From what I have heard, if you are over 18, you can use better, more powerful batteries such as lithium ion. I would be very happy if someone to confirm this. Also, I was just wondering how dangerous it would be to use batteries like these? Would they cost too much to even think about using?
Yes, a rule was passed to allow the use of other forms of batteries. I looked quickly and did not find the email explaining the specifics (can someone else please post them?).
Bottom line is, yes, you will be able to use a number of different kinds of batteries. The idea is not to allow more power (but it will) but to create more options. The other effect will be that now there are way more classes of cars on the track. If you show up at a race with lith ion (or other) batteries and you are the only one at the race with them you will either not be allowed to race (check with the promoter before hand) or you will be racing in a group that will not be in your class.
I looked earlier and found some Lithum Poly for about $1200 per battery pack and then you need the proper charging equpt.
If this is a student project, I would limit the design to LiFePO4 batteries. Most of the other battery technologies have serious safety problems when they pushed outside their design limits or mechanically deformed .... IE they can be EXPLOSIVE ... especially Li-Poly and Li-Ion.
You will need the proper BMS to protect the batteries.
I'm not sure why anything other than LiFePO4 were approved as an advanced battery class for student use, as they require a REAL engineer to properly design them in a system for safety reasons. Even LiFePO4's should be used carefully, as they can source high enough currents to start some amazing fires in shorted wiring.
I have used Lithium (Lipo) for the last 2 races held in the Tampa, FL area. I have been using lithium batteries in RC airplanes for over 5 years. I also have lithium in 3 of my bicycles and also in my motorcycle. I am NO engineer. However, I do understand the chemistry and know the rules of using and charging. My batteries cost around $400.00 plus shipping from China. Almost the same price as my Yellow Tops. They are actually from 2 of my bikes so technically they cost me nothing to use them in the Electrathon. They have almost identical watt/hours as the lead but are 58 lbs lighter. Really the only difference I noticed with the lipo is a better acceleration, due mostly to the 58 lb less battery weight, but also better voltage holding under load. Also it handles a good bit better with the weight out of there.
Lithium is NOT for everyone. If you don't have experience with it, I recommend you stay away!
An Li-Poly cell is a time bomb once it has been stressed past safe limits ... it will not always fail immediately, sometimes a few hours or days later. The packs for an RC car or plane are small, but still can create a significant fire without much warning.
The packs for an EA car are huge, and that HUGE amount of energy can, and will, end up creating a large fire expectedly when an Li-Poly (aka Lipo) pack has been stressed past safe limits.
I have two concerns about Li-Poly packs in student cars ... the first is that students are much more likely to create a wiring fault that will trigger a pack failure. The second is that in a one hour race, that wiring fault can trigger a fire with the student strapped inside the car with the batteries on fire. Most students will not react to this failure promptly enough to avoid serious injury or death.
That kind of a failure during a race is very unlikely with AGM and LiFePO4 batteries - almost impossible.
Lithium-Ion batteries have a long history of fires and explosive failures too, sometimes from just getting too warm. Both in computers and in cell phones. There are special battery managment circuits that monitor the battery charge and temperature to avoid these failures.
Both students, and adults that are not engineers, may be unaware of the full risks when they construct high current Li-Ion or Li-Poly packs for an EA racer.
A small Li-Ion phone battery is only 3.7V at 2AHr ... about 7 watts of power worst case ... that creates significant fires when over charged or over heated:
The overheating problem creating a fire in these events should be a concern for EA racing ... unless the pack is specifically built to cool properly on charge and discharge, it can overheat and fail during a race with the driver strapped in the car with it.
The gases when Li-Ion and Li-Poly burn are not safe to breath ... the time it takes to stop and get out of the car can make the difference between serious lung and burn injury.
These Li-Ion and Li-Poly batteries fail when subjected to being crushed, high vibration, and high g-shock loads. They are not safe in a high speed crash unless contrained in a crush proof, shock absorbing battery container. In a multi-car crash, not only the operator of an Li-Ion or Li-Poly car is at risk, all those involved in the crash may be at risk as well.
