3.2 lb. LiFePO4 Track Battery
04-25-2011, 02:17 PM
#1
Momentum Keeps Me Going
Thread Starter
3.2 lb. LiFePO4 Track Battery
The RX-8 was designed to be lightweight, so it’s hard to shave even more pounds to lighten the car for the track. While still keeping the car basically stock, I’ve been working at reducing overall weight of my VR Grand Touring model for the last eight years. For my track setup, I added an Odyssey PC680 battery (-22lbs.), lightweight wheels (-40lbs.), lightweight Corksport exhaust system (-10lbs.), two-piece lightweight brake rotors up front (-9 lbs.), remove the back seats (-24lbs.), took everything out not screwed down plus a few things that were, and I'm at around -127lbs. Add back in a few other mods and the total savings is about -105lbs. Not bad, but short of gutting the car interior, or using CF body panels, there was little left to change.
Lately I began to reconsider my full time use of the Odyssey PC680 battery. It seems to fail like clockwork every two years, and I seem to run it down every now and then due to leaving something electrical on the car or just not using the car for a period of time. That’s a pain. I guess it happens because of its small 16 AH rating and the cars parasitic current draw that conspires to drain it. Bottom line, even though it only weighs 16lbs., it’s still a 16lbs more than I’d like. To reduce it means converting to a different, lighter weight energy source.
[16lb Odyssey battery w/heat wrap]
Until recently there had been no readily available alternative. However, Porsche has recently started offering a lithium ion battery as an optional $1700 upgrade in some of their track oriented models.
From Porsche's website http://www.porsche.com/microsite/tec...lectedVariant=
A press release from Porsche sums up the advantages of this 13 lb. jewel.
“With its nominal capacity of 18 Ah, the lithium-ion battery, through its specific features, offers a level of practical output and performance not only comparable to that of a 60 Ah lead battery, but rather even better in many cases.
On a conventional car battery only about 30 per cent of the total capacity is actually available for practical use due to the configuration of the system, while this restriction does not apply to the lithium-ion battery. On the contrary, through its characteristic structure – and, in particular, the independence of the chemical composition of the electrolytes from the charge status – a lithium-ion battery consistently offers almost 100 per cent of its capacity.
Delivery of power by the lithium-ion battery throughout its useful charge range is likewise significantly better, providing its full power, for example, when starting the engine almost independently of the current charge level. After the engine has started, the new Porsche battery shows further benefits in the charge process, being able through its smaller internal resistance to take up more power than a conventional battery and thus re-charge more quickly.
Yet a further benefit is that a lithium-ion battery allows a significantly greater number of charging and discharging cycles, plus the two further advantages that the self-discharging effect is lower and the service life of the battery longer.”
That being far, far out of my price range I had to come up with some other more reasonable solution by focusing only on track use, building the unit myself, and minimizing capacity and component costs. Of course, beside Porsche, I found other ready made premium (managed) Lithium battery replacements like the VoltPhreaks products that BRODA has discussed here https://www.rx8club.com/showthread.p...hlight=lithium. Unfortunately these units are $800 to $1500 and up. Yikes again! And while offering real benefits, my pocketbook was just not ready for that sizeable an outlay! There are also many other (unmanaged) LiFePO4 products out there, but they seemed overpriced for what you get.
I learned that like any technology, Lithium batteries excel at certain things - but not everything. Principally, they cost a lot, and they need some special TLC. In practical terms, they can never be overcharged, over discharged, or overheated. Still, for a track car it would appear to be an almost perfect fit and a tempting conversion.
With a bit of research this winter I discovered a variation of the Lithium technology - the Lithium Iron Phosphate battery, or LiFePO4 battery for short, offers great promise. The LiFePO4 battery, like the Lithium Ion, wins on its power and low weight, but it is also lower cost, and is far safer due to its unique chemistry. So why isn’t everybody using them? For one, they are quite new and still somewhat expensive, but also you need to understand what a battery actually does and doesn’t do in a car, and how LiFePO4 plays into that. First, it needs to supply a lot of current (=>100amps) to start the car. Second, with the motor running, a battery does nothing, and is just dead weight, as the alternator powers electrical needs. Third, a battery runs accessories when the car's not running.
