# [EVDL] Battery SOC/Discharge question



## EVDL List (Jul 27, 2007)

Having just finished my EV, wait, is it ever REALLY finished? I wanted some insight into what voltage I should be running my 144V pack down to before charging? As I mentioned in another post I am using a PakTrakr and the fuel gauge isn't very accurate at the moment. At least I don't trust it.

What I do have is a pack voltage reading that seems pretty accurate. What voltage, not sag voltage, should I be running my pack down to indicate 80DOD? I just don't want to damage my batteries thinking that I should be able to get more range that I'm really capable of.



Thanks!
Ben
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## EVDL List (Jul 27, 2007)

I hope this spacing works. I copied it from my spreadsheet here:
http://spreadsheets.google.com/ccc?key=pRk3hQKpzKD_bgtNSWZy-KA&hl=en

SOC %	DOD %	V per cell	V per 144V
equalize 2.5	180
charge 2.4	172.8
float 2.25	162
100	0	2.116	152.35
90	10	2.083	149.98
80	20	2.07	149.04
70	30	2.053	147.82
60	40	2.033	146.38
50	50	2.01	144.72
40	60	1.983	142.78
30	70	1.958	140.98
20	80	1.93	138.96
10	90	1.885	135.72
0	100	1.75	126

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## EVDL List (Jul 27, 2007)

That's a nice little cheat sheet! Gonna print it out to take in the car with me.

Ben

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Jon Glauser
Sent: Thursday, October 30, 2008 2:23 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Battery SOC/Discharge question

I hope this spacing works. I copied it from my spreadsheet here:
http://spreadsheets.google.com/ccc?key=pRk3hQKpzKD_bgtNSWZy-KA&hl=en

SOC % DOD % V per cell V per 144V
equalize 2.5 180
charge 2.4 172.8
float 2.25 162
100 0 2.116 152.35
90 10 2.083 149.98
80 20 2.07 149.04
70 30 2.053 147.82
60 40 2.033 146.38
50 50 2.01 144.72
40 60 1.983 142.78
30 70 1.958 140.98
20 80 1.93 138.96
10 90 1.885 135.72
0 100 1.75 126

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## EVDL List (Jul 27, 2007)

Hi Ben,

Voltage is a bad indicator of battery SOC, it is much better to
measure amps over time (Ah).
There are dedicated meters which do that.
You can guesstimate how far you can drive to run your pack
down 20%, so you still have 80% SoC.
You need either to measure how much the controller draws from
the batteries or give us a vehicle type, then we can give a
rough figure how much it should consume if it is running well
(wheels aligned, brakes not dragging, drivetrain in good shape).
One simple test is: at level ground you should be able to push
your vehicle by hand a couple feet with one hand (even better is
if it can be done with only a few fingers) without leaning into
the pushing. If you stop pushing and the car drives back a short 
distance then your alignment is not optimal.
Push forward and backward to cancel out a slope.

Then, tell us how much Ah batteries (or which type) and how
many (which pack voltage) so we can figure total energy (kWh)
of your pack.
Try always to stay well below 50% of that (theoretical) max
energy level to avoid premature death of batteries run down
to zero SoC.

Regarding charging: typically as often as practical, typically
every day that you have driven the car unless it was less
than a few miles only, then you can wait till a next time.

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040) 23117400x109 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Willis, Ben
Sent: Thursday, October 30, 2008 11:39 PM
To: 'Electric Vehicle Discussion List'
Subject: [EVDL] Battery SOC/Discharge question

Having just finished my EV, wait, is it ever REALLY finished? I wanted
some insight into what voltage I should be running my 144V pack down to
before charging? As I mentioned in another post I am using a PakTrakr
and the fuel gauge isn't very accurate at the moment. At least I don't
trust it.

What I do have is a pack voltage reading that seems pretty accurate.
What voltage, not sag voltage, should I be running my pack down to
indicate 80DOD? I just don't want to damage my batteries thinking that I
should be able to get more range that I'm really capable of.



Thanks!
Ben
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## EVDL List (Jul 27, 2007)

Warning!

You received a list without specification under which load
and for what battery type this is valid.
Different situations give *very* different results, exactly
the problem the PakTrakr is suffering from!

The list you have goes down to 1.75V per cell.
This is a totally dead cell if this voltage is reached
under no-load condition. But when running not too much load,
like 1/4C (for example 25A on a 100Ah battery) then it is
a good level to stay above to avoid draining the battery too much.

