# [EVDL] Measuring Pack Capacity



## EVDL List (Jul 27, 2007)

One of the easier ways might be to just pick a route that you can drive under
repeatable conditions, and that discharges your pack to about 30% SOC or so. 
Do this maybe once per quarter to twice per year to accumulate data. You
need controlled conditions, so charge your pack to the same voltage each
time, minimize stop lights and other variables such as wind, drive the same
speed each time, etc. Also do it the same time of the year at the same
ambient and pack temperatures. At the end of the drive measure cell
voltages. If pack capacity decreases over time, you should see these
voltages showing a clear drift to lower values over the years with some
variability superimposed on it. Would be good to measure cell voltages at
the end of charge, before the drive, too, to ensure they are charging to
about the same voltages each test.



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## EVDL List (Jul 27, 2007)

Option 1: You can get a meter from EVTV or elsewhere which will charge and
then drain a cell. You get to choose the high and low voltages. It will
tell you the capacity of the cell in amp hours. Once you find your weakest
cell you can measure it's capacity periodically.

Option 2: (assuming you have some sort of low voltage cell
protection/alarm/controller cutback) Charge the car, get in and drive
normal to the nearest highway and then drive a set speed until the car
cries weeee. Record the miles. Repeat each year.

Option 1 is a bit more scientific and accurate but the meter costs money.




> Mike Nickerson <[email protected]>wrote:
> 
> > I have a question based off the current discussion about how much capacity
> > lithium cells lose and how fast.
> ...


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## EVDL List (Jul 27, 2007)

Hello Mike,

When I pick up my first EV back in April of 76, it was suggested to make a 
EV Log Book that you record your daily travels. So that's what I did and 
place it on a table next to the EV. Lay it out in a spreadsheet design 
which contains:

Date - Miles - AH - SOC - Bat.Volts - Charge Cycles - Charge Time


Other Data: Ambient Temperature
Battery Temperature
Controller Temperature
Motor Temperature

Highest battery ampere
Highest motor ampere
Highest motor rpm

Battery Data: Type
Weight
No of Cells
Maximum Charge Voltage
Minimum Discharge Voltage

Road Conditions: Grades
Type of surface - rough to smooth
Wet
Ice
Depth of Snow
Wind

Mechanical Changes: Motor type
Transmission type
Transmission gear ratios
Overall gear ratios
Type of wheels
Type of tires
Weight changes

I now have been recording this data since April 76 and just now about 10 
minutes ago recorded the Date - Miles travel - AH use - Remaining SOC% - 
Battery Volts at rest - Charge Cycles - Charging Time for driving up and 
down a hill for 2.2 miles that I have been doing for more than 20 years for 
a EV with a 180V battery pack.

12 years ago, the AH/Mile started out at 2.6 AH and in 8.6 years of running, 
the AH/Mile increase to 3.9 AH with a longer charge time which I made a new 
battery pack change.

My new pack also started out at about 4 AH/mile and after three years it is 
now up to about 4.3 AH/mile before I did some weight reduction and 
mechanical changes.

By using a EV log data, you can calculated the estimate range and life of a 
battery pack. Mechanical changes can also improve the life and range of a 
battery pack. I decrease the weight of the wheels and tires by 50% per wheel 
and increase the overall gear ratio which increase my range by 25%!!! which 
resulted in a 2.9 AH/mile about 30 minutes ago.

Roland









On Fri, Jul 27, 2012 at 1:11 AM, Mike Nickerson 


> <[email protected]>wrote:
> 
> I have a question based off the current discussion about how much capacity
> lithium cells lose and how fast.
> ...


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## EVDL List (Jul 27, 2007)

> Mike Nickerson wrote:
> 
> > My question:
> >
> ...


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## EVDL List (Jul 27, 2007)

> tomw wrote:
> > One of the easier ways might be to just pick a route that you can drive under
> > repeatable conditions, and that discharges your pack to about 30% SOC or so.
> > Do this maybe once per quarter to twice per year to accumulate data. You
> ...


