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Lithium vs lead batteries
Posted: Mon Aug 18, 2008 1:35 pm
This is a question for all those who have used or are using LiFePO4 batteries. Do you feel they are worth the added cost over lead acid batteries and if so, why? Do you have an estimate of your amortized cost/mile for them over their expected lifetime? What is the expected lifetime? I am trying to decide if they are worth the extra cost.
Posted: Mon Aug 18, 2008 2:35 pm
I've used 3 different brands of LifePo4, and i'd highly reccomend any of them above lead acid.
Cycle life is far far greater, which alone ofsets cost issues. (3000 cycles plus likely from LifeBatt cells). Much Much lighter too, and you get the real rated capacity from the pack too (lead gets you about 65% rated capacity if you go easy on em!)
Available power out is way way higher, at least from the more reputable suppliers (A123/LifeBatt), so for any lightweight fast vehicle they are a must. A 50Ah pack of lifebatts can supply over 500A and still hold its nominal voltage.
At the end of the day, if you build a vehicle with lead acid, you will always be wondering how much better it would be with LifePo4.
Of all packs available right now, I'd say LifeBatt are the most easily available, have the best warranty (3 years?), decent BMS/packaging, and great aftersales support.
A123 cells have a higher discharge rate (ideal for drag racing!:)), and will last equally as long, but dont have a public sales department, dont offer ready to run packs, and are very small cells (you need LOTS to make a pack).
I'm sure theres more reasons too, its just so long since I gave up on lead acid that I cant remember all the bad points:P
Hope this helps,
Posted: Mon Aug 18, 2008 4:34 pm
PHEV wrote: Available power out is way way higher, at least from the more reputable suppliers (A123/LifeBatt), so for any lightweight fast vehicle they are a must. A 50Ah pack of lifebatts can supply over 500A and still hold its nominal voltage.
Whilst I wholeheartedly agree about LiFePO4 being much better for practical EVs, I think that lead acid almost certainly still has the edge when it comes to maximum power output, simply because the maximum discharge current can be much higher than for current LiFePO4 cells. Lead acid cells have a pretty high power to weight ratio, despite having a very low energy to weight ratio. Paul summed this up well in another thread on a hill climb race car conversion - it hadn't occurred to me before.
LiFePO4 chemistry is getting there, with 10C possible from the better cells, but it's still some way behind lead acid at the moment.
In terms of energy density then LiFePO4 wins hands down, although some other lithium technologies can be better, albeit with a potential safety management issue.
Posted: Mon Aug 18, 2008 6:04 pm
Having used Lithium since 2003 I could never go back to anything with less useable capacity. Yes pure grunt is still missing from the cheaper end of the market, but if your current demands are reasonable then for pure range and AH per kg Lithium is the only choice IMO.
Posted: Mon Aug 18, 2008 11:10 pm
I appreciate the performance of the lithium cells but the cost is horrific. I think you need to decide whether your needs could be met by lead acid & consider lithium if not. My gut feeling at the moment is a cost ratio of about 20:1 in terms of Ã‚Â£/kWh, I'd be interested to hear what others think. That is comparing the lifebatt website with UPS/caravan batteries from the battery man in Rochdale.
I'm doing my first fullsize EV now & will start with lead acid - I only want a 15 mile range for my commute ;^)
I think if you are trying to get 100 miles range lithium makes things feasible.
Posted: Mon Aug 18, 2008 11:33 pm
Don't forget yo may need to replace the lead 10X or more in the life of the lifebatts. They are garanteed to 3000 cycles!
Jeremy, I'll repharase that then, you can push them harder than lead whilst still keeping close to maximum capacity. I'd hate to see what capacity loss there is a lead acid battery discharged fully in 6 minuits:)
Personally I've not found any lead that will do 10c without sagging terribly, but I must admit I gave up trying after I tried my first A123 cell! (they do 30C continuous and still deliver 90% of capacity)
Posted: Tue Aug 19, 2008 9:07 am
I'd always choose Lithium or NiMH over lead any day!
Posted: Tue Aug 19, 2008 9:17 am
A warmed up 42Ah Hawker Genesis will hold 10 volt with a 1000 amp load, some 700W/Kg.
The JCI Inspira batteries produced for the proposed 42 (really 36) volt automotive systems were a great deal more powerful, a 7Ah battery supporting over 1000 amp at peak power (50% voltage sag). Whilst these were available, they were THE battery of choice for the drag racers.
Next along was the Boulder TMF. These were a lead acid cell the same size as an industrial 'C' that would deliver 1000 amp for 10 seconds and weighed around 200g. These were what really put Killacycle on the map, but weren't a commercial sucess. I think a Korean company now owns the licence.
In terms of watts for you hard earned pound, you really can't beat lead.
Posted: Tue Aug 19, 2008 5:39 pm
I love my lead batteries. They cost me Ã‚Â£220 for a 120 volt, 200 amp/hr pack five years ago and are still going strong. They give me a range of 30 miles and I use them every day. If you do not require a long range or you also run an internal combustion car, then financially it probably is not worth the extra cost of Lithium.
Posted: Tue Aug 19, 2008 6:35 pm
Peter, I think it's worth mentioning for those who don't know that you drive a very smart milk float
Those ex power supply batteries are fantastic value, but mostly come up for sale in large sizes, so the picture is different for smaller, lightweight vehicles. The lead acid batteries on my bike cost around Ã‚Â£400 for just 60V 26 Ah. A larger pack of LifeBatt (60V 30 Ah) would cost just over Ã‚Â£1200 (at the recently offered individual cell price). The lithium pack would weigh half as much and deliver one and a half times the range per charge. Over its useful lifetime it should be capable of delivering around six times the total range of lead acid.
If you want a relatively inexpensive runabout with less than say 30 miles range, lead still makes excellent sense. If you're looking for better performance and/or longer range then it's worth doing the sums for your particular application to see whether lithium would make a better choice. The relative merits vary widely depending on your needs.