DC-DC Chargers For Camper Vans (With Wiring Diagrams)

Charging auxiliary batteries from the vehicle’s alternator is essential to a comprehensive camper van electrical system. Solar power harvesting can sometimes be unreliable (especially during winter and cloudy days), and shore power is not always available. But as long as you have gas in the tank and a DC-DC charger, you can have a reliable source of electricity during van life.

This post covers everything you need to know about charging your camper van’s leisure batteries from an alternator. It includes what you’ll need, selecting the correct sizes, and successfully installing a DC-DC charger efficiently and safely in your camper van.

Along the way, we’ll include graphics and wiring diagrams to help you on your alternator charging journey. Let’s get to it!

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What Is Alternator Charging?

If you’ve ever heard the term “charge while driving,” it means charging the batteries while the engine is running. At first glance, this is problematic because an engine creates kinetic energy that propels a vehicle forward, but a battery needs electrical power to charge. Therefore, an intermediary device is required to convert kinetic to electrical energy.

This is the purpose of a vehicle’s alternator.

An alternator is a generator that attaches to the engine’s drive belt and converts kinetic energy into electrical energy. Its original purpose is to keep the vehicle’s starter battery charged to power all the internal electronics in the van, such as the radio, headlights, and power windows.

But how do you siphon power intended for the starter battery to charge the auxiliary battery? To do this, you’ll need another intermediary device, like a DC-DC charger or a split charge relay.

Purpose of DC-DC Chargers & Split Charge Relays

With an intermediary device, like a DC-DC charger or a split charge relay, you can direct some of the alternator’s power to charge the auxiliary battery.

The purpose of these types of intermediary devices is two-fold:

1. Ensure the alternator adequately charges the auxiliary battery.
2. Isolate the auxiliary battery when the engine is off to prevent draining the starter battery.

Point #2 is essential because, without this intermediary device, you could quickly drain the starter battery, which can prevent the engine from starting.

Split Charge Relays vs. DC to DC Chargers

You will need either a split-charge relay or a DC-DC charger to manage the power the alternator provides to charge the auxiliary battery. While both devices offer the same function, there are critical differences between them that you should be aware of before you buy.

Split-Charge Relays (SCR)

Split-charge relays are generally cheaper – often less than $70 – because they only provide a simple function: to join the starter and auxiliary battery together when the engine is on and to disconnect the two batteries when the engine is off. The technology is relatively simple because the power from the alternator is PASSIVELY flowing to the auxiliary battery via the starter battery.

This simple (or “dumb”) technology means, however, that split-charge relays have limited abilities and face technical restrictions. For example, they are:

• Not recommended with many modern vehicles. Newer vehicles have ‘smart alternators’ that automatically regulate the voltage output. This is good for power efficiency (and environmental regulations), but this varying voltage confuses the split charge relay, leading to an inefficient auxiliary battery charge.
• Not recommended with lithium batteries. When activated, split charge relays connect the starter battery (lead-acid/AGM) with the auxiliary battery. If the auxiliary battery is lithium-based, the relay will connect two batteries with different chemistries if the auxiliary battery is lithium-based. This leads to problems like sub-optimum charges of the lithium battery due to different battery charge profiles and overworking the alternator due to the lithium battery’s lower internal charge resistance.

DC-DC Chargers

These high-tech (or “smart”) devices receive power from the alternator and ACTIVELY charge the auxiliary battery. Instead of allowing the auxiliary battery to charge passively, like a split-charge relay, a DC-DC charger supplies a purposeful, voltage-regulated power supply to the auxiliary battery.

This fundamental difference from a split-charge relay means that a DC-DC charger can be used on a broader array of usage environments, including modern alternators AND lithium batteries.

Comparison Table

	DC-DC Chargers	Split Charge Relays
Cost	More expensive	Cheaper
OK with modern alternators?	Yes	No
OK with AGM batteries?	Yes	Yes
OK with lithium batteries?	Yes	No
Installation1	Easier	More difficult
Popular model	Victron Orion	Victron Cyrix-ct
Which do we recommend?	Yes!

Table Footnotes:
1. SCRs require an additional connection to a port that is activated only when the ignition is on

Key takeaway: Although DC-DC chargers are more expensive, we recommend them if you are serious about building a robust camper van electrical system. We’ve already established in our electrical system guide that lithium batteries are substantially better than AGM batteries. That reason alone is enough to invest in a DC-DC charger.

DC-DC Charger Amp Ratings (“Charge Speeds”)

Most DC-DC chargers have an ampacity rating between 20A and 60A, which tells you how fast the unit can charge the auxiliary batteries. The higher the amp rating, the quicker the charge. This rating information is often found on the charger’s front panel.

