Spock - analysis: switching from Lead acid to Lithium batteries

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Spock - analysis: switching from Lead acid to Lithium batteries

Rob Trahms
Hi all -
I won't be switching my EV to LiFePO4 batts in the near term, but I wanted to do a thought experiment using the current TS-LFP100AHA and TS-LFP160AHA to see what my range increase would be.  Please review my logic/numbers, and let me know if they make sense.   Thanks!
Rob

Current EV (16 US125XC batteries - 96V)
Total curb wgt (including current LA batteries): 1452 kg
Curb wgt w/o batteries: 967 kg

Stats on the US125XCs:
286mm (H) 260mm (L) x 181mm (W)
30.3 kg each, 6.2V each
Pack (16) = 99.2V, 23KWhr (20-hr rate)
Pack weight: 485 kg
Realistic pack energy (< 50%): 9 KWhr
Realistic energy usage: 550 Whr/mi
Realistic range: 16 mi

TS-LFP160AHA Lithium option (a decrease in weight, increase in range):

279mm (H) x 71mm (W) x 182mm (L)
5.6 kg each, 3.2V each
(space to replace every LA unit with 3 LFP units)
Pack (48) = 144V, 23 KWhr
Pack weight: 269 kg (0.55 today's pack)
Curb weight ratio factor: 0.85
Realistic pack energy (70%): 16 KWhr
Realistic energy usage: 468 Whr/mi (0.85 * 550Whr/mi)
Realistic range: 34.5 mi

TS-LFP100AHA Lithium option (a little cheaper, lighter, and slight increase in range):

217mm (H) x 68mm (W) x 145mm (L)
3.2 kg each, 3.2V each
(space to replace every LA unit with 3 LFP units)
Pack (48) = 144V, 14.4 KWhr
Pack weight: 154 kg (0.32 today's pack)
Curb weight ratio factor: 0.77
Realistic pack energy (70%): 10 KWhr
Realistic energy usage: 423 Whr/mi (0.77 * 550Whr/mi)
Realistic range: 23.5 mi

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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Willie McKemie
On Sat, May 02, 2009 at 03:24:39PM -0700, Rob Trahms wrote:
> TS-LFP160AHA Lithium option (a decrease in weight, increase in range):
>
> 279mm (H) x 71mm (W) x 182mm (L)
> 5.6 kg each, 3.2V each
> (space to replace every LA unit with 3 LFP units)
> Pack (48) = 144V, 23 KWhr

Nominal voltage would be 48*3.2=153
Peak would be 48*3.65=175.2

> Pack weight: 269 kg (0.55 today's pack)
> Curb weight ratio factor: 0.85
> Realistic pack energy (70%): 16 KWhr

17 KWH

> Realistic energy usage: 468 Whr/mi (0.85 * 550Whr/mi)

Those numbers seem very high for a VW.  Have you factored in lead
oddities?  With LFP, you get to use all the stored energy.

> Realistic range: 34.5 mi

I would guess your "mileage" would be no worse than 350 wh/m.
17000/350 = 48 miles
17000/300 = 57 miles

Our Hyundai Accent has 26 kwh of available energy and uses a bit less
than 300 wh/m.  Both observed and calculated range is about 90 miles to
30% SOC.  http://www.evalbum.com/2314

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  504 days 12 hours 07 minutes

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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Rob Trahms

Willie McKemie-3 wrote
On Sat, May 02, 2009 at 03:24:39PM -0700, Rob Trahms wrote:
> TS-LFP160AHA Lithium option (a decrease in weight, increase in range):
>
> 279mm (H) x 71mm (W) x 182mm (L)
> 5.6 kg each, 3.2V each
> (space to replace every LA unit with 3 LFP units)
> Pack (48) = 144V, 23 KWhr

Nominal voltage would be 48*3.2=153
Peak would be 48*3.65=175.2

> Pack weight: 269 kg (0.55 today's pack)
> Curb weight ratio factor: 0.85
> Realistic pack energy (70%): 16 KWhr

17 KWH

> Realistic energy usage: 468 Whr/mi (0.85 * 550Whr/mi)

Those numbers seem very high for a VW.  Have you factored in lead
oddities?  With LFP, you get to use all the stored energy.

