Alternator Charging Technology

Alternator Charging

Video on compelling benefits of 48V Systems

In modern engines with smart alternators, the ECU changes the way the alternator charges. It may change the charging set-point between 9V and 16V.

This is done to meet engine emmissions control regulations and optimize fuel consumption.

These regulations require the starter battery to be charged at no more than 80% when running under power. When the engine is "braking" and there is no acceleration , the ECU directs a high charging voltage and the battery can then max out at 100% capacity. When back under acceleration, the ECU will direct a lower charge voltage to put less load on the engine from the alternator saving fuel and reducing carbon emmissions. The ECU will also direct a voltage change if the vehicle has auto start-stop.

To charge a second battery system requires a battery charging profile at a series of set voltage levels.

A DC to DC alternator controller bridges these two conditions so the battery is charged correctly. Some units, particularly the Victron unit, can be switched between "power supply" and "battery charging" mode. In power supply mode, the unit applies power regardless of the battery condition and is commonly used to put power into a flat battery.

In battery charging mode, the DC to DC applies a load to the alternator. Whilst the level of load can be pre-set in some models, it is generally on or off. Victron DC to DC have an engine detection system based on a voltage range that automatically turns the unit on and a separate range for isolating the starter battery, that is called "lock out".

Fixed power DC to DC units are generally kept at a low level os less than 600W (50A nominal). This is because if on when the engine is idling, the load may cause the alternator to overheat as there is less air flow. Fixed power DC to DC units range in efficicency of 85-90%. The generate significant heat.

Placing 4 units in parallel as suggested in the brochure of an Australian manufacturer, would produce around 15% of 3000W in heat which is 450W. That amount of heat is difficult to manage.



Time To Charge

The time taken for a DC to DC power (amps) to charge the target battery charging capacity (amp hours) is easy to calculate. Typical values are 5 - 8 hours for charging from a low State of Charge (SOC) to 100% SOC. That has worked well in the past when touring involved long drives and battery capacities were small to moderate.

However, increased battery capacities now see 400-800Ahs in a caravan and at least 200Ah in a canopy. Touring patterns have also changed with shorter drives between locations or short drives frm a stationary base camp. Charging in 1-2 hours is very convenient. This requires 100-250A of charging at 12V. For this level of charging, the batteries have to be Lithium.

Some Lithium batteries are designed to charge at a 0.5C or lower rate. There may be a variety of reasons for this but generally it is cost based. Going to the effort to increase the charge rate and then find that the Lithium battery system cant accept that level of charge would be a major disappointment.

In the discussion that follows, it is assumed that the Lithium battery bank can accept the level of power (amps). 

It is now possible to charge a 400Ah Lithium bank in less than 2 hours in one of two ways:

1) Direct Control of the Alternator combining an alternator regulator and battery charger.

2) Using a "Buck Boost" planar transformer that can vary the load on the alternator and charge a battery bank.

Direct Control of the Alternator

This is an external alternator regulator and battery charger combined. There are several brands that achieve this with a high degree of efficiency. It could be argued they are 99% efficient as there is only a minute amount of heat loss. However, there are pre-cautions needed in designing systems that use them. For that reason they are used by system designers who provide and end to end solution. The designer must be very knowledgable on the Lithium battery BMS technology being used. If the BMS calls for a "stop charge" and the charging circuit opens suddenly, the accumulated energy in the alternator has to be dumped suddenly. Such a load dump may damage the system.

In the marine environment, these controllers have been used for some time. The product Safiery supports has extensive range of parameters to program for big alternators on small engines as in sailing boats. The largest alternator power Safiery supports is 12.5kW for marine. That needs to be a 48V alternator for practical cable management. At this level, 250A will be flowing.

Dual alternators for port and starboard engines can be controlled in sync with a CANbus connection between them.

In the vehicle environment, the alternator is small compared to the engine but the charging process is more complex. Understanding the algorithm to move from a bulk or absorption charge level to float and then back again to re-bulk requires a carefull choice of parameters. The power level is high and the system design requires quality products that all talk togther. 

Toyota Lancruisers, both the 79 and 200 series have an easy to control alternator. With a replacement alternator at 250A output, it is easy to extract 220A+ from them for charging.