For the track, the only thing we care about is starting the car and light weight, nothing else. In other words, while very lightweight lithium batteries (under 4lbs) do lack the AH capacity for long term parasitic draw and to power large current draw accessory loads for long periods when the car is not running, that shortcoming is irrelevant when the car is in regular use or on short term use on the race track. So I decided the LiFePO4 is the cheapest, safest, lightest battery that gets the job done on track.
With that in mind, the criteria for this mod was set... but for the RX-8 it also needed to be the right size and shape for safe placement, yet easy to construct, install and maintain from readily available parts. After looking at everything available in the exploding LiFePO4 battery marketplace, I found nothing ready-made that was a 100% fit and certainly nothing that fit my budget! So I had the fun of designing and building a custom unit. The result is an unmanaged unit with these specs:
Weight: ~3.2 lbs. (less case and attached cables)
Continuous current: 120 amps (RX-8 starter current is <100amps)
Maximum current: 200 amps
Nominal Capacity: 8AH or ~Lead Acid equivalent 27AH
Dimensions: 80mm x 80mm x 152mm (can of beans size)
Cost: ~$100 (does not include optional charger/balancer ~$80)
And the best part......
Cost of weight savings over stock: ~$3/lb or 33lbs. = $100
[It takes four 38120P 3.2v cells to make a 12.8v battery - each weighs 300g]
[Plastic case, cell holders, and hardware to construct the battery]
[Showing internal layout of cells - 5 wire cable is for charging when not connected]
[Short 4 gauge 18" flex leads (red/blk) make under dash connection easy]
[The short cables/case/hardware add a bit to the weight]
So theoretically I’d morphed the OEM 38 lb. dead weight into a 16 lb. one and then finally into a featherweight 3.2 lb. one (4.4 with case and attached cables). My original intent was just to replace the stock battery in place. But the problem with that is that lithium batteries don’t like to be overheated. The RX-8 engine bay can be one hot place. If you overheat a lithium battery past ~160F, you kill it. Not just maybe - but for sure. Even though our battery box is ventilated (but only when the car is moving), it also sits right on top of the radiator wash, which could approach boiling point temperature. That’s way too hot for a lithium battery. I had to find another location.
My first thought about placing the battery in the trunk was less than ideal from the perspective of losing weight. Battery cables are heavy, running them is a pain, and a dual 14 ft. run back to the trunk even with lightweight 4 gauge wire would weigh ~5lbs. That’s an additional 156% more than the battery cells themselves - yikes! If I ground the battery in the trunk and only run the positive wire back to the engine compartment, I was afraid the large voltage drop under high starting currents would be a problem. If I used a heavier gauge positive wire, weight goes up again.
The solution was to find a closer mounting place, and I found one great one - directly behind the glove box. I used a short 5 ft., 4 gauge positive run to the battery box, and an even shorter 3 ft. ground wire directly to a point on the engine intake runner, where my already installed grounding kit goes back to the battery box. Total cable weight (inc. attached cables) - 1 lb. 6 oz. - for a total battery and cable weight of ~5 lbs.
[Move a few bits and there's a nice space here behind the glove box.]
[Cables coming thru firewall in a hole behind the washer tub^]
[The battery fits nicely there and there's a metal brace to hang the battery from]
[Cables thru firewall attach to the short battery cables & are hidden]
As far as Lithium battery TLC, with the design set for short term track use, I was able to forgo the expensive over voltage and over discharge battery management electronics. Our alternators already regulate output to ~14.5 volts, and that’s safe for charging 12.8 volt LiFePO4 cells directly. Regular car use will keep the battery charged and so there’s no possibility of over discharge. The intent is for the regular battery to be swapped back in for daily use, or for a car left in storage, or when large current draw accessories are used without the engine running.
All this effort put into saving a few pounds begs the question, “Does losing ~30 lbs. really matter to performance that much?” The answer is no, it really doesn’t matter all that much, being only a ~1% overall weight savings. But any improvement is better than no improvement. Further, a track situation is a special case for a number of reasons. To wit, during a track session or race, all the car does is brake, turn, then accelerate, brake, turn, and accelerate. Mass is the enemy, and any gain or loss in performance, however small, is multiplied over and over again, possibly hundreds of times during a session. So by ‘simply’ increasing your cornering speed a bit and/or straight line acceleration and top speed by a fraction of a mile per hour, you’re making headway. All these small improvements can add up quickly in the track environment and cut seconds over time when you are exercising your car to the fullest extent possible.
