LiFePO4 Batteries
 

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?

Re: LiFePO4 Batteries
 

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.

Re: LiFePO4 Batteries
 

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

Re: LiFePO4 Batteries
 

Are the cells American?

Re: LiFePO4 Batteries
 

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

Re: LiFePO4 Batteries
 

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?

Re: LiFePO4 Batteries
 

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

Re: LiFePO4 Batteries
 

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.

Re: LiFePO4 Batteries
 

Sorry about the confusion :o. 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?

Re: LiFePO4 Batteries
 

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

Re: LiFePO4 Batteries
 

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.

Re: LiFePO4 Batteries
 

i'd be down for buying some.

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

Re: LiFePO4 Batteries
 

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 :D


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?

Re: LiFePO4 Batteries
 

Copy and Paste from Google Mail Sucks :D. 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

Re: LiFePO4 Batteries
 

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

Re: LiFePO4 Batteries
 

I was looking at the a123 batteries before. They seemed quite repute. However, I didn't know where to get high-capacity cells, and the decent capacity ones were expensivo

Re: LiFePO4 Batteries
 

I'd be ready, however, I do not think anymore that they will be priced as low as a dlooar a piece, more like $5 under ideal circumstances, plus I will need to ship them to, I believe, Pennsylvania? However, I will keep you posted about this, as I think that even $5 is a decent price for 10ah cells :]

Re: LiFePO4 Batteries
 

Devyash

You should carefully consider the size of the individual batteries and the number that you have to connect in series/parallel to get the energy you want.

The smaller the batteries, the more "strings" you will have and the more connection points you will have. Connection points are the most common failure point in electrical/electronic systems. I have only seen strings of batteries connected in parallel at the two ends of the strings. This allows the use of Battery Management Systems to be used to monitor each cell. I have never seen the intermediate points connected in parallel since it would prevent the monitoring of individual cells.

Since you are using these in a vehicle, you will be concerned with system weight and volume. A pack made up of smaller batteries might weigh more and take more space than one made up of larger batteries. The shell of the battery may constitute a larger percentage of it's weight than in a larger battery. You will have to study the detailed specifications carefully and estimate your overall weight and size. A BMS for small batteries is about the same size and weight as the BMS for a larger battery so a pack made up of small cells will have more weight and volume taken up with the BMS.

If you are using high discharge rates, the smaller batteries will have more surface area per unit of energy storage, making it easier to keep the battery pack within it's specified operating temperature limits.

The flat discharge curve followed by a rapid voltage drop is a good reason to use a BMS to prevent you from damaging the battery pack.

Re: LiFePO4 Batteries
 

Maybe I could calculate a function to solve for the battery "percentage" and the range of the vehicle. There will be 10 amps of reserve, enough for about 5-10 miles, depending on your driving style. Also, if I add regenerative braking, I shall add more range. Also, since these batteries will be weighing in at about 100 kgs, do any of you know of any high power, commercially available motors that will bring this 200-300 kg car to 60mph? I was looking at this: http://www.hobbyking.com/hobbyking/s...ner_Motor.html
However, it required a very high voltage (52 volts) at 250 amps! that's a lot of juice! The batteries won't provide enough energy for more than maybe an hour of runtime, dropping the range to about 60-100 miles!

Re: LiFePO4 Batteries
 

I don't know of any motors myself. However, I will again point you to the SAE Clean Snowmobile Challenge, which has a zero-emissions category (AKA electric). They're building for range, power, and lack of emissions--and I bet they know some good motors if you're able to contact one of the teams. There might even be one near you.

Re: LiFePO4 Batteries
 

thanks, just pm me in chief delphi when you are ready to order. i'm in williamsport pa. i'll gladly pay for shipping.

Re: LiFePO4 Batteries
 

How are you calculating your numbers? What is your requirement? Before you continue to keep looking at motors and batteries, you have to start with a set of requirements to point your research in the right direction. Until you list out the requirements, we can't really help you solve your problem.

You said the car has to go to 60 mph, but how long does it need to travel at that speed? What is the acceleration required? How many stop-start cycles will be required? What is the vehicle weight constraint? How many wheels will there be?

Re: LiFePO4 Batteries
 

Devyash

You need to study up on the various types of motors available (DC, AC) and the advantages and disadvantages of each type. You then need to study the types of controllers available for each type of motor. Since you are aiming at maximum efficiency, you will have to select the motor and controller very carefully. As Tim above says, you need to have clear specifications for what you are trying to do before you start.

