[Frank06]

I'm trying to understand battery types better and am hoping someone here can help me.

Does anyone know how the latest battery technologies stack-up efficiency wise? i.e. how much A.C. energy is actually used for charging?

AC Propulsion has a paper on their site saying that some NiMH packs can use up to twice as much charging energy as PbA packs. We know that wet-cell technology isn't that great (80-85%?) and I know from our home solar setup (and Trimetric monitor) that AGM's are excellent (99%).

Of course we all like the idea of less weight, extended range, etc. but if EV's are to truly be part of a national energy/greenhouse-gas strategy, charging efficiency is part of the equation. The best way to compare technologies would be a Life Cycle Analysis but I don't know if this has been done.

I'd appreciate any comments, links, etc.

TIA

 

[DanMan32]

Charging efficiencies are important, but it takes a back seat (unless really terrible) compared to power density, battery lifecycle and cost.

I would rather wait an extra 10 minutes to get a full charge that will get me 200 miles on a full charge than not wait on those 10 minutes and only go 100 miles. I would also rather wait an extra 10 minutes for a full charge and not have to spend $1000 or more for 7 years than not have to wait 10 extra minutes, but have to replace the battery in 3 years costing $1000 or more.

 

[Frank06]

Dan, thanks for your thoughts.

http://www.acpropulsion.com/white_papers.htm

Here's the link to the article I was referring to (third from the bottom in this list). Their conclusion (in 2000) was that PbA was better and more economical for the average person, hence my quest to understand current state-of-the-art better.

 

[Jeffand]

When it comes to battery efficency of charging and discharging. For instance lead acid batteries are rated in amp hours (ah). For lead acid batteries they typicaly rated at 20 hours discharge rate. If the battery is discharged at a faster rate amp hour rating goes down. This has to do to that when a lead acid battery is charged it will produce hydrogen gas. The faster the battery is charged the more gas is produced. This is waisted energy and does reduce battery efficiance.
For a battery to be charged a greater voltage has to be applied to the terminals. Current will flow into the battery. This causes a chemical reaction. Some heat is typical produced due to the internal resitance of the battery. This is more wasted energy. Batteries that have a low internal resistance will be able to supply higher current output with out over heating. Batteries with low internal resistance are ideal for hybrid drive systems.

The efficency of the battery can be calculated by this formula.

(Energy out in watts) / (Energy in watts) * 100 = Efficency %

When it comes to longevity. The new batteries that can be found in the new higher voltage cordless tools as an example. Now have waranties of one year on the batteries, instead of the traditional 90 days. Battery charge capacity has more than doubled.

 

[clett]

Charge / discharge efficiency is low for lead acid, but great for lithium-ion.

With some lithium-ion you can get as much as 98% back out of what you put in, even with high discharge rates. Lead acid sometimes as little as 80%, Prius NiMH somewhere in between.