That's almost the end of this mod story; however there is one small thing left. LiFePO4 battery cells tend to charge at slightly different rates, and are more apt to do so during high discharge/charge cycles. Over time, this can result in cell damage or battery failure. So in the design I added a special charger that rebalances the four internal cells during recharge. This only needs to be done every now and again to keep the battery in perfect health. When maintained correctly it said a LiFePO4 battery can last up to 5 times longer than a lead acid battery such as the Odyssey PC680. I’m not sure if this extra step of careful charging is necessary, but it isn’t that costly either, so I decided it was worth trying.
[Basic 14.5v LiFePO4 charger shown w/balancing circuit during testing]
Finally, by saving 33 lbs. over the OEM battery, or 11 lbs. over the PC680, my net weight saving is up to 116 lbs. With a half tank of gas, I’m ready to rock with a track weight of 2871 lbs, not including myself.
I'm looking foward to another great track season testing this design in practice. And I hope this inspires other to have a go at trying something few have done before (except Porsche owners, race car drivers, and a few well healed others)... I always believe where there's a will, there is usually a way, so go for it! LiFePO4 technology is new, exciting, and holds great promise as a lightweight energy source for track addicts!
Cheers
Lately I began to reconsider my full time use of the Odyssey PC680 battery. It seems to fail like clockwork every two years, and I seem to run it down every now and then due to leaving something electrical on the car or just not using the car for a period of time. That’s a pain. I guess it happens because of its small 16 AH rating and the cars parasitic current draw that conspires to drain it. Bottom line, even though it only weighs 16lbs., it’s still a 16lbs more than I’d like. To reduce it means converting to a different, lighter weight energy source.
[16lb Odyssey battery w/heat wrap]
Until recently there had been no readily available alternative. However, Porsche has recently started offering a lithium ion battery as an optional $1700 upgrade in some of their track oriented models.
From Porsche's website http://www.porsche.com/microsite/tec...lectedVariant=
A press release from Porsche sums up the advantages of this 13 lb. jewel.
“With its nominal capacity of 18 Ah, the lithium-ion battery, through its specific features, offers a level of practical output and performance not only comparable to that of a 60 Ah lead battery, but rather even better in many cases.
On a conventional car battery only about 30 per cent of the total capacity is actually available for practical use due to the configuration of the system, while this restriction does not apply to the lithium-ion battery. On the contrary, through its characteristic structure – and, in particular, the independence of the chemical composition of the electrolytes from the charge status – a lithium-ion battery consistently offers almost 100 per cent of its capacity.
Delivery of power by the lithium-ion battery throughout its useful charge range is likewise significantly better, providing its full power, for example, when starting the engine almost independently of the current charge level. After the engine has started, the new Porsche battery shows further benefits in the charge process, being able through its smaller internal resistance to take up more power than a conventional battery and thus re-charge more quickly.
Yet a further benefit is that a lithium-ion battery allows a significantly greater number of charging and discharging cycles, plus the two further advantages that the self-discharging effect is lower and the service life of the battery longer.”
That being far, far out of my price range I had to come up with some other more reasonable solution by focusing only on track use, building the unit myself, and minimizing capacity and component costs. Of course, beside Porsche, I found other ready made premium (managed) Lithium battery replacements like the VoltPhreaks products that BRODA has discussed here https://www.rx8club.com/showthread.p...hlight=lithium. Unfortunately these units are $800 to $1500 and up. Yikes again! And while offering real benefits, my pocketbook was just not ready for that sizeable an outlay! There are also many other (unmanaged) LiFePO4 products out there, but they seemed overpriced for what you get.
I learned that like any technology, Lithium batteries excel at certain things - but not everything. Principally, they cost a lot, and they need some special TLC. In practical terms, they can never be overcharged, over discharged, or overheated. Still, for a track car it would appear to be an almost perfect fit and a tempting conversion.
With a bit of research this winter I discovered a variation of the Lithium technology - the Lithium Iron Phosphate battery, or LiFePO4 battery for short, offers great promise. The LiFePO4 battery, like the Lithium Ion, wins on its power and low weight, but it is also lower cost, and is far safer due to its unique chemistry. So why isn’t everybody using them? For one, they are quite new and still somewhat expensive, but also you need to understand what a battery actually does and doesn’t do in a car, and how LiFePO4 plays into that. First, it needs to supply a lot of current (=>100amps) to start the car. Second, with the motor running, a battery does nothing, and is just dead weight, as the alternator powers electrical needs. Third, a battery runs accessories when the car's not running.
