Battery Choices

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Need to know what type to use or size or capacity then again place your thoughts here
MalcolmB
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Postby MalcolmB » Fri Mar 21, 2008 1:27 pm

As you say, battery technology still has a long way to go before we can convert Jeremy Clarkson.

Here are some figures for my motorcycle that might help a little. All-up weight including me is around 200 kg.

I currently have a 1.68 kWh lead acid battery pack (5 x 12V/28 Ah), which weighs 47 kg. If I'm careful with the throttle I can actually get 1.20 kWh hours out of this pack, giving a range of 15 miles at 80 Wh/mile. That means a useful energy density of 25 Wh/kg for lead acid.

Lead acid will typically only deliver around 60% of its rated capacity at EV discharge rates. It's not the ideal chemistry for this application.

When prices come down I plan to switch to lithium ion, probably lithium iron phosphate. From all the reports I've read, including user experience, these cells should deliver the current I need with only a 10% reduction in nominal capacity. Nominal energy density is 80 Wh/kg, so a conservative estimate of useful energy density would be 70 Wh/kg. That means almost a threefold improvement over lead acid.

Lithium polymer cells are even lighter and have a nominal capacity of 100 Wh/kg and higher, but they can't yet handle high discharge rates and they require careful management.

hyve
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Battery Choices

Postby hyve » Sat Mar 22, 2008 9:09 am

Thanks for the useful data, Malcolm. That 60% useful capacity for lead acid figure is particularly helpful. What sort of speeds do you generally travel at ?
I recently bought a car battery from a very helpful and reasonable chap in Llandudno, http://www.electroquestuk.com. On their site are a wide range of batteries including Trojan and impressive "Odyssey" motorcycle lightweights. From data gathered here I conclude that marine so-called dual purpose, starting & deepcycle batteries are somehow the two types combined, going by the weight. So my original premise that an EV needs a set of both seems born out here.
To me the weight penalty is unacceptable and I have to think, like you, about the Lithium alternatives. I note you say LiFePO4 have an energy density of 80wh/kg. The sums I did on the figures given me by Ian Goodman came out at 59wh/kg. What was your source ?
Otherwise I like the long life they offer - matching the life of any car easily and making the price justifiable.

Further to the Singapore source, NRG: I got a price of US$1.50/wh, which comes out at about £800/kwh ! For my use this would add only about 55kg, but mean an investment of at least £8000. This sort of performance is clearly the F1 of EV batteries. Out of reach unless sponsored.

There is a long term consideration. If investing in a set of Lithium batteries which are expected to last the life of the vehicle, this could mean ten years or more. At some point in the future, quite possibly the next decade, the government is going to find that so many people have switched from fuel to electricity that their colossal tax take from fuel is being significantly eroded. While they're happy initially to encourage us to switch, in the end they depend very heavily on this easy money because only one tenth of it is spent on roads. They WILL begin to get it off us EV people again in some other way, believe it.
If there is any cost benefit in an EV, it may not last long enough for us to enjoy it. Buy sooner rather than later would seem the moral of this story.
Peter Ph

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qdos
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Re: Battery Choices

Postby qdos » Sat Mar 22, 2008 9:33 am

hyve wrote:There is a long term consideration. If investing in a set of Lithium batteries which are expected to last the life of the vehicle, this could mean ten years or more. At some point in the future, quite possibly the next decade, the government is going to find that so many people have switched from fuel to electricity that their colossal tax take from fuel is being significantly eroded. While they're happy initially to encourage us to switch, in the end they depend very heavily on this easy money because only one tenth of it is spent on roads. They WILL begin to get it off us EV people again in some other way, believe it.



Hence all the cameras appearing at every significant road junction. Regardless of any petitions or what the public want we are going to be charged per mile for road use. Yes at circa 80% road tax (which equates to at least 8 pence a mile in tax alone of fuel costs) the government makes a colossal ammount of money from the motorist. I'd hazzard a guess at it being the most lucrative and reliable source of income they have

MalcolmB
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Re: Battery Choices

Postby MalcolmB » Sat Mar 22, 2008 12:36 pm

hyve wrote:What sort of speeds do you generally travel at ?

