Lithium vs Lead on Bike - DIY Electric Car Forums

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#1
05-07-2008, 12:23 PM
 hypnotoad Junior Member Join Date: May 2008 Posts: 7

Something I never seem to read about is how many more lithium batteries a motor needs to use to achieve higher range then a lead acid battery.

Let's just make up some number here...

Motor = 48-72 VDC 10hp/40hp peak single-shaft 62lbs.
Weight = 200lb minus batteries
Range = 70 mile safe / 100 mile max(drained batteries)

Now then.. Using Optima Blue/Yellow Top 12v 50ah batteries. It would take 6 of them in series to power the vehicle. Each at 45lbs adding 270lbs to the bike. This should get the bike close half the range we are looking for.

Time to jumble with lithium battery. Using a Lithium D battery 3.6v 1ah(guessing it's ah). It will take 20 of these in series to reach 72v. Each at 3oz x 20 = 60oz OR 3.75lbs. Obviously, these 20 batteries could turn the motor. However, they would be able to handle pushing that kind of weight for more then a block.

Here is the actual forum question I am asking..

Keeping in mind that 50% of my numbers are completely made up. How many lithium batteries would it take just to equal the 6 lead acid batteries?

300?

Also, would that mean running 15 packs of 20 lithium batteries in parallel?

I didn't get to goto MIT like Lennon(emoto) did. So I just work it out as a go.

Thanks

#2
05-07-2008, 03:35 PM
 mattW Super Moderator Join Date: Sep 2007 Location: Sydney, Australia Posts: 882 Blog Entries: 18
Re: Lithium vs Lead on Bike

Hmmm it's probably easier to explain the difference between the two without using your numbers. The main difference between lithium and lead acid (besides weight, size and cost) is what's known as the Puekert's effect. What it means is the quicker you use your energy, the less total energy you will get out. For lead acid batteries you will only get about 55% of the capacity out at the rate we use them. For lithium you get around 95% of the energy in the pack. Lets say you have a 50Ah lead acid battery. The actual usable energy in the battery is only 27.5Ah (x 12V). For a lithium battery to be the same capacity it only needs 29Ah because puekert's will bring it down to 27.55Ah. And thats not taking into account the added efficiency of a lithium pack. Most lithium cells run at 3.2V and they can come in many different Ah, the LionEV packs are up to 200Ah. 72V of lithium would mean 24 batteries @ about 30Ah to match (exceed) your lead acid pack.
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If I was giving a kWh for every suggested idea of perpetual motion I read, I would probably ironically be able to travel perpetually...
#3
05-07-2008, 04:11 PM
 emoto Junior Member Join Date: May 2008 Posts: 16
Re: Lithium vs Lead on Bike

Might want to check out what others are getting with lithium:

http://www.evalbum.com/battt/LION
http://www.evalbum.com/battt/LIPO

-Lennon
#4
05-07-2008, 06:23 PM
 hypnotoad Junior Member Join Date: May 2008 Posts: 7
Re: Lithium vs Lead on Bike

Well, firstly let me thank you for replying. Yeah, my numbers are not exact. I just wanted to express my thoughts out loud so I could be corrected.

Which you guys did.

One of the harder things I have come across is actually finding sources to purchase these batteries. Most places I have found give little to no real information about the battery.

I'd rather build a lithium power system then a lead acid. I think I could afford this on a motorcycle. I don't make enough to say the same thing about running a automobile atm.

Even if I takes me one full year to slowly get all the batteries I need. It should be worth it in the long run.

Thoughts? Feelings?
#5
05-07-2008, 07:38 PM
 ngrimm Senior Member Join Date: Oct 2007 Location: Medford Oregon Posts: 296
Re: Lithium vs Lead on Bike

That was a great idea looking at the Evalbum for ideas. I noticed this one in particular since he gave some weights etc. http://www.evalbum.com/1017
#6
05-07-2008, 11:58 PM
 mattW Super Moderator Join Date: Sep 2007 Location: Sydney, Australia Posts: 882 Blog Entries: 18
Re: Lithium vs Lead on Bike

I am probably going with Chinese lithium on my bike... Using the El ninja as a guide I worked out that if you can get 40 miles on 6 85Ah Lead batteries then 50 or more will be possible on a 60Ah Lithium pack due to the Puekerts. Another thing to look at is the number of cycles, Lifepo4 has almost 3 times the apparent life of Lead acid so it may actually be cheaper in the long run than Lead.

Make sure you buy your batteries all at once even if it takes a whole year to save for them so they are more likely to be balanced with one another.
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If I was giving a kWh for every suggested idea of perpetual motion I read, I would probably ironically be able to travel perpetually...

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