For the track, the only thing we care about is starting the car and light weight, nothing else. In other words, while very lightweight lithium batteries (under 4lbs) do lack the AH capacity for long term parasitic draw and to power large current draw accessory loads for long periods when the car is not running, that shortcoming is irrelevant when the car is in regular use or on short term use on the race track. So I decided the LiFePO4 is the cheapest, safest, lightest battery that gets the job done on track.
With that in mind, the criteria for this mod was set... but for the RX-8 it also needed to be the right size and shape for safe placement, yet easy to construct, install and maintain from readily available parts. After looking at everything available in the exploding LiFePO4 battery marketplace, I found nothing ready-made that was a 100% fit and certainly nothing that fit my budget! So I had the fun of designing and building a custom unit. The result is an unmanaged unit with these specs:
Weight: ~3.2 lbs. (less case and attached cables)
Continuous current: 120 amps (RX-8 starter current is <100amps)
Maximum current: 200 amps
Nominal Capacity: 8AH or ~Lead Acid equivalent 27AH
Dimensions: 80mm x 80mm x 152mm (can of beans size)
Cost: ~$100 (does not include optional charger/balancer ~$80)
And the best part......
Cost of weight savings over stock: ~$3/lb or 33lbs. = $100
[It takes four 38120P 3.2v cells to make a 12.8v battery - each weighs 300g]
[Plastic case, cell holders, and hardware to construct the battery]
[Showing internal layout of cells - 5 wire cable is for charging when not connected]
[Short 4 gauge 18" flex leads (red/blk) make under dash connection easy]
[The short cables/case/hardware add a bit to the weight]
So theoretically I’d morphed the OEM 38 lb. dead weight into a 16 lb. one and then finally into a featherweight 3.2 lb. one (4.4 with case and attached cables). My original intent was just to replace the stock battery in place. But the problem with that is that lithium batteries don’t like to be overheated. The RX-8 engine bay can be one hot place. If you overheat a lithium battery past ~160F, you kill it. Not just maybe - but for sure. Even though our battery box is ventilated (but only when the car is moving), it also sits right on top of the radiator wash, which could approach boiling point temperature. That’s way too hot for a lithium battery. I had to find another location.
My first thought about placing the battery in the trunk was less than ideal from the perspective of losing weight. Battery cables are heavy, running them is a pain, and a dual 14 ft. run back to the trunk even with lightweight 4 gauge wire would weigh ~5lbs. That’s an additional 156% more than the battery cells themselves - yikes! If I ground the battery in the trunk and only run the positive wire back to the engine compartment, I was afraid the large voltage drop under high starting currents would be a problem. If I used a heavier gauge positive wire, weight goes up again.
The solution was to find a closer mounting place, and I found one great one - directly behind the glove box. I used a short 5 ft., 4 gauge positive run to the battery box, and an even shorter 3 ft. ground wire directly to a point on the engine intake runner, where my already installed grounding kit goes back to the battery box. Total cable weight (inc. attached cables) - 1 lb. 6 oz. - for a total battery and cable weight of ~5 lbs.
[Move a few bits and there's a nice space here behind the glove box.]
[Cables coming thru firewall in a hole behind the washer tub^]
[The battery fits nicely there and there's a metal brace to hang the battery from]
[Cables thru firewall attach to the short battery cables & are hidden]
As far as Lithium battery TLC, with the design set for short term track use, I was able to forgo the expensive over voltage and over discharge battery management electronics. Our alternators already regulate output to ~14.5 volts, and that’s safe for charging 12.8 volt LiFePO4 cells directly. Regular car use will keep the battery charged and so there’s no possibility of over discharge. The intent is for the regular battery to be swapped back in for daily use, or for a car left in storage, or when large current draw accessories are used without the engine running.
All this effort put into saving a few pounds begs the question, “Does losing ~30 lbs. really matter to performance that much?” The answer is no, it really doesn’t matter all that much, being only a ~1% overall weight savings. But any improvement is better than no improvement. Further, a track situation is a special case for a number of reasons. To wit, during a track session or race, all the car does is brake, turn, then accelerate, brake, turn, and accelerate. Mass is the enemy, and any gain or loss in performance, however small, is multiplied over and over again, possibly hundreds of times during a session. So by ‘simply’ increasing your cornering speed a bit and/or straight line acceleration and top speed by a fraction of a mile per hour, you’re making headway. All these small improvements can add up quickly in the track environment and cut seconds over time when you are exercising your car to the fullest extent possible.