> Realistic range: 34.5 mi

I would guess your "mileage" would be no worse than 350 wh/m.
17000/350 = 48 miles
17000/300 = 57 miles

Our Hyundai Accent has 26 kwh of available energy and uses a bit less
than 300 wh/m.  Both observed and calculated range is about 90 miles to
30% SOC.  http://www.evalbum.com/2314

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  504 days 12 hours 07 minutes

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Yes, first thing I noticed was that 48 batts would be 153.6V instead of 144V - duh.
So my revised numbers are below.  I do draw 550 Whrs in this hilly area, at speeds of 40MPH.
If there are other lead 'oddities' I should be accounting for, then that is just another upside of switching to LFP!

The VW cabbies are also a tad heavier than their rabbit cousins, due to the beefer body structure.

I am curious about your comment regarding pulling all of the energy out of lithium batteries.  Advised?  Or do you prematurely shorten their lives by doing so?  I was just looking at this also a little more on the conservative side.

New numbers:

TS-LFP160AHA Lithium option:

279mm (H) x 71mm (W) x 182mm (L)
5.6 kg each, 3.2V each
(space to replace every LA unit with 3 LFP units)
Pack (48) = 153.6V, 24.6 KWhr
Pack weight: 269 kg (0.55 today's pack)
Curb weight ratio factor: 0.85
Realistic pack energy (70%): 17.2 KWhr
Realistic energy usage: 468 Whr/mi (0.85 * 550Whr/mi)
Realistic range: 36.7 mi

TS-LFP100AHA Lithium option:

217mm (H) x 68mm (W) x 145mm (L)
3.2 kg each, 3.2V each
(space to replace every LA unit with 3 LFP units)
Pack (48) = 153.6V, 15.4 KWhr
Pack weight: 154 kg (0.32 today's pack)
Curb weight ratio factor: 0.77
Realistic pack energy (70%): 10.7 KWhr
Realistic energy usage: 423 Whr/mi (0.77 * 550Whr/mi)
Realistic range: 25.4 mi



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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Roger Heuckeroth
In reply to this post by Rob Trahms

On May 2, 2009, at 6:24 PM, Rob Trahms wrote:

>
> Hi all -
> I won't be switching my EV to LiFePO4 batts in the near term, but I  
> wanted
> to do a thought experiment using the current TS-LFP100AHA and TS-
> LFP160AHA
> to see what my range increase would be.  Please review my logic/
> numbers, and
> let me know if they make sense.   Thanks!
> Rob
>
> Current EV (16 US125XC batteries - 96V)
> Total curb wgt (including current LA batteries): 1452 kg
> Curb wgt w/o batteries: 967 kg
>
> Stats on the US125XCs:
> 286mm (H) 260mm (L) x 181mm (W)
> 30.3 kg each, 6.2V each
> Pack (16) = 99.2V, 23KWhr (20-hr rate)
> Pack weight: 485 kg
> Realistic pack energy (< 50%): 9 KWhr
> Realistic energy usage: 550 Whr/mi
> Realistic range: 16 mi
>
> TS-LFP160AHA Lithium option (a decrease in weight, increase in range):
>
> 279mm (H) x 71mm (W) x 182mm (L)
> 5.6 kg each, 3.2V each
> (space to replace every LA unit with 3 LFP units)
> Pack (48) = 144V, 23 KWhr
> Pack weight: 269 kg (0.55 today's pack)
> Curb weight ratio factor: 0.85
> Realistic pack energy (70%): 16 KWhr
> Realistic energy usage: 468 Whr/mi (0.85 * 550Whr/mi)
> Realistic range: 34.5 mi
>
> TS-LFP100AHA Lithium option (a little cheaper, lighter, and slight  
> increase
> in range):
>
> 217mm (H) x 68mm (W) x 145mm (L)
> 3.2 kg each, 3.2V each
> (space to replace every LA unit with 3 LFP units)
> Pack (48) = 144V, 14.4 KWhr
> Pack weight: 154 kg (0.32 today's pack)
> Curb weight ratio factor: 0.77
> Realistic pack energy (70%): 10 KWhr
> Realistic energy usage: 423 Whr/mi (0.77 * 550Whr/mi)
> Realistic range: 23.5 mi
>

You can go to 80% DOD if you want with LiFePO4 without sacrificing  
much longevity.

