LiFePO4 Batteries

[yash101]

I am working on designing a tiny electric concept vehicle, inexpensive enough for most people to afford. I was looking at Howell Energy batteries and found a 200 amp 12 volt battery for approximately $1000. Do you guys think that this is overpriced and maybe even let me know where I can buy a cheaper Lithium Ferrous Phosphate Batteries?

[G33K]

I'd check out LiFePo4 batteries for hobby applications initially. Here's an 8.4Ah, 4-cell pack (13.2V nominal) on HobbyKing: http://hobbyking.com/hobbyking/store/__14074__ZIPPY_Flightmax_8400mAh_4S2P_30C_LiFePo4_ Pack.html
With a 30C constant discharge rating, it should be able to crank out 252 amps continuously.

[AlexH]

if you want to buy american, ep buddy and battlepack.com both sell LiFe cells and packs.

http://battlepack.com/

http://www.buddyrc.com/battery/a123-life-batteries.html


K2 battery has a pack that has a board in in that makes LiFe cells act like a sla battery. they also sell single cells.

http://store.peakbattery.com/index.html

[AdamHeard]

Originally Posted by AlexH

if you want to buy american, ep buddy and battlepack.com both sell LiFe cells and packs.

http://battlepack.com/

http://www.buddyrc.com/battery/a123-life-batteries.html


K2 battery has a pack that has a board in in that makes LiFe cells act like a sla battery. they also sell single cells.

http://store.peakbattery.com/index.html

Are the cells American?

[AlexH]

i think so. but i guess i phrased it wrong. what i meant to say was if you want to buy cells that won't take 4 weeks to arrive from china without currency exchange charges, these companies sell LiFe cells

[protoserge]

What are your requirements? You only gave a load and the description "tiny".

What else needs to be taken into consideration? Do you have a characterization of the motor(s)? How long would you need it to last? How long to charge? What is the lifespan requirement? What is the weight restriction? What are the operating conditions?

[philso]

If you are considering a concept for an EV that people would drive on a daily basis, you should get in touch with the EAA. There is a Scottsdale chapter. A Basic Membership is only $35 a year ($25 for students).

There are typically a bunch of members who have done an EV conversion or are planning one. They are generally pretty enthusiastic about helping each other. It should not be very hard to find someone in your local group who can direct you to a more economical source for the batteries you need. You should be able to get larger batteries and in larger quantities than what you would want to buy from a hobby supplier. Someone should also be able to help you with other issues such as the Battery Management System (BMS) and chargers.

If you are lucky, you may be able to get in on a "group buy" where someone takes on the responsibility of importing several pallets of batteries then ships them to all the participants. One of the members here in Houston saved several thousand dollars this way.

www.electricauto.org

[EricH]

There is one thing to remember about LiFePO4 batteries, and this will probably affect number and lifetime used. Particularly as you're modifying a vehicle.

They will run at nearly full voltage right up until they're just about discharged (slight decrease, not a whole lot). At which point, the voltage will drop like a rock. If you're using them in a vehicle, you probably want to account for this phenomenon.


Something a little more helpful: When I was doing my senior design project (a robot that could run 10 minutes at a time) we found some 40 A (continuous)/40 Ah LiFePO4s for about $500 for a pair. And, with some digging through some copies of data on that build, I was able to track down our source: http://www.batteryspace.com/12-8v-li...-to-200ah.aspx There are a couple up around $1K; most are $200-$600.

[yash101]

Sorry about the confusion . I am aiming for maximum distance that can be travelled. What I meant by 200 ah is the battery holds 200 amps of charge. Otherwise, i did start at hobbyking. They don't have too big batteries and the big ones are overpriced. Also, doing some looking into the manufacturer's website, if I mass order lifepo4 cells (1000s of cells), i can get 10 amp 3.2 volt cells for $1 a piece. That means that Philso mentioned, if i get into a group buy if this mass, we all could get these 10 amp cells dirt cheap! $4 for a 12v equivalent battery of 4 amps is a ridiculous price, especially for one who mostly shops at hobbyking. Also, these tiny cells that I found (10ah a piece) are rated for 2C, more than what is required because they will more-or-less be wired parallel, distributing the load to all ~100 cells. Also, how dangerous are the fires or explosions of these batteries. They are not as bad as lithium LiCoO2 batteries (cell phone battery chemistry, i think). That's why i'm using these. Also, can I permanently wire these batteries in parallel? Won't the cells distribute the charge equally and maintain the same voltage throughout? Also, anyone know about any electric vehicle enthusiast communities?