That's almost the end of this mod story; however there is one small thing left. LiFePO4 battery cells tend to charge at slightly different rates, and are more apt to do so during high discharge/charge cycles. Over time, this can result in cell damage or battery failure. So in the design I added a special charger that rebalances the four internal cells during recharge. This only needs to be done every now and again to keep the battery in perfect health. When maintained correctly it said a LiFePO4 battery can last up to 5 times longer than a lead acid battery such as the Odyssey PC680. I’m not sure if this extra step of careful charging is necessary, but it isn’t that costly either, so I decided it was worth trying.
[Basic 14.5v LiFePO4 charger shown w/balancing circuit during testing]
Finally, by saving 33 lbs. over the OEM battery, or 11 lbs. over the PC680, my net weight saving is up to 116 lbs. With a half tank of gas, I’m ready to rock with a track weight of 2871 lbs, not including myself.
I'm looking foward to another great track season testing this design in practice. And I hope this inspires other to have a go at trying something few have done before (except Porsche owners, race car drivers, and a few well healed others)... I always believe where there's a will, there is usually a way, so go for it! LiFePO4 technology is new, exciting, and holds great promise as a lightweight energy source for track addicts!
Cheers
Last edited by Spin9k; 04-25-2011 at 02:30 PM.
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sharingan 19 (03-23-2024)
04-25-2011, 04:10 PM
#4
I run the 15lb Braille battery in the trunk. Yes the cables add some weight and there are lighter options, but going smaller and lighter is not worth the money or convenance tradeoffs for me. My battery set up still saves about 15lbs, plus a little weight in the right rear isn't really a bad thing.
I could always pull the passenger seat for track days if I was that worried. -38lbs.
Until I lose the extra 30lbs I am carrying around I'm not too worried about the 5-10lbs I could take out of the car.
As it sits, my car is 2900 lbs with a half tank of fuel no back seats. Racewheels and tires -40lbs,front bbk with f&r 2 piece rotors -25lbs, header and header back exhaust is about -20 lbs. Mazdaspeed body kit, splitter, Apr wing, supercharger and extra body bracing add some weight.
The next weight savings project on my list is custom aluminium f&r crash bars hoping for -15lbs and rumor has it there might be a new light weight catback option -15-25lbs off stock and lightweight ppf hoping for -15lbs, hitting the market this year.
After all that and the 30lbs of dead driver weight I will consider lexan windshield and rear Windows -25 lbs I think, plus the weight is high.
I could always pull the passenger seat for track days if I was that worried. -38lbs.
Until I lose the extra 30lbs I am carrying around I'm not too worried about the 5-10lbs I could take out of the car.
As it sits, my car is 2900 lbs with a half tank of fuel no back seats. Racewheels and tires -40lbs,front bbk with f&r 2 piece rotors -25lbs, header and header back exhaust is about -20 lbs. Mazdaspeed body kit, splitter, Apr wing, supercharger and extra body bracing add some weight.
The next weight savings project on my list is custom aluminium f&r crash bars hoping for -15lbs and rumor has it there might be a new light weight catback option -15-25lbs off stock and lightweight ppf hoping for -15lbs, hitting the market this year.
After all that and the 30lbs of dead driver weight I will consider lexan windshield and rear Windows -25 lbs I think, plus the weight is high.
Last edited by Highway8; 04-25-2011 at 04:16 PM.
04-25-2011, 04:42 PM
#5
Momentum Keeps Me Going
Thread Starter
04-25-2011, 04:47 PM
#6
Momentum Keeps Me Going
Thread Starter
Guys! I appreciate everyone has worked to lighten their car for track use. There are many ways to go about it, so good for all of your efforts.
But!!! I'd prefer this not be a thread with posts focused on "How I also reduced the weight of my car" or "My car is already lighter than yours and this is how" type of back and forth. There are plenty of those threads about that. This is about lightweight battery technology, how to use it, where to put it, and how light it can be and still work for the track.
Thanks.