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## EVDL List (Jul 27, 2007)

For bench-testing the capacity of individual 12v batteries, I use a "Watt's 
Up" meter. These sell in the $50-60 range. 

They can handle up to 60 volts. The manufacturer says they can measure up 
to 100a, but since the supplied source and drain pigtails are only #14 wire, 
I'm skeptical. I don't exceed 20 amps.

At any rate, I connect the meter between a fully charged battery and a 12v 
inverter. The inverter powers a 250w incandescent lamp and an old plug-in 
alarm clock. I set the clock for 12:00:00 and let 'er rip. The inverter 
shuts down when the battery falls to 10.5 volts - essentially flat - and the 
clock tells me how long it was able to supply 250 watts. From that I can 
calculate the battery's capacity in watt-hours. 

The only flaw is that it's entirely manual. I think it's Lee who uses an 
old Rudman Regulator to automate a capacity testing jig that repeately 
cycles the battery and logs the results.

For 24v lithium batteries, I use a similar rig with a 24v inverter instead. 
The inverter shutdown is ~21v, but the 24v LiFePO4 batteries I'm tinkering 
with have a BMS with an undervoltage shutdown.

David Roden - Akron, Ohio, USA
EVDL Administrator

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## EVDL List (Jul 27, 2007)

"It sounds like you are making the argument that SOC can be divined from 
cell voltage?"
Yes I am. If Mike plans to track them for enough years that he sees a
10-20% change in capacity, then the discharge to 30% will gradually turn
into discharge to 22% SOC (10% capacity loss) or 12.5% SOC (20% capacity
loss), and you will definitely see significant changes in cell voltages over
this range of SOC.



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## EVDL List (Jul 27, 2007)

I like toms approach, but to keep things predictable between tests, why not
find someone with a dyno ?


> "tomw" <[email protected]> wrote:
> 
> > One of the easier ways might be to just pick a route that you can drive
> > under
> ...


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## EVDL List (Jul 27, 2007)

Mike Nickerson wrote
> 
> I could theoretically measure pack capacity... what should be the
> procedure?
> 

Your digital BMS will that for you. You do have a BMS, right?

An analog BMS (such as the MiniBMS, EV Power, Pacific EV) is nice and easy.
But a digital BMS costs only marginally more yet it has all sort of
additional features, such as measuring your pack's effective capacity on an
ongoing basis.

The Elektromotus, Lithiumate Pro, Lithiumate Lite, Orion BMS, Lithium
Balance or REAP BMSs will simply show you your pack's effective capacity on
their Graphics User Interface application.

The Anhui, Claiton power, Electric Blue, EVPST, GWL Power BMSs will show it
to you on the included display.

The REC, Rozwiazania and Tritium BMSs will report it on a data bus.

Source: http://liionbms.com/php/bms-selector.php



-----
Davide Andrea
Elithion 
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## EVDL List (Jul 27, 2007)

Hi Davide,

I do have a BMS. The car had MiniBMS modules installed when I bought it.
They are working well enough that I don't see the need to replace them.

I see how the digital BMS can do a fine job of used energy, miles, Ah, kWh,
etc. All that can certainly give great data on the amount of pack capacity
that has been used on a particular drive. However, I don't see how they
could know total pack capacity (used capacity plus remaining capacity)
unless they see the pack discharge nearly completely. Would that be your
proposal, to drive the vehicle until the pack is nearly discharged?