Also, levels change with temperature.
At low temp it will be no problem to reach 180V equalization.
But leave this voltage on for a while or charge while it is
warm and you will not be able to reach this voltage.
All battery voltages are temperature dependent, so the
cheat sheet should say not only under which load and
for which type of batteries (golfcart flooded lead acid
for example) but also at which (battery) temperature.

So, use with care.

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040) 23117400x109 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Willis, Ben
Sent: Friday, October 31, 2008 12:02 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Battery SOC/Discharge question

That's a nice little cheat sheet! Gonna print it out to take in the car
with me.

Ben

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Jon Glauser
Sent: Thursday, October 30, 2008 2:23 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Battery SOC/Discharge question

I hope this spacing works. I copied it from my spreadsheet here:
http://spreadsheets.google.com/ccc?key=pRk3hQKpzKD_bgtNSWZy-KA&hl=en

SOC % DOD % V per cell V per 144V
equalize 2.5 180
charge 2.4 172.8
float 2.25 162
100 0 2.116 152.35
90 10 2.083 149.98
80 20 2.07 149.04
70 30 2.053 147.82
60 40 2.033 146.38
50 50 2.01 144.72
40 60 1.983 142.78
30 70 1.958 140.98
20 80 1.93 138.96
10 90 1.885 135.72
0 100 1.75 126

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## EVDL List (Jul 27, 2007)

I agree.. I should have put all those caveats in there with it, but I
made the assumption that you have flooded golf cart batteries (if you
had expensive batteries you would buy an Ah counter to help protect
them), and you just have a volt meter in your car. The original
spreadsheet has a temperature adjustment built in, I just sent you
*typical* voltages at 80F. The voltages can vary by manufacturer.

I've been watching kWhs in my car, always keeping the voltage above
1.75 V/cell under load. Speaking of that, I'll start another thread
with a question I have.

-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555

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## EVDL List (Jul 27, 2007)

I have 12 Trojan T-1275 batteries.


________________________________________
From: [email protected] [[email protected]] On Behalf Of Cor van de Water [[email protected]]
Sent: Thursday, October 30, 2008 2:41 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Battery SOC/Discharge question

Warning!

You received a list without specification under which load
and for what battery type this is valid.
Different situations give *very* different results, exactly
the problem the PakTrakr is suffering from!

The list you have goes down to 1.75V per cell.
This is a totally dead cell if this voltage is reached
under no-load condition. But when running not too much load,
like 1/4C (for example 25A on a 100Ah battery) then it is
a good level to stay above to avoid draining the battery too much.

Also, levels change with temperature.
At low temp it will be no problem to reach 180V equalization.
But leave this voltage on for a while or charge while it is
warm and you will not be able to reach this voltage.
All battery voltages are temperature dependent, so the
cheat sheet should say not only under which load and
for which type of batteries (golfcart flooded lead acid
for example) but also at which (battery) temperature.

So, use with care.

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040) 23117400x109 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Willis, Ben
Sent: Friday, October 31, 2008 12:02 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Battery SOC/Discharge question

That's a nice little cheat sheet! Gonna print it out to take in the car
with me.

Ben

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Jon Glauser
Sent: Thursday, October 30, 2008 2:23 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Battery SOC/Discharge question

I hope this spacing works. I copied it from my spreadsheet here:
http://spreadsheets.google.com/ccc?key=pRk3hQKpzKD_bgtNSWZy-KA&hl=en

SOC % DOD % V per cell V per 144V
equalize 2.5 180
charge 2.4 172.8
float 2.25 162
100 0 2.116 152.35
90 10 2.083 149.98
80 20 2.07 149.04
70 30 2.053 147.82
60 40 2.033 146.38
50 50 2.01 144.72
40 60 1.983 142.78
30 70 1.958 140.98
20 80 1.93 138.96
10 90 1.885 135.72
0 100 1.75 126

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## EVDL List (Jul 27, 2007)

I am still wondering about Ben's original question. Which I believe 
was about discharging the battery. If I recall correctly from 
"Convert it" the procedure is to check the pack voltage without any 
load. For example at a stop of while coasting.

Using this method, (because one currently only has a volt meter and 
an ammeter) what is the "resting" do not go below voltage (per cell 
of a floodie) to avoid battricide.



> Joe Downing wrote:
> > Trojan explains in detail how to adjust charging voltage to
> > accommodate change in temp from 80 degrees. You can also search the
> > EVDL archives since this has been covered several times.
> ...