But!!! I'd prefer this not be a thread with posts focused on "How I also reduced the weight of my car" or "My car is already lighter than yours and this is how" type of back and forth. There are plenty of those threads about that. This is about lightweight battery technology, how to use it, where to put it, and how light it can be and still work for the track.
Thanks.
04-25-2011, 04:57 PM
#8
Momentum Keeps Me Going
Thread Starter
I think this opens up other possibilites for those with turbos, etc. Maybe it will help you...
04-25-2011, 05:21 PM
#10
Guys! I appreciate everyone has worked to lighten their car for track use. There are many ways to go about it, so good for all of your efforts.
But!!! I'd prefer this not be a thread with posts focused on "How I also reduced the weight of my car" or "My car is already lighter than yours and this is how" type of back and forth. There are plenty of those threads about that. This is about lightweight battery technology, how to use it, where to put it, and how light it can be and still work for the track.
Thanks.
But!!! I'd prefer this not be a thread with posts focused on "How I also reduced the weight of my car" or "My car is already lighter than yours and this is how" type of back and forth. There are plenty of those threads about that. This is about lightweight battery technology, how to use it, where to put it, and how light it can be and still work for the track.
Thanks.
Regarding batteries, I agree the lightweight racing batteries like Barille and odessey have their short comings like battery discharge rate. I keep a smart charger on it when it sits for more then 1 night.
I like your cost effective method and I am interested in seeing how it works out for you long term.
Regarding trunk installs, I really don't mind the extra few pounds back there as it is the lightest corner on the car, plus there are lightweight cables available that work well but pricey.
Not saying your battery effects balance, but sometimes having the proper weight distribution is more important then removing weight. It's important to weigh your car and focus on pulling and placing weight in the Ideal positions and then corner balance.
04-25-2011, 05:38 PM
#11
Momentum Keeps Me Going
Thread Starter
^ No problem. I was thinking about balance as well Highway8. The idea of the battery on the passenger front made me think of keeping it on that side as well, and so I went searching. But the trunk was just too far away and sacraficed too many of those pounds LiFePO4 was saving. With such a small size possible with LiFePO4 why not make the most of it and fit it as best as possible?
Mazda did go to great lengths (but didn't do all they could unfortunately) to reduce weight, the enemy of performance, because it wasn't designed 'just' as a track car.
For track use, I don't think there is really a good argument for saying, "Well, that extra weight is OK in this case". Extra weight is not OK, esp. in our severely underpowered car compared to current offerings and new lightweight technology.
That's why Mazda has made the commitment to lose 100kg of all new cars. For us stuck with 8 yr old technology, and esp. for track use where practicality isn't so much of a concern, LiFePO4 technology lets us lose lots of those "grams" that Mazda says is tried to rid the car of.
LiFePO4 just happens to let us "lose" some 15,000 of those grams, at least on the track! That's major.
Mazda did go to great lengths (but didn't do all they could unfortunately) to reduce weight, the enemy of performance, because it wasn't designed 'just' as a track car.
For track use, I don't think there is really a good argument for saying, "Well, that extra weight is OK in this case". Extra weight is not OK, esp. in our severely underpowered car compared to current offerings and new lightweight technology.
That's why Mazda has made the commitment to lose 100kg of all new cars. For us stuck with 8 yr old technology, and esp. for track use where practicality isn't so much of a concern, LiFePO4 technology lets us lose lots of those "grams" that Mazda says is tried to rid the car of.
LiFePO4 just happens to let us "lose" some 15,000 of those grams, at least on the track! That's major.
Last edited by Spin9k; 04-25-2011 at 05:41 PM.
04-25-2011, 06:41 PM
#13
Momentum Keeps Me Going
Thread Starter
^ link? ... there are lots of options out there, but I doubt those specs, the market levels price/capabilities quite well... but what you got 
04-25-2011, 07:39 PM
#14
Finally own one :)
04-25-2011, 08:39 PM
#15
Momentum Keeps Me Going
Thread Starter
Yes, that looks like the real deal as far as power. There are however a few problems with Lithium Polymer batteries for automobile use, and esp. 'hobby' use by non-professional individuals (most all of us car nuts).
__________________
Being Lithium Polymer composition, they can explode, catch fire and burn extremely rapidly if over charged / discharged or punctured / damaged or overheated.
>>LiFePO4 cannot burn or explode due to their unique chemisty, they just stop working in a benign fashion if mistreated.
