Electrical Systems

Setting up a Dodge Sprinter Vans electrical systems for camping is kind of interesting.  We decided to rely more on electrical appliances and not use propane.   Propane is restricted in some tunnels, including some in this area  - such as the Big Dig in Boston.  It is also a concern on some ferry boats.  We are a little concerned about the safety issues too.

Over the last 10 years or so, big inverters have become readily available and a lot cheaper than they used to be.  An inverter changes the 12 volt direct current (dc) that is available in the battery to 120 volt alternating current (ac) about like you use in a house.  Once you do this, you can use regular household appliances instead of buying special stuff for campers (or boats).

Certain kinds of 12 volt things are readily available and reasonably priced, things like car radios are an obvious example of something commonly used.   Buying a 12 volt TV is not that unreasonable, but getting a 12 volt microwave, refrigerator, or crockpot may be more expensive, and not replaceable everywhere. You can get a 12 charger for your laptop computer, but they are usually at an extra cost compared to the 120vac charger that comes with it.

You can even get a refrigerator that uses 12 volt dc, 120 volt ac or propane to run it.   They are a lot more expensive than a 120 vac refrigerator.

Lighting is readily available in 120 volt ac and also 12 volt dc.     Some of the new LED lighting runs on dc, even many of the 120 vac units have a little transformer that cuts the voltage down to 12v or less.

Of course, if you hook all these things up to your main battery and use them all, you might use all the energy available in the battery and not be able to start the van the next morning.       Sprinters have the option of a second battery available for the “back” of the van.   Mine didn’t come that way, so I found a battery to install in the back for these uses.      Batteries are usually rated in amp hours, which is simply amps multiplied by  hours of use.     For an example, a 100 amphour batery could possible deliver 50 amps for 2 hours, of 4 amps for 25 hours, etc.   It would also be very bad for a battery to use up all the rated amp hours,  For long battery life, using half would be a lot more prudent and lead to a longer battery life.  

You can hook up the battery  to  the van alternator to  charge up the back battery too, the trick is to have both batteries charge when the vehicle is running and only have the back battery discharge for the “back” uses, thereby saving the main battery for starting the vehicle when needed.    There are several devices that will do this, one is a relay, the other is a diode.    The new electronic “battery isolators” can do this without any of the disadvantages of the other older methods.  It is a kind of an electronic relay.

 Boats (or vehicles) used to have the operator turn a switch to use or charge one, the other, or both batteries.  That is subject to more “operator error”.

 I went with a device called a battery isolator and it works fine.   It even has the possibility of flipping a switch and using the back battery to start the van if for some reason the front battery goes dead.  When either battery is charging, both will be charged too.  They are less than $100.

The next thing to consider is the battery.   A front battery may be rated at 100 amphours.  I chose a larger battery for the back.  It is an 8d (size) battery rated at around 250 amphours and weighing around 155#.

This shows the black refrigerator and the battery in the white box forward of it.

Refrigerator and battery

Refrigerator and battery

Other choices could be a smaller battery, or two 12 volt batteries in parallel, or two 6 volt batteries in series or even four 6 volt batteries in series parallel.     

The size of the back batteries depends on the  anticipated use,   and amphours can be calculated.   Without getting too involved, remember that Watts = volts times amps.   or w=v times a.       To use a refrigerator for an example,  I got a 4.4 cu ft dorm type refrigerator with a decent freezer for the van.  My  measurement, at 120 vac, says it uses 440 watts for starting, then goes right to  65 watts, and since it is only on around half the time, I measured that it takes an average of 30 watts.    Not counting losses in the inverter, or anywhere else, using our formula  Watts = volts times amps, we can say amps =watts/volts or 30/12 = 2.5 amps at 12 volts.   Using it for 18 hours (for example) means 2.5 times 18 or 45 amphours will be taken from the battery - wich is well less that than half the 250 amphour rating.  I can probably run it for 2 days easily if I decided to stay another day without running the van or charging the battery.

The other appliances, chargers, and lighting can be calculated too.    This brings up another consideration, the charging rate from the van alternator.    The Springer alternator in my van is the “small” one rated at 90 amps. Optional ones are available at 150 or 200 amps.  Aftermarket ones are available for other vehicles in similar sizes.   That indicates the  maximum charging capacity.    As the battery starts to get charged, the battery voltage increases and therefore the charging rate or amps decreases.   If it was putting out 90 amps, it would put 90 amphours in the batteries in one hour.  In practice it takes longer than that because the charging rate decreases and the alternator is also  charging both batteries.   From posts on several websites, it seems that having an alternator that is twice the size of the 90 amp  alternator,  the charging time only decreases by a relative small amount.  This is because batteries won’t take much more than 90 amps for more than a few minutes, unless you have a huge battery bank.

Another main part of the electrical system is the  inverter.  I got a 1500 watt inverter with 3000 watt peak capability.   It is wired directly to and very  close to the big back battery using the recommended wire size, # 4 AWG for a very short run.  Remember that a 12 volt system has to use 10 times the current that a 120 volt system for the same wattage.       For example, it you had a 1200 watt coffee maker and ran it from a home, it would use 1200/120 or 10 amps,   Ordinary size 14 wire would be fine.   Using that at 12 volts would require 1200/12 = 100 amps from the battery  to the inverter- way beyond the capacity (15 amps) of 14 wire.  From the inverter, an ordinary coffeemaker plug and wire would be fine.

