Explaining converters, inverters and generators – Part 1

Explaining converters, inverters and generators – Part 1

By Wolfe Rose
There is a lot of confusion for new RVers as to whether they need a converter, inverter or generator. What’s the purpose of each, and if one is needed, what type or size? How do inverters vary from the converters built into RVs, or are they the same thing? To answer all of that, we first have to understand that trailers have two complete power systems, and why.

Starting at your shore cord, you take in 120V Alternating Current (AC), similar to your 15A wall power at home. This is the 30A or 50A designation you may hear referenced. You can pull much more power through that cord than the outlets you’re used to at home, but it’s the same “type” of power – 120V provided as a sine wave. This type of power runs your RV’s outlets, air conditioner and microwave. These are normally allowed to go dead whenever you’re unplugged from shore power. When your water heater or refrigerator are in AC mode, those too may be powered by this – but remember each of those can also usually run just fine off propane as well.

The second power system your trailer contains are your batteries, which provide 12V DC – the same type of power as in your car, which has polarity (+ and – terminals). This power runs your lights, fans, furnace blower and the control electronics for your refrigerator and hot water even when they are primarily powered from propane. These are all run from your batteries because “camping” trailers were originally assumed to need to be independent from shore power, even if that capability is only used by some RVers while in transit these days. Those who still camp away from power use this power independence to “dry camp” at sites without electricity, or “boondock” without a designated campsite. The problem is that your battery quickly runs down since it’s not being replenished – especially with high-drain loads like your furnace blower. This is why boondockers often install solar or wind power to recharge their batteries.

Recharging the battery (and preventing it from running down in the first place) is the job of the converter, which can be thought of as a beefy AC-to-DC battery charger. Some folks replace or augment their converters with “smart” multi-stage automotive chargers. A 40A converter designation means the converter can compensate for up to 40A of DC draw, running your lights and furnace without pulling power from the battery. Think of this function as a “wall adapter” for your battery-powered trailer. In addition to carrying the load for your batteries, the converter also recharges your battery from prior drains. The converter is an important bridge between the AC and DC power systems, in order to maintain the DC battery charge.

That said, our boondocker in the woods still can’t use his microwave or air conditioning, because they exclusively gulp down AC, not the relatively meager DC that’s available. In the next installment, I’ll discuss how to create AC power without a shore connection.

Facebooktwitterpinteresttumblrmail

Related

15 thoughts on “Explaining converters, inverters and generators – Part 1

  1. Charles Young

    Wolfe,

    Thanks for the work and articles going into this series. When you get to generators, I hope you go into how they can impact a surge protector. I have a pair of Yamaha 2000 watt generators joined with the cable designed to join them for 30 amp service., and they trip the surge protector. I made a ground-neutral/Edison plug for the 20 amp plug on the generator,but still is tripping the surge protector. I am getting very little help from neither the generator manufacturer nor the surge protector manufacturer. Any help you can give would be appreciated. Surge protector works fine with shore power.

    Thanks – Charles

    1. Wolfe

      What an interesting question, and I may defer this to Mike Sokol for confirmation.

      Artificially bootleg-grounding at the plug should not be necessary (and there are some reasons against it). Rather than trying to double bond the ground, providing a “real” earth ground to the chassis of the generator is better if there’s a grounding issue.

      What I’m *guessing* your problem is, although I haven’t heard of this before, is that your buddy cable allows your two generators to drift too far out of phase. This could activate the sensitive GFCI function of your surge protection when power doesnt zero-sum as expected by the GFCI. My single genny never pops the protection, so I suspect the buddying. If its activating the surge protection function, this may involve defective hardware I can’t diagnose here. I would demand whoever sold the generators to assist you, since you paid for a working system, although they may beg off just saying their setup isn’t GFCI compatible. Let us know what you find out!

      1. Mike Sokol

        I do understand your problem and over the last several years I’ve talked with Yamaha, Honda and Progressive Industries tech support at length about solutions. Sounds like a topic for my RV Electrical column. Tune in next week for an explanation of how this works and how to fix it.

        1. CY

          Love you guys for looking into this. I have gotten quite the runaround and am stumped. Looking forward to your article .
          Thanks – CY

  2. Steve

    I am seeing several comments about solar and these are great. But I would like to see the staff expand on some of the info provided, in particular the discussion about the refrigerators. An RV 12 Volt DC (battery powered) / LP frig as compared to the residential frig in many 5th wheels which is only 120VAC. And how this affects your battery / inverter system – if you have one.

    I understand these systems, but it is obvious from many blogs that this is not clear to many people.

