Power in a battery

Patman3 · January 2008

I searched the forums but maybe not good enough. I just want to calculate the 'KwH' in a battery. Do I just multiply the nominal voltage by the amp hour rating? Say a T105 or US-145, 6V, 220 amp hour 6*220=1.3KwH? Of course that's over 20 hours. I'm using my EV for maybe an hour, drawing 100 amps it will be dead after that 1 hour so is the power then 6V*100amp=600Watt? Do I have Peukurt to blame for this? I use 400 watts/mile so I want to know how far I can theoretically go in miles. I have 20 batteries, 600W each, 12Kwh pack size? I can only go 30 miles?

niel · January 2008

Re: Power in a battery

yes, it pretty much works the same as the current ratings in amphours, but you multiply it by the battery voltage for watthours. if at say a 20hr rate you can figure the average wh by dividing 20hrs from the product of the 20hr ah rating x the voltage.

crewzer · January 2008

Re: Power in a battery

Patman3,

You’re on the right track, but we need to address a few issues.

A battery’s energy content is pretty much as you suggest: 6 V x 220 Ah = 1.32 kWh, based on the “20 hour” rate and 77 F ambient temperature. However, a good rule of thumb is to not consume more than 50% of a battery’s energy, although an occasional 80% discharge appears to be OK with Trojan. So, the useable amount of energy is in the 660 Wh to 1.056 kWh range.

The Peukert Exponent for the T-105 is ~1.24. Based on Trojan specs, I estimate the 100A discharge period to be ~1.34 Hours, for a total capacity of ~804 Wh. 80% of that is ~643 Wh.

However, the working capacity of your battery bank will also be affected by the series/parallel configuration of your 20 batteries. Are you operating “2 x 10” at 12 V x 2,200 Ah, or “4 x 5” at 24 V x 1,100 Ah, or what?

For example, it's one thing to pull 100 A from one battery, but it's another to pull 100 A from four batteries in parallel, which results in 25 A / battery. Trojan rates the 25 A discharge period of the T-105 at 447 minutes, for a capacity of 25 A x 6 V x 447 minutes/60 mins/hr = 1.117 kWh. 80% of that is 894 Wh. :cool:

Let us know about the battery configuration, and we’ll be able to complete this exercise.

HTH,
Jim / crewzer

References: http://www.geocities.com/CapeCanaveral/Lab/8679/battery.html and http://www.trojanbattery.com/Products/ProductSpec.aspx?Name=T-105

Solar Guppy · January 2008

Re: Power in a battery

The S-10 EV is 120V I think, so its a series string

30-40 miles is typical for LeadAcid in the S-10 EV, the Nickle batterys do about 50-60

Patman3 · January 2008

Re: Power in a battery

I love this forum, thanks you guys! Yes, its all 20 in series. I often pull 250 amps going uphill, but 100 amps is faily normal. I'm thinking the power in these batteries is around 640 WattHours. I thought it would be more, but drawing larger amounts of current makes the battery actually have less power. I went 33 miles (33miles*350w/m=11.5Kw) and the indicator was yellow - voltage with a 100 amp load near the end of the drive was 100V or less. I did this in 1 25 minute drive there, a 1 1/2 rest where I put in approx 1Kw and a 35 return journey. The 1kw charge was a drop in the bucket. I think I hurt them guys and was lucky to get home. These batts are over 2 years old now. Anyone (Solar Guppy?) know where I could get similiar size NickleMHydride replacements? Thanks again...

Solar Guppy · January 2008

Re: Power in a battery

Well the nickle pacs are like 15K Plus shipping and its reconditioned, not new batterys, I think its www.evbones.com, they support the S-10 EV

Now your finding out why the S10/Ranger EV's are so cheap on eBay and other places, the battery packs cost big bucks and the range is very limited.

I'm waiting for the next generation of EV's before I buy one

There is also some promising new batteys comming to market

http://www.wired.com/cars/futuretransport/news/2007/07/batteries?currentPage=all

Power in a battery

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