What type of EV do you have that only gets 550 wh/mile?
 

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Re: Spock - analysis: switching from Lead acid to Lithium batteries

martinwinlow
In reply to this post by Rob Trahms
-----Original Message-----
Subject: [EVDL] Spock - analysis: switching from Lead acid to Lithium
batteries
--------------------------


Hi Rob,

I would be very surprised if you don't get a big increase in range comparing
LA with LiPo4 cells based on the weight reduction of the pack alone,
particularly if you haven't got regen, use the EV in hilly terrain (which
you mentioned you do) and do a lot of stop/go driving.  All that saved
energy not having to accelerate (both horizontally and vertically) that
large extra mass must add up to a good few extra miles of range.  I'd be
interested to see the numbers but don't have sufficient knowledge to crunch
'em.

Good luck.

Regards, Martin Winlow, Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk


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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Rob Trahms
In reply to this post by Roger Heuckeroth

Roger Heuckeroth wrote
On May 2, 2009, at 6:24 PM, Rob Trahms wrote:

>
> Hi all -
> I won't be switching my EV to LiFePO4 batts in the near term, but I  
> wanted
> to do a thought experiment using the current TS-LFP100AHA and TS-
> LFP160AHA
> to see what my range increase would be.  Please review my logic/
> numbers, and
> let me know if they make sense.   Thanks!
> Rob
>
> Current EV (16 US125XC batteries - 96V)
> Total curb wgt (including current LA batteries): 1452 kg
> Curb wgt w/o batteries: 967 kg
>
> Stats on the US125XCs:
> 286mm (H) 260mm (L) x 181mm (W)
> 30.3 kg each, 6.2V each
> Pack (16) = 99.2V, 23KWhr (20-hr rate)
> Pack weight: 485 kg
> Realistic pack energy (< 50%): 9 KWhr
> Realistic energy usage: 550 Whr/mi
> Realistic range: 16 mi
>
> TS-LFP160AHA Lithium option (a decrease in weight, increase in range):
>
> 279mm (H) x 71mm (W) x 182mm (L)
> 5.6 kg each, 3.2V each
> (space to replace every LA unit with 3 LFP units)
> Pack (48) = 144V, 23 KWhr
> Pack weight: 269 kg (0.55 today's pack)
> Curb weight ratio factor: 0.85
> Realistic pack energy (70%): 16 KWhr
> Realistic energy usage: 468 Whr/mi (0.85 * 550Whr/mi)
> Realistic range: 34.5 mi
>
> TS-LFP100AHA Lithium option (a little cheaper, lighter, and slight  
> increase
> in range):
>
> 217mm (H) x 68mm (W) x 145mm (L)
> 3.2 kg each, 3.2V each
> (space to replace every LA unit with 3 LFP units)
> Pack (48) = 144V, 14.4 KWhr
> Pack weight: 154 kg (0.32 today's pack)
> Curb weight ratio factor: 0.77
> Realistic pack energy (70%): 10 KWhr
> Realistic energy usage: 423 Whr/mi (0.77 * 550Whr/mi)
> Realistic range: 23.5 mi
>

You can go to 80% DOD if you want with LiFePO4 without sacrificing  
much longevity.

What type of EV do you have that only gets 550 wh/mile?
 

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Thanks Roger!  That is great news -  my estimated range just got longer!
My EV is a 1989 VW Cabriolet.  The body is heavier than a rabbit, but the real reason for 550 Wh/mi is the hilly terrain and stop-go driving that I do on my daily commute.  

