Lithium vs Lead; the Great Cost Debate.

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Posted 02-03-2009 at 01:21 PM by mattW

Tags lead, lithium, thundersky, trojan

I've decided to try and work out the cost comparisons for a Lithium pack vs a Lead pack for a set range and a set number of years. Is Lead Acid actually cheaper or does is just seem that way up front? This article aims to find that out. The method is to get 10kWh of usable energy, I’ll try to get that with Lead and with Lithium and see what we find is cheaper in the long run. Assuming an efficiency of 250Wh per mile (a compact car) we should get a range of 40 miles (65km) with either pack. I’ll be using Australian prices since I’ve already researched them, but the comparison is probably close in other countries too.

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The first step is to source a lithium pack with 10kWh of usable energy. The Lithium batteries I have chosen get 2000 cycles to 80% DoD and I estimate that at the 1 hr rate they will deliver 95% of their rated energy due to the Peukert’s effect. So to give our total energy we multiply our usable energy by 1.35 meaning we need 13.5kWh to get out 40 mile range with lithium batteries. If we assume a 120V conversion this means we need 112.5Ah. The cheapest Lithium batteries I have seen in Australia are Thundersky LiFePo4 LFP prismatic cells $2.50 per 3.2V per Ah. So our 13.5kW pack would take 38 3.2V cells at ~110Ah and would cost $10450 at normal prices (no group discount), without shipping or BMS.
For a Lead Acid pack we also need to keep the batteries at less than 80% DoD and at the 1hr rate we can only expect to get 55% of the rated energy of the pack back due to the Peukert’s effect. That means we need to multiply the usable energy by 2.25 to get our total energy, in this case its 22.5kWh. Trojan T605 batteries could make up a 22.5kWh pack with 18 batteries (108V, 210Ah) at $225 each or $4050, it didn’t say how many cycles it would take on the website but let’s guess around 650 to 80%. That means we’ll need to replace our lead Acid pack around three times for every lithium pack we buy, meaning our total cost for the lead packs goes up by a factor of 3 to $12150 over 2000 cycles.
Now I must admit that I didn’t look very hard for the cheapest batteries and I am only guessing the cycle life of the Trojans but even if it’s not precisely accurate it does show that the myth that Lead is clearly cheaper than lithium is not well founded. Lithium’s greater efficiency and cycle life makes up for its higher initial cost. I didn’t know what the results would be like before I started. The10kWh number was chosen just to make it easy to calculate, it has little influence on the result one way or the other. I thought the results would be close but not this close. Please note that the Lithium pack would require a BMS, which would cost $1270 but that still means you are going to pay around $12k whether you go with Lithium or Lead. It would also be worth mentioning that you would be paying for more electricity over that time with Lead; 36MWh costing $3600 compared to 21.6MWh $2160 @ $0.10 per kWh and recharging 80% of capacity. You would also need to water the batteries if you went with the Trojans, while the lithium’s would be maintenance free. It’s also worth mentioning that there are apparently disputed copyright issues with the thundersky cells and their previous record with customer support apparently not good, but this was just a cost comparison and the number look pretty convincing.
The total cost per km for the 2000 cycles is $15 750/ 130 000km = 12.1c per Km (19.7c/mile) for Lead Acid and $13888/ 130 000km = 10.7c per km (17.4c/mile) for the LiFePO4. These would obviously increase slightly when factoring in tire and brake wear. Just for comparison a the cost per km of a bunch of small ICE cars are listed here the cheapest being 41.44c/km but only 33.5% of that cost was for fuel and servicing (the rest being common cost for EVs as well) so that’s 13.9c/km for the cheapest ICE using fuel at $1.25/L. Clearly then EV have a price advantage over ICE’s especially now that normal unleaded is averaging $1.48/L.
In summary, while Lead Acid may be cheaper up front new lithium packs are more cost effective in the long run as well as being lighter, smaller and maintenance free. Obviously battery choices are highly dependant on individual conversions and budgets but it should not be assumed that Lead is the budget option, since it’s just not true anymore.

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	Metric mind makes/carries a BMS system that at least one TS conversion used to date.
	Posted 07-18-2008 at 06:54 AM by david85

Maybe I'm totally wrong about this, but, all the cost projections are going forward. What if we go backwards? ie, instead of thinking about the costs at the end of a certain time period, think about the cost per cycle.