Mike

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Elithion
> Sent: Sunday, July 29, 2012 3:50 PM
> To: [email protected]
> Subject: Re: [EVDL] Measuring Pack Capacity
> 
> 
> Mike Nickerson wrote
> >
> > I could theoretically measure pack capacity... what should be the
> > procedure?
> >
> 
> Your digital BMS will that for you. You do have a BMS, right?
> 
> An analog BMS (such as the MiniBMS, EV Power, Pacific EV) is nice and
easy.
> But a digital BMS costs only marginally more yet it has all sort of
additional
> features, such as measuring your pack's effective capacity on an ongoing
> basis.
> 
> The Elektromotus, Lithiumate Pro, Lithiumate Lite, Orion BMS, Lithium
> Balance or REAP BMSs will simply show you your pack's effective capacity
on
> their Graphics User Interface application.
> 
> The Anhui, Claiton power, Electric Blue, EVPST, GWL Power BMSs will show
it
> to you on the included display.
> 
> The REC, Rozwiazania and Tritium BMSs will report it on a data bus.
> 
> Source: http://liionbms.com/php/bms-selector.php
> 
> 
> 
> -----
> Davide Andrea
> Elithion
> --
> View this message in context: http://electric-vehicle-discussion-
> list.413529.n4.nabble.com/Measuring-Pack-Capacity-
> tp4656800p4656880.html
> Sent from the Electric Vehicle Discussion List mailing list archive at
> Nabble.com.
> 
> _______________________________________________
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## EVDL List (Jul 27, 2007)

> Mike Nickerson <[email protected]> wrote:
> > Hi Davide,
> >
> > I do have a BMS. The car had MiniBMS modules installed when I bought it.
> ...


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## EVDL List (Jul 27, 2007)

Evan Tuer wrote
> 
> It's not actually a BMS that you need to measure capacity accurately,
> but an energy meter, and it just happens that more sophisticated BMSs
> include one "for free".
> 

True.

Here is a stand-alone meter that Justin sells:
http://www.evolveelectrics.com/E-Xpert%20Pro.html




-----
Davide Andrea
Elithion 
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## EVDL List (Jul 27, 2007)

> Elithion <[email protected]> wrote:
> >
> > Evan Tuer wrote
> >>
> ...


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## EVDL List (Jul 27, 2007)

>> Here is a stand-alone meter that Justin sells:
>> http://www.evolveelectrics.com/E-Xpert%20Pro.html



> Evan Tuer wrote:
> > That looks pretty neat!
> 
> This is a remarked version of the classic E-meter / Link-10 / Link-Lite
> ...


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## EVDL List (Jul 27, 2007)

> Lee Hart <[email protected]> wrote:
> >>> Here is a stand-alone meter that Justin sells:
> >>> http://www.evolveelectrics.com/E-Xpert%20Pro.html
> >
> ...


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## EVDL List (Jul 27, 2007)

Evan,

Did some quick Googling.
Look at the bottom of this page:
http://thesolarstore.com/monitors-metering-c-49.html

Indeed, this is not like the original Link-10 (E-meter)
with red LED digits, as can be seen for example on the following page:
http://www.righthandeng.com/hm_rxbgo.htm

And btw, why should you pay $100 more for a resistor and a shifted
decimal point? 
But that is a whole 'nother story.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Evan Tuer
Sent: Tuesday, August 07, 2012 12:58 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Measuring Pack Capacity

On Mon, Aug 6, 2012 at 10:23 PM, Lee Hart <[email protected]>


> wrote:
> >>> Here is a stand-alone meter that Justin sells:
> >>> http://www.evolveelectrics.com/E-Xpert%20Pro.html
> >
> ...


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## EVDL List (Jul 27, 2007)

>>>> http://www.evolveelectrics.com/E-Xpert%20Pro.html



> Lee Hart wrote:
> >> This is a remarked version of the classic E-meter / Link-10 / Link-Lite
> >> / Link-Pro / XBM series of meters. For the price, and given the long
> >> evolution, it *should* work pretty good.
> ...


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## EVDL List (Jul 27, 2007)

> On 7 Aug 2012 at 10:44, Lee Hart wrote:
> 
> > Throughout, the actual manufacturer (first Cruising Equipment, then
> > Heart Interface, then Xantrex) has sold relabelled versions with other
> ...


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