----------



## EVDL List (Jul 27, 2007)

Ben and All,
As I've said before, I got 20,000 miles out of a 144 volt pack of T-145's, and one
of the things I did to achieve this mileage, is to limit the voltage to 128 volts or
higher on my analog volt meter (under load). 
With a 144V pack, and at 1.75 volts per cell (VPC) as the minimum voltage, 
that would be 126V (72 cells x 1.75), but I add a couple of volts for meter inaccuracy,
and because you always have a runt in the litter!
Suck Amps,
BB

>Date: Thu, 30 Oct 2008 14:09:27 -0400
>From: "Willis, Ben"
>
>Having just finished my EV, wait, is it ever REALLY finished? I wanted some insight into what voltage I should be running my 144V pack down to before charging? As I mentioned in another post I am using a PakTrakr and the fuel gauge isn't very accurate at the moment. At least I don't trust it.
>
>What I do have is a pack voltage reading that seems pretty accurate. What voltage, not sag voltage, should I be running my pack down to indicate 80DOD? I just don't want to damage my batteries thinking that I should be able to get more range that I'm really capable of.

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## EVDL List (Jul 27, 2007)

Thanks, That is very helpful.

You say "one of the things" , any other items that are no brainers 
from the EV veteran point of view.

John


On Oct 30, 2008, at 9:04 PM, Dave (Battery Boy) Hawkins wrote:

> Ben and All,
> As I've said before, I got 20,000 miles out of a 144 volt pack of 
> T-145's, and one
> of the things I did to achieve this mileage, is to limit the 
> voltage to 128 volts or
> higher on my analog volt meter (under load).
> With a 144V pack, and at 1.75 volts per cell (VPC) as the minimum 
> voltage,
> that would be 126V (72 cells x 1.75), but I add a couple of volts 
> for meter inaccuracy,
> and because you always have a runt in the litter!
> Suck Amps,
> BB
>
>> Date: Thu, 30 Oct 2008 14:09:27 -0400
>> From: "Willis, Ben"
>>
>> Having just finished my EV, wait, is it ever REALLY finished? I 
>> wanted some insight into what voltage I should be running my 144V 
>> pack down to before charging? As I mentioned in another post I am 
>> using a PakTrakr and the fuel gauge isn't very accurate at the 
>> moment. At least I don't trust it.
>>
>> What I do have is a pack voltage reading that seems pretty 
>> accurate. What voltage, not sag voltage, should I be running my 
>> pack down to indicate 80DOD? I just don't want to damage my 
>> batteries thinking that I should be able to get more range that 
>> I'm really capable of.
>
> _______________________________________________
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> Usage guidelines: http://evdl.org/help/index.html#conv
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> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>

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## EVDL List (Jul 27, 2007)

Another thing that might possibly explain why you get such long range from a
pack is that you don't require a long range from your pack. I don't know
your specific needs, so I'm just throwing that out there, but let me
explain.

Let's say we both drive the same conversion; an S-10 with 12kwh pack, same
motor, same controller, etc.

To make the math easy let's say the pack is good for 500 cycles at 100% DoD
to 80%, and 1000 cycles at 50% DoD.

Let's say our trucks both average 500wh/mile.
My daily commute is 20mi round trip no charging at work, so I absolutely
require at least 10kwh's in my pack. 
Your daily commute is 15mi round trip no charging at work, so you absolutely
require at least 7.5kwh's in my pack.

After 500 cycles I will have driven 10,000 miles, and you will have driven
7500 miles. My pack is now degraded to 9.6kwh capacity and is dead as far as
I'm concerned. However your pack is still going strong for your needs, you
have used slightly more than half of it. You will be able to get close to
15000 miles from your pack, you could even get another "WAG" 5000 miles from
my *dead* pack.

I am not trying to say that what you have written is not good advice, indeed
quite the opposite. In my above fiction, we would both have to take the
measures that you outline below in order to meet our goals. I'm just saying
that there's more to the story than proper care and feeding of your
batteries...having the proper size pack is really important. Something the
newbies need to understand. We don't want guys to throw in 4 12 volt
batteries, drive 'em til they're dead and then wonder why they only last a
month.


Stay Charged!
Hump



Dave (Battery Boy) Hawkins wrote:
> 
> Ben and All,
> As I've said before, I got 20,000 miles out of a 144 volt pack of T-145's,
> and one
> of the things I did to achieve this mileage, is to limit the voltage to
> 128 volts or
> higher on my analog volt meter (under load). 
> With a 144V pack, and at 1.75 volts per cell (VPC) as the minimum voltage, 
> that would be 126V (72 cells x 1.75), but I add a couple of volts for
> meter inaccuracy,
> and because you always have a runt in the litter!
> Suck Amps,
> BB
> 
>>

-- 
View this message in context: http://www.nabble.com/Battery-SOC-Discharge-question-tp20252506p20270111.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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## EVDL List (Jul 27, 2007)

> On 31 Oct 2008 at 10:00, Tim Humphrey wrote:
> 
> > I'm just saying that there's more to the story than proper care and
> > feeding of your batteries...having the proper size pack is really
> ...


