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Boondocking Basics: Electrical Use While Unplugged

With all the solar retrofits and additional batteries being installed on some units, people are looking at their stock Class Bs and wondering if they’re hopelessly outdated. The answer is no – Class Bs have been out there for decades without all these recent innovations, functioning just fine, as long as you know how to use them, and what they can and can’t do. Some people are afraid to even try, and miss out on some excellent camping spots which don’t have electrical plug-ins.

This is a quick review of the basics of electrical use while unplugged. Electricity is a resource, just like water or propane, and in many respects the use of electricity works pretty much the same. You need to know how much you have and how fast you’re using it. With  a few simple tools, you’ll know enough to stay out of trouble, and still use electrical devices while unplugged.

RVs store power in batteries; most Class Bs have one or two “coach” batteries in the back somewhere, as opposed to your “chassis” battery which is where it is on all vans, usually under the hood.  The two types of batteries are connected by an isolator or separator, which lets power from your RV’s alternator charge all the batteries while driving, but prevents electricity use while parked from draining the chassis battery, the one you use to start your vehicle.  Class Bs usually have a battery size called Group 27, which holds about 100 amp-hours of electricity.  Two batteries mean you have about 200 amp-hours.

Instead of getting all these technical terms mixed up, let’s talk about watt-hours  – one watt of electricity use for one hour. Your 200 amp-hours at 12 volts is 2400 watt-hours. You can safely use 50% of your electricity before recharging because running the batteries too low will drastically shorten their lives, so let’s say you have 1200 watt-hours of chassis battery storage.  That’s twelve hours of use for your 100 watt refrigerator, or 1200 hours of use for your one watt LED interior light.

Add up your watt-hours and you’ll get a good idea of what you can run, and for how long.  One thing though – appliances that produce heat are generally electricity hogs, like microwaves, toasters, coffee pots and hair curlers. I boil water on the stove with the propane and make my own drip coffee rather than use a Mr. Coffee type coffee pot.  If you really want to use one, though, you can (usually) always crank up the generator.  It depends on who your neighbors are, and what time it is 😉

This is an LED light I modified to fit the spotlight-type lights over the front seats. Most other interior lights will plug right in.
This is an LED light I modified to fit the spotlight-type lights over the front seats. Most other interior lights will plug right in.

Many Class B owners switch the bulbs in their interior lights because of the 10-to-1 advantage LED technology gives you – you can get a LED bulb that produces the same amount of light as your 10 watt incandescent bulb and uses one watt. Because lights are on for long periods of time, energy savings here add up fast.  Many new Class Bs come with LED lights as standard equipment.

Try http://www.superbrightleds.com/ or other online sources – get the bulb number off your old bulb and look it up. Most folks prefer the “warm white” color – the “cool white” looks too much like florescent lighting.  LED lights are allergic to water, though, and to shorting to ground against the back of the circuit board, so your porch light must be well insulated and sealed to use one.

To get a more accurate idea of what your state of charge is, a cheap multimeter will give you a voltage reading accurate to 1/100 volt, which is a better indicator than the standard four idiot light display Class Bs usually come with. The one that plug into your cigarette lighter, though, are measuring your chassis battery, not your coach battery, so measure it at the coach batteries or somewhere the coach batteries supply, like a light socket.

Most tables correlating battery state of charge in percent to voltage aren’t accurate for real-world use because they assume you take all load off the battery and let it rest an hour before measuring voltage. 12.0 volts is not fully discharged when the battery is under load. I set the low voltage cutoff on my inverter at 11.3 volts, and that’s being conservative.   The only way to know for sure is to use a hygrometer – a (cheap) device available in auto stores which measures battery electrolyte density – and correlate these readings with measured voltage. There is a good discussion of this issue here for the obsessively technically minded.

With great power comes great responsibility. Use the power wisely ;-)
With great power comes great responsibility. Use the power wisely 😉

I have made many simplifications and generalizations in this brief summary, but it will give you the general idea. Think of your stored electricity as another water or propane tank, and calibrate your use/recharge cycles according to how much you use.Avoid electricity hogging devices and consider adding a second battery if your rig only has one. You’ll be boondocking in no time once you know what’s going on with your electrical system.

Additional links with more information are here:

http://www.marine-electronics.net/techarticle/battery_faq/b_faq.htm#4

http://www.vonwentzel.net/Battery/00.Glossary/index.html

10 thoughts on “Boondocking Basics: Electrical Use While Unplugged”

  1. Campskunk: Great article. I really like how you look at watt/hours instead of amp hours. Too many people get tied up in the battery ratings of amp/hours and don’t understand the difference if they have 6 volt verses 12 volt when looking at amp/hours. Watt/hours is the energy that the battery truly holds and is independent of voltage. One issue I did see is you related a 40W 120V to 400W at 12 volts. This would be true for current, but not watts. Power is power and does not change. The only difference in the power at 12 volts would be the losses in the inverter. This can be calculated using the efficiency rating of the inverter. Good inverters usually run 90-95% so not much loss.

    Sorry if I bored some, I just really enjoy electronics. I have a degree in electronics and work at a semiconductor manufacturing facility were I utilize my education in it. But my passion lately is to get a class B that will be well equipped to boondock in. And that is why I was excited to read you article. Thank you very much for sharing your experiences.

    1. thanks, bob, and as you noticed, i rounded a lot of things off and glossed over some technical details in trying to get this where people without a technical background can follow along and maintain an understanding (and interest). watt-hours is a convenient way of looking at it because the watts used by various appliances is information readily available. and you’re right – i fooled myself on the 12v/120v conversion. amps change and watts don’t. i fixed it. battery storage capacity and output vary according to temperature, rate of discharge, and many other factors. one detail i glossed over is that two 6 volt batteries in series usually have about 220 amp-hours, compared to the 12 volt batteries’ 200, so there’s a slight advantage to using six volt batteries.

  2. Thanks so much…just discussed this subject with my son on the weekend. My knowledge of electricity is so limited and he agreed to provide me with a written explanation. Now I can share this info with him. Perfect timing!

  3. Mary Zuschlag

    Great article I boondock a lot and my solar charge controller tells me the voltage of my batteries. I know that is is not completely accurate when it is charging, I have the battery charge table posted. I try to check it before I go to bed at night. Usually my batteries are about 12.3- 12.4 when I go to bed at night and I have a small fan on the back of my fridge that runs intermittently at night. It seems like I am topped off everyday, I’ll get a surface charge of 13.6 or so and the amps on my solar charger will ramp down to a float charge. I never use the inverter because I don’t need it. I have always wondered how accurate the solar controller is for voltage read. I have wondered if it is worth getting a battery monitor. All my lights are LED and usually have only one on plus my 12v tv for a 2-3 hours.

  4. Dorothy Inglis

    This was very helpful. I’m not the technical type but, out of necessity, have had to learn lots about my rig. I recently switched to the LED light bulbs; they are much brighter and I like them a lot. Have one question: I don’t know how to replace the bulbs in those swivel lights in the back of the rig. Can anyone help me?

  5. led light bulbs for home

    get the bulb number off your old bulb and look it up. Most folks prefer the “warm white” color

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