Start / Finish point

Motorway

Voltage variations associated with vehicle regenerative braking / smart alternator Systems (Energy Recovery System) and what a Sterling Battery to Battery Charge does to rectify this problem.

Regenerative Braking - Introduction to the problem and the solution.

12

12.5

13

13.5

14

14.5

96.00 101.00 106.00 111.00 116.00 121.00 126.00 131.00 136.00

Battery Voltage

Volts

Sterling Battery to Battery charger

Actual data from Ford Transit with active regenerative braking

Older Standard vehicle with no regenerative braking

Volts

start 5 10 15 20 25 30 35 40

Time in mins

ActualVehicle data

euro 6

The Solution

Sterling’s Battery to Battery Charger: The battery to battery charger is designed to boost the low voltage from the alternator up to the correct voltage for the battery chemistry regardless of the massive voltage swings delivered by the alternator, this ensures a constant and much faster charge from the system, also this is even more important the further back the auxiliary battery banks is in the vehicle to also compensate for cable voltage drops, the end result is a much faster charge rate (over 10 times faster).

The Objective

The object is to graphically display the effect regenerative braking (smart alternators) has on auxiliary battery charging systems.

This is not an inditement of any particular vehicle or system. To my knowledge all vehicle smart alternators are based on roughly the same principle - to intelligently use the alternator’s voltage and onboard starter battery to reduce carbon footprints in order to enable them to comply with the latest EU engine emissions standards.

The object is to recover as much “free” energy as possible. This is achieved by heavily loading the alternator during deceleration / braking to get as much “free power" as possible boosted into the engine starter battery. Then release this “free power” into the vehicle’s system by reducing the alternator’s load (by dropping the voltage) during smooth driving stages. It effectively uses the vehicles inertia to boost electrical energy efficiency, thus improving MPG and CO2 emissions.

This works well, but with any improvement on one side there is usually a cost somewhere else. In this case the standard vehicle’s efficiency is undoubtably improved as one would expect, however, the down side is a massive reduction in performance of the auxiliary battery charging system (if installed).

The Test

Vehicle used in test (use graph for illustration)Vehicle tested was a new (2013) Ford Transit van. Most, if not all vans and cars are now operating on this principle (nothing special about the Transit).Route chosen:The route involved some urban, then town, then motorway driving over about 40 minutes.Graph / Voltage measured.Blue line: Is the voltage measured at the battery from the Ford Transit using the regenerative system over the journey (acquired on actual journey).Green line: Is the typical voltage one would see from a standard older vehicle not operation under regenerative braking control.Red line: This is the voltage on the auxiliary battery sustained by the Sterling Battery to Battery charger regardless of the voltage on the input to the unit (or what ever voltage the unit is set for depending on the aux battery chemistry). The important thing to gleen from this is that the Sterling unit is still boosting to 14.8V even when the input voltage drops to 12.6V.Conclusion: One can clearly see the voltage swing associated with the regenerative braking. Swing from 12.6V - 15.0V. At 12.6V the auxiliary charging would simply be useless - at 15.0V it would destroy AGM batteries.

The simple fact is the new system relies on a 20% empty engine starter battery for the new system to work as it needs the space to “dump” the fast energy build up during braking, this is in direct conflict with the requirement / desires for the secondary battery system. Problem with using voltage sensitive relays? As one can see the voltage sensitive relay would have 2 major issues: 1) The 2-3 minute time delay before activation is the first problem so simply getting the relay to activate could be an issue in itself. 2) Even if the relay engages the massive voltage swings would prevent the second battery from getting any serious charge when on low voltage and would certainly damage AGM batteries when at high voltage.

The Transit Van’s Route

R.B.FRegenerative raking riendly B F

Please turn over

R.B.FRegenerative raking riendly B F

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