Difference between revisions of "EV Batteries"

Latest revision as of 08:47, 9 July 2018

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EV Batteries List

Lead-Acid

Standard lead acid batteries are designed for massive bursts of startup current (denoted as locked rotor, or cold crank amps) usually in excess of 500 Amps. Electric Vehicles, on the other hand require relatively steady discharge, from fully charged all the way down to mostly flat, before recharging again. The lead plates inside the battery required for this purpose are thicker than standard car batteries and are usually referred to as "deep cycle".

• Standard Lead Acid Battery
• Deep Cycle Lead Acid Battery

carbonfoam-acid (Firefly)

The Carbon foam battery was in mid 2010 put forward as a lighter more energy dense replacement for the lead acid battery. Unfortunately the firefly company was unable to convince the Department of Defence (who were funding the research?) that it's product was worthwhile and the Firefly company subsequently went out of business.

Lithium Ion Battery

Lithium Ion are rechargable batteries that are popular in consumer electronics and power tools. They have a higher energy density (pack more amp hours per kg) than lead acid batteries. For an Electric Vehicle, this means more miles and less weight, but the upfront cost is substantially higher.

Nickel-hydride

Nickel Hydride, or more exactly Nickel Metal Hydride (NiMH) batteries replaced NiCd (Nickel Cadmium) batteries in most consumer products in during the 1990's. Nickel Cadmium batteries suffered from memory effects (the battery would "remember" where it was last charged from, and only discharge back down to that level). NiMH batteries have for the most part been supplanted by Li-Ion Batteries, with usage dropping from around 60% in 2000 to 22% in 2011 due to Li-Ion having higher energy density. Ref

LiFePO4

Lithium Iron Phosphate are preferred for larger application such as electric vehicles and do not suffer from over discharge combustion problems seen in other Lithium battery types. From a weight point of view, typically a 30AH 48V pack is around 16KG compared to the similar Lead Acid of 46KG for the same energy storage, so a big weight saving will apply, but cost would be substantially higher.

The peak current however for a the LiFePO4 will not be as high as the Lead Acid. Lead Acid CCA (cold crank amps, or peak short term current) for a 30AH pack is 200 Amps, whereas the equivalent LiFePO4 battery would have a surge rating of 90A.

Discharge Depth will also vastly impact your battery life expectancy. A 30% discharge and recharge will give around 2000 discharge cycles, while a 100% discharge and recharge will shorten this to around 1/3. Lead Acid Batteries life also depend on discharge depth. A 100% discharge will shorten your Lead Acid to 300 recharges.

Shelf Life of Lithium Batteries will be around 2 years, meaning whether you use them or not, the batteries will degrade just from sitting around. This compares with around 5 years for Lead Acid.

Cells are 3.2V each, so a pack and must be made up of a large number of cells. Usually a Battery Management System (BMS) would be included in the pack to prevent thermal and overcurrent damage.