----------



## EVDL List (Jul 27, 2007)

> Tim Humphrey wrote:
> > Another thing that might possibly explain why you get such long range from a
> > pack is that you don't require a long range from your pack. I don't know
> > your specific needs, so I'm just throwing that out there, but let me
> ...


----------



## EVDL List (Jul 27, 2007)

Dave,
Do you live in an area with no hills? Or do you go very few miles on a
charge? Otherwise, I find it hard to believe you can drive a 144v
vehicle without going under 126v under load. (Let alone 128 to be
safe!)

On Thu, Oct 30, 2008 at 9:04 PM, Dave (Battery Boy) Hawkins


> <[email protected]> wrote:
> > Ben and All,
> > As I've said before, I got 20,000 miles out of a 144 volt pack of T-145's, and one
> > of the things I did to achieve this mileage, is to limit the voltage to 128 volts or
> ...


----------



## EVDL List (Jul 27, 2007)

> On 31 Oct 2008 at 15:38, Robert MacDowell wrote:
> 
> > My view is batteries for a homebrew EV'er should be bulletproof and
> > idiot-proof.
> ...


----------



## EVDL List (Jul 27, 2007)

Storm (and All),
Yes we have hills, and leaving my little town of Lyons, I would pull 
big hills for the first five miles on US36 on the way to The Peoples 
Republic of Boulder. Also, I once drove West up US36 to Estes Park,
which I think I have posted about. 
Anyway, during that 20,000 miles, I could do 60 miles on a charge 
along the Front Range, but keep in mind that the T-145 is the most 
robust of the 6V golf car battery, and doesn't sag like the T-105 
and T-125, and don't even get me started on the 8V batteries,
which should not be used in a heavy vehicle, if at all!
Suck Amps,
BB

-----Original Message-----
>From: storm connors 
>Sent: Oct 31, 2008 5:56 PM
>
>Dave,
>Do you live in an area with no hills? Or do you go very few miles on a
>charge? Otherwise, I find it hard to believe you can drive a 144v
>vehicle without going under 126v under load. (Let alone 128 to be
>safe!)
>
>On Thu, Oct 30, 2008 at 9:04 PM, Dave (Battery Boy) Hawkins


> >wrote:
> >> Ben and All,
> >> As I've said before, I got 20,000 miles out of a 144 volt pack of T-145's, and one
> >> of the things I did to achieve this mileage, is to limit the voltage to 128 volts or
> ...


----------



## EVDL List (Jul 27, 2007)

Dave,
I think this is a private response - no need to fill everybody's inboxes.
I moved back to PA in '93, till then I lived in CSPGS, the Black Forest right near the AFB. My Conference office was in Denver - managed two conference centers - one in the Forest, one near Breckinridge.
Bought a few horses from an outfitter in Estes Park.
Anyway, reading your "travelogue", made me a bit reminiscent.
Ran those roads a LOT, traveled @ 50K a year, all along the front range, up into Wyoming, over to Casper, then down unto Utah. And 3/4 of my travel was by air.
Now I'm in the mountains of Northeast PA.
Don't need anything, just thought I'd say hi. I used to ask people where they were from - I typically found just a couple dozen a year who were actually born in CO. (I was - in Aurora at Fits. Army Hosp. - Dad was Air Force til he retired)
Bob
evalbum.com/2004



----- Original Message -----
From: "Dave (Battery Boy) Hawkins" <[email protected]>
To: [email protected]
Sent: Saturday, November 1, 2008 3:12:28 PM GMT -05:00 US/Canada Eastern
Subject: Re: [EVDL] Battery SOC/Discharge question

Storm (and All),
Yes we have hills, and leaving my little town of Lyons, I would pull 
big hills for the first five miles on US36 on the way to The Peoples 
Republic of Boulder. Also, I once drove West up US36 to Estes Park,
which I think I have posted about. 
Anyway, during that 20,000 miles, I could do 60 miles on a charge 
along the Front Range, but keep in mind that the T-145 is the most 
robust of the 6V golf car battery, and doesn't sag like the T-105 
and T-125, and don't even get me started on the 8V batteries,
which should not be used in a heavy vehicle, if at all!
Suck Amps,
BB

