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Mercedes Sprinter: Charging Battery System via 2nd Alternator

2017-07-06 updated 2017-08-30 • SEND FEEDBACK
Related: Mercedes 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

My final conclusion was to NOT install a 2nd alternator: cost, complexity and increased risk of failure way down remote areas that can require (if available at all) $2000+ tows out. The stock Mercedes Sprinter alternator is working GREAT in severe conditions over 6 weeks of intensive use.

The primary built-in alternator can do the job for charging a battery bank albeit at a slower rate than a dedicated 2nd alternator and regulator. The 6 cylinder engine is an easier install; the 4 cylinder slightly more complicated. If more rapid charging and/or very high amperage is a requirement (such as for rooftop-mounted air conditioning), then the Mercedes Sprinter van has provisions for a 2nd alternator.

The stock Mercedes alternator peaks at 14.2 volts plus or minus a tiny bit, and supplies up to 140 amps of charging power while driving (and at 35-60 amps at 800 rpm idle, depending on what it senses for voltge). It charges a single Lithionics lithium battery from 20% SoC to 100% in about 4 hours of driving—plenty fast for my needs.

Update December 2018: with dual 400 amp batteries, charging takes too much idling and fuel, particularly for topping off from 70% on up where the alternator drops output due to already good voltage. Idling is the kiss of death for the Sprinter (oil vaporizes in the turbo during DFP regeneration), so 3 or 4 hours a day of idling in very cold temps is just problematic. Also, the engine never gets to full operating temperature in very cold conditions, which is also Not Good.

Fast charging of batteries is a 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 a lot of amperage; the Lithionics lithium battery accepts 360 charging amps (about 5100 watts), far more than a primary or secondary alternator can deliver or even the 150 amps supplied by a charger/inverter like the Xantrex 3012 via shore power. When fast charging is possible, one can enjoy ample electrical power every day, without fretting over how long the batteries will last. But it looks quite challenging to charge the Lithionics lithium battery anywhere close to its potential speed. 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. That’s harder than it sounds. In the end, and after 6 weeks of intensive field use in remote areas, I concluded that the extra cost and complexity and risk of failures of a 2nd alternator were not a good choice for my particular needs. So I never installed one. And it turns out that the Lithionics battery powers my computing gear for at least 20 hours.

The simplicity of charging off the Mercedes primary alternator reduces failure points at the cost of greater charging time versus using a 2nd alternator with higher amperage, one dedicated to fast recharge. This has great appeal for me in terms of reducing failure points far down a dirt road, where a failure like a thrown belt or tensioner problem means a $2500 tow.

For fastest charging, the most elegant and powerful solution is to install a 2nd alternator like the Nations 280XP. A little driving or even idling can shovel a lot of power back into the battery system. The Sprinter is built to take a 2nd alternator; no other solution comes close in cost or convenience or speed of charging and at almost 280 amps charging power, the Nations 280XP can deliver up to 86% faster charging versus using shore power or generator through the Xantrex 3012 (150 amps).

Dual alternator kit with 280XP high-amp alternator for
Mercedes Sprinter van, 2007-UP 3.0L DIESEL
  • 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). [NOT TESTED, those are claims stated to me, and I think the true values are lower and would require a regulator that does not drop amps in response to near-full voltage].
  • 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 @AMAZON 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 but even witih the Xantrex 3012 the charging amps top out at 150 amps. 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.

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