Only using 1/3rd of batteries?

tonybelding · 11-28-2006, 09:35 AM

Quote:

In order, to make the batteries last the lifespan of a car, engineers use complex control software that manages the charging and discharge of the cells in the battery to maximize the lifespan. Tesla, for example, has sized their battery pack to be three times what is actually needed and then uses different segments of the battery over the lifespan of the car in order to make it last.

Could that be true? If it is, then it's a real eye-opener -- and I, for one, will have to rethink everything I thought I understood about li-ion battery capacity and the potential for future improvements.

iisjsmith · 12-01-2006, 08:20 AM

I have never heard anything that would make me think the Roadster uses various sections of the pack only. In fact, their ESS lifespan numbers calculate complete charge/discharge cycles using the 500 cycle number...which is pretty normal for Li-ion cells.

I doubt they would build the ESS 3X more massive than they needed. If they could build a battery pack that gave a 250 mile range, with a 125000 mile lifespan, and only weighed 300lbs I'm sure they would do it.

doug · 12-01-2006, 08:35 AM

There was quite a bit of info about the batteries in yesterday's blog entry:

http://www.teslamotors.com/blog1/?p=39

Embassy · 12-04-2006, 11:30 AM

I think what is meant is that the batteries are being charged and discharged in the 3-4.15 volt range, which is about a third of the total voltage available. The author of the piece doesn't realize that that's what batteries do and how they're supposed to operate, and that restricting maximum voltage to 4.15 and minimum to 3.0 benefits battery life at a very small reduction in total capacity. Which is what the blog post basically said.

TEG · 06-28-2007, 10:34 AM

Yeah - I imagine that they could change the software to let the batteries drain down to say 2v instead of 3v.
That would:

#1: Increase the range per charge (yeah!)
#2: Make the batteries wear out much sooner (boo...)
#3: Have the car produce less power and performance when charge was low (boo...)

The downsides outweigh the upside. 3v is about as low as they would want to go without really damaging the batteries and hurting performance.

They also made the same decision on the full charge. The batteries could go to 4.2v for a little extra range, but they last longer if they only top them off at 4.15v. They picked a compromise between range and battery lifespan. The projected 100k+ mile lifespan for the battery pack is no accident. Anything less would likely scare customers away.