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#31
05-07-2012, 05:17 PM
 DIYguy Senior Member Join Date: Sep 2008 Location: Kitchener, Ontario, Canada Posts: 2,468
Re: Lithium over Lead? It's really not that clear.

Quote:
 Originally Posted by meanderingthemaze diyguy: Well, I must have missed those discussions because I've been here awhile too. Linking to posts would be more useful here. The Wiki has some information, but its kind of a mess too. Plus some of the info doesn't cite its source.
I did an advanced search in the Battery section for "Cost", in titles only and got 250 hits. (it's capped at 250) There are thousands. . Including cost per mile, charge efficiency, cycle life discussions, plenty of conjecture, but lots of data from ppl also.

As for the Wiki.......... it doesn't seem too messy to me....

Step 3: Make allowances for your battery type.
Electric conversions use deep-cycle batteries which have some important characteristics that affect how they can be used in EVs. The two major factors are the Depth of Discharge (DoD) limitations and the Peukert effect:

EV batteries do not like being emptied down all the way and so emptying them completely will drastically shorten their life (the number of times you can use them). In order to counter this most EV conversions arrange things so that their battery pack never goes below 20% full. This is usually known as 80% DoD, or depth of discharge. So for our battery pack we need to make sure that when we have traveled our full range we still have 20% of our energy still in the batteries. To make sure this happens we take the the Ah rating we worked out in part 2 and multiply it by 1.25. This will mean when we have traveled our required distance we still have 20% left in the batteries. So for our previous example we worked out the Amp-hours to be 83.3Ah so we multiply by 1.25 to give us about 104Ah.

The Peukert effect sounds fancy but it simply means that the faster you use up the energy in the battery the less you will get out in the end. Battery Amp-hour ratings are usually given for a pretty slow discharge over 20 hours. However most EV conversion will use up their power much faster than that, usually in about 1 hour. Because the faster you use the energy the less you get altogether most EVs using Lead Acid batteries will only be able to use about 55% of the energy of the 20hr rate and we need to again compensate for this in our total pack size, by multiplying by 1.8. So our the amp-hour value in our example of 104Ah becomes 187Ah. When sizing the battery pack we need to make sure that the batteries we choose have an Amp-hour rating of 187 or better to achieve our range of 40 miles.

Lithium based batteries perform much better under high strain loads so you should be able to use 95% of the 20C energy rating. This means for a lithium pack you only need to multiply by about 1.05 to compensate, so a smaller pack is needed compared to a Lead Acid pack.

The third step in Sizing a battery pack is compensating for the characteristics of the batteries we choose, for Lead acid batteries this can be achieved by multiplying our Amp-hour rate from step 2 by 2.25, For Lithium batteries this can be achieved by multiplying our Amp-hour rate from step 2 by 1.32.
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Look, lead has been around for over a hundred years and you cannot even nail down HOW LONG IT LASTS! You will get everything from 100 cycles to 1000 cycles. . . and they are probably all true! You really think you will get a difinitive answer on the life expectancy of Lithium?

It has been documented that researches are predisposed to getting the results they anticipate from a study because they inadvertently do things to influence the outcome. . . with out even knowing it sometimes. Sure, u can say it's all baloney. . . or u can say it's all true. If your heart is set on something, by all means, go ahead and do it.
I've had two lead packs and one lithium in my first build. What have you had? How did it work?
While your at it, you can factor in the extra cost of boiling those floodies. . . and the watering system. . . and the difference in Rolling Resistance from the weight. . or not being able to run to the market when u get home from work or or or or......
The main reason I sometimes jump into the battery discussion (and it's gonna be less. . I can tell . . lol) is that I agree with JR on another point also. . . that Lead Acid builds actually do more to harm the adoption of EV's than they do to help it. These builds, in most cases, exemplify all those common beliefs about EV's. Make a car that will exemplify the best traits that an EV can have. . . or don't do one. Just one man's opinion. . . but I'm allowed . . . my wife said I could ...
#32
05-07-2012, 05:53 PM
 Ziggythewiz Senior Member Join Date: May 2010 Location: Houston Posts: 3,752
Re: Lithium over Lead? It's really not that clear.