    Just a suggestion

    1. Wolfe

      I’ll address solar and wind in a followup to this series, but for now I was trying to keep it as “simple” as it already fails to be. 🙂 Yes, “green” energy can be a great way to maintain your batteries without a generator when shore power isn’t feasible.

      As for your question about 120V single power, LP/Battery & 120V dual-power fridges (as most RV iceboxes are…), and the implied triple power (dual plus full 12V), I could summarize that “energy is energy, and refrigerators need a good amount to move heat around.” None actually “make cold” so much as moving it from inside the box to outside, plus some extra heat for doing that work.

      120V only models are similar to your home fridge, running a compressor just like your air conditioner does. Dual-power models use an evaporative process (pretty clever if you want to research it now), in which *heat* from an 120V heater OR propane paradoxically drives the cooling process — but recall that LP mode still needs 12V power to run the control electronics. Purely DC powered fridges can produce cooling by a small compressor, by heating the evaporative cycle like dual-power fridges, or by a piezoelectric effect called Peltier heat transfer (in which DC power moves heat across sides of a metallic substrate. Peltier modules are really cool devices (pun unintended) if you want to research those, but they are best applied to smaller “can coolers” or (in my experimenting) a refrigerated baseball cap.

      Thanks for the questions!

  3. Ron B

    We are new to RVing. We purchased a 2002 27-foot Fleetwood RV recently and decided to purchase a Dometic 40 us portable ref/freezer to enhance our regular ref/freezer. It will run on 120 AC or 12 volts.

    We are planning to place it in our rear storage area.

    We don’t have a wall plug in the compartment, but do have two lights powered by 12 volt DC. I turned on my battery power and checked a receptical in our sleeping area just above the compartment that works off generator or shore power and realized my receptacles in my RV will not work on 12v. I have a converter. Do I need to switch over to a inverter?

    1. Wolfe

      Ron: You’re on the right track — the 120VAC “wall outlets” (and anything else 120VAC) in your RV do not run on 12V automatically, and I address why in my next column. Your confusion is why I wrote the series. Sorry for the tease, but stay tuned for why an inverter may not help!

      As for your fridge running off 120V or 12V, understand refrigerators draw a fair amount of power (mine is 360W when cooling). Do NOT tap into the convenient lighting circuit you mentioned, as it is not meant to carry significant amperage. Even if you ran new wiring, you’d still run down your batteries quickly if you use it without shore power or engine running.

      1. Ron

        Thanks for your reply Wolfe. I do hope to
        read up on your next topic on how the inverter works.

  4. J Hamme

    I prefer shade when I camp so for that very practical reason I carry portable solar panels. I have a generator and use the 200 watts to keep batteries charged. It saves me money on generator fuel and maintenance. I have Renogy kit.

  5. Tommy Molnar

    I think the roof is the best place to install solar. If you sit them on the ground they’re susceptible to theft. If installed properly on the roof you’ll have no issues with your roof. I’ve had solar on my roof for 16 years (on my old trailer) with no issues. I’ve had the panels on my 2012 trailer since a month after I bought it – again with no issues. Since the only warranty issue in question IS the roof, if the solar is done right, it won’t matter because you won’t have an issue.

  6. Dr4Film ----- Richard

    I have one solar panel on my one piece fiberglass roof. The wires do not go through the roof. They are fed down through the fridge vent opening. This method should not void any roof warranty whatsoever.

  7. Bob Novak

    Can you or one of the other readers elaborate on adding solar? Two of the vendors at the Hershey show said putting solar on the roof was a no no. It voids the warranty because of the TPO roof seal. We visited a local Grand Design dealer last weekend and the sales person said roof mounted solar would void the warranty. Is there a 5th wheel manufacturer that offers roof mounted photovoltaic panels as an option? I installed a 30W panel, wiring and charge controller on my 1998 Chinook with no issues. I use it mainly to maintain the batteries while it is in storage. The Chinook has a fiberglass roof. Only staying in campgrounds that provide electric hookups really limits the options. Do I need to “void the warranty” to install solar on the roof? Comments?

    1. Joe Call

      Northwoods Manufacturing (Arctic Fox 5ers):does factory installed solar I think. I bought a 2013 27-5L last year that came with a single small panel, and they were very helpful in providing info to help me expand n

    2. Wolfe

      Boy, I step away for one moment… LOL…

      Bob: Solar may void your roof warrantee because it requires putting holes through the roof membrane or shell in order to screw the panels into place. Manufacturers can’t guarantee you’re careful doing that, so they wave their hands if you intentionally poke holes for any reason. Secondarily, solar panels are dark to collect the sun, and what doesn’t go into electricity still collects as intense HEAT. Most panels get scorching, and improperly failing to vent underneath them can cook your roofing materials as well.

Leave a Comment