VANPOWERCALC

DC-DC Charger Calculator for Campervans

DC-DC Charger Size Calculator

The wrong DC-DC charger can burn your alternator (especially with Lithium). Calculate the safe charger size for your van.

Optimal Safe Charger
0 Amps
Absolute Maximum Charger
0 A

Lithium batteries have very low internal resistance. Without a properly sized DC-DC, your alternator will burn out at idle.

Euro 6 alternators drop voltage when the starter battery is full. A "Smart" DC-DC charger is MANDATORY.

Which vans have smart alternators?

Rule of thumb: any Euro 6+ van sold in EU since 2016, plus select US models. Quick check: if idle voltage drops below 13.5V after a minute, you have a smart alt.

  • •Mercedes Sprinter VS30 (2019+): standard on all models
  • •Mercedes Sprinter NCV3 (2014–2018 US): OM651 4-cyl with option code M47 (E33 is unconfirmed — check your VIN sticker)
  • •Ford Transit: 2014+ EU Euro 6 = true SRC; 2015+ US = PCM variable-voltage (SRC-ish but not identical)
  • •VW Crafter / MAN TGE (2017+): all Euro 6 variants
  • •Iveco Daily (2015+ Euro 6): standard (smart alt introduced with MY 2015)
  • •Fiat Ducato / Peugeot Boxer / Citroën Jumper (2016+ Euro 6): Start&Stop models only

Gear for your DC-DC build

The selection I use in my vans: Victron charger + protection fuse + sized cable. All tested, all reliable.

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Victron Orion DC-DC Charger 30A

Charges battery from alternator with correct Li profile.

$56 on Amazon*

LiFePO4 200Ah 12V Battery

200Ah true capacity, 200A built-in BMS, 5000+ cycles.

$773 on Amazon*

Victron BMV-712 Battery Monitor

Real-time SOC, history, Bluetooth alarms. Must-have.

See product*

ANL Fuse 250A + Fuse Holder

Mandatory inverter protection. 250A with integrated fuse holder.

$13 on Amazon*

Battery Cable 50mm² Red+Black

50mm² cable for 2000W+ inverter. Red and black, 1m each.

$33 on Amazon*

Why limit your DC-DC charger?

A vehicle alternator is not designed to run at 100% capacity for long periods, unlike a generator. If you install a Lithium battery (which offers almost zero resistance) with an oversized charger or a simple split relay, the alternator will instantly provide maximum current.

In traffic jams or at idle, the alternator's cooling fan spins slowly. As a result, it quickly overheats beyond 120°C (250°F) and melts, risking an engine fire. It is crucial to select a DC-DC charger that draws no more than 40% (ideally 25-30%) of your alternator's native capacity.

DC-DC charger guide →Calculate Wire Size →Back to Main Power Audit