-----Original Message-----
>From: storm connors 
>Sent: Oct 31, 2008 5:56 PM
>
>Dave,
>Do you live in an area with no hills? Or do you go very few miles on a
>charge? Otherwise, I find it hard to believe you can drive a 144v
>vehicle without going under 126v under load. (Let alone 128 to be
>safe!)
>
>On Thu, Oct 30, 2008 at 9:04 PM, Dave (Battery Boy) Hawkins


> >wrote:
> >> Ben and All,
> >> As I've said before, I got 20,000 miles out of a 144 volt pack of T-145's, and one
> >> of the things I did to achieve this mileage, is to limit the voltage to 128 volts or
> ...


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## EVDL List (Jul 27, 2007)

Hi Jon and everyone,
I use a similiar spreadsheet, so someone please correct me if I am wrong,
but according to everything I have seen daily charge voltage per cell is
suppose to be 2.47 and equalizing is 2.6 volts per cell. I am pretty sure
we are talking about flooded cells here.
Cheers,
Paul





> Jon Glauser-2 wrote:
> >
> > I hope this spacing works. I copied it from my spreadsheet here:
> > http://spreadsheets.google.com/ccc?key=pRk3hQKpzKD_bgtNSWZy-KA&hl=en
> ...


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## EVDL List (Jul 27, 2007)

I think it depends on manufacturer (some recommend a bit higher than others)
and also on the duration of the charge and equalization, and your tolerance
for water use......

I vary the charge voltage a bit depending on whether the charge is a 2 hour
absorption then dropping to float, or whether it stays at charge voltage all
day (i.e. whether you have a two stage, three stage, four stage, or bad-boy
charger......)



> Paul Kirchman <[email protected]> wrote:
> 
> >
> > Hi Jon and everyone,
> ...


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## EVDL List (Jul 27, 2007)

Hump and All,
Without looking at my battery log, I'm thinking that on average, most of my 
trips were around 50% DOD, but the 20,000 mile mark was when the pack dropped
to 80% of it's new range, which I think is a standard number. Keep in mind that
with the high cost of lead, I've continued to use this pack well past that 
20,000 mile mark, but I'm only driving like three to four miles now!
Suck Amps,
BB

>Date: Fri, 31 Oct 2008 10:00:52 -0700 (PDT)
>From: Tim Humphrey 
>
>Another thing that might possibly explain why you get such long range from a
>pack is that you don't require a long range from your pack. I don't know
>your specific needs, so I'm just throwing that out there, but let me
>explain.
>
>Let's say we both drive the same conversion; an S-10 with 12kwh pack, same
>motor, same controller, etc.
>
>To make the math easy let's say the pack is good for 500 cycles at 100% DoD
>to 80%, and 1000 cycles at 50% DoD.
>
>Let's say our trucks both average 500wh/mile.
>My daily commute is 20mi round trip no charging at work, so I absolutely
>require at least 10kwh's in my pack. 
>Your daily commute is 15mi round trip no charging at work, so you absolutely
>require at least 7.5kwh's in my pack.
>
>After 500 cycles I will have driven 10,000 miles, and you will have driven
>7500 miles. My pack is now degraded to 9.6kwh capacity and is dead as far as
>I'm concerned. However your pack is still going strong for your needs, you
>have used slightly more than half of it. You will be able to get close to
>15000 miles from your pack, you could even get another "WAG" 5000 miles from
>my *dead* pack.
>
>I am not trying to say that what you have written is not good advice, indeed
>quite the opposite. In my above fiction, we would both have to take the
>measures that you outline below in order to meet our goals. I'm just saying
>that there's more to the story than proper care and feeding of your
>batteries...having the proper size pack is really important. Something the
>newbies need to understand. We don't want guys to throw in 4 12 volt
>batteries, drive 'em til they're dead and then wonder why they only last a
>month.
>
>
>Stay Charged!
>Hump
>
>
>
>Dave (Battery Boy) Hawkins wrote:
>> 
>> Ben and All,
>> As I've said before, I got 20,000 miles out of a 144 volt pack of T-145's,
>> and one
>> of the things I did to achieve this mileage, is to limit the voltage to
>> 128 volts or
>> higher on my analog volt meter (under load). 
>> With a 144V pack, and at 1.75 volts per cell (VPC) as the minimum voltage, 
>> that would be 126V (72 cells x 1.75), but I add a couple of volts for
>> meter inaccuracy,
>> and because you always have a runt in the litter!
>> Suck Amps,
>> BB

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