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Old 06-10-2009, 02:55 PM   #1 (permalink)
electricman
 
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Lead-Acid Batteries Voltage Sag Formulas

Hi everyone, There seems to be a number of people responding to the Electric Car threads, so I wondered if anyone knows of some formulas that can be used to determine - ahead of time - how much the voltage will sag on a Lead Acid Battery, under some specific load or varying load?

While I have a PakTrakr - and a Woodward Enhanced PakTrakr Display - with Data Logging - I have a lot of empirical data, but no formula - maybe someone can look at the data and come up with a formula?

Electricfly - MyElectricfly.com and NoGas96volts

PakTrakr Multi Battery Monitor Battery Pack Monitor and

Thanks for you help, ahead of time! Robert

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Old 06-11-2009, 01:35 AM   #2 (permalink)
PaulH
 
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Where are the data points? I could try to come up with a formula for voltage drop. It would at least be a function of current and temperature, and perhaps current and temperature and state of charge.
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Old 06-13-2009, 01:07 AM   #3 (permalink)
electricman
 
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Data Points

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Originally Posted by MPaulHolmes View Post
Where are the data points? I could try to come up with a formula for voltage drop. It would at least be a function of current and temperature, and perhaps current and temperature and state of charge.
I have the files from the display as it logs them in .csv format - as well as eddited and trimmed data files in .csv or excel spreadsheet formats. They can be quite long - since the paktrakr delivers one data line per second, so an hour would be 3600 lines. Luckily - the actual drive to work testing I am currently doing is just a copuple minutes, and I used to let the logger keep coing for the whole 8 hour shift - but lately started to simply log a few seconds before the actual drive and about 10 - 30 seconds or so after most times, so they are now just little 28kb files or so each trip.

I could make them posted in my electricfly site for access if you like?

Robert
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Old 06-13-2009, 01:38 AM   #4 (permalink)
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ya! Post those buggers!
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Old 10-08-2011, 11:27 AM   #5 (permalink)
electricman
 
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One Weeks Summar Log of the Loads with Electricfly

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Originally Posted by MPaulHolmes View Post
ya! Post those buggers!
Ok - here is a Summary Sheet - in Excel, and a Tabloid Sized (11" x 17") pdf print of the same data.

It is just a set of key highlights, but fishing though a table in Excel with 32,000 lines is no fun, trust me!

True - actually having a Packtracker on a battery, with the woodward display - logging the data, while doing a load test on a Lab Bench would be even more definative, and controllable, but here are some high points, and you can be sure the max current points and minimum voltage points are within a few seconds of each other for the most part.

By the way - Have you checked out EV Fest 2011 yet?

Robert

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