The alternator controller is perfect for second alternator systems. There are a standard option on nearly all the USA "muscle" trucks, Mercedes Benz Sprinters, VW Craters, Ford transit Vans, Isuzu trucks, MAN trucks and even the new Hilux can have a powerfull second alternator. The largest system installed by Safiery is a 9kW alternator and charging on a MAN Expedition vehicle. The typical size installed is 5kW.

Using a "Buck Boost" planar transformer

Vehicles with some degree of electification require multiple voltage systems with high power transfer between them. A "mild hybrid" vehicle uses a 48V battery bank to drive the motor on a ring gear of a petrol engine for added torque. The motor may used be used to start vehicles and becomes as a generator when the engine is braking. Both the Dodge RAM 1500 and 2500 have such a system. Performance vehicles like the Aston Martin Valkrie have electric super chargers that are likely to be powered at 48V from lithium. The Bentley Bentayga and Audi S6 also are mild hybrids at 48V.

Mild hybrid technology suits the Australian 4WD market well as range is increased with more efficient petrol engines yet torque can be added by the 48V battery. 

The "buck Boost" Safiery uses hails from the electric vehicle market and is manufactured to "automotive grade" which is a very high standard. Being an automotive product it requires ECU control. It wont operate with out that. Safiery have an ECU embedded in the case that controls the Buck boost with CANbus (as all vehicles do) at 500Bps. It can switch direction in the power flow in less than 25ms.

A "buck boost" demands power when the low side "pin" voltage is less than the available alternator voltage. This makes it very effective for alternator control. The largest "Buck Boost" installed by Safiery is 3,000W or 250A on the 12V DC alternator side.

Compliance to Emmision's Control

Back to where this article started, emmissions control, particularly with European engines has a strict requirement on the ability of the vehicle to reduce alternator load at times. Adding charging of a second battery with a regular DC to DC will immediately change the fuel consumption level. In many countries this is presently allowed. However, it may be restricted in the future. Safiery has (Patent Pending) technology that will only operates the "Buck Boost" when the vehicle is in regenerative braking and then puts no load on the alternator when it is not. This makes this technology absolutle leading edge and future proof.

CANbus Control

Lithium batteries may have a BMS that communicates with CANbus. There are several advantages:

  • No Shunts are required as the current measurement using hall effect sensors is in the battery itself.
  • An accurate voltage, current and temperature measurement can be transmitted by CANbus - there is no loss
  • A pre-warning of BMS action to "stop charge" can be issued by CANbus

Safiery links CANbus Lithium batteries both at 12V and 48V with the 1) Buck Boost, 2)Alternator controller and the 3) Victron GX operating system. It is a simple and elegant system that is all digital. The design is modelled on a vehicle's CANbus system.

Scotty Application Notes 2.1

In version 2.1 of this product, the following features are now standard. The software in version 1.0 is upgradeable over the CAN.


  • Billet machined IP65 Case is complete. This will be refined further with the final anodized colour being a burnt orange. Scotty can be engine bay mounted for vehicle immersion in water crossings.
  • Short pre-crimped cables from Scotty for 300mm.  1 x 70mm2 12V +, 1 x 50mm2 12V – and 1 x 35mm2 24 or 48V +. These will be crimped with lugs to match optional megafuse holders. This reduces installation costs and means the Scotty case does not have to be opened.
  • Optional mega fuse holders with facility to hold a spare Mega Fuse on side of cover:
     300A on 12V side and 125A on 48V side. If this is 24V then Fuse will be 150A.
  • CANbus wiring is complete internally with CANbus Pin out on the RJ connector. This simplifies installation. A CANbus patch lead runs from Scotty to CANbus Lithium 48V.
  • Any voltage from 12-70V DC can be applied to the “Ignition or Power in”; there is a 12V power supply inside Scotty for the CAN controller.
  • The Auxiliary-In wire can now be switched high to 12V to switch the operating mode of Scotty. This wire input goes to the harness.
  • There will be a simplified harness for Scotty with Alternator connections AND Battery & Current Sense connections.
  • There will be a range of optional compact battery post Integrated Fuse Blocks at up to 300A for connection from Alternator/Starter battery to Scotty on 12V side.