Rob
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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Willie McKemie
In reply to this post by Rob Trahms
On Sat, May 02, 2009 at 05:11:34PM -0700, Rob Trahms wrote:
> So my revised numbers are below.  I do draw 550 Whrs in this hilly area, at
> speeds of 40MPH.

On what do you base the 550 whr/m number?  It sure seems excessive to
me, though I have little experience with steep hilly country; our
elevation changes amount to a few hundred feet in several miles with
slopes rarely exceeding 2%.  We are able to recover much of our
potential energy at the tops of hills by avoiding braking while
coasting downhill.

> If there are other lead 'oddities' I should be accounting for, then that is
> just another upside of switching to LFP!

I was referring to Peukert's Law where energy is lost as the current
goes up.  With LFP, there is no such loss.
 
> I am curious about your comment regarding pulling all of the energy out of
> lithium batteries.  Advised?  Or do you prematurely shorten their lives by
> doing so?  I was just looking at this also a little more on the conservative
> side.

Again, I was referring to Peukert's Law.  With LFP, if your available
energy is 17 KWH, then all of that 17 KWH can be applied to motive
power.  I was NOT recommending drawing a LFP pack below 20 or 30% SOC.

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  505 days  3 hours 30 minutes

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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Lee Hart
Willie McKemie wrote:
> I was referring to Peukert's Law where energy is lost as the current
> goes up.  With LFP, there is no such loss.

All batteries have Peukert effects. It's just more severe with lead-acid.

Peukert's equation basically accounts for the fact that the higher the
current, the greater the voltage drop. If you establish a particular
voltage as the cutoff point, then you reach that point sooner at higher
currents.

The reduction in amphours predicted by Peukert's equation amphours
aren't "lost". They are still in the battery; you just can't get them at
high current without the voltage falling below your "dead" voltage
limit. If you reduce the load current, the voltage rises, and you can
sell get them.

>> I am curious about your comment regarding pulling all of the energy out of
>> lithium batteries.  Advised?  Or do you prematurely shorten their lives by
>> doing so?  I was just looking at this also a little more on the conservative
>> side.
>
> Again, I was referring to Peukert's Law.  With LFP, if your available
> energy is 17 KWH, then all of that 17 KWH can be applied to motive
> power.

This is not the case. All batteries have an internal resistance. Under
load, the external voltage sags due to this resistance. This creates
loss inside the battery. It heats the battery, and reduces the power and
energy available to external loads.

The limited life data we have so far on lithium batteries shows a
reduction in life as you discharge them deeper. The exact numbers are
hard to get, because the battery chemistries keep changing, and no one
wants to do life testing and publish their data.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Willie McKemie
On Sun, May 03, 2009 at 11:04:16AM -0400, Lee Hart wrote:
> Willie McKemie wrote:
> > I was referring to Peukert's Law where energy is lost as the current
> > goes up.  With LFP, there is no such loss.
>
> All batteries have Peukert effects. It's just more severe with lead-acid.

Would you be happier with the statement "With LFP, the loss is
insignificant"?  My TBS fuel meter has a Peukert parameter which it
uses to estimate the energy removed based on current.  For LFP, the
parameter is to be set to "1", meaning no Peukert effect.  At that
setting, it does seem to accurately estimate energy remaining in the
pack.  That is, we do not run out of energy unexpectedly.

>
> Peukert's equation basically accounts for the fact that the higher the
> current, the greater the voltage drop. If you establish a particular
> voltage as the cutoff point, then you reach that point sooner at higher
> currents.
>
> The reduction in amphours predicted by Peukert's equation amphours
> aren't "lost". They are still in the battery; you just can't get them at
> high current without the voltage falling below your "dead" voltage
> limit. If you reduce the load current, the voltage rises, and you can
> sell get them.