__________________
These Lithium Polymer cell are called "pouch cells", meaning they are a bag with electrode material inside. Therefore they expand under high charge/discharge cycles, possibly resulting in electrode delamination, and reduction of reliability, output, and cycle life. Therefore to achieve rated performance, Lithium Polymer pouch cells must include an external casing to retain their shape. These don't appear to have any.
>>On the other hand, the metal case of cylindrical cells like these particular LiFePO4s cannot delaminate by design, in fact they press even more firmly together under stress, increasing output. This means these LiFePO4's actually produce MORE power as they warm up!
__________________
Lithium Polymer batteries must be charged carefully. That's why for RC use they sell special chargers that have a low steady output that diminishes over time. I'm not sure if it's safe to charge them with a high output car alternator, the spec doesn't say the maxium charge rate. After a high current starting discharge, a car's alternator would simply charge them as fast as it could at the highest rate possible. That could be dangerous.
>>The LiFePO4 cells I used allow a 80A charge rate, which is a great match for a car's alternator output.
==============
Understand, I'm not simply raining on your parade so to speak, but I've spent considerable time researching and understanding the terminolgies and characteristics of Lithium technology. I've found there are a bunch of "Gotchas" with serious implications for many types that make them less then "nice".
But great find nontheless - thanks for bringing it up - I hadn't investigated that variation until now due to trying to stay with the safer Lithium technologies.
__________________
Being Lithium Polymer composition, they can explode, catch fire and burn extremely rapidly if over charged / discharged or punctured / damaged or overheated.
>>LiFePO4 cannot burn or explode due to their unique chemisty, they just stop working in a benign fashion if mistreated.
__________________
These Lithium Polymer cell are called "pouch cells", meaning they are a bag with electrode material inside. Therefore they expand under high charge/discharge cycles, possibly resulting in electrode delamination, and reduction of reliability, output, and cycle life. Therefore to achieve rated performance, Lithium Polymer pouch cells must include an external casing to retain their shape. These don't appear to have any.
>>On the other hand, the metal case of cylindrical cells like these particular LiFePO4s cannot delaminate by design, in fact they press even more firmly together under stress, increasing output. This means these LiFePO4's actually produce MORE power as they warm up!
__________________
Lithium Polymer batteries must be charged carefully. That's why for RC use they sell special chargers that have a low steady output that diminishes over time. I'm not sure if it's safe to charge them with a high output car alternator, the spec doesn't say the maxium charge rate. After a high current starting discharge, a car's alternator would simply charge them as fast as it could at the highest rate possible. That could be dangerous.
>>The LiFePO4 cells I used allow a 80A charge rate, which is a great match for a car's alternator output.
==============
Understand, I'm not simply raining on your parade so to speak, but I've spent considerable time researching and understanding the terminolgies and characteristics of Lithium technology. I've found there are a bunch of "Gotchas" with serious implications for many types that make them less then "nice".
But great find nontheless - thanks for bringing it up - I hadn't investigated that variation until now due to trying to stay with the safer Lithium technologies.
Last edited by Spin9k; 04-25-2011 at 08:52 PM.
04-25-2011, 09:25 PM
#16
Finally own one :)
Thanks. The spec says they can charge at 50A. Even if you double up for 100A charging capacity that is still only 2.6 lbs, maybe $170-180 shipped, 10AH capacity and 450/900 Amps.
Wire the batteries with diodes. Thats solves the direct charging problem.
Then use a relay or remote switch to disable usage after the alternator is energized and even use an self maintaining 1-5 farad audio capacitor for a buffer for the alternator if you wanted too.
Now if you wanted it to be permanent then run the charger off the alternator, the battery would be disconnected once the car is running anyways. The starter is rated for 2 kw and a normal start takes say 3 seconds. that's 6000 joules. At 12V and 100A that's 1200 joules a second recharge plus the slow trickle at the end of charge. Plus you wouldn't even come close to meeting the max rated discharge rate. So it would weigh maybe 10 pounds max, but if it's a permanent solution then who cares. I rather have something permanent then absolute weight loss. Besides I can lose a few pounds that would gladly make up for the weight gain under the hood.
Wire the batteries with diodes. Thats solves the direct charging problem.
Then use a relay or remote switch to disable usage after the alternator is energized and even use an self maintaining 1-5 farad audio capacitor for a buffer for the alternator if you wanted too.