[AdamHeard]

Originally Posted by EricH

There is one thing to remember about LiFePO4 batteries, and this will probably affect number and lifetime used. Particularly as you're modifying a vehicle.

They will run at nearly full voltage right up until they're just about discharged (slight decrease, not a whole lot). At which point, the voltage will drop like a rock. If you're using them in a vehicle, you probably want to account for this phenomenon.

This is one of the reasons I love this chemistry. It's a huge bonus, not a negative.

[EricH]

Originally Posted by AdamHeard

This is one of the reasons I love this chemistry. It's a huge bonus, not a negative.

It's a huge bonus, up to a point. For a normal vehicle, the rough equivalent would be running out of gas right when the warning light went on. Now, if you had the warning light on at quarter-tank, you might get quite a few false positives--but some sort of low-battery indicator would be useful, and it's just a little harder when the curve is flat up until an asymptotic curve.

As this is a vehicle application, this particular item is something that should be a pretty high driver of the size and number of batteries, particularly when combined with the desired range.

A couple of other comments:
-When using LiFePO4s in my aforementioned senior project, we used quite a bit of institutional knowledge from the college's SAE Clean Snowmobile team, who used a large bank of them under the seat of a snowmobile to power the drive motor. If I'm not mistaken, SAE's Collegiate Design Series competitions each have their own mini-forums... And wouldn't ya know it, http://forums.sae.org/access/dispatc...EAN_SNOWMOBILE can be read by the public. (You'll probably want the Archives, and zero-emissions entries.)

-From experience, they're actually pretty safe, particularly compared to normal LiPOs used in R/C aircraft. However, shipment can be a pain--as I recall, the originator has to have some sort of permit to ship them.

[AlexH]

Originally Posted by yash101

Sorry about the confusion . I am aiming for maximum distance that can be travelled. What I meant by 200 ah is the battery holds 200 amps of charge. Otherwise, i did start at hobbyking. They don't have too big batteries and the big ones are overpriced. Also, doing some looking into the manufacturer's website, if I mass order lifepo4 cells (1000s of cells), i can get 10 amp 3.2 volt cells for $1 a piece. That means that Philso mentioned, if i get into a group buy if this mass, we all could get these 10 amp cells dirt cheap! $4 for a 12v equivalent battery of 4 amps is a ridiculous price, especially for one who mostly shops at hobbyking. Also, these tiny cells that I found (10ah a piece) are rated for 2C, more than what is required because they will more-or-less be wired parallel, distributing the load to all ~100 cells. Also, how dangerous are the fires or explosions of these batteries. They are not as bad as lithium LiCoO2 batteries (cell phone battery chemistry, i think). That's why i'm using these. Also, can I permanently wire these batteries in parallel? Won't the cells distribute the charge equally and maintain the same voltage throughout? Also, anyone know about any electric vehicle enthusiast communities?

i'd be down for buying some.

http://visforvoltage.org/ is a ev community

[yash101]

right now, i am just requesting a quote. I did contact the company yesterday and I did get a reply. However, the only answer I got would be "the price would be high" because of all the shipping and price + tariffs and other moneyhogs. However, I asked for a quote of just 200 batteries. It'll probably be cheaper if I order in bulk because the expensive price of shipping won't change much if I buy a couple thousand batteries versus 200 of them.

Here is the important excerpt of the reply. I agree the English sucks, but the email was sent from china, so I am quite impressed they know English


We leading Batteries manufacture for years,USA is one of our main market .
we can send to you by TNT without problem. only the cost will a bit high.
Our standard specs:

Model Material voltage capacity life cycles Max. charge voltage cut-off discharge voltage weight approx. measurement(D*H)
HWF42110 LifePO4 3.2V 10Ah up 2000 3.65V 2.3V 330g 42*110mm

Do you assembled the 200cells by yourself ?
And by the way ,may i know some information about your company please?

[yash101]

Copy and Paste from Google Mail Sucks . The table is completely missing, however, if you are really looking into these specs, you may look hard or even look at the manufacturer, Howell's website

[yash101]

Originally Posted by G33K

I'd check out LiFePo4 batteries for hobby applications initially. Here's an 8.4Ah, 4-cell pack (13.2V nominal) on HobbyKing: http://hobbyking.com/hobbyking/store/__14074__ZIPPY_Flightmax_8400mAh_4S2P_30C_LiFePo4_ Pack.html
With a 30C constant discharge rating, it should be able to crank out 252 amps continuously.

That is a good idea. That way, if the car crashes or flips over, I won't have as big of an explosion. Also, I would put a few of these in parallel, for capacity and for discharge rate