For 12V auxiliary batteries, you can calculate how much power the DC-DC charger can deliver to the batteries by multiplying its amp rating by 12. For example:

• 20A charger * 12V = 240W charging
• 30A charger * 12V = 360W charging
• 40A charger * 12V = 480W charging

Sizing A DC-DC Charger (How To Calculate)

The size of your DC-DC charger should correspond to the size of your van’s electrical system. The larger the system, the larger the charger. Two significant factors to consider when sizing a DC-DC charger are:

• Daily power usage. Larger electrical systems with high power requirements should aim for a charger with a larger amp rating.
• Are you installing solar panels? A smaller DC-DC charger can be used if battery charging is supplemented with solar panels.

Recommended DC-DC Charger Size

Sizing a DC-DC charger is not an exact science. There is no “right” and “wrong” answer. But based on our experience, we recommend following the table below. First, identify the size (Ah) of your battery bank (assuming 12V), then locate your ideal DC-DC charger amp rating based on whether or not you will be installing solar panels.

Battery Size (Ah)1	With Solar Panels2	Without Solar Panels
100Ah	18A/20A	18A/20A
200Ah	18A/20A	30A
300Ah	30A	40A
400Ah	40A	60A

Table Footnotes:
1. Use our battery size calculator to help.
2. Use our solar size calculator to help.

Recommended DC-DC Chargers

We love our Victron DC-DC charger (30A) in our camper van. It works and has never failed us, and we use the unit’s Bluetooth accessibility to view our alternator charging statistics on our smartphones daily. It is a big reason why we’ve never run out of power during our five years on the road.

Victron products are not the cheapest, and we realize that not everyone has the same budget flexibility. If staying within a tight budget is essential, Renogy chargers provide good value. You do not get Bluetooth accessibility, and additional wiring is required (the D+ wire to the ignition), but these units will get you the most for your dollar.

Below, we recommend our top four DC-DC chargers. Each unit has a different amp rating (charge speed). For sizing help, you can refer to the sizing table in the previous section.

DC-DC Charger Installation Guide

This section will teach you how to install a DC-DC charger (Victron 30A) in a camper van. We’ll provide helpful wiring diagrams and material lists to help you finish your installation quickly and safely.

Wiring Diagram

Below is the DC-DC charger wiring diagram we will follow. Here, we connect the starter battery to the Victron 30A DC-DC charger with 6 AWG wires and a 60A fuse. From the charger, we will be wiring the bus bars with more 6 AWG wire and a 60A breaker.

The bus bars are wired to the auxiliary batteries. For more information on this step, visit our 12V system guide for wiring diagrams and recommended components.

We’ll discuss each component in the above diagram below. But if you just want a quick list, visit our DC-DC charger parts list.

Recommended Wire Size

For 12V systems, which we recommend for first-time van conversions, Victron recommends using 6 AWG wires when installing 18A & 30A DC-DC chargers. Below is an excerpt from the Victron Orion manual assigning 16mm² wire (6 AWG) for cable lengths between 5 and 10 meters.

We love electrical wires from Windynation, which are made in the USA. They are 100% pure copper wires with an exceptionally high strand count for ultra-flexibility and resistance to driving vibration. Windynation’s 6 AWG wires are what you’ll need.

Using Renogy’s 40A/60A charger? Use 4 AWG wires instead (per Renogy’s manual)

Recommended Fuse Size

Referring to the same Victron Orion table below, we can see that the manufacturer recommends a 60A fuse. So this is the size we also recommend.

Use A Fuse Or Breaker?

Both fuses and circuit breakers are designed with the same end purpose: to protect the circuit wiring from overheating and catching on fire. Fuses are cheaper and are generally recommended by DC-DC charger manufacturers in their manuals.

However, we substituted the fuse with a 60A circuit breaker between our DC charger and the bus bars. This is not essential, but we wanted to manually disconnect the circuit for various reasons, including long-term vehicle storage and conducting electrical maintenance.

Recommended Lug Sizes

If you follow our DC-DC charger wiring diagram, you will need lugs with a 6 AWG neck size and 3/8″, 5/16″, and 1/4″ ring diameters. We color-coded our lugs to help you identify which lug sizes go where.

• 60A circuit breaker: 1/4″ lug
• 60A fuse: 5/16″ lug
• Bus bars: 3/8″ lug

Since there are three different lug sizes, buying an assorted lug set is the most convenient and affordable option. The set we recommend below will have the lugs you’ll need to complete this section and the other parts of your camper van’s electrical system.

Essential Tools To Install a DC-DC Charger

The three tools we recommend below are to help you crimp the terminal lugs onto the 6 AWG wire.

For a step-by-step tutorial (with video), read: How to crimp lugs onto electrical wire.

FAQ

Conclusion

We hope you found this DC-DC charger installation guide helpful. Charging your auxiliary batteries while driving is a great feature, and we recommend them for every camper van’s electrical system. This ensures you have a backup plan if your solar panels can’t adequately charge your house batteries.

If you have any questions about wiring a DC charger in your van conversion, please don’t hesitate to let us know in the comments section below.

Happy building!