Scotty - Alternator Charging Technology

Alternator Charging

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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.


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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.


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.

Technical Detail

Safiery Scotty Wiring Install and Operation Manual



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




Examples of alternator control

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