I can't find any hard numbers for Trojan t-105 life cycles, but somewhere here or on evdl somebody said it's 300-500 80% cycles, so that's what I'm going with.

A 144V 225AH pack of T-105's is 24 batteries. If they cost $150, the pack comes to $3600. If they get a minimum of 300 cycles, that comes out to $3600/300 = $12 per cycle.

A 144V 200AH pack of LiFePO4's is 48 batteries (3V cells at beeps.com). Those cost $500 so the pack costs $24,000. They claim a minimum of 2000 cycles. That also comes out to $24,000/2000 = $12 per cycle.

I know there is skepticism about the claims of the Lithiums, but if the claims are true, it looks like the costs are fairly even. Will you get more than 300 cycles from the T105's. Probably. Will you get more than 2000 cycles from the LiFePO4's? There are claims that they can get 3000 cycles if you only discharge them to 70%.

So, my conclusion is that if the Lithium batteries perform as the people selling them claim, then they are a better solution, because your ev will perform better with half the battery weight, and by the time you need to replace your pack, the prices should be less than today.

Posted 08-07-2008 at 08:52 PM by mark1030 mark1030 is offline

Regarding pro`s `n`con`s personally I will go for lead and just "wait it out" and in 3-4 years when my leads goes up crap creek i`m confident a good Lithium solution is within my reach - money wise.
I would`nt be happy if one of the TS goes bad,and should wait for a new one from freakin`China.

Nope I rather buy one from the shelf at the local HW-store.I think the potential "downtime" is to big a risk/cost at present.

And for you die hard Lithium-freaks a company in Denmark is currently developing a BMS !!

www.lithiumbalance.com

It`s in English

just my 2c`s

Molle

Posted 08-12-2008 at 03:17 PM by Molle303 Molle303 is offline

Quote:

Originally Posted by Molle303

And for you die hard Lithium-freaks a company in Denmark is currently developing a BMS !!

www.lithiumbalance.com

It only balances up to 500amps. That may be pushing it if you have a Logisystems or Zilla. It also can only monitor up to 120 cells, although maybe you can stack them. So if you use cyllindrical cells you can't manage every single cell.

Has anyone gotten a price quote from them?

Posted 08-12-2008 at 06:52 PM by saab96 saab96 is offline

Just thought I'd point out that in the last few weeks 2 of the LiFePO4 suppliers I've had my eyes on have lowered their prices. At beeps.com the 200AH cell went from $500 to $459 and the 100AH went from $250 to $225. It seems the 50AH one is no longer available. At elitepowersolutions.com the 160AH cell went from $288 to $272. Their other sizes also all went down to $1.70/AH.

So, the prices are dropping. I don't think the same can be said for lead acid batteries. Keep watching!

Posted 08-19-2008 at 04:23 PM by mark1030 mark1030 is offline

Quote:

Originally Posted by mark1030

Does anyone have good data on the price of LiFePO4 (and Lead) over time? I'd like to see a graph on the price trend... it's tempting to wait a few more months to go for the Lithium on my conversion.

Posted 08-19-2008 at 07:15 PM by ClintK ClintK is offline

All right guys, help me out here. I'm trying to figure out how much lithium I need to do about the same job of all the lead I'm hauling around. It takes power to move mass, but if my car is so much less massive, then I don't need as much power.

I am not going for a 100 mile range, I'm just trying to build a lithium pack that does what my lead pack does: 70 mph max speed, and a solid 40 mile range.

Currently my Bug has 128v worth of 8v Energizer (Johnson Controls) batteries. Motor is an L91-4001. Attached is the rating Johnson Controls gave: 170 at the 20aH rate, 75 minutes @ 75 amps. We all know that due to Peukert factor, that the capacity isn't really what the label says.

So how much lithium do I REALLY need to do the same amout of work? Escpecially since my pack is going weigh 300-400 lbs vs. 1100 lbs.

How does this tie into the "Great Debate"? Because it helps determine if the Lithium is better in the long run. Too many people are trying to buy a lithium pack that does MORE than their lead pack would, which isn't a fair cost comparison.

Is the 60ah lithium the closest equivilant capacity to what I have now? Or is it 30? Or 90?

