brand new performance stats.

2088 Views 3 Replies 4 Participants Last post by EV_dub, Feb 7, 2011

lou-ace

Discussion Starter · Dec 2, 2010

Ok EV wizards it’s time to educate the ol’ Lou-ace here. “Red Sparky” is officially on the road, that is my 1994 Mazda b2300 truck conversion, 120 volt, AMD 9’ motor, Crown GC225 (6volt) pack, Curtis 1231c charger. I’ve made a few runs now and am trying to figure out my performance. Here are my assumptions, please feel fee (as I know you guys will!!) to check them. According to Bob Brant, a depleted cell measures 1.75 volts and a nominal fully charged cell measures 2.1, therefore my swing, at 60 cells is from 105v to 126 volts. #2 if my pack is 225 amps, than a drop of 1 volt =10.75 amps, with 105v being “empty” and 126v being full. My last run ( on hilly terrain) was 13 miles and after 30” equalization I read 122.3 volts remaining before charging therefore I used 42.8 amps or 5136kwt, using these assumptions, this works out to 395wts/mi. Like I said I’m just starting to calc. my performance but this sounds too good to be true. Of course I will be tracking and trending all of my trips to get more data, but if these numbers hold than my theoretical range is 68 mi. this seems also to be too good to be true. I realize that floodies don’t like to give up their last 20% therefore 225amps really becomes 205 amps useable, and makes the theoretical range 62 miles. Am I doing any of this right ? thanks again. Ps the temp here is only 40F. and my batteries are brand new.

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EVfun

· #2 · Dec 2, 2010

Please don't try to use pack voltage to measure amp hour removed. That is a marginal route to a rough guess.

A lead acid cell reads 1.75 volts under load when it is discharged. Actually, since we don't have a constant load even that isn't really accurate (but a real good target to try and stay above when driving.) A resting lead acid battery at about 10% state of charge will read about 2.0 volts per cell, about 1.95 vpc is please-don't-even-make-it-run-your-dome-light dead. The curve goes off a cliff at that point.

A fully charged lead acid battery reads about 2.14 volts per cell. That is the charged and rested voltage, right off charge it may read 2.25 vpc and work its way down over 24 hours. The fully charged voltage is variable, depending on the alloy metals and the specific gravity. A fully charged (and rested) Optima yellow top used to specced at 2.2 volts per cell.

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GerhardRP

· #3 · Dec 2, 2010

lou-ace said:
Ok EV wizards it’s time to educate the ol’ Lou-ace here. “Red Sparky” is officially on the road, that is my 1994 Mazda b2300 truck conversion, 120 volt, AMD 9’ motor, Crown GC225 (6volt) pack, Curtis 1231c charger. I’ve made a few runs now and am trying to figure out my performance. Here are my assumptions, please feel fee (as I know you guys will!!) to check them. According to Bob Brant, a depleted cell measures 1.75 volts and a nominal fully charged cell measures 2.1, therefore my swing, at 60 cells is from 105v to 126 volts. #2 if my pack is 225 amps, than a drop of 1 volt =10.75 amps, with 105v being “empty” and 126v being full. My last run ( on hilly terrain) was 13 miles and after 30” equalization I read 122.3 volts remaining before charging therefore I used 42.8 amps or 5136kwt, using these assumptions, this works out to 395wts/mi. Like I said I’m just starting to calc. my performance but this sounds too good to be true. Of course I will be tracking and trending all of my trips to get more data, but if these numbers hold than my theoretical range is 68 mi. this seems also to be too good to be true. I realize that floodies don’t like to give up their last 20% therefore 225amps really becomes 205 amps useable, and makes the theoretical range 62 miles. Am I doing any of this right ? thanks again. Ps the temp here is only 40F. and my batteries are brand new.

Hi Lou,
First, congratulations for getting on the road.
A good source for understanding batteries is http://www.batteryfaq.org/. There you can find State-of-Charge vs. voltage and temperature. Your ending voltage of 122.3 at 40F indicates just over a 50% SOC, so your range when driven as you did will be about 25 miles. Remember that this is Peukert effect corrected capacity, so you probably used 50 A-hr of charge.
Gerhard
PS study up a little so you can distinguish Amps and Amp-hr and similarly watts from watt-hours.

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EV_dub

· #4 · Feb 7, 2011

Hi lou-ace

Well done with getting the truck on the road

As Ev-fun metioned, there is a major difference between an OCV (open circuit voltage- without load) and CCV (closed circuit voltage- under load)

A batteries IR (Internal resistance) is equal to the difference between OCV and CCV divided by the load.

The equation is not linear since a batteries IR always becomes greater as the battery becomes discharged, due to the lowering of the CCV. The OCV can remain constant whilst the CCV drops therefore the difference between the two increases, hence IR increases.

The OCV will not drop significantly untill roughly 75%dod.

To make a accurate calculation you need to consider discharge time as well as other things such as temp etc..

I couldnt find much info on the crown batteries but i expect they are simular to the trojan t-105s so have made calculations based on this.

So lets assume you discharge the batteries in 1hr. Using the Batteries Reserve capacity we can work out the 1hr rating of the batteries is around 127ah the peukerts exponent= 1.23

127*120v= 15240wh pack total usable energy in 1hr

say you average 40mph in the 1hr duration which means you would have travel 40miles.

15240wh/40miles = 381wh per mile or 3.1ah per mile. I think figure would be more for a truck like yours though.

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brand new performance stats.

lou-ace

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