Obviously my understanding of Peukert is incomplete.  Perhaps you can
add to my education.  My mental model, based on my not exhaustive
readings, is that the Peukert effect is due to internal resistance in
the cells.  You put in X KWH and you get out less than X KWH and the
difference is dissipated as heat within the cells.  If that is the
case, then the energy is indeed "lost" and not recoverable.

> >> I am curious about your comment regarding pulling all of the energy out of
> >> lithium batteries.  Advised?  Or do you prematurely shorten their lives by
> >> doing so?  I was just looking at this also a little more on the conservative
> >> side.
> >
> > Again, I was referring to Peukert's Law.  With LFP, if your available
> > energy is 17 KWH, then all of that 17 KWH can be applied to motive
> > power.
>
> This is not the case. All batteries have an internal resistance. Under
> load, the external voltage sags due to this resistance. This creates
> loss inside the battery. It heats the battery, and reduces the power and
> energy available to external loads.

Perhaps you would agree that the losses due to internal resistance are
negligible in LFPs (at rated draw rates) and highly significant in
lead acid (at draw rates necessary to propel a car)?
 
> The limited life data we have so far on lithium batteries shows a
> reduction in life as you discharge them deeper. The exact numbers are
> hard to get, because the battery chemistries keep changing, and no one
> wants to do life testing and publish their data.

Agreed.  I wonder how best to deal with the situation?  Continue to use
lead acid?  Or try LFPs.  Manufacturer's ratings indicate that a single
set of LFPs might last as long as 5 to 10 sets of lead acid batteries.  
So far, the anecdotal data on LFPs is highly promising.

Here is a bit of anecdotal data: I have a Jet Electra that is over 25
years old.  There are about 12K miles on it.  No telling how many sets
of batteries.  Wayne just rebuilt the motor that suffered being
exposed to an acid mist.  Indeed, the whole car suffers from exposure
to an acid mist.  The Hyundai (LFP) has been in use for just 4 months
and has about 4K miles.  We are at about 100 cycles on the Hyundai.  
That should be about 3% of the rated life.  For lead acid, that 100
cycles would be 10%-20% of rated life.  Each cycle has taken us at
least twice as far as would be possible with lead acid.

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  505 days 23 hours 57 minutes

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Re: Spock - analysis: switching from Lead acid to Lithium batteries

Morgan LaMoore
On Mon, May 4, 2009 at 6:44 AM, Willie McKemie <[hidden email]> wrote:
> Obviously my understanding of Peukert is incomplete.  Perhaps you can
> add to my education.  My mental model, based on my not exhaustive
> readings, is that the Peukert effect is due to internal resistance in
> the cells.  You put in X KWH and you get out less than X KWH and the
> difference is dissipated as heat within the cells.  If that is the
> case, then the energy is indeed "lost" and not recoverable.

Nope, Peukert says that you have an X Ah cell and you get less than X
Ah, and the reason is that the increasing internal resistance means
that you can't draw more of your amp-hours without bringing the
voltage below the cutoff point.

The power dissipated in the internal resistance further reduces your
available energy, but that is in addition to Peukert's, and in lead,
it is generally less significant.

In LiFePO4, the traditional Peukert's effect has little effect; for a
Headway 38120S cell (as tested at www.endless-sphere.com), you get
about 95% of the C/10 capacity at 3C. You only get 82% of the energy,
though, due to voltage sag.

Comparing an Odyssey PC1500 AGM at C/10 to 3C, on the other hand,
gives 62% of the C/10 capacity at 3C and 60% of the energy.

In AGM (and other lead), Peukert's effect will significantly reduce
the amp-hour capacity of the battery, but the voltage sag due to
internal resistance will only slightly further reduce the available
capacity.

In LiFePO4, on the other hand, Peukert's effect will have minimal
effect on capacity, but voltage sag will significantly reduce the
available energy at higher currents.

I took the Odyssey data from Hawker's website:
http://www.odysseybatteries.com/battery/pc1500series.htm

I took the Headway data from DrBass's battery tests:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=7655&start=45

-Morgan LaMoore

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