Quote:
 Originally Posted by meanderingthemaze Thanks mora. But I thought lead could be discharged more than 50%. There doesn't seem to be consensus on that. Also, you give the best case scenario for Lead. But, what is the worst case scenario for Lithium?
He was being far too generous for the lead. You can only use 50%, but because of peukert you only get around 60% of that.

Also, why would you compare best case for lead with worst case for lithium? Best case for lithium would be lasting for decades. That's part of the reason we run numbers, but are still doubtful of some of the projected results.

For example, some of my calcs would give a lithium pack at 80% DOD a longer lifespan (16 years) than at 70% DOD (12 years) because I could charge every other day, using 3 cycles/week instead of every day at 6 cycles/week.

There is simply not enough data to answer all our questions, and that's not going to change any time soon. I'm not aware of anyone with the resources to do a good test besides a manufacturer. A good test would involve about a dozen cells, from a dozen different batches (so 100-150/test) run in a dozen different use cases. Since the manufacturers never publish the results of more than a couple of their tests, the only data we will ever have is anecdotal from us, and it will take 8-20 years to collect that through actual use.

Theoretically I could size a pack so I could charge every 2 days while using at 70% DOD, and it would last around 24 years (and then I could switch to charging every day and get another 12 years?). However, at some point the shelf life matters as much as the cycle life and I don't think they could possibly last that long.
__________________
1 EV - 8,530 e-miles in 2 years (2/11/13) - http://www.evalbum.com/4000
#33
05-07-2012, 11:06 PM
 GizmoEV Senior Member Join Date: Nov 2009 Location: Kelso, WA Posts: 858
Re: Lithium over Lead? It's really not that clear.

I got only 5000 miles out of the set of T-875s that came in my Gizmo. If I add the miles which were on the odometer when I got it the total would be 7500 miles. A pack of six T-875s looks to cost around \$900 right now. I put 2500 miles/year with the lead acid pack so this would mean I could get 3 years use before the range went below useful for me. In January of 2010 I installed a LiFePO4 pack of 40 TS-LFP100AHA cells in a 2p20s configuration. I wasn't sure of what I needed due to the need for ballast and keeping the C rate down so I went over board on pack size. I spend \$5000 on the pack and another \$800 for a BMS (which I'm not using at the moment, btw). Now that I have had this pack for the past 29 months I'm quite sure I could have done fine with a pack half this size which means the cost would have been \$2500 + \$800 or \$3300. Basically three times the cost of a lead acid pack which I took out.

Using just these numbers would mean I would need to have this pack last 9 years to break even on costs. What the numbers don't show you is that now I drive my rig over twice as much as I did with a lead acid pack. This means that over 2500 miles/year is not being put on my gas rigs. This would most likely be at ~25mpg but lets use 32mpg of my Corolla. That equates to ~\$300/year in fuel savings alone. This makes the equivalent cost of driving my Gizmo with a T-875 pack to be \$600/year (\$300 for the amortized battery cost and \$300/year in extra fuel costs for my car). \$3300/(\$600/year)=5.5 year cost break even point. For the LiFePO4 pack I did install it would be \$5800/(\$600/year)=9.7 year break even point. And this is using numbers which don't favor using lithium. Right now I would have to drive my 15mpg truck since my Corolla is not available so my break even point would be even sooner. The extra fuel costs for my truck would be \$650/year so the cost of driving my Gizmo with a T-875 pack would be \$300+\$650=\$950/year. This makes my break even point at \$3300/(\$950/year)=3.5 year break even or \$5800/(\$950/year)=6.1 year break even point.

All of this ignores the vastly improved drive-ability and significantly reduced maintenance of battery watering and cleaning terminals. Add to this the fact that my range with half the LiFePO4 pack I put in would be 35 miles and this could diminish to 20 miles before it would give me the useful range of the T-875 pack before it died. With my 200Ah pack my useful range is 70 miles driving any way I want except only up hill. 70 miles is not the farthest it could go on a charge at a constant optimum speed. This is a real put it in the bank drive any way you want range. It could drop to 20 miles or less than 30% of its original range before the pack would be unusable for me.

So what do you think. Was it worth my investment? It was to me, that is for sure.

