First lithium-powered electric car on PriusChat?

Thanks for the great information on the lithium packs. I think the cells you are using are these.

Foxx Specs

I was considering them for an electric conversion, but I am starting to wonder what the benefit is if you have a very short drive. Your case seems to be an excellent example. Your vehicle is lighter but performance seems to be unchanged at best. You do get a lot more cycles but it is probably not any better than the amount of Lead batteries you could buy to get the same range over time. The only benefit I see is in range or power. You could easily have built a pack that weighs the same as the original lead pack but have double the capacity. Except if the original pack meets your range requirement then why do it. You could also have went to much higher voltage and a similar capacity but you are limited by the existing motor and controller.

I think I am actually trying to talk myself into lead at this point, so don't take this as a knock on your project.

Steve

 

Daniel,

What I meant to say was the packs you got from EWI distribution, appear to come from the manufacturer at the link I provided.

I didn't know the Xebra was so rough on the Lead batteries. It certainly makes sense financially if you are not getting the expected number of cycles out of the Lead Batteries.

I also don't have to deal with cold weather, so I don't have to worry about the poor performance of Lead in cold weather. I felt like the vehicle performance in my situation would be the same on Lead versus Lithium so the Lithium would need to last at least three times as long. I am not sure I am willing to bet on that just yet.

By the way, I do use LiFePO4 (Dewalt A123) cells on my daily commuter (bicycle) and they work great. I would never go back to Lead on the bicycle. Unfortunately, scaling these cells up to a pack of the size you have would cost about $10,000 and I would have to build the packs.

Steve

 

Great information on your testing so far. Would you happen to remember what the minimum voltage drop under load was and what the current was at the time?

This would be really useful is designing my pack.

Thanks,

Steve

 

Thanks Daniel, that would be great.

Steve

 

Hi Daniel,

Congratulations on the new battery. BTW, Voltage only limits a motor RPM. Its current that sets the torque. Voltage limits the RPM because as a motor turns it generates a socalled back-emf. The amount of current that can flow is limited by the difference between the battery potential and the back-emf. This why motors have a torque curve that is flat up to some RPM, and then a straight line from that point to zero.

So it does not neccassarily follow that the lower voltage battery would result in the car with less umph, just a lower top speed.

 

Hi Daniel,

You could change the gear ratio to get the motor speed down, and this would allow you to stay in the torque flat to a higher speed. Which would help with accelleration, I would think. I am no expert though. But you might also need a motor with bigger windings for the bigger current and you should check the mechanical Max RPM too. There might be some room to maneuver within the rating of the motor. You might want to check out that EV car chat board for more specific experience on your car.

 

Daniel,

It is hard to tell on the website but it looks like they used 24 cells to build the 72V pack in your car, which is good because I have seen many places that rate the LiFePO4's at 3.2V per cell or higher nominal so they would probably have used at least 1 less cell. My experience has been that a very good LiFePO4 cell (like the A123) will hold right at 3V under a 5c load.

I am sure you don't want to throw money at it, but four more cells would put you back to 84V and your performance should be better than it was with th 84V lead pack. I suspect they could do this for you for under $1000.

I always recommend using 4 LiFePO4 cells in series for every 12V lead battery you replace. This should guarantee you the same top speed as your lead pack but acceleration should be much better with the lighter weight. I would see how many cells there are in the pack if this is something you can do without too much trouble.

What is the voltage of the pack fresh off a charge? I think they may not be utilizing the full capacity of the cell which is why they quote such long cycle life. Nothing wrong with this approach, it is exactly what Toyota does with the Prius.

Steve

 

I thought that Doc Willie had the first litium-powered car. Oh, wait, sorry I was thinking of Dilithium power. Never mind.

 

Well, actually, I do have the first lithium powered Chevy Volt.

The battery problem has been solved. The wind tunnel thing is still a bit of an issue . . .

 

Perhaps you were the first one on Priuschat with a lithium-powered "car" but I may have been the first one with a lithium-powered vehicle!

Check it out.

 

It is both a battery assist and has a throttle so you don't have to pedal. Of course your range is way bigger if you pedal. It has four levels of assist.

There is a little computer attached to the handlebars that is a speedometer, odometer and controls the settings.

In assist mode it automatically senses how hard you are pedaling and provides a certain amount of thrust depending on what level you set it. I use level 4 (the most assistance) on my commute. It really flattens the hills and keeps my speed up on level ground.

With the heavy battery and motor (plus my panniers) it is a heavy bike, but I can easily get around without having any battery power. My speed is just cut in half when going up hills. It's on a 27-speed hybrid bike so overall, it is easy to pedal.

 

congrats on your upgrade!!

my Zenn only does 36 mph max and it accelerates about the same as yours...its actually pretty fast (since i beat most people off line for first block or so) up to about 30 mph...then drifts to 36)

and as you know, there are compromises... but that is what EV's are all about. they have been thwarted at every opportunity...

funny how an hybrid SUV still qualifies for 100 % hybrid tax credit, while pure EV's get ZERO...(tax credit ended in 2006).... and it aint because EV's have sold any particular amount of cars either.

but daniel, you are right, if we dont start an EV movement, no one will know or care (its hard to care about something you are completely unaware of!!)

since driving my Zenn, i have had a lot of interest shown with people i run into while tooling around and one guy actually turned me on to option that i would do today if i knew that plug ins were not coming down the pike... once again, its a three wheeler, but much faster with greater range (cost as much as a Prius!@!)

check it out TWIKE.us


another thing daniel, i am a member of three different Zenn user groups and there is this guy in the bay area who cracked the Zenn software code and now his Zenn will do up to 45 mph on its standard 25 mph motor and will coast up to 53 mph down hills. (the Zenn is governed so mine for instance will only do 37 mph down hills, iow, no real increase at all) ... check around, see if altering the software will make it run better.

 

ZENN is a great little Canadian company.