Smart Charger Significantly Increases E-Bike Battery Lifetime
MARYLAND, USA – E-bike battery lifetime is predominantly determined by stress and cell temperature and cell quality. For existing batteries, only stress can be addressed. Stress substantially increases above 80% and below 20% State of Charge (SoC). E-bike batteries are rarely below 20% but are always charged to 100%, even during storage. This reduces the e-bike battery lifetime.
CALCE, a major reliability and lifetime test lab at the university of Maryland, USA performed a year-long test. The study proved that charging to 80% doubled cycle lifetime compared to 100%. This resulted in the E-bike Battery Saver (EBS) Smart Charger, where the user can select charging 40 to 100% in 5 steps each time. 40% is the ideal SoC for storage as the degradation of the battery is neglectable between 30 and 50%. 60, 70 and 80% save lifetime during normal operation, while the user would only use the 100% switch for longer trips.
'Solution for the range versus lifetime dilemma'
E-bike consumers strongly oppose the short lifetime
With e-bikes, the range is an important marketing factor. Consumers often base their decision on how far they can ride, even though they rarely -if at all- use the full range. Electric vehicles (EV) typically operate between 20 and 80% of the charge/discharge cycle, because they believe that they can only sell their EV’s with a substantial warranty: 8 years.
E-bike battery warranty is mostly 2 years, sometimes 3 years and rarely 4 years or more. E-bike consumers strongly oppose the short lifetime, but there was no alternative.
Alternative: EBS Smart Charger
James Post, CEO ECOpro Technology BV: “To solve the range vs lifetime dilemma, we designed a charger with a microcontroller, that allows the user -before each charge- to select the charge percentage that fits their trip that day. For the typical daily use, 60% will prove to be sufficient in most cases, but 70% and 80% are also available switch positions. Before a long trip, users would select 100%. 40% is the ideal storage charge percentage”.
Models & Availability
The first EBS Smart Charger for 36V batteries is available now but for with DC 5.5 x 2.5, DC 5.5×2.1, DC video (RCA) and XLR-5 connectors. Models for different connectors will be added from time to time.
For batteries, where a manufacturer restricted access to the charge port, EBS Smart Chargers can be created in cooperation with the manufacturer in question.
Pricing, Warranty & CE Compliance
The 42V 2A EBS Smart Charger has an MSR price of € 79.50 including VAT and will be sold via the retail channel. All EBS Smart Chargers carry 8 years pro rata warranty** and are tested for CE compliance at a certified laboratory (test report available for OEM customers).
Even though the EBS Smart Charger adds substantial complexity (comparable to a BMS), the price is not significantly different from standard chargers. E-bike manufacturers, who consider switching to the EBS Smart Charger, will appreciate the minor price difference.
How it works
Determining the voltage, corresponding to each charge percentage, is far from easy. The difference in voltage between 40% and 60% is just 1V, but moreover the voltage/charge % characteristics change with the cell manufacturing technology. The only way to do it right is to measure the battery capacity and thus determine the accurate voltages for each charge percentage. In this respect, the EBS Smart Charger has the function of a 2A battery tester!
The accuracy of the EBS Smart Charger is best when the battery is empty before charging. Because only then the full charge range can be measured and accuracy is then +/- 2%, which is more than enough for this application.
Most battery manufacturers require that batteries are charged regularly, especially when the concerned batteries have a high self-discharge. This is done to avoid deep discharge, which can ruin the battery. For consumers it is not easy to have to think about this, but besides, it is bad for the battery lifetime to store at 100% capacity.
The EBS Smart Charger solves this elegantly: The battery is charged until 40%; then the battery is automatically disconnected. Once the SoC hits 30%, the battery is recharged to 40% automatically. This way the consumer just sets the charge position to 40% and can forget about the battery all winter. This feature alone justifies the purchase.