior to heading down the road. The “house” battery or batteries will run the fridge then.