As for calculating true energy available: Using my CycleAnalyst I take the Wh used and divide by the Ah used on a 40-60 mile run where the average current draw is around 130A or 0.65C and I generally get 64V (3.2vpc) to 62V (3.1vpc) when the pack is below 10°C. This is why using 3.2vpc is a realistic nominal voltage for energy calculations with LiFePO4 cells. The peukerts is so low that I don't notice any difference in heavy or light discharges so if a battery is rated at 100Ah that is what you will get, worst case 95Ah assuming you aren't abusing the cell.

The T-875 has a 170Ah rating at the 20 hour rate. The 5 hour rating is only 145Ah. Tests have shown that a 50% DOD gives the most miles for the life of a lead acid pack. If you are trying to minimize pack life this is the value you should use but understand that you can't use the 20 hour rate. A 1 hour rate would be more like it. The 1 hour rate for a LiFePO4 cell is very close to its 2 hour rate which is very close to its 5 hour rate. For my calculations for using LiFePO4 I take the Ah rate at face value and use 80% for extremes or 70% for conservative values. With lead acid I use 50% of the 20 hour rate as equivalent to 80% DOD.

With LiFePO4 you can always buddy pair a second cell with an initial pack for more range. It won't matter that the old cell and new cell have slightly different capacities. They will work as a single cell once paralleled as long as neither cell is damaged and both are the same chemistry. That is not something I would even consider doing with a lead acid pack.
#34
05-08-2012, 06:50 AM
 piotrsko Senior Member Join Date: Dec 2007 Posts: 848
Re: Lithium over Lead? It's really not that clear.

you also need to amortize the charger cost and whether or not you bms. I won't even talk about wiring them together. there is a huge series of threads about drilling, materials used and <corrosion>.

My charger cost \$40 to make, no bms. Betcha yours cost more.

How well can you abuse the LIpo batteries? Can you drastically over charge, draw them down to below 2 voltsthen expect them to work? Cell reversal? Can you go down to Joebobs house of batteries in your town and just buy a new one? Do they even have a warranty? Have you tried to return a defective cell? Do you need to speak a different language or learn another culture to buy Pb's?

Yeah it is 100 year old technology, and it kinda sucks, but my vehicle is rolling under its own power.

Finally: Many of the lipo fanatics used PB chemistry once.
#35
05-08-2012, 08:00 AM
 Frank Senior Member Join Date: Dec 2008 Location: Maine Posts: 118
Re: Lithium over Lead? It's really not that clear.

Another factor not yet mentioned is that PbA conversions typically have to (or at least, should) be in pickup trucks so as to not exceed GVW. Lithium lets you choose the vehicle you want. My small Toyota has 1320# of T125's (not quite a "ton" but pretty damm heavy nonetheless.) An equivalent amount of energy could be contained in maybe 400# of LiFePO4's (not LiPo's) which are a pretty safe cell. Taking 900# out of my truck would make it infinitely more useable. Sure, it does okay on the flat but is a pig going up hills. I'd be surprised if any PbA conversion does well on hills. When the batteries get totally pooched (they're getting weak now, in the 6th year of usage) I'll transplant the EV stuff in another chassis with prismatic LiFePO4's. BTW, I'm convinced the only reason the batteries have lasted as long as they have is that I'm paranoid about not abusing them.

My latest m-cycle conversion uses 72V of 100AH T-Sky's. It's a bit more battery than I need but the bike is pretty fun. I use CellLog's to monitor, no BMS and the cells stay very close together. There's no need for chargers to be more complex than PbA chargers and voltage stays more stable than it would with any PbA pack. When your PbA pack wears out, have a serious look at prismatic LiFePO4's, you won't regret it.
#36
05-08-2012, 02:50 PM
 mora Senior Member Join Date: Nov 2009 Location: Jyvaskyla, Finland Posts: 222
Re: Lithium over Lead? It's really not that clear.

