Battery Amp-Hour Requirements for Electric Vehicles

I am not very familiar with 3 phase power, but would assume that it would be a simple power conversion equation. Power in=Power out + loss, you know your output power, and can assume say a 5% loss from inverting (please check, as stated I am unfamiliar with 3 phase), your input power is V.I.=648xI, this will run for the same number of hours and since the batteries are in series to obtain your required voltage, this current flows through all of them. therefore each battery will require Ix 3 Amp hours.

Your batteries must be maintaining the 10.8 Volt output voltage at the end of the 3 Hours working period.

Each cell of 6 are 2.4 Volt when full charged and 1.8 Volt when considered they are empty.

This means you will see 14.4 Volts when charged and 10.8 Volts when empty at the battery output terminals.

If the batteries are tractional type shallow charge. than you should calculate a 5 Hours working capacity. Such as 119 Amps x 5 Hours.

However if they are deep charge type, you can lower this value to 4 hours of full working time. such as 119 Amps x 4 Hours.

Ensure the batteries are not warmed during working period. Higher and lower temperatures are very effective on the capacity calculation.

I suggest that you do a little research on batteries before proceeding. 120 Amps from 54 batteries for 3 hours is a lot! (I was gonna say, "a ton" instead of "a lot," but I think it would be a good bit more than a ton -- pun intended.)

See this tutorial on batteries.

Take this for example: This battery is rated at 150 AH for 20 hrs, and it weighs 96 lb. You want 120 A from each battery for 3 hr -- not very practical.

Search for submarine batteries, and be prepared to make your electric vehicle about as large as a submarine.

Even though Iam not an expert in this,what I can say that for constant load current ,

AH=I X K X L X T, where

I =load current ,

K= a constant for a given back up for a given end cell voltage,taken from graph.

L=Life factor or ageing factor taken as 1.25

T=Temperature correctionwhen ambient is less than 27'C(changes from 1.6 to 1.01 as temp. changes from -10'c to 25'c),value is 1 when ambient temperature is more than 27'c .

Three hours continuously at 119 Amps motor current - AND it's a 440 VAC motor.

I make that somewhere over 70kW electrical power which means you will need 210kW/Hr battery pack.

I hope that the vehicle is a semi trailer because most EVs have between 12 and 30kW/hr packs and the latter are usually Lithium packs - not Lead Acid.

A Lead Acid 14kW/Hr pack is around 500kG weight.

Are you sure you need this power continuously?

Based on the information provided:648vDC(12vx54);440vAC;119amps

AC motor full load current=119amps;power out(AC)=72.550kw,lets round up to 75kw.

Assume Power in battery(battery power)=Power out(motor power), IV=P, Ix648v=75kw, I=75000w/648v=115.74AH, For 3 hours=115.74AH x 3 = 347.22AH.

U need about 347.22AH (or 350AH) Battery capacity for yr above project.But i have only seen and used 200AH,so if u dont have 350AH,connect 2x200AH,12v batteries in parallel to get 400AH 12v.Series the sets of parallel batteries to maintain yr 648v and 400AH,if u cant get a single 12v 350AH Battery.

Must u use 648vDC for the job? If not,other arrangement for the batteries and amps could be made to get it better and cheaper.

Patrick Whowha

Based on the information provided:648vDC(12vx54);440vAC;119amps

AC motor full load current=119amps;power out(AC)=72.550kw,lets round up to 75kw.

Assume Power in battery(battery power)=Power out(motor power), IV=P, Ix648v=75kw, I=75000w/648v=115.74AH, For 3 hours=115.74AH x 3 = 347.22AH.

U need about 347.22AH (or 350AH) Battery capacity for yr above project.But i have only seen and used 200AH,so if u dont have 350AH,connect 2x200AH,12v batteries in parallel to get 400AH 12v.Series the sets of parallel batteries to maintain yr 648v and 400AH,if u cant get a single 12v 350AH Battery.

Must u use 648vDC for the job? If not,other arrangement for the batteries and amps could be made to get it better and cheaper.

Patrick Whowha

Thank you,

I am going to have to de-rate my amp hours. The full load amps were as stated, 119@440VAC , but for cruising and eveyday driving I am not sure what percentage to de-rate.

The LiFePo4 battery price quotes that I am receiving ($150K) for 400AH. and for $17K 50AH.

The 630 volt buss is required for the efficient inverting to 440 V 3 phase AC (according to Siemens and Hitachi VFD Representatives).

Does anyone have a cheap(er) LiFePo4 manufacturing source and a Feq drive source?

I am going to be using Headway Lithium Iron (LiFePO4). 12 packs of 32 cells (16S2P) - making each pack 48V20AH. I am expecting 80km range at 60 km/hr and 60km range at 80km/hr. The pack can deliver 150 Amps for several minutes but flat and level travel at 60 km/hr only requires 10 to 12 Amps (6kw). 100km/hr is expected to draw about 20 to 30 Amps (15 to 18kw). The kw/hr rating of the pack is just under 12kw/hr. So while you need a large amount of current short term, the continuous cruising requirements are a lot lower.

Concerning LiFePO4 batteries,

Can you give me an idea abt the weight comparison with the same capacity of ordinary Pb Acid car batteries.

Regards

The 48V20AH packs weigh 12kg each. It works out to a faction less than half the weight of Lead Acid. The Lithiums should last 1500 cycles at 80% DOD and 3000 cycles at 50% DOD. Lead would be lucky to get 500 cycles at 50% DOD and due to Peukert effect you only really get about half the capacity with lead - see: http://en.wikipedia.org/wiki/Peukert%27s_law Price is higher of course (isn't that the way?) Lots of great discussion here: http://www.aeva.asn.au/forums/

Thanks for the detailed info.

I am working on the info, you supplied.

I already know abt. the Peukert effect. What I don't know is if Peukert calculations are also applicable for those new type of Lithium Ion and NiMh batteries.

Best Regards

The Peukert effect is apparently minimal in Lithium and NiMh chemistries. Folks on the AEVA forum have measured some reduced discharge capacity at high currents (3C) but it is a faction of that experienced with Lead Acid. From memory a 10Ah high current cell (Headway 38120) surrenders 9Ah at 50 Amps (5C). Same cell was just over 10Ah at 10 Amps (1C). These figures should be verified on the AEVA forums (or/and elsewhere) before any commitment. This thread has some testing: http://www.aeva.asn.au/forums/forum_posts.asp?TID=1113