Lead-Acid Batteries Voltage Sag Formulas

[electricman]

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

[MPaulHolmes]

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.

[electricman]

Originally Posted by MPaulHolmes

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

[MPaulHolmes]

ya! Post those buggers!

[electricman]

Originally Posted by MPaulHolmes

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