Adding regenerative braking will roughly double the complexity of your controller. It will also roughly double the losses in your controller while transferring power from the battery to the motor, reducing your overall efficiency. Unfortunately, I have yet to find a commercially available AC or DC motor controller for EV applications that has regenerative braking.

Re: LiFePO4 Batteries
 

hobbyking brushless motors are grossly over spec'ed. the wattage they give is just stall current times maximum voltage.

Re: LiFePO4 Batteries
 

It's not overspec'd, just deceptive. It's max input wattage instead of max mechanical output power :-(

Re: LiFePO4 Batteries
 

I got two "3000 watt" HK Sk3 motors for an gokart.

Any good ways to find the max mechanical output power?

Re: LiFePO4 Batteries
 

Put it on a dynamometer?

If you know the stall torque and the free speed, and you believe the speed vs torque is linear, then the max output mechanical power in watts is stall torque times free speed divided by 4 (if using SI units).

Re: LiFePO4 Batteries
 

I completely agree. I was planning on using Brushless (AC) motors because they are a tad more efficient and because there are no brushes that wear out over time. The only stress is the bearings, and using something like a ball bearing could last quite a long time.

Re: LiFePO4 Batteries
 

This is the reason why I do not like HK motors. They do not give what they say. Also, I think that their motors are meant for high RPM, not high torque. That would also mean that the bearings have a whole greater load to withstand. Our BAG motors on our shooter keep failing because the motors can get up to 14,000 RPM Also, the motors are ridiculously priced (the ones that seam that they might work)

Anyways, does anyone know where I could buy a car motor? I do not want to use CIMs because they overheat after continuous usage, and they just do not provide the torque required

Re: LiFePO4 Batteries
 

How are your BAG motors reaching 40krpm?

Re: LiFePO4 Batteries
 

Darn It! Typo. 14,000. Let me edit the post above :D

Re: LiFePO4 Batteries
 

go to a "u pull it"

find a prius

extract motor?


http://www.cloudelectric.com/product...em200-d135.htm

this would be the motor to use if you are doing what i think you are doing.

Re: LiFePO4 Batteries
 

That seems like a legit motor. Also, is it advisable for me to use two motors, one controlling each side of the car? If so, that would allow easier computer control of the car. Also, I am planning to implement an autopilot routine, (in the future years), to just follow the roads straight and automatically stop and start in traffic jams. The following will probably use a camera and the stopping will be done either with a ping or a laser rangefinder.

Re: LiFePO4 Batteries
 

Hey, can someone post about how safe/unsafe these batteries are against AGM/FLA/VRLA (Lead Acid) bateries? I do not want this car that I am building be a bomb in ceratin cases!::ouch::

Re: LiFePO4 Batteries
 

Living in the middle of Arizona, a desert, I am probably unlikely to find Snowmobile Designers? :confused: :deadhorse:

Re: LiFePO4 Batteries
 

You can find them in some unlikely places (though I admit that I don't see any registered teams from anywhere south of Illinois). And remember, there's this wonderful invention called the Internet, which can help you connect with folks who actually have winter. (As a matter of fact, I remember having a couple of folks from Arizona on my Aero team--which worked in the same room as the Snowmobile team--during my final year of college in South Dakota, one of whom may have graduated from your FRC team--I can never keep 1164 and 1165 straight.)


As far as safety, AFAIK, they're pretty comparable as long as you don't do anything utterly stupid. The risk of flammability is a bit higher, but not nearly as bad as LiPOs. If you're shipping them, you have to have someone who's registered to do that, though I don't think that'll be too big of an issue if you're not shipping them. Charging is more of common sense--use the right charger, and make sure it stops when it needs to.

Re: LiFePO4 Batteries
 

There are quite a few people out there who have been building electric cars for a long time. Many of them are members of the EAA (I gave you the link in my first post in this thread). You are best to start by getting in touch with a bunch of them in your area.

Re: LiFePO4 Batteries
 

how big is this car? are we talking go kart size or like a actual car size.

assuming you construct the pack correctly, as long as you don't draw more amps than the cells "c" rating or discharge the cells below 2.8v you shouldn't have problems.

Re: LiFePO4 Batteries
 

I am thinking a little bigger than a a go-kart, but way smaller than a regular cart. that is the project, basically. that way, the car will be small enough to drive even inside a building :D!::ouch::

Re: LiFePO4 Batteries
 

Hey, before, I was looking at Howell batteries because of their price. After doing a couple hours more of research, I came upon Winston Batteries (LiFeYPO4 instead of LiFePO4). Does anyone have experience with these batteries or this manufacturer?

Also, where can I buy these for the best possible price?