> EV Basics – Basic Physics vs. Promotional Claims!

> Money, money, money makes the world go round.

> Perhaps, a simpler way to express this is Fact vs.

> Fiction!

> This month, we look at some of the claims by EV manufacturers

> to identify which ones are realistic and which ones raise

> questions. These are claims regarding range, cost per mile, and

> time to recharge. These are the major concerns by the EV

> consumer.

> Next month, we will look at the engineering required to size a

> motor for on-road applications. How does rolling resistance,

> aerodynamic drag, hill climbing, and acceleration affect the

> motor hp? Why is higher voltage better?

> We recently have seen many claims by EV companies that are

> looking for customers. For example, the Chevy Volt claims 230

> mpg. Since it gets 40 miles on a charge without any gasoline,

> couldn't it get 1000 miles (25 charges) with no gasoline? GM also

> claims that it will go 40 miles on about 8 Kw-hr of electricity.

> That is 5 miles/ Kw-hr; which is twice the typical EV conversion.

> Most EV conversions get about 2-3 miles/ kw-hr, so I question

> the 5 miles/ kw-hr. It is achievable - but probably not at highway

> speeds or in stop and go traffic.

> This month, I received a promotional email on the Tesla sedan

> for 7 people that made strong claims:

> 300 mile range

> $4 for a charge (300 miles)

> 45 minute recharge

> http://www.teslamotors.com/models/index.php

> In my 22 years in the EV business, there have been many

> exaggerated claims in order for companies to obtain investors

> as well as customers. To validate if a claim is reasonable, an

> individual needs to understand EV Basics.

> To obtain a 300 mile range, a typical EV conversion would

> require 100-150 Kw-hr battery pack. Most EVs carry 15-25 KW-

> hrs lead acid battery packs weighing 800 -1400 lbs. So a 100 KW

> hr battery pack would weigh 5600 lbs! Which is consistent with

> our claims that it takes 15-20 lbs of lead to get 1 mile in range.

> Lithium batteries are about 1/3 the weight of lead acid. So that

> would mean ~1900 lbs of lithium batteries. But if we assume that

> the Tesla also gets 5 miles/ kw-hr (same as Chevy Volt) then you

> have ~1000 lbs of lithium batteries. Check this against the

> specifications on the Tesla website. So our conclusion is (1) that

> the Tesla will require about 1000 lbs of Li batteries and approximately 60
> kw-hrs of energy (300 miles/ 5 miles/ kw-hr).

> The average cost of electricity in the U.S. is 12 cents/ kw-hr.

> Ref: http://www.eia.doe.gov/cneaf/electricity/epm/table5_6_a.html

> So 60 kw-hr x $0.12 = $7.20

> This is almost twice the $4 charge claimed by Tesla. In order to

> achieve the $4, Tesla has to achieve 9 miles/ kw-hr which is

> almost twice as efficient as the Chevy Volt and almost 4X the

> efficiency of a conversion. Or they had to assume 7 cents/ kw-hr.

> So this claim is questionable.

> Now we get to the 45 minute recharge. Most EVs require 8 hours

> to recharge using a 230VAC power supply and 20 kw-hr battery

> pack. Let's go back to our assumption of 5 miles/ kw-hr yielding

> a 60 kw-hr battery pack. The problem becomes how fast can we

> recharge a 60-kw-hr battery pack.

> A 115VAC circuit typically is 15 amps, so that is 1725 watts.

> Even if we assumed 2000 watts or 2 Kw, it would take 30 hrs to

> charge the 60 Kw-hr battery pack.

> If we assume a 230VAC and 30 amps, that is 6900 watts or ~

> 7Kw. That is 8.5 hours to charge the 60 kw-hr. Not even close

> to 45 minutes.

> Let's work backwards.  60 Kw-hrs/ 0.75
> hrs (45min) = 80 Kw of

> charge. That is 80,000 watts. If we assume a 480VAC circuit that

> is 166 amps.

> The Tesla Roadster with a smaller battery pack requires 3.5 hrs to

> charge completely. So you really do have to question how they

> are able to claim 45 minutes.

> The Nissan Leaf makes very realistic claims: 100 miles/ charge

> and 4-8 hrs recharge (230VAC).
> http://www.nissanusa.com/leaf-electric-car/?dcp=ppn.39666654.&dcc=0.2...

> So the Nissan Leaf goes 100 miles and requires 4-8 hrs to

> recharge; the Tesla goes 300 miles and can be recharged in

> 45 minutes. There does seem to be a question.

> Next month, I will discuss the basic engineering associated with

> identifying the hp required for an EV. Meanwhile, question

> everyone - including me, by simply asking for the engineering to

> back up their claims.

> Full article:

> http://us.mc657.mail.yahoo.com/mc/welcome?action=&YY=927331124&YY=224...