There are two kinds of inverters, modified sine wave and pure sine wave.   The modified sine wave is ok for many uses, but the pure sine wave will work with any 120volt ac device.   I have run my refrigerator with the modified sine wave device, but it looks as though a pure sine wave device will work better with some devices, microwaves and refrigerators or example.    The modified sine waves are less than half the price of pure sine wave devices for a given wattage output.  Just checked and found a pure sine wave inverter for $259 that puts out 1000 watt continuous and 2000 watt peak.     Using that and a big box store refrigerator is cheaper than buying a specialized “RV Refrigerator”.

Finally got a modified sine wave inverter and it was fine - we just run the microwave when we plug in at nite.  The ordinary big box store (dorm style) refrigerator worked great  (for less than $100).  

The following photo shows the battery, the isolator, and the inverter.

Battery. isolator, and inverter

Battery. isolator, and inverter

The refrigerator is on the left and the drivers seat on the right.  The isolator is the small device on the right of the battery, the inverter is the black box under it.   The charging wire from the Sprinter alternator runs under the van and follows other wires up thru a sleeve under the drivers seat and out from there.  There are some relays under the Sprinter driver’s seat.  I also wired another 12 volt outlet in the front of the battery box.    There is one on the Sprinter console near the shift lever and another in the ashtray.


There are devices that measure amphours in and out of a battery, and they have also come down in price, have seen them for around $50. There is an also a device made for houses that will give a lot of information- called the Kill A Watt.   It is a very handy device for checking the electrical use of any household appliance and you can get one for less than $20.    You simply plug them into a wall and plug the appliance in to them.     They will read the wattage at any given time or the kilowatt hours for any lenght of time you chose - and will keep track of that time.

I used it to figure out the wattage and amphours of the rerigerator.     Then I started thinking about an electric coffeemaker and the energy use.      It is the kind that will make 10 cups and turn itself off because it has an insulated carafe.   It takes 1000 watts for a short time - for a total of .11 kilowatthours or 110 watthours.     Although there are some losses in the battery and inverter, etc,  a rough estimate would be 110 divided by 12 or roughly 10 amphours.     This and the refrigerator use would still leave us with plenty for the battery.

We also thought of using a crockpot while underway.  It would obviously have to be very secure, down in some area where a quick stop wouldn’t leave it scattered all over us and the windshield.   Since the van would be charging while underway, it would not run down the battery .  We measured ours and it took 75 watts on low and 150 on high.    Dividing by 12, that would give is the amps required - around 7 and 14 amps.     That is well less that the alternator’s output.   Running it for 4 hours with the van off would be a lot more significant.

Lighting with LEDs would be almost insignificant.     Computer speakers would take less than 10 watts or 1 amp hour and maybe 1/3 of that.   Six hours may be only 2 amphours.

Another good edition will be a vent fan for the back, we got a “Fantastic Fan”.

Hope these numbers are helpful for anyone setting up their own van.     We will use this info for setting up ours.

Camper Van - Plug In, Generator, or Neither?

September 17th, 2008

Whether you need more power that can be stored in the extra battery(s) or not depends on the kind of camping you will be doing.  Our planned Alaska trip will be one where we will drive at least every other day - and probably drive someplace most days.    Even taking the van for a trip to a store or to see a nearby site will charge the battery enough to make it last another nite.  We may not need a generator or even a plug-in.

Parking someplace for several days without moving - with the refrigerator  on - may discharge the battery more than we want.   Aside from the solution of turning the refrigerator off, most campers have a big cord with a plug for a campsite outlet and they typically supply 30 amps at 120 volts or 3600 watts.   This can easily run anything we will bring with us as well as recharge the battery.    For a one or two nite use, you can buy an adapter (for less than $10) that will plug into the campground outlet and adapt to a common extension cord.  If you were going to plug in every nite, it would be better to use a big cord with a socket in the side of the van.

If you want to park in other than a campground, getting a generator is another possibility.   You can get a diesel, gas, or propane generator that is built into a camper that will provide as much power as you want. Another solution is taking a portable gasoline generator with you and plugging into that.  For example, Honda makes a compact 2000 watt generator that is relatively light and quiet, and they sell new for around $1000,  That is a lot less than one that is built in.  Running a generator all nite in a crowded campground does not provide the kind of solitude that most people desire when camping, and many campgrounds have quiet hours.

PS  April 09

We did decide to do a simple plug in for shore power.  Bought a power strip with an 8 ft cord and a surge protector.  Under the driver seat in the Sprinter is a sleeve running many wires up thru the floor,  so I put the plug end out thru that and resecured the sleeve with a wire tie.  A few more wire ties held the plug end up close to the underside of the van right by the back end of the drivers door.   A good 20 amp, 50 ft extension cord will be carried for plugging in when we feel it is needed.