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Re: conversion is quite efficient.....
Posted by Reality (more from Reality) on Thu, 14 Jun 2012 19:38:28
In Reply to: conversion is quite efficient....., Mark from Toronto, Thu, 14 Jun 2012 15:48:29
Less than half the vehicle's kinetic energy can be turned into electricity (before storage) in typical regenerative braking, because:

1. Regenerative braking can only be used on driven wheels;

2. Regenerative braking can not be used at very low speed, because there is not enough braking force to stop the vehicle;

3. Regenerative braking can not be relied upon when significant amount of braking force is called for either, because the drive train power capacity is much much less than the braking force that can be applied by the tire contact patch, and the electrical part only accounts for a small percentage of the drive train in a typical hybrid. It would be quite absurd for a car to take as long to do 60-0 as it does for 0-60; would be ploughing through people with that long of a braking time. Not to mention typical hybrids' best 0-60 is achieved with help of ICE not on electric motor alone.

After that half is cut out, we are looking at what is essentially a system comparable to an alternator for converting mechanical energy to electric energy, only the range requirement would be even wider / more hostile than the typical alternator. The typical alternator has an efficiency of 50-62%

Lithium battery charging efficiency is 80-90% under the most ideal conditions. In-car application certainly is not ideal. Let's take 80%.

Lithium discharging efficiency is 80-90% under the most ideal conditions. In-car application certainly is not ideal. Let's again take 80%.

Other types of battery typically have lower charge/discharge efficiency. NiMH battery charge/discharge efficiency is around 66% each way. So giving 80% for each is rather generous, considering that up to this point most hybrid electric car models on the market with Lithium batteries face fire threats (Volt and Karma)

Then finally the electric energy is used to drive wheels again, so after drive train losses, let's say again 80% efficient. So let's tally Up

50% x 50% x 80% x 80% x 80% = 13%

posted by 75.67.1...
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