I mostly use the bike for running around town, with the odd short stretch of urban motorway. Average speed around 25 mph, max 55 mph.
The batteries I use are Enersys SBS, they have the same pure lead plate construction as the Odyssey deep cycle batteries, which are very popular in EV circles. The SBS range are the same ones that Peter Eggleston mentioned earlier, I think.

hyve wrote:The sums I did on the figures given me by Ian Goodman came out at 59wh/kg. What was your source?

Lifebatt 10Ah cells weigh around 370 g each and have a nominal voltage of 3V, so 30 Wh/0.37 = 81 Wh/kg. Maybe you did your sums based on the weight of the ready-built Lifebatt packs? I'm not sure how much the packaging weighs, but I wouldn't expect it to be that heavy. Whether you use lead acid or lithium you'll need some sort of containment for them, whether it's off the shelf or homebuilt.

I agree, the amnesty on electric vehicles won't last long, so lets enjoy it while we can!

hyve
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Lifebatts

Postby hyve » Mon Mar 24, 2008 10:18 am

Lifebatt 10Ah cells weigh around 370 g each and have a nominal voltage of 3V, so 30 Wh/0.37 = 81 Wh/kg. Maybe you did your sums based on the weight of the ready-built Lifebatt packs?

Correct. Note that this includes BMS. I wonder what the figure for Thundersky includes ?
However, you remind me that weights can be quoted at all sorts of stages of installation. I guess finished all up vehicle weights are the only true comparison.

I'm impressed that you can get up to 55 mph on just 1,2kwh. Thanks again Malcolm.
Peter Ph

bobc
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Postby bobc » Tue Mar 25, 2008 6:15 pm

The lithium phosphate batteries look very nice but the price is horrendous! I just looked on the "lifebatt" page where 12V at 10Ah comes in at a princely £204... Thats around 20 (twenty) times the cost per joule of lead acid.
Do we expect economies of scale to close this gap much in the forseeable future?
Bob

electricvehicles
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Postby electricvehicles » Wed Mar 26, 2008 8:58 am

bobc wrote:The lithium phosphate batteries look very nice but the price is horrendous! I just looked on the "lifebatt" page where 12V at 10Ah comes in at a princely £204... Thats around 20 (twenty) times the cost per joule of lead acid.
Do we expect economies of scale to close this gap much in the forseeable future?
Bob


I notice that you can buy the 12V10Ah batteries directly from LifeBatt in the States for only $250. What with the exchange rate being so good and even taking into consideration the shipping costs you could make yourself some considerable savings. What with the price of lead going through the roof, hence the increase in PB batteries, looks like Lithium might finally become a reality :)

hyve
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Lifebatts costs

Postby hyve » Fri Mar 28, 2008 11:50 am

A couple of posts back I reported that Worley Parsons in Singapore quoted me US$1.50/watt hour for their NRG cells. I thought this was horrendous until I did the sums for Lifebatts. Even the USA price mentioned above makes them $2.08/watt hour.
When you add in the fact that the NRG's are near one quarter the weight of the Lifebatts and remember that a typical battery pack can be 300kg, the extra range provided by the weight saving alone makes NRG very attractive.
Anyone else know anything about them ?
Peter Ph

MalcolmB
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Postby MalcolmB » Fri Mar 28, 2008 12:39 pm

Hi Peter
The quoted energy density for the NRG cells would be fantastic if they were readily available, but I can't find any information about these cells, either on the Worley Parsons site or from googling NRG cells. Can you point me to a source of more info?

hyve
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NRG cells

Postby hyve » Sat Mar 29, 2008 8:00 am

I got this quote from [url]John.Grzan@WorleyParsons.com[/url] He's a director there. He said I could find more info on their website: [url]WorleyParsons.com/AES[/url]
I did find batteries eventually; they seem to do everything ! But the price put me off.
Remembering that Ian's Lifebatt packs come with voltage management systems perhaps the price is not so awful and the weight advantage for NRG not so great, but it still looks like they would cut 200kg from a 300 kg pack. Well worth having !
Peter Ph


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