Version 2.3.2-9 is a major break-though


On-Road/ Off-Road Feature (Patent Filed and Pending)

  • When the Auxiliary Input is switched on, Scotty changes mode to support Enhanced Fuel Economy. It will feed power and energy from the secondary 48V battery to the vehicle starter battery when the engines ECU reduces Alternator output voltage calling for power from the starter battery. When this occurs, there is zero or very low load on the alternator. This, in turn, reduces the load on the engine, particularly at idle or in “start stop” mode. This, in turn, improves fuel consumption. This is a key feature in Euro 6 engines’ compliance.
  • The first installation will be in the first week of October 2020 on a new Ford Ranger.
  • When the Auxiliary Input is switch off, Scotty changes mode to off-road and pulls as much power as possible from the alternator. Fuel consumption will increase at idle.
  • Alternator Temperature is now enhanced with a pull back feature for “off-road” mode if the temperature goes high at idle.
  • Response time is significantly improved to load demands to less than a second.



Its generally once in a lifetime that we see a revolutionary product that changes the game. Scotty is such a product. The On-road /Off-road feature is a significant game changer that will both save fuel costs when power and energy in the canopy/vehicle is not critical (driving around town during the week) AND flick a switch for abundant power on the weekend off-road. The fuel saving adds value to the product.

There are the ways to apply Scotty to suit:

 LC200 or LC79 Series

  1. Use existing 12V alternator for up to 1,800W (130A at 14.6V) of power charging. This has Scotty directly connected to the Alternator/Battery.
  2. Upgrade the Alternator to either the brushless 200A or brushed 250A 12V alternator. This will pull up to 3,000W (200A+ at 14.6V) of power charging. This has Scotty directly connected to the Alternator/Battery.
  3. Upgrade Alternator to 48V 100A. This will pull up to 5,000W (100A+ at 52V) of power charging directly to 48V batteries. Connect the 12V Pin of Scotty directly to the Starter Battery and disconnect the Alternator/Starter battery wiring. (The original 12V alternator is kept as a spare and can be refitted at any time if the 48V unit malfunctions)


There are the ways to apply Scotty to suit:

Ford Ranger/BT 50/ Y 62/ VW transporter and any vehicle with LINbus controller Alternator

  1. Use existing 12V alternator for up to 3,00W (200A+ at 14.6V) of power charging. If the alternator is only 130A, then 1,800W of power. This has Scotty directly connected to the Alternator/Battery.
  2. Use the 1.5kW DC to DC for 12V ONLY power. This is not the Scotty product at present. We will have a 1.5kw Scotty in 2Q 2021. In the meantime up to 1,500W van be extracted for 12V charging but there is no on road/ off road mode. Package and price shown on website for this.

These options mean there is no modification to the alternator.


These are the ways to apply Scotty to:

  • Mercedes Sprinters
  • MAN TGE (VW Crafter collaboration)
  • Dodge Ram
  • Ford F Trucks
  • Any vehicle with second alternator support.
  1. Use existing 12V alternator for up to 3,00W (200A+ at 14.6V) of power charging. If the alternator is only 130A, then 1,800W of power. This has Scotty directly connected to the Alternator/Battery.
  2. Upgrade the Primary Alternator to 250A 12V alternator. This will pull up to 3,000W (200A+ at 14.6V) of power charging. This has Scotty directly connected to the Alternator/Battery.
  3. Install a second Alternator at 12V 250A. This keeps the existing alternator and “Factory Warranty” Intact. This will pull up to 3,000W (200A+ at 14.6V) of power charging. This has Scotty directly connected to the Alternator/Battery.
  4. Install a second Alternator at 48V 100A. This will pull up to 5,000W (100A+ at 52V) of power charging directly to 48V batteries. Connect the 12V Pin of Scotty for 12V power in vehicle and also use for winch support.


Winch Support

16,000lb winches require up to 400A at 12V. When combined with the Alternator, Scotty will deliver 250A + Alternator capacity for continuous winch operation.


There is 5 years warranty on Scotty. This is a manufacturer’s express warranty and is listed on our website.

Coomera 29th September 2020



Examples of alternator control

“Simplicity is at the very heart of this system”

Use your 4WD as a power station for your caravan or camper trailer “plug in and run 240V”.