Now if you wanted it to be permanent then run the charger off the alternator, the battery would be disconnected once the car is running anyways. The starter is rated for 2 kw and a normal start takes say 3 seconds. that's 6000 joules. At 12V and 100A that's 1200 joules a second recharge plus the slow trickle at the end of charge. Plus you wouldn't even come close to meeting the max rated discharge rate. So it would weigh maybe 10 pounds max, but if it's a permanent solution then who cares. I rather have something permanent then absolute weight loss. Besides I can lose a few pounds that would gladly make up for the weight gain under the hood.
04-26-2011, 07:02 AM
#18
Momentum Keeps Me Going
Thread Starter
^ Well I'd say then go for it then. Seriously. But I can tell you that the vast majority of aftermarket Lithium batteries intended for aftermarket Lead Acid replacement are LiFePO4, typically a bunch of A123 or prismatic type cells. There have to be good reasons why that's the case, but that doesn't mean you can't try something different. I certainly have with these cells I'm using, they're neither of the above.
I can also appreciate the desire to have a more permanent solution too, just that's not what this mod is about. As I said, I hope I inspire others to give a try with Lithium technology.
So build your idea, whether it be a better track solution or a more permanent one using these RC batteries, and let us see it. Good luck!
I can also appreciate the desire to have a more permanent solution too, just that's not what this mod is about. As I said, I hope I inspire others to give a try with Lithium technology.
So build your idea, whether it be a better track solution or a more permanent one using these RC batteries, and let us see it. Good luck!
04-26-2011, 05:18 PM
#19
Finally own one :)
Thanks. Once I get a few other mods out of the way, I may give it a try if I do enough track days. Honestly depends whether I'll use its advantage enough to be worth the cost.
05-24-2011, 09:51 AM
#22
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Ive just joined this forum and this is a great writeup.
I am looking to do the same but fit a lifepo4 battery to a UK Vauxhall Monaro which has an LS1 engine and M6 transmission.
I have a few questions though,
Did you use the 12Ah cells, and is the battery still running okay?
Also where did you purchase the case from as it looks like a perfect fit.
Thankyou
I am looking to do the same but fit a lifepo4 battery to a UK Vauxhall Monaro which has an LS1 engine and M6 transmission.
I have a few questions though,
Did you use the 12Ah cells, and is the battery still running okay?
Also where did you purchase the case from as it looks like a perfect fit.
Thankyou
05-24-2011, 11:32 AM
#23
Momentum Keeps Me Going
Thread Starter
- I used four 8Ah 3.2v cells to make the 12.8v battery. I choose 'only' 8Ah size because of their amazing C ratings, better than the higher Ah cells.
Ratings: Continuous Discharge @15C (120A) and Max Discharge @25C (200A <30sec), and Charge max 10C (80A). That's much better than the higher Ah cells. The amazing thing is the cells weigh just 10 1/2 ounces each - talk about power packed!
- The case is a Cobalt Friction race pad shipping box. I like to recycle + you couldn't design much better packaging.
- Yes, but it's not been used really - it's been a weather thing here - just rain and gloomy ): ...more to come...
Ratings: Continuous Discharge @15C (120A) and Max Discharge @25C (200A <30sec), and Charge max 10C (80A). That's much better than the higher Ah cells. The amazing thing is the cells weigh just 10 1/2 ounces each - talk about power packed!
- The case is a Cobalt Friction race pad shipping box. I like to recycle
+ you couldn't design much better packaging.- Yes, but it's not been used really - it's been a weather thing here - just rain and gloomy ): ...more to come...
06-10-2011, 12:32 AM
#24
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thanks for the reply.
Out of interest how much current does an rx8 alternator output?
I have just found out that my monaro alternator has a rated output of 140 Amps, so i might email headway to ensure that this is safe if not if they have anything suitable
Out of interest how much current does an rx8 alternator output?
I have just found out that my monaro alternator has a rated output of 140 Amps, so i might email headway to ensure that this is safe if not if they have anything suitable
06-10-2011, 05:46 AM
#25
Momentum Keeps Me Going
Thread Starter
Here you go... in other places they reference making sure your tester can take 120A or more. Sooo...~100A. Of course you need a low enough resistance in the sink to be able to draw that much. The cells I used can accept 80a max. and as I intend they never be totally discharged in the car, that is more than sufficient.
Last edited by Spin9k; 06-10-2011 at 05:54 AM.
