Electric Car Batteries

[shemandr]

With all the battery expertise on this forum I'm interested in some opinions regarding electric cars.
First, what kind of batteries are they using? Is there any special technology that makes the car batteries different from those in our boats? What kind of charging regimens are they using? Are they practical? How does the charging regimen affect the battery life?
I am not considering buying an electric car. I am aware of the inefficiencies involved in transfering energy from generation with any fuel, or anything else, and transporting energy, and converting energy, so I hope this thread can be about the batteries.
Its winter and really cold outside. Humor me.

 

[Ed Schenck]

You are wondering about lithium-ion batteries for your boat? BoatUS recently had a preview of the Mastervolt lithium-ion battery for marine use. Talking big bucks here: http://www.madmariner.com/blogs/boat_shows/37777 .

 

[shemandr]

Is that what the cars are using?
It's not about my boat batteries so much. I'm just interested in learning about the technology in cars and if it will eventually trickel down to boats. $ 7,500 - yikes!

 

[Ed Schenck]

The Chevy Volt does. Not sure about my next door neighbor's two Prius'.

 

[kenn]

The Prius apparently uses Nickel Metal Hydride battery technology.

For electric autos, energy density (amount of energy for a given weight of battery) is key, which is why new, lighter battery technology has been crucial in making EVs physically practical.

However, for marine applications, especially keelboats, battery weight isn't near as big an issue. If your boat has 1,000 pounds of lead in the keel, it's not ridiculous to suggest that maybe 200 pounds or more of that weight could be in the form of lead-acid batteries.

It's my understanding that the newer battery technologies need to be charged and managed more carefully, whereas the lead-acid technology is more tolerant of the erratic charge/discharge cycle of the recreational cruiser.

So, while I expect that the EV battery technology will eventually trickle down to boats and other uses, lead-acid batteries will still be more economical and reliable for a while, at least until lead replaces gold as the backstop of our currency.

 

[Bill Roosa]

Lead acid have specific charge regimes that other batteries do not. Specifically they get harder to charge as they approach full charge. aka the internal resistance goes up with SOC.
Most other batteries do not have this problem (advantage) so you can blast lots of amps into them even when they are fully charged and make them catch on fire. This requires some battery safety circuits to make sure that does not happen.
The bottom line is if you embrace something other than lead acid you are going to have to embrace a different charge regime and equipment to do that.
All battery types have their own unique cell voltages so you move away from 12 volts as a standard. Not much of a problem as most marine instruments are 10-32 volt operable. The motors will not care much either. Your cell phone charger and inverter may complain mightily though as they have turn on and turn off voltages that are fixed and are expecting the 12 volt auto lead acid standard.

 

[kloudie1]

Agree that some technology will trickle (charge :~) down to boating, but there are two real differences that are not optimized for boats.. The first is that the batteries are optimized for really big current flows .. doesn’t sound like a problem but they are not nearly as efficient at long term very low current draw, and will not reach their stated AH capacity in low/slow mode. The second is that they typically have a much higher static discharge rate than would be desirable for sailboat use. They would not be nearly as tolerant as conventional batteries when sitting and not being constantly replenished.. They discharge themselves much quicker than normal technology. Yes, they do require sophisticated charging controllers, which the auto guys have built into the cars to enable the batteries to get to warranty end .. The conventional stuff (flooded lead/acid, AGM, Gel, etc) that is available today is a better solution until some changes are made in the new technology to make them better for long slow, low ampere generation..

 

[tommays]

The older Prius batterys are starting to reach end of life at around 3k to 4k cost depending on who you believe

 

[JohnShannon]

The Prius uses Nickel metal hydride batteries, the Tesla uses LiFePo from A123. Both these chemistries have higher energy density and power density than lead acid. Managing the charge termination is harder than with lead acid. Nickel chemistries in quick charge have termination based on a sudden increase in battery temperature, or a sudden drop in battery voltage. Lithium chemistries end up being kind of sorta like lead acid, except each cell in the string (4.2V) has to be monitored individually and cell voltage has to be regulated to 50mV. So no cell in the string is allowed to go over 4.25V. Once the Li cell is charged you want to "float it" meaning disconnect charging energy which is unlike a Pb cell where a temp dependent 13.8 ish float voltage is desired.

Anyway higher performance with higher cost and higher complexity. Is that a deal or what? Maybe for the racers, maybe for the cruisers.

 

[Bill Roosa]

There is always NiCad!

I did some research a while back and NiCads have some possibilities. They take a charge quickly right up to full so you can reduce your engine run time. they don't care if you store them discharged, charged or somewhere in between. They have charge controllers and regulators on the market as they are used in a wide range of standby power applications. They hold voltage throughout the discharge cycle so you can't tell how charged they are by looking at a volt meter and they have a higher self discharge rate however.
the biggest plus was the number of cycles you can get from them. Using the 50% max rule you can get 5000+ cycles!!! Lead-acid is more like 300. So while they are slightly more expensive they last much longer. If you "cruiser cycle" at 75-80 (you don't have to though because of the lack of increasing internal resistance with SOC) you get around 7000 cycles. cycle them at 90+% and 10000 cycles is possible.

 

[JohnShannon]

Yes one of the benefits of the new chemistries is the higher charge acceptance means you can build capacity in shorter time so switching to a giant alternator would allow you to run your diesel charging for less time at higher load. NiMH is an improvement over NiCad.

 

[joker460]

The trickle down from EV cars is EV boats.

http://www.youtube.com/watch?v=GdEDZuvk7wE