Crashes pose high risk of a shorted battery wiring that the normal over current protection may not stop unless there are special precautions to fuse the battery pack internally. These accident shorts risk battery explosions, as high current discharge will overheat them quickly. This places both the driver, and those around them at risk.
LiFePO4 batteries do not have the safety problems that Li-Ion and Li-Poly have.
Even in the RC community there are voices that strongly suggest using LiFePO4 batteries for safety reasons. In particular, one brand, A123 that have both exceptional safety and cycle life. Many a DeWalt battery pack was taken apart for RC uses until the cells became common place China exports last year.
The safety is inherient in the chemistry of the LiFePO4 battery, and choice of materials. Tests show them being heated to red hot, and nails driven thru them, with only passive failures. None of the explosive results you get from torturing Li-Ion and Li-Poly batteries the same way.
Dr. John Goodenough and his team at University of Texas patented LiFePO4 in 1996. In a few short years it has been commericalized and become the defacto safe battery alternative for many consumer uses, rapidly replacing both Li-Ion and Li-Poly as production ramps up. The most interesting result has been the wide spread patent infringement in China for this technology.
I have heard that Odyssey batteries age good quality. I don't think I have seen a set being used yet. If I remember correctly there was not a good set available under the old weight limit. not sure now that it has been raised.
When you are looking at automotive battery applications, like 75/35 or 75/25, the double number means that it has top and side posts.
The only thing you gain with this is more weight. As much as 2 or 3 pounds.
Unless you are going to get a great deal on the price always go with a straight 25 or 35 application. It will be a top post only battery. 25 or 35 relates to the possition of the pos. neg. posts for installation in an automobile or truck.
I am glad to see some discussions about new batteries. At this point, I have a team of students running a set of LiFeMnPO4 batteries, and I am happy with what I am seeing thus far. Our original purpose for purchasing the batteries were for financial reasons: At the asking price of $904 with a battery management system and battery charger included, we would actually save money in the long run over using the Yellow Top batteries. (The LiFeMnPO4 batteries by themselves are $254 each).Their life cycles are estimated at 5 times over the yellows. There is, of course, an initial high cost to get this system. Provided that you take care of these batteries, I expect to save money in the long run. All aside, these are newer technology batteries that do not share the same safety hazards as Lithium Ion batteries. Because of this, they do not have near the same energy density. I highly recommend that a Battery Management System be purchased with these batteries to increase both safety and useful life. As advertised, these batteries are rated at 40Ah with a nominal voltage of 25.6 volts and weighing in at 44.1 pounds. These kids of mine are in a class by themselves and are not awarded for their lap count since other teams we roll with are not yet running these types of batteries. They commented that the discharge curve is much flatter than the lead-acids and seem to provide a consistent rate. When the batteries reach a certain voltage, they are done. GBS (manufacturer of the batteries) claim that the LiFeMnPO4 batteries do not experience memories issues like the lead-acids do. Over time, we will be tabulating data to compare with yellows and create a conclusion about longevity and associated costs. But, at this point, I am betting on the LiFeMnPO4 batteries. I am quite tempted to purchase another set next year. What these kids are doing reminds me of Electrathon Americas Mission Statement: To create and develop a sport that improves public awareness and understanding of electric vehicles through continuously improving vehicles and rules.
John Pappas - There is no arbitrary age limit related to battery type.
Jim - According to rule # 27 in the Electrathon America handbook, your batteries are too heavy and therefore illegal. Lithium-Ion 15lb; Lithium Polymer 15lb; Lithium-Iron-Phosphate 29lb.
Running advanced batteries in the Open Standard class is like running a Corvette against a bunch of 4-cylinder Pintos. You SHOULD win, but the victory is hollow and meaningless.
The reason for the weird weight limits with the experimental batteries is to try and keep the watt hours down to about 1000 watt hours. I've gotten close with my yellow top batteries on a couple occasions which meet the 73 pound limit, but other lead acid combinations need to be weight to meet the requirement.
Nickel Cadium I think comes in at 42 pounds (correct me if I'm wrong), and I know Lithium Ion and Lithium Polymer both come in at a mer 15 pounds because they are so potient in engergy compared to a lead acid type. I know there are other battery types on the list that can be used but I don't remember the rest of what was on the list. Those four stuck out to me the best.