Quote:
 Originally Posted by meanderingthemaze what is the worst case scenario for Lithium?
Few cycles and ready for replacement (overcharge few times or even once). Over discharge isn't that bad unless you run down to 0V resting voltage. Your car stops moving way before that happens though. Opposite for lead. Drain a lead battery too empty once and it is nothing but downhill from that point. Care must be taken to ensure good cycle life no matter chemistry. Maybe some old flooded NiCds are exception though.
#37
05-09-2012, 12:03 AM
 GizmoEV Senior Member Join Date: Nov 2009 Location: Kelso, WA Posts: 858
Re: Lithium over Lead? It's really not that clear.

Quote:
 Originally Posted by piotrsko you also need to amortize the charger cost and whether or not you bms. I won't even talk about wiring them together. there is a huge series of threads about drilling, materials used and .
No matter what chemistry you have to get a charger. Why would you need to amortize the charger cost? It is a capital expense like buying the car in the first place. Do you amortize the seats, doors, windows, etc?

What are you talking about with the drilling, materials used etc part?
#38
05-09-2012, 06:23 PM
 piotrsko Senior Member Join Date: Dec 2007 Posts: 848
Re: Lithium over Lead? It's really not that clear.

my charger cost 40 USD. Not a big expense. I havent seen many lipo chargers for that price. What happens during an over charge? Can you say bang?? Not an issue with lead. So I am saying that the cost of the charger and BMS system (if you use one) is an integral part of LIPO useage and sort of irrelevant with lead.

My battery connections including the ones to the controller, all made from 2-0 cable cost about 100 usd, and took about an hour to make. Haven't seen the equivalent for LIPO. Then there can be the too long screw issue, corrosion, materials disimiliarity, swelling, strapping, boxing, whatever.
#39
05-09-2012, 07:12 PM
 TomA Senior Member Join Date: Mar 2009 Posts: 270
Re: Lithium over Lead? It's really not that clear.

What about corrosion and chassis leaks to ground so common with floodies?

I haven't seen or heard of a single LiFePO4 pack that has needed ventilation, emitted acid vapor, has caused corrosion on the terminals, battery racks or battery boxes, or been the source of a chassis ground leak other than by contact of the HV wiring to the chassis. Long term, that's worth something to me.

Still, this is all minutiae. The simple fact is that the conversion I want to do (Daewoo Matiz) isn't possible with lead batteries. Can't do it. Hard stop. Oh, sure, it could be done at 72V with a 20 mile range and terrible performance, but that isn't the conversion I want to do. Its only possible to do a 130V HPEVS powered car, and have about a 16kWh pack and 50+ mile range, with lithium-based cells.

So the question "Lithium over Lead?" is only "really not that clear" if the performance envelope of the conversion you want to do (like with a small pickup) is feasible with lead. The smaller the glider, the harder it is to make lead work. For a 4 seat glider under 1700lbs stock, its practically impossible.
#40
05-10-2012, 12:33 AM
 GizmoEV Senior Member Join Date: Nov 2009 Location: Kelso, WA Posts: 858
Re: Lithium over Lead? It's really not that clear.

Quote:
 Originally Posted by piotrsko my charger cost 40 USD. Not a big expense. I havent seen many lipo chargers for that price. What happens during an over charge? Can you say bang?? Not an issue with lead. So I am saying that the cost of the charger and BMS system (if you use one) is an integral part of LIPO useage and sort of irrelevant with lead.
So did you not see that I included the BMS in my analysis? When done properly there is not going to be an overcharge issue. Furthermore, with lead there is thermal runaway with too much overcharge. In addition, with every full charge of a flooded lead acid and flooded NiCd packs there is corrosive acid vapors to deal with and highly combustible H2. Have you seen the bulging pickup bed and lids blown off battery boxes? I have. That is just one why you should have a temperature compensated charger for lead. Also, LiFePO4 have different characteristics than LiPo.

Quote:
 My battery connections including the ones to the controller, all made from 2-0 cable cost about 100 usd, and took about an hour to make. Haven't seen the equivalent for LIPO. Then there can be the too long screw issue, corrosion, materials disimiliarity, swelling, strapping, boxing, whatever.
Again, LiPo is not the only chemistry out there. I have had my LiFePO4 pack in place for well over 2 years and over 12k miles and haven't had any pack connection issues or battery failures like I did with lead acid.

What again is the problem with LiFePO4?

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