When you first move into an RV or take it on an extended vacation, there can be an unexpected learning curve regarding how devices and appliances are powered. It’s important to understand how your RV house batteries work. Questions like “What does the RV battery actually power?” or “Do RV batteries charge when plugged into shore power?” are reasonable questions to ask. Today we’re taking a look at these questions and more in hopes of demystifying them a bit.
Do RV Batteries Charge When Plugged into Shore Power?
Your house batteries do indeed charge when plugged into shore power. House batteries are the ones that power your 12-volt accessories… interior lights, water pump, vent fans, etc. They can also power 120V AC appliances… IF your rig is equipped with an inverter.
If you have a motorized RV (class A, B, or C), plugging into shore power may or may not charge your chassis battery. That’s the one that starts the engine, and powers headlights, taillights, windshield wipers, horn, and other driving-related equipment. Many RVs do charge chassis batteries, but not all.
If your rig’s chassis battery (or batteries, in larger motorhomes) aren’t charged by shore power, which is more common in smaller rigs, they’ll only be charged by the alternator when the engine is running.
Before you plug into the nearest shore power outlet, it’s crucial to protect your RV’s electrical system! In our last post, we talked about RV power cords and included more information about protecting your rig from “bad” shore power. You can check that out, or look into the Hughes products we use to protect our RV.
Understanding the RV Electrical System
Understanding your rig’s electrical system isn’t overly complicated, but if you’re not used to how it works, it can seem a bit daunting. In essence, most RV appliances run off one of two simple power sources: 12-Volt direct current (12V DC) or 120-Volt alternating current (120V AC).
12V DC Power
Your RV’s 12V house battery bank directly powers anything that runs off 12V DC. Again, this includes the water pump, interior lights, and vent fans.
Even if your battery bank consists of 6V batteries, they’ll be wired together in pairs to produce 12 volts. Some RVs actually run 24V systems, but that’s rare enough that it’s unlikely your rig will be equipped that way.
Your house batteries store & provide power whether or not you’re plugged into shore power, making it simple to run many of the devices you use daily. However, it’s important to note that your 12V DC system probably can’t power all of your appliances (think air conditioning for example) and also has limits on storage capacity depending on the number, size, and type of batteries you have.
This is why it’s so beneficial to be able to recharge your house batteries with access to shore power, a generator, solar power, or while driving.
120V AC Power
The 120V AC system operates the more power-hungry appliances. Your microwave oven, air conditioner(s), and 120V household power outlets all work from this system.
120V AC power in an RV is available from one of three sources: Shore power, generator power, or an inverter.
The easiest option for powering the 120V AC system is plugging into shore power. Your rig will typically have either a 30-amp or 50-amp plug that connects to a corresponding outlet, although the smallest RVs might be equipped with a 15-amp plug, just like a typical household appliance.
If you don’t have access to shore power, all is not lost. Many RVs have an onboard generator, which can power your 120V AC system when you’re boondocking or are otherwise away from a power pedestal. You can also purchase a portable, stand-alone generator if your rig lacks an onboard generator.
How is the RV Battery Charged on Shore Power?
When you plug your rig into shore power, the battery charges via a device called a converter, which converts AC power into DC power so that your battery charges correctly.
You can also charge your house batteries with an appropriate 12V battery charger that’s applied externally. But most RVs have a built-in converter (also typically known as a converter-charger). Larger RVs, which often come equipped with inverters (which produce 120V AC from your 12V DC battery bank), frequently combine all of these features into one unit, known as an inverter-charger. We’ll leave the detailed dive into that device for another day!
RV Converter / Converter-Charger
Your RV’s converter is a multitasker. When plugged into shore power, it feeds power to your appliances AND charges your house batteries.
Now not all RVs are wired the same way, but the basics are the same. Typically, the converter is part of the power center, which is where the 120V AC breakers and the 12V DC fuses/breakers are located. This is what allows the differing power systems to send the appropriate current to the right appliances: 12V power is sent to the DC devices, and 120V power to the AC ones.
