PROJECT PRESENTATIONBattery Swapping Reliability

Wesley LavenderEMIS 7305

Presentation Outline• Overview

• Scope• Problem

• Analysis• Overview• Industrial Robots Performing Swap• Charging Stations

• Results• Conclusions• Questions

Overview

Battery swapping stations have been proposed by Better Place as a solution to the problem of electric vehicle batteries’ limited range. The Better Place switch stations are currently in the demonstration phase and use a mix of mature and immature technology. Better Place Switch Station

Scope• Original Scope:

• Reliability, Maintainability, Supportability• Analyzing the battery identification process, battery swapping

process, and the charging of depleted batteries

• Refined Scope:• Reliability only• Analyze battery swapping process (including the clamping

mechanism, the retrieving mechanism, and the moving tray) and charging stations

Problem• Battery swapping is new and immature• Little testing completed on reliability of battery swapping

systems• Complex system with a lot of moving parts

ANALYSISOverview, Industrial Robots Performing Swap, and Charging Stations

Overview• Selected Model: Exponential

• commonly used for electronic equipment • constant failure rate model• used in analyzing the ‘useful life’ period of an item’s life

• Failure rates and MTBFs used were measured during testing

Industrial Robots Performing Swap• 3 Primary Components:

• Clamping mechanism: holds vehicle in place while swapping battery

• Retrieval mechanism: retrieves/inserts batteries• Moving tray: contains clamping and retrieval mechanisms and

moves batteries to and from vehicle

  Failure Rate (λ) MTBF (in hours)

Clamping mechanism 0.00005 20,000

Retrieving mechanism 0.0001 10,000

Moving Tray 0.0000625 16,000

FIGURE 1: Industrial Robots failure rates and MTBFs

Industrial Robots Performing Swap

Reliability Function:

t

e )t(R

  R(t)

Clamping mechanism 0.966

Retrieving mechanism 0.905

Moving Tray 0.911

Industrial Robots Performing Swap

Components in a series configuration:

Product Rule of System Reliability:

RS(t) = (0.966)*(0.905)*(0.911) = 0.796

Failure rate: = 0.000213

MTBFS = 4,706

n

ii

n

iiS tRAPtR

11

)()()(

Clamping Mechanism

Retrieval Mechanism

Moving Tray

n

1iiS )t(

Charging Stations

• 5 identical, independent charging stations

• Need at least 3 in operation at all times

• R-out-of-N configuration (n=5, r=3)

S1

S1

S1

S1

S1

3 out of 5

Charging Stations

Results

  R(t) Failure Rate (λ) MTBF (in hours)

Industrial Robots 0.796 0.000213 4,706

Clamping mechanism 0.966 0.00005 20,000

Retrieving mechanism 0.905 0.0001 10,000

Moving tray 0.911 0.0000625 16,000

Charging Stations 0.796 0.00049 1,958

FIGURE 4: Summary of reliabilities, failure rates, and MTBFs

Conclusions• Technology too immature for widespread commercial

implementation• Industrial robot system should use redundancy to improve

reliability• Charging stations should improve reliability of individual

stations to improve overall reliability

Questions?

References:

"Better Place." Wikipedia. Wikipedia Foundation, Inc., 07APR2012.

Better Place official website. www.betterplace.com.

EMIS 7305 class notes.