Lithium Compatible Alternator Regulators

Alternator Battery Charging Background

1st Generation Alternator Regulators and Managing Temperature Rise

Situation Overview

In the first generation alternator regulators, the main objective was to limit the voltage output of the alternator. For example, it would charge the battery up to a design voltage of 14.0V and maintain it at that level until the engine is turned off. The alternator's current supply is determined by its design, engine speed, and the battery's capacity to absorb the current. Once the set voltage is reached, the current tapers off.

In terms of temperature management within the alternator casing, these alternators were designed to provide a high current for a short duration after an engine start to recharge the lead-acid battery. Afterwards, they would operate at a much lower amperage to support basic electrical loads such as lights, wipers, and entertainment systems. This approach ensured that the alternator did not overheat.

Potential Issues with Additional Batteries

However, adding an auxiliary battery in the vehicle and/or a house battery in the caravan and directly charging them from the alternator could lead to prolonged high currents flowing through the alternator, causing overheating. Watch this video by Victron on more about alternators overheating due to battery charging. Furthermore, the use of LiFePO4 batteries exacerbates the problem, as their charging voltage does not rise as much or as quickly as lead-acid batteries during the charging cycle.

Potential Issues with Modified Voltage Regulation

In some cases, vehicle owners may attempt to increase the alternator voltage by adding a diode to the field winding circuit. This modification raises the upper limit of voltage regulation by the forward voltage drop of the diode. The purpose of this modification is often to compensate for voltage drop in long cables running from the front of the engine bay to a battery located at the back of a long caravan. However, this modification can worsen the situation, especially if the alternator's vents are partially blocked due to high mileage. This problem becomes particularly pronounced when charging the battery while the vehicle is idling at high temperatures.

2nd Generation Alternators and Vehicle Electronics

In the 2nd generation alternators, the voltage regulator is controlled by the vehicle electronics. These electronics are specifically designed to support the standard factory vehicle and contribute to reducing emissions. As part of this design, the voltage is lowered once the battery has been fully charged.

Therefore, similar to the 1st generation alternators, the alternator system is not suitable for charging additional batteries. Modifying the system becomes more challenging due to limited access, warranty considerations, and the restrictions imposed by emission control legislation, which prohibit modifications to the vehicle systems.

Vehicle Alternator Regulators and Charging Challenges

Vehicle alternator regulators generally have a generic charging characteristic, which means they do not provide the specific charge characteristics and voltages specified by battery manufacturers for deep cycle and LiFePO4 batteries. To overcome the challenges mentioned earlier, a common approach is to use a DC to DC charger that is configured with the required charge characteristics and voltages for charging deep cycle or LiFePO4 batteries from the vehicle alternator.

DC to DC chargers offer the flexibility to set the maximum charge current output according to the size of the auxiliary battery and/or the capability of the alternator. This feature is particularly important in situations such as conversions of older vehicles like a 1970's VW combi van, where preventing alternator overheating is crucial.

It's worth noting that some DC to DC chargers have a bypass setting, which directly connects the input of the DC to DC charger to the output. In this mode, all the available current from the alternator is passed to the auxiliary battery until the voltage reaches a pre-determined level. After that, the bypass is opened, and the DC to DC charger resumes its charging function. However, it's important to consider that prolonged activation of the bypass mode could lead to alternator overheating, especially when charging a large LiFePO4 battery. Therefore, specific consideration must be given to the alternator's capacity, the type of DC to DC charger being used, and the potential charging time at maximum alternator amps for a fully drained auxiliary LiFePO4 battery.

Upgrading to an Adaptive Regulator for Enhanced Battery Charging

In cases where it is both possible and permitted, the original voltage regulator installed in the vehicle can be replaced with a more advanced and adaptable regulator. These upgraded regulators offer selectable charge characteristics specifically designed to accommodate deep cycle and LiFePO4 batteries, which can now be utilized as the vehicle's main battery for engine starting and standard electrical loads. One notable company leading in this field is Wakespeed, offering two primary products: the WS100 and the WS500.

The focus here is on the WS500, which features a CAN Bus interface that enables integration with a LiFePO4 battery management system. Through this interface, the battery management system can set both the voltage limit and current limit coming from the alternator. The significant advantage of this setup is that the battery management system actively lowers the charge current while the battery cells are being balanced. Since the balance current is typically only a few amps, it is ideal to reduce the charge current to a similar level to avoid any voltage imbalances between the cells that could lead to runaway cell voltages.

Comparatively, the older, less refined method of preventing cell overvoltage involved inhibiting the charger when the highest cell reached a pre-set voltage. However, this approach posed a problem: the voltage of an excessively charged cell would drop rapidly the moment the charging was halted. In such scenarios, a battery management system that lacks control over the charge current can cause rapid cycling of the charging process, turning it on and off repeatedly while the cell balancer tries to balance the cells.

The REC BMS, which is programmed with user-defined limits for charge current and voltage, plays a crucial role in determining whether the charge current needs to be reduced for balancing and topping off the battery pack. It communicates these voltage and current limits to the WS500 regulator accordingly. Additionally, the WS500 monitors the alternator temperature to ensure the well-being of the alternator. If necessary, it will further decrease the current output to prevent overheating.