Battery Life

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Greenbeast
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Battery Life

Postby Greenbeast » Tue Jun 23, 2009 10:50 am

If i plan a system that will cover a couple of days driving (approx 32 miles) and therefore only charge every other day, i'll be doing 365 charge cycles every two years.

If the batteries are capable of 2000 cycles, they should last for 5.5 years, correct?

I'm trying to do cost comparisons to running our citroen C1, which gets 60mpg.

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Jeremy
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Postby Jeremy » Tue Jun 23, 2009 12:35 pm

Yes and no.......

Battery cycle life is very dependent on depth of discharge. For an extreme example, take the Prius. It limits battery charge discharge to only the middle 30% of the battery capacity, it never fully charges the batteries and never discharges them below about 50%. The result is that the cycle life is well in excess of 20,000 cycles, probably closer to 30,000 cycles, although the individual cells are probably rated at around 1000 to 2000 cycles when fully charged/discharged.

The other point is to do with the accuracy of battery specifications. Stated cycle life may well be under conditions far removed from those in normal EV use, so some sort of correction might be required to get a sensible estimate of battery life.

Finally, there's the issue of cycle life versus calendar life. For lithium batteries it may well be that calendar life dominates, as age-related loss of capacity might be greater than cycle-related loss of capacity.

Overall, charging "little and often" and not discharging the batteries deeply, will give a better cycle life, with the possible exception of some cell types that like the occasional deep discharge/charge.

Bear in mind that some battery types require careful cell monitoring and control to get the best life from them. Lithium cells, in particular, are very fussy about being charged and discharged within very closely controlled limits. Looked after, they have a long service life, allowed to get out of balance and their life can be very short indeed, which will play havoc with your running cost comparison.

Jeremy

Greenbeast
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Postby Greenbeast » Tue Jun 23, 2009 1:49 pm

Thanks for the detailed response.

There's so much to get my head around, even just to complete a basic comparison against my current petrol car.

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MB
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Postby MB » Tue Jun 23, 2009 8:06 pm

A lot of it will depend on the sort of batteries, the sort of driving and so on, but you would be better off topping up the batteries every day rather than just when they are running flat.

That said, with lead acid batteries at least, it is a good idea to discharge them to much lower levels once a week or so - otherwise you'll find your overall range will reduce.

What sort of batteries were you planning to use?
My new book is out: The 2011 Electric Car Guide is available from Amazon and all good bookshops.

Greenbeast
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Postby Greenbeast » Wed Jun 24, 2009 6:52 am

Ok i see, daily charging wouldn't be a problem its just that the max range i was looking at would (for a particular journey) would enable 2 daily work commutes.

As to battery tech, i'm not sure.
I just got a quote from LiFeBatt to do a car with 60 mile range, but as i told the guy quoting me afterwards the misses has vetoed the car replacement scheme of mine because she doesn't want any restrictions (i.e. she might want to drive to the moon and back on a whim without bothering anyone else for a lift)

So i'm looking at a scooter/bike/trike for my own daily use, but to be really worthwhile i would need to be able to do 60 miles still (there is one return journey i make once or more a month that would make having my own vehicle very useful and if i couldn't do it the vehicle would be surplus to requirements as we currently survive with 1 car)

I think a proper registered trike would be good because it has a bigger, more stable platform for batteries and i believe i could ride it on a car licence (no bike licence yet)

andylaurence
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Postby andylaurence » Wed Jun 24, 2009 1:39 pm

Greenbeast wrote:I think a proper registered trike would be good because it has a bigger, more stable platform for batteries and i believe i could ride it on a car licence (no bike licence yet)


Does this fit the bill? I don't know if there are any on the road but they say it can be road-legal and they say they will build one for you (assuming you don't want to build it yourself). DIY price is ~£1500, so ready-built would be an order of magnitude more.

Cheers,
Andy
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Jeremy
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Postby Jeremy » Wed Jun 24, 2009 4:56 pm

Qdos should be along any minute now to illuminate us further on the MEV trike, I hope!

I'd be interested to hear how it's going, too, especially as there's now a motorcycle sized >10kW continuous hub motor becoming available that would seem to suit it rather well.

Jeremy

Greenbeast
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Location: Sittingbourne, Kent

Postby Greenbeast » Thu Jun 25, 2009 7:14 am

wow, that etrike looks pretty decent!

I'd be interested in more details

like how to get it road legal, how to insure, what licence i'd need to drive?
how difficult it is to build?

duxuk
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Postby duxuk » Sun Jun 28, 2009 5:25 pm

I am building an electric trike to my own design. I have built 4 previos trikes with scooter engines. The MSVA test is quite tricky but plenty of people manage it. Insurance is easy. I'd suggest you get a copy of "Complete Kit Car", it's full of the kind of info you need. I will post info about my trike when I get it running at the end of the summer. I hope for a range of at least 40 miles. If a Vectrix can manage that wtih only 3750 Wh of capacity then my 72V 7920Wh system must stand a chance!

Greenbeast
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Joined: Tue Jun 23, 2009 7:52 am
Location: Sittingbourne, Kent

Postby Greenbeast » Sun Jun 28, 2009 9:20 pm

can i have more info on the battery pack?
i'd love 40 mile range


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