The converter also acts as a charger, sending 12V DC power to your house batteries, allowing them to charge up whenever you’re connected to shore power. Most RVs today will come with a converter/charger that provides a balanced, 3-stage charging profile in order to recharge your battery(ies) properly so that you can get the most life out of them.
Other Ways to Charge Your RV Batteries
As previously mentioned, in addition to plugging into shore power there are multiple ways to charge your RV’s house batteries.
With a Generator
Motorhomes frequently have an onboard generator that’s wired to an on-off switch inside your rig’s cabin. Your generator provides 120V power to your electrical appliances, including your onboard converter/charger. With the generator running, the converter/charger replenishes the power in your house batteries, just like shore power would.
If your RV doesn’t have a built-in generator, you can get any number of small, portable generators that you can plug your RV into. Effectively, it’s like plugging into shore power… except you’re limited to the output capacity of the generator, so you’ll be limited in what you can run. Regardless, it’s plenty of power to charge your batteries.
With either situation (onboard or portable generator), be aware that when you supply 120V power to the RV, the onboard charger will most likely start charging your battery(ies) right away (or after a few minutes of “thinking”), replenishing the power you’ve used. It’s good to be aware of this fact so that you don’t accidentally overload your generator: don’t turn on too many high power-draw appliances until you’re sure the generator can handle it (or until the charger has gotten closer to finishing it’s charging cycle)
Through the Alternator
Many motorhomes are wired so that the engine’s alternator charges both your vehicle (chassis) battery and your RV (house) batteries when you’re driving down the road. There are two common systems that RV manufacturers use: a BiRD (Bi-directional Relay Delay) or an echo charger.
- A BiRD system uses a high-capacity relay to link the chassis & house batteries together, allowing the house battery to charge off the alternator when the engine is running (and vice versa when plugged into shore power).
- An echo charger takes a portion of the charging current from the chassis battery (once it nears being fully charged) and supplies it to the house battery bank, and can be installed after-the-fact if your RV didn’t come with one (like this unit from Xantrex, available on Amazon).
Either system is convenient, especially if you move around a lot. Just be aware that your RV may not be wired this way… it may only charge the chassis battery when the engine is running, not both battery banks.
With Solar Power
Solar power is another commonly chosen option for charging RV batteries. While most RVs don’t come off the lot with pre-installed solar panels (or at least not enough solar for spending any reasonable time off the grid), it’s become a wildly popular add-on for many RVers, including us!
Solar is a game-changer for camping off the grid. With our (admittedly large) system, we can function virtually as if we were plugged into shore power (as long as there’s sun), without having to run our generator to do it. With a residential refrigerator (power hog), that’s pretty impressive.
You can either add permanently-mounted solar panels to your RV’s roof or opt for portable solar panels that you place in the sun.
Use a Battery Monitor to Prevent Draining Your Batteries Too Far
Some RVs come with a battery monitor; most don’t. This monitor (and we’re not talking about the “idiot lights” that show your battery status in 25% increments), however, can be a critical piece of equipment, whether you have a single house battery or a bank of multiple batteries.
The reason you want to monitor your batteries (especially flooded lead-acid batteries) is that you don’t want to drain them too low. Lead-acid batteries can be seriously damaged if you use more than 50% of their rated capacity, dramatically reducing their useful lifespan. This isn’t the case with lithium batteries which can be drawn down much further without issue.
- Read your battery bank like a fuel gauge
- Provides critical information about the status of your battery bank
A battery monitor does just what the name implies: it monitors your battery, giving you insight into the amount of power that remains so you can avoid draining them too far (and know that you have enough power to get you through the night).
There are many variables to understanding your RV’s electrical system. “Do RV batteries charge when plugged into shore power?” is just one of many power-related questions every RVer should be able to answer. We hope running through some of the basics here has offered you a helpful start to understanding a bit more about your RV’s electrical system.
And, in case you missed it (or skipped to the end)… the answer to the question “Do RV batteries charge when plugged into shore power?” is YES! 😉
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