Then there's the issue of sag (internal resistance). What kind of voltage drops do lithiums exhibit? My nominal voltage is 135 volts...well, it's 140v when the car is fresh in the morning after charging the night before. When loaded, I drop from 135 volts to 120-115 volts. If lithium sags so much less, then maybe I don't need so many cells. If 120v is a good enough performance point for me, and the IF lithium batteries only sag 5 volts at the max, then I only need 125 volts worth of 3.2v units. That would be 39 units instead of 43 units which reduces my costs even further. I have a 500 amp controller, but I'm really only looking to pull 200 battery amps for short periods of time. My motor won't take much more and that's good enough acceleration for me.

So...if you all can help me tailor a lithium pack to replace my lead pack so I can calculate my costs, I'd be very grateful. I haven't had a lot of luck with this on the EVDL.

Posted 08-20-2008 at 07:44 AM by EVBug EVBug is offline

What DoD do you go to on your lead pack? As far as voltage sag goes real world anecdotal evidence seems to suggest thundersky lithiums sag 0.2v per 1C of current per 3.2V cell. If you are going to 50% DoD then you have 170 x 0.55 x 0.5 = 46.75 usable Ah. If you multiply by 1.32 for the lithiums you should get around 62Ah to match your Lead pack- not counting the weight savings... if you are already doing 80% DoD then it will take about 100Ah to match the LA.

Then you just need to work out whether they will give you enough current at 3-5C.

Posted 08-20-2008 at 08:23 AM by mattW mattW is offline

Quote:

Originally Posted by EVBug

Then there's the issue of sag (internal resistance). What kind of voltage drops do lithiums exhibit? My nominal voltage is 135 volts...well, it's 140v when the car is fresh in the morning after charging the night before. When loaded, I drop from 135 volts to 120-115 volts. If lithium sags so much less, then maybe I don't need so many cells. If 120v is a good enough performance point for me, and the IF lithium batteries only sag 5 volts at the max, then I only need 125 volts worth of 3.2v units. That would be 39 units instead of 43 units which reduces my costs even further. I have a 500 amp controller, but I'm really only looking to pull 200 battery amps for short periods of time. My motor won't take much more and that's good enough acceleration for me.

I was going to give my 2 cents on the Ah equivalence, but I'd trust mattW's answer far more than mine.

I do have a few questions on your motor though... I just picked up an L91-4003 (with no manual of course). Do you have any documentation on it? How is your motor hooked up? What are each of the A1, A2, S1, and S2 connections for? How has your motor performed with the 128V pack (heat / etc...)? I'm wondering because the motor is only rated 72-120. Are you staying under the 120V by counting on the sag from the batteries?

I've been keeping a close eye on the 128V 90Ah LiFePO4s packs for my conversion but have been worried about the extra 8V on the motor.

Posted 08-20-2008 at 08:36 AM by ClintK ClintK is offline

Thanks Matt, that's helpful. I run my pack between 50 and 80%. I think if I get the 60 ah units and maybe 40 instead of 39, I'll do ok. Heck, I can add some later if I have to. How do I find out if the lithiums can give 3-5C?

Clint,

I've looked at my motor and seen the connections but I forget how it's tied in right now. I'd have to look at it again. I know that one of the S terminals is tied to another terminal on the motor. The whole voltage/amperage rating is just an arbitrary point on a temperature curve. You can run higher voltages at lower amperages to meet the same temperature and duty cycle or you can run higher voltages and amperages for shorter duty cycles.

In my experience, limiting my take-off amps to 160 battery amps and cruising amps to 40-80 battery amps keeps the motor comfortably warm to the touch. On the hottest summer days (high 90's), it gets uncomfortably warm to touch. I keep the RPM's high, and the amps low to control the temperature. These amperages are in line with keeping my batteries healthy too.

Posted 08-20-2008 at 10:17 AM by EVBug EVBug is offline

The batteries can put out 3-5C bursts of current, you just need to work out your 'C' (capacity) so that you can get enough power out of them to accelerate. A 60Ah pack can put out 180A at 3C and 300A at 5C... a 100Ah pack with do 300 and 500 amps.

If you are driving at 160A max then it sounds like a 60Ah pack will do everything you need without straining the batteries much at all and you still have some room to play with for acceleration.

Posted 08-20-2008 at 09:29 PM by mattW mattW is offline

Sounds good. Based on the figures you stated earlier (.2v sag per 1c per 3.2v unit) That would result in a drop to 120v from 128v in a 40 unit (128v) pack at 1C. So if I draw 3C, that's a sag of 24 volts which puts me at 104 volts. That's lower than I want my lowest voltage to be so I think I'm going to end up adding one or two more modules.

Wait a sec...I have a question now. Lead batteries are 2.4 or 2.5v per cell. I mean, I'm using 8v batteries but they're really at 9.6v when fully charged. Do lithiums behave this way or is "3.2 v" really the nominal, fully charged voltage?

I'll have to recrunch the numbers depending on what the answer is.

Posted 08-21-2008 at 05:47 AM by EVBug EVBug is offline

	The TS batteries run between 2.5 - 4.25 operating voltage, 3.2 nominal. http://www.thunder-sky.com/products_en.asp So fully charged a 40 unit pack might start out around 168 volts I guess. My "48" volt lead pack starts around 51 volts fully charged.
	Posted 08-21-2008 at 06:55 AM by JRP3

	Holy cow. Then yes, 39 or 40 units would definitely be plenty. I never achieve those voltages even now. Between the lighter weight, and the higher starting voltage, my car would -fly- compared to how it is now. JRP I'm a big fan of your 6-wheeler. That thing is awesome!
	Posted 08-21-2008 at 07:09 AM by EVBug

	And.......here comes probably my biggest complaint about Lithium batteries: Minimum purchases. I can go to any store and buy a single lead battery. It seems like every lithium vendor has a minimum order. I'd gladly buy a couple of units per month until I had my pack but I don't think I can do that. If I can, someone please point me in the right direction.
	Posted 08-21-2008 at 07:32 AM by EVBug

	Thanks, it is a lot of fun Buying a few every month till you get your pack means you end up with a bunch of older batteries in your pack. I think you'd be better off just saving up and buying at once, plus as time goes on they seem to get cheaper and by getting quantity you might get a further discount.
	Posted 08-21-2008 at 11:40 AM by JRP3

The way they are trying to remove lead from every aspect of life, there may not be an argument is a few years.

Tonight in the paper they had an article about removing the use of lead in wheel weights.

That should make the price of Lithium go even higher, since one competitor will be phased out.

I really can't see the big deal about lead. We had all lead pipes going to people's homes in this small northwestern town, since the water supply was put in.

We finished removing the last lead pipe to a home, that the inhabitants had raised children and the folks lived to be in their late 80s.

Not how did we all servive with lead pipes all that time??

We also used to put lead pellets in our mouths, when hunting birds with our pellet guns.

A bullet was sometimes not removed, if it was in a bad place to operate.

Time for nickle-iron batteries....

Posted 08-29-2008 at 08:57 PM by Coley Coley is offline

Nickel iron batteries are very reliable and long lived, but they are not very efficient. In the tune of only 50% by some sources. Some fuel cells or even diesel engines can do better. NIMH is around 60%, lead acid can be as high as 95% (low current charging) and lithium is even higher.

With lithium, the net efficiency of the vehicle is much higher and that means lower operating cost in addition to lower maintenance when compared to lead acid.

Not sure how the voltage sag of NiFe compares, but its probably not as bad as lead.

Incredibly tough, but alas it is an old technology that was not updated over the years. If it can be purchased for a reasonable price than its worth considering, but I still think lithium is the front runner to keep an eye on because information technology demands more performance at a lower cost every day. Indeed this battery is advancing almost at the pace of IT itself.

Where can you get nickel iron batteries?

Nickel zinc is another one, but I'm even less up to date on that one.

Posted 08-29-2008 at 09:23 PM by david85 david85 is offline

	Quote: Originally Posted by Coley Not how did we all servive with lead pipes all that time?? Quote: there may not be any obvious symptoms, but the lead can still cause serious health problems over time, such as difficulty sleeping or lowered IQ http://www.nlm.nih.gov/MEDLINEPLUS/e...cle/002473.htm Lead is a poison, like it or not.
	Posted 08-29-2008 at 09:55 PM by JRP3