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Sprinter Electrical: Charging House Battery System via 2nd Alternator

Last updated 2017-07-06 - Send Feedback
Related: Sprinter

Photographer and cyclist and Mac expert and software engineer Lloyd Chambers is available for consulting on general Sprinter considerations at his usual consulting rates via phone, or in person in the Palo Alto, CA area. Save yourself hours and mistakes by discussing issues up-front. More about Lloyd....

Get your batteries and 2nd alternator and regulator (the whole kit!) from

All information here is preliminary, suppled to the best of my ability to understand and verify with multiple sources. Conflicting sources muddy the water however.
When the gear is in hand, installed and verified, this page will contain all “as it actually works” details.

The primary built-in alternator can the job for charging a battery bank albeit at a slower rate*, but if rapid charging is a requirement, then the Mercedes Sprinter van has provisions for a 2nd alternator. The 6 cylinder engine is an easier install; the 4 cylinder slightly more complicated.

* So far, I’ve had conflicting info on whether the primary alternator is up to the job of charging a large lithium battery. This is an open question to which I do not have a proven answer as yet. The ansser I most trust as of 10 July 2017 is that the primary alternator is NOT up to the job of charging a 400 amp lithium battery. I’ve also gotten conflicting information on whether a lithium battery can achieve a 100% charge from the alternator (versus 90% or 95%), without having to be topped off by other means.

Fast charging of batteries is a huge win: you get to enjoy ample battery power without worrying about draining the batteries and waiting all day or longer to recharge.

A good battery bank can soak up well over 300 amps, some can do far more. Thus any recharge system needs to be able to shovel in high amperage, or the charging will take a much longer time and you’ll avoid using electricity—a no-fun time-waster. When fast charging is possible, one can enjoy ample electrical power every day, without fretting over how long the batteries will last. For example, I want to run a ~300 watt computing system for hours for two days and know that I can recharge that system in an hour or two of driving.

There are many ways to charge the batteries in a Sprinter van or RV, and a lot of ill-conceived notions surrounding that goal.

Dual alternator kit with 280XP high-amp alternator for
Mercedes Sprinter van, 2007-UP 3.0L DIESEL

By far the most elegant and powerful solution is to install a 2nd alternator—a little driving or idling can shovel a lot of power back into the batteries. The Sprinter is built to take a 2nd alternator; no other solution comes close in cost or convenience or speed of charging.

  • A good alternator like the 280XP can deliver 140 amps or so at idle into the batteries (about 1850 watts) , and up to 280 amps when running strongly (about 3700 watts).
  • A generator is bulky and requires its own fuel, taking space in the van. Also, regular maintenance. No one likes hearing or smelling a generator, even the owner. Reasonable size generators generally cannot do more than 160 amps for charging, which means the charge rate is slower than with a 2nd alternator. Thus a generator makes little sense if a 2nd alternator is onboard along with a suitable battery pack. An exception might be parking for days or weeks or for continuous direct power (those annoying RV campers droning on for hours). But for Sprinter owners, it’s just easier and faster to drive for an hour or two to charge a battery bank, say for food or fun outings you’ll likely be doing anyway.
  • Shore power (plug into the grid) is great if you’re a wired campground type, but I never stay in such campgrounds, so shore power is useful to me only when home to keep the batteries topped-off. And charging via most shore power chargers is generally limited to 100 amps DC—much less than idling the Sprinter.
  • Solar power is marginal in many ways.

2nd Alternator

Driving for one hour with a 2nd alternator can deliver much more power than solar delivers for two days.

Available for the Sprinter and other vans, the 280XP alternator is the most elegant and most powerful solution for Sprinter van and other van owners. Nothing else will charge as fast, nothing else is as convenient (just drive around a bit).

Installation should be professionally done, including heavy gauge wiring to the batteries suitable for high current